Bug - Borne Diseases
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Leishmaniasis is a parasitic disease spread by the bite of infected sand flies.
There are several different forms of leishmaniasis. The most common forms
are cutaneous leishmaniasis, which causes skin sores, and visceral
leishmaniasis, which affects some of the internal organs of the body (for
example, spleen, liver, bone marrow).
What are the signs and symptoms of cutaneous leishmaniasis?
People who have cutaneous leishmaniasis have one or more sores on their
skin. The sores can change in size and appearance over time. They often
end up looking somewhat like a volcano, with a raised edge and central
crater. Some sores are covered by a scab. The sores can be painless or
painful. Some people have swollen glands near the sores (for example,
under the arm if the sores are on the arm or hand).
What are the signs and symptoms of visceral leishmaniasis?
People who have visceral leishmaniasis usually have fever, weight loss,
and an enlarged spleen and liver (usually the spleen is bigger than the
liver). Some patients have swollen glands. Certain blood tests are abnormal.
For example, patients usually have low blood counts, including a low
red blood cell count (anemia), low white blood cell count, and low platelet
count.
How common is leishmaniasis?
The number of new cases of cutaneous leishmaniasis each year in the
world is thought to be about 1.5 million. The number of new cases of
visceral leishmaniasis is thought to be about 500,000.
In what parts of the world is leishmaniasis found?
Leishmaniasis is found in parts of about 88 countries. Approximately
350 million people live in these areas. Most of the affected countries
are in the tropics and subtropics. The settings in which leishmaniasis
is found range from rain forests in Central and South America to deserts
in West Asia. More than 90 percent of the world's cases of visceral leishmaniasis
are in India, Bangladesh, Nepal, Sudan, and Brazil.
Leishmaniasis is found in some parts of the following areas:
- in Mexico, Central America, and South America -- from northern Argentina
to southern Texas (not in Uruguay, Chile, or Canada)
- southern Europe (leishmaniasis is not common in travelers to southern
Europe)
- Asia (not Southeast Asia)
- the Middle East
- Africa (particularly East and North Africa, with some cases elsewhere)
Leishmaniasis is not found in Australia or Oceania (that is, islands
in the Pacific, including Melanesia, Micronesia, and Polynesia).
Could I get leishmaniasis in the United States?
Probably not. It is possible but very unlikely that you would get leishmaniasis
in the United States. Very rarely, people living in rural southern Texas
have developed skin sores from cutaneous leishmaniasis.
No cases of visceral leishmaniasis are known to have been acquired in
the United States.
How is leishmaniasis spread?
Leishmaniasis is spread by the bite of some types of phlebotomine sand
flies. Sand flies become infected by biting an infected animal (for example,
a rodent or dog) or person. Since sand flies do not make noise when they
fly, people may not realize they are present. Sand flies are very small
and may be hard to see; they are only about one-third the size of typical
mosquitoes. Sand flies usually are most active in twilight, evening,
and night-time hours (from dusk to dawn). Sand flies are less active
during the hottest time of the day. However, they will bite if they are
disturbed, such as when a person brushes up against the trunk of a tree
where sand flies are resting. Rarely, leishmaniasis is spread from a
pregnant woman to her baby. Leishmaniasis also can be spread by blood
transfusions or contaminated needles.
Who is at risk for leishmaniasis?
People of all ages are at risk for leishmaniasis if they live or travel
where leishmaniasis is found. Leishmaniasis usually is more common in
rural than urban areas; but it is found in the outskirts of some cities.
The risk for leishmaniasis is highest from dusk to dawn because this
is when sand flies are the most active. All it takes to get infected
is to be bitten by one infected sand fly. This is more likely to happen
the more people are bitten, that is, the more time they spend outside
in rural areas from dusk to dawn. Adventure travelers, Peace Corps volunteers,
missionaries, ornithologists (people who study birds), other people who
do research outdoors at night, and soldiers are examples of people who
may have an increased risk for leishmaniasis (especially cutaneous leishmaniasis).
If I were bitten by an infected sand fly, how quickly would I become
sick?
People with cutaneous leishmaniasis usually develop skin sores within
a few weeks (sometimes as long as months) of when they were bitten.
People with visceral leishmaniasis usually become sick within several
months (rarely as long as years) of when they were bitten.
Can leishmaniasis be a serious disease if not treated?
Yes, it can be. The skin sores of cutaneous leishmaniasis will heal
on their own, but this can take months or even years. The sores can leave
ugly scars. If not treated, infection that started in the skin rarely
spreads to the nose or mouth and causes sores there (mucosal leishmaniasis).
This can happen with some of the types of the parasite found in Central
and South America. Mucosal leishmaniasis might not be noticed until years
after the original skin sores healed. The best way to prevent mucosal
leishmaniasis is to treat the cutaneous infection before it spreads.
If not treated, visceral leishmaniasis can cause death.
What should I do if I think I might have leishmaniasis?
See your health care provider, particularly if you have traveled to
an area where leishmaniasis is found and you have developed skin sores
that aren't healing. Be sure to tell your health care provider where
you have traveled and that you might be at risk for leishmaniasis.
It is very rare for travelers to get visceral leishmaniasis.
How will my health care provider know if I have leishmaniasis?
The first step is to find out if you have traveled to a part of the
world where leishmaniasis is found. Your health care provider will ask
you about any signs or symptoms of leishmaniasis you may have, such as
skin sores that have not healed. If you have skin sores, your health
care provider will likely want to take some samples directly from the
sores. These samples can be examined for the parasite under a microscope,
in cultures, and through other means. A blood test for detecting antibody
(immune response) to the parasite can be helpful, particularly for cases
of visceral leishmaniasis. However, tests to look for the parasite itself
should also be done. CDC staff can help with the laboratory testing.
Diagnosing leishmaniasis can be difficult. Sometimes the laboratory tests
are negative even if a person has leishmaniasis.
How is leishmaniasis treated?
Your health care provider can talk with CDC staff about whether your
case of leishmaniasis should be treated, and, if so, how. Most people
who have cutaneous leishmaniasis do not need to be hospitalized during
their treatment.
How is leishmaniasis prevented?
The best way for travelers to prevent leishmaniasis is by protecting
themselves from sand fly bites. Vaccines and drugs for preventing infection
are not yet available. To decrease their risk of being bitten, travelers
should:
- Stay in well-screened or air-conditioned areas as much as possible. Avoid
outdoor activities, especially from dusk to dawn, when sand flies are the
most active.
- When outside, wear long-sleeved shirts, long pants, and socks. Tuck your
shirt into your pants.
- Apply insect repellent on uncovered skin and under the ends of sleeves
and pant legs. Follow the instructions on the label of the repellent.
The most effective repellents are those that contain the chemical DEET
(N,N-diethylmetatoluamide). The concentration of DEET varies among
repellents. Repellents with DEET concentrations of 30-35% are quite
effective, and the effect should last about 4 hours. Lower concentrations
should be used for children (no more than 10% DEET). Repellents with
DEET should be used sparingly on children from 2 to 6 years old and
not at all on children less than 2 years old.
- Spray clothing with permethrin-containing insecticides. The insecticide
should be reapplied after every five washings.
- Spray living and sleeping areas with an insecticide to kill insects.
- If you are not sleeping in an area that is well screened or air-conditioned,
use a bed net and tuck it under your mattress. If possible, use a bed
net that has been soaked in or sprayed with permethrin. The permethrin
will be effective for several months if the bed net is not washed.
Keep in mind that sand flies are much smaller than mosquitoes and therefore
can get through smaller holes. Fine-mesh netting (at least 18 holes
to the inch; some sources say even finer) is needed for an effective
barrier against sand flies. This is particularly important if the bed
net has not been treated with permethrin. However, it may be uncomfortable
to sleep under such a closely woven bed net when it is hot.
NOTE: Bed nets, repellents containing DEET, and permethrin should
be purchased before traveling and can be found in hardware, camping,
and military surplus stores.
If I have already had leishmaniasis, could I get it again?
Yes. Some people have had cutaneous leishmaniasis more than once. Therefore,
you should follow the preventive measures listed above whenever you are
in an area where leishmaniasis is found.
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Lymphatic filariasis is a parasitic disease caused by microscopic, thread-like
worms. The adult worms only live in the human lymph system. The lymph
system maintains your body's fluid balance and fights infections.
Lymphatic filariasis affects over 120 million people in 80 countries
throughout the tropics and sub-tropics of Asia, Africa, the Western Pacific,
and parts of the Caribbean and South America. You cannot get the worms
in the United States.
How does infection occur?
The disease spreads from person to person by mosquito bites. When a
mosquito bites a person who has lymphatic filariasis, microscopic worms
circulating in the person's blood enter and infect the mosquito. If the
infected mosquito bites you, you can get lymphatic filariasis. The microscopic
worms pass from the mosquito through your skin, and travel to your lymph
vessels. In your lymph vessels they grow into adults. An adult worm lives
for about 7 years. The adult worms mate and release millions of microscopic
worms into your blood. Once you have the worms in your blood when a mosquito
bites you, you can give the infection to others through mosquitoes.
Who is at risk for infection?
You need many mosquito bites over several months to years to get lymphatic
filariasis. People living or staying for a long time in tropical or sub-tropical
areas where the disease is common are at the greatest risk for infection.
Short-term tourists have a very low risk. An infection will show up on
a blood test.
What are the symptoms of lymphatic filariasis?
At first, most people don't know they have lymphatic filariasis. They
usually don't feel any symptoms until after the adult worms die. The
disease usually is not life threatening, but it can permanently damage
your lymph system and kidneys. Because your lymph system does not work
right, fluid collects and causes swelling in the arms, breasts legs,
and, for men, the genital area. The name for this swelling is lymphedema
(limf-ah-DE-ma). The entire leg, arm, or genital area may swell to several
times its normal size. Also, the swelling and the decreased function
of the lymph system make it difficult for your body to fight germs and
infections. You will have more bacterial infections in your skin and
lymph system. This causes hardening and thickening of the skin, which
is called elephantiasis (el-ah-fan-TIE-ah-sis).
What is the impact of this disease?
Lymphatic filariasis is a leading cause of permanent and long-term disability
worldwide. People with the disease can suffer pain, disfigurement, and
sexual disability. Communities frequently shun women and men disfigured
by the disease. Many women with visible signs of the disease will never
marry, or their spouses and families will reject them. Affected people
frequently are unable to work because of their disability. This hurts
their families and their communities. Poor sanitation and rapid population
growth in tropical and subtropical areas of the world, where the disease
is common, has created more places for mosquitoes to breed and has led
to more people becoming infected.
How can I prevent infection?
Prevention includes giving entire communities medicine that kills the
microscopic worms and controlling mosquitoes. Avoiding mosquito bites
is another form of prevention. The mosquitoes that carry the microscopic
worms usually bite between the hours of dusk and dawn. If you live in
an area with lymphatic filariasis:
- Sleep under a mosquito net.
- Use mosquito repellant on your exposed skin between dusk and dawn.
- Take a yearly dose of medicine that kills the worms circulating in
the blood. The medicine will kill all of the microscopic worms in the
blood and some of the adult worms. It does not kill all of them.
What is the treatment for lymphatic filariasis?
If you have adult worms, you should take a yearly dose of medicine that
kills the microscopic worms circulating in your blood. While this does
not kill the adult worms, it does prevent you from giving the disease
to someone else. Even after the adult worms die, you can have swelling
of your arms, legs, breasts, or genitals. You can keep the swelling from
getting worse.
- Carefully wash the swollen area with soap and water every day.
- Use anti-bacterial cream on any wounds. This stops bacterial infections
and keeps the swelling from worsening.
- Elevate and exercise the swollen arm or leg to move the fluid and
improve the lymph flow.
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Also called American trypanosomiasis , Chagas disease is an infection
caused by the parasite Trypanosoma cruzi. It is estimated that
16-18 million people are infected with Chagas disease; of those infected,
50,000 will die each year.
How is Chagas disease spread?
Reduviid bugs, or "kissing bugs" live in cracks and holes of substandard
housing primarily found in South and Central America. Insects become
infected after biting an animal or person who already has Chagas disease.
Infection is spread to humans when an infected bug deposits feces on
a person's skin, usually while the person is sleeping at night. The person
often accidently rubs the feces into the bite wound, an open cut, the
eyes, or mouth. Animals can become infected the same way, and they can
also contract the disease by eating an infected bug.
How can I become infected?
- By infective feces contacting your eyes, mouth, or open cuts.
- By infected mothers passing infection to their baby during pregnancy,
at delivery, or while breastfeeding.
- By blood transfusion or organ transplant.
- By eating uncooked food contaminated with infective feces of "kissing
bugs."
Is Chagas disease a serious illness?
Yes. Chagas disease primarily affects low income people living in rural
areas. Many people get the infection during childhood. The early stage
of infection (acute Chagas disease) usually is not severe, but sometimes
it can cause death, particularly in infants. However, in about one-third
of those who get the infection, chronic symptoms develop after 10-20
years. For these persons who develop chronic symptoms, the average life
expectancy decreases by an average of 9 years.
What are the symptoms of Chagas disease?
There are three stages of infection with Chagas disease; each stage
has different symptoms. Some persons may be infected and never develop
symptoms.
Acute:
Acute symptoms only occur in about 1% of cases. Most people infected do
not seek medical attention. The most recognized symptom of acute Chagas infection
is the Romaña's sign, or swelling of the eye on one side of the face, usually
at the bite wound or where feces were rubbed into the eye. Other symptoms
are usually not specific for Chagas infection. These symptoms may include
fatigue, fever, enlarged liver or spleen, and swollen lymph glands. Sometimes,
a rash, loss of appetite, diarrhea, and vomiting occur. In infants and in
very young children with acute Chagas disease, swelling of the brain can
develop in acute Chagas disease, and this can cause death. In general, symptoms
last for 4-8 weeks and then they go away, even without treatment.
Indeterminate:
Eight to 10 weeks after infection, the indeterminate stage begins. During
this stage, people do not have symptoms.
Chronic:
Ten to 20 years after infection, people may develop the most serious symptoms
of Chagas disease. Cardiac problems, including an enlarged heart, altered
heart rate or rhythm, heart failure, or cardiac arrest are symptoms of chronic
disease. Chagas disease can also lead to enlargement of parts of the digestive
tract, which result in severe constipation or problems with swallowing. In
persons who are immune compromised, including persons with HIV/AIDS, Chagas
disease can be severe. Not everyone will develop the chronic symptoms of
Chagas disease.
How soon after infection will I have symptoms of Chagas disease?
Symptoms may occur within a few days to weeks. Most people do not have
symptoms until the chronic stage of infection, 10-20 years after first
being infected.
Can I take medication to prevent Chagas disease?
No. There is neither a vaccine nor recommended drug available to prevent
Chagas disease.
What should I do if I think I have Chagas disease?
See your health care provider who will order blood tests to look for
the parasite or for antibodies in your blood.
What is the treatment for Chagas disease?
Medication for Chagas disease is usually effective when given during
the acute stage of infection. Once the disease has progressed to later
stages, medication may be less effective. In the chronic stage, treatment
involves managing symptoms associated with the disease.
Where can I contract Chagas disease?
Chagas disease is locally transmitted in Argentina, Belize, Bolivia,
Brazil, Chile, Colombia, Costa Rica, Ecuador, El Salvador, French Guiana,
Guatemala, Guyana, Honduras, Mexico, Nicaragua, Panama, Paraguay, Peru,
Suriname, Uruguay, and Venezuela.
Who is at risk for Chagas disease?
Those people who sleep in poorly constructed houses found in the rural
areas of the above-mentioned countries are at elevated risk of infection.
Houses constructed from mud, adobe, or thatch present the greatest risk.
Travelers planning to stay in hotels, resorts, or other well-constructed
housing facilities are NOT at high risk for contracting Chagas disease
from reduviid bugs.
How can I prevent Chagas disease?
- Avoid sleeping in thatch, mud, or adobe houses.
- Use insecticides to kill insects and reduce the risk of transmission.
- Be aware that, in some countries, the blood supply may not always
be screened for Chagas disease, and blood transfusions may carry a
risk of infection.
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There are two types of African trypanosomiasis (also called sleeping
sickness); each is named for the region of Africa in which they are found.
The disease is caused by a parasite named Trypanosoma brucei rhodesiense
(tri-PAN-o-SO-ma BREW-see-eye rho-DEE-see-ense), carried by the tsetse
fly. Worldwide, approximately 40,000 new cases of both East and West
African trypanosomiasis are reported to the World Health Organization
each year. However, the majority of cases are not reported due to a lack
of infrastructure and it is likely that there are more than 100,000 new
cases annually. Since 1967, twenty-one cases of East African trypanosomiasis
have been reported within the United States, all among individuals who
had traveled to Africa. (See also West African trypanosomiasis.)
How is East African trypanosomiasis spread?
An individual will get East African trypanosomiasis if they are bitten
by a tsetse fly infected with the Trypanosoma brucei rhodesiense parasite.
The tsetse fly is common only to Africa.
Is East African trypanosomiasis a serious illness?
Yes. If a person fails to receive medical treatment for East African
trypanosomiasis, death will occur within several weeks to months.
Where can you become infected with East African trypanosomiasis?
East African trypanosomiasis is found in parts of Eastern and Central
Africa, including Uganda, Kenya, Tanzania, Malawi, Ethiopia, Zaire, Zimbabwe,
and Botswana. Areas where infection is spread are largely determined
by the location of the infected tsetse fly and wild animal population.
What are the symptoms of East African trypanosomiasis?
A bite by the tsetse fly is often painful and can develop into a red
sore, also called a chancre (SHAN-ker). Fever, severe headaches, irritability,
extreme fatigue, swollen lymph nodes, and aching muscles and joints are
common symptoms of sleeping sickness. Some people develop a skin rash.
Progressive confusion, personality changes, slurred speech, seizures,
and difficulty in walking and talking occur when infection has invaded
the central nervous system. If left untreated, infection becomes worse
and death will occur within several weeks or months.
How soon after infection will I have symptoms of East African trypanosomiasis?
Symptoms begin within 1 to 4 weeks of getting an infected tsetse fly
bite.
What should I do if I think I may have African trypanosomiasis?
If you suspect that you may have East African trypanosomiasis, immediately
consult with your health care provider who will order several tests to
look for the parasite. Common tests include blood samples, a spinal tap,
and skin biopsies, especially if you have a chancre.
What is the treatment for East African trypanosomiasis?
Medical treatment of East African trypanosomiasis should begin as soon
as possible and is based on the infected person’s symptoms and laboratory
results. Medication for the treatment of East African trypanosomiasis
is available through the CDC. Hospitalization for treatment is necessary.
Periodic follow-up exams that include a spinal tap are required for 2
years.
Once infected, am I immune to East African trypanosomiasis?
No one is immune from East African trypanosomiasis. Even if you had
the disease once, you can get re-infected.
Who is at risk for contracting East African trypanosomiasis?
East African trypanosomiasis is usually found in woodland and savannah
areas away from human habitation. Tourists, hunters, game wardens, and
other persons working or visiting game parks in East and Central Africa
are at greatest risk for illness.
Can I take a medication to prevent East African trypanosomiasis?
There is neither a vaccine nor recommended drug available to prevent
East African trypanosomiasis.
How can I prevent African trypanosomiasis and prevent other insect
bites?
- Wear protective clothing, including long-sleeved shirts and pants. The
tsetse fly can bite through thin fabrics, so clothing should be made of thick
material.
- Wear khaki or olive colored clothing. The tsetse fly is attracted
to bright colors and very dark colors.
- Use insect repellant. Though insect repellants have not proven effective
in preventing tsetse fly bites, they are effective in preventing other
insects from biting and causing illness.
- Use bed netting when sleeping.
- Inspect vehicles for tsetse flies before entering.
- Do not ride in the back of jeeps, pickup trucks or other open vehicles.
The tsetse fly is attracted to the dust that moving vehicles and wild
animals create.
- Avoid bushes. The tsetse fly is less active during the hottest period
of the day. It rests in bushes but will bite if disturbed.
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There are two types of African trypanosomiasis (also called sleeping
sickness); each named for the region of Africa in which it is found.
Individuals can become infected with West African trypanosomiasis if
they receive a bite from an infected tsetse fly, found only in Africa.West
African trypanosomiasis, also called Gambian sleeping sickness, is caused
by a parasite called Trypanosoma brucei gambiense (tri-PAN-o-SO-ma
BREW-see-eye GAM-be-ense) carried by the tsetse fly. Worldwide, approximately
40,000 new cases of both East and West African trypanosomiasis are reported
to the World Health Organization each year. However, the majority of
cases are not reported due to a lack of infrastructure and it is likely
that there are more than 100,000 new cases annually. Few cases of West
African trypanosomiasis have been reported in the United States.
How can I get West African trypanosomiasis?
An individual gets West African trypanosomiasis through the bite of
an infected tsetse fly, found only in Africa. On rare occasions,
a pregnant woman may pass the infection to her baby, or an individual
may become infected through a blood transfusion or organ transplant.
Is West African trypanosomiasis a serious illness?
Yes. West African trypanosomiasis is fatal if it is not treated.
Where can I contract West African trypanosomiasis?
West African trypanosomiasis can be contracted in parts of Western and
Central Africa. The tsetse fly lives only in Africa; areas where infection
is spread are largely determined by where the infected tsetse fly is
found.
What are the symptoms of West African trypanosomiasis?
A bite by the tsetse fly is often painful. Occasionally, within
1 to 2 weeks, the infective bite develops into a red sore, also called
a chancre (SHAN-ker). Several weeks to months later, other symptoms of
sleeping sickness occur. These include fever, rash, swelling around the
eye and hands, severe headaches, extreme fatigue, aching muscles and
joints. You may develop swollen lymph nodes on the back of your neck
called Winterbottom's sign. Weight loss occurs as the illness progresses.
Progressive confusion, personality changes, slurred speech, irritability,
loss of concentration, seizures, and difficulty in walking and talking
occurs when infection has invaded the central nervous system. These symptoms
become worse as the illness progresses. Sleeping for long periods of
the day and having insomnia at night is a common symptom. If left untreated,
infection becomes worse and death will occur within several months to
years after infection.
How soon after infection will I have symptoms of West African trypanosomiasis?
Symptoms occur within months to years after getting an infected tsetse
fly bite.
What should I do if I think I have African trypanosomiasis?
If you suspect that you may have West African trypanosomiasis, see your
health care provider who will order several tests to look for the parasite.
Common tests include blood samples and a spinal tap. Your physician may
also take a sample of fluid from swollen lymph nodes.
Is treatment available for West African trypanosomiasis?
Medication for the treatment of West African trypanosomiasis is available.
Hospitalized treatment of West African trypanosomiasis should begin as
soon as possible and is based on the infected person’s symptoms and laboratory
results. Hospitalization for treatment is necessary. Periodic follow-up
exams that include a spinal tap are required for 2 years.
Who is at risk for contracting West African trypanosomiasis?
Tsetse flies can be found in Western and Central African forests, in
areas of thick shrubbery and trees by rivers and waterholes. Risk of
infection increases with the number of times a person is bitten by the
tsetse fly. Therefore, tourists are not at great risk for contracting
West African trypanosomiasis unless they are traveling and spending long
periods of time in rural areas of Western and Central Africa.
Can I take medication to prevent West African trypanosomiasis?
There is neither a vaccine nor recommended drug available to prevent
West African trypanosomiasis.
How can I prevent African trypanosomiasis and other insect bites?
- Wear protective clothing, including long-sleeved shirts and pants. The
tsetse fly can bite through thin fabrics, so clothing should be made of thick
material.
- Wear khaki or olive colored clothing. The tsetse fly is attracted
to bright colors and very dark colors.
- Use insect repellant. Though insect repellants have not proven effective
in preventing tsetse fly bites, they are effective in preventing other
insects from biting and causing illness.
- Use bed netting when sleeping.
- Inspect vehicles for tsetse flies before entering.
- Do not ride in the back of jeeps, pickup trucks or other open vehicles.
The tsetse fly is attracted to the dust that moving vehicles and wild
animals create.
- Avoid bushes. The tsetse fly is less active during the hottest period
of the day. It rests in bushes but will bite if disturbed.
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Disease:
The West Nile virus (WNV) is spread by mosquitoes to birds and other
animals through a mosquito bite. The virus normally passes between mosquitoes
and birds. However, people may also be infected if they are bitten by
a WNV-infected mosquito.
The most likely route of WNV infection to humans is through the bite
of an infected mosquito. In addition, WNV may be spread through organ
transplantation, blood transfusion, or possibly breast milk. Transplacental
(mother-to-fetus) infection has occurred. Workers are at risk of WNV
infection if their skin is penetrated or cut while handling WNV-infected
tissues. Turkey breeder farm workers have been infected with WNV. The
mode of transmission to these farm workers is uncertain.
Most human infections cause either mild flu-like symptoms or no symptoms
at all. Mild symptoms may include fever, fatigue, headache, and muscle
or joint pain. Although rare, some people may become severely ill. Severe
symptoms may include high fever, stiff neck, disorientation, tremors,
muscle weakness, and paralysis. Severely affected persons may develop
encephalitis, meningitis, or meningoencephalitis—inflammation of the
brain, membranes of the brain or spinal cord, or both, respectively.
Severe cases of WNV may be fatal. Persons over the age of 50 are at higher
risk of severe illness.
History: From 1999 to 2001 in the United States, 149 cases of
illness and 18 deaths due to WNV were reported in humans. In 2002, more
than 4,100 cases of WNV in humans and 280 deaths due to WNV were reported
by State health departments to the Centers for Disease Control and Prevention
(CDC). In 2003, more than 9800 cases and 264 deaths were reported.
Location: WNV is commonly found in Africa, West Asia, and the
Middle East. It was first reported in the Uited States in New York State
in 1999. The geographic range of WNV has expanded annually. In 2003 it
was reported in most of the continental United States.
Occupational Risk Occupational exposure to WNV is possible. Workers
at risk of WNV exposure include those working outdoors when mosquitoes
are actively biting—farmers, foresters, landscapers, groundskeepers and
gardeners, painters, roofers, pavers, construction workers, laborers,
mechanics, and other outdoor workers. Turkey breeder farm workers have
been infected with WNV. The mode of transmission to these farm workers
is uncertain. Laboratory workers who handle WNV-infected tissue and fluids
are also at risk of WNV infection if skin penetration or laceration occurs.
Occupational groups at risk should receive training that describes and
reinforces the potential occupational hazards and risks of WNV exposure
and infection. The importance of timely reporting of all injuries and
illnesses of suspected occupational origin should be emphasized. A medical
surveillance system should be in place which includes the reporting of
symptoms consistent with WNV infection and employee absenteeism.
Who Is At Risk Of WNV Exposure?
Anyone who lives or works in an area where there are WNV-infected mosquitoes
is at risk of WNV infection. Persons over 50 years of age have the highest
risk of severe disease due to WNV infection. Even though older workers
may be at higher risk, all workers should be careful to follow the recommendations
listed below.
Which Outdoor Workers Are At Risk Of WNV Exposure?
Workers at risk of WNV exposure include those working outdoors when
mosquitoes are actively biting—farmers, foresters, landscapers, groundskeepers
and gardeners, painters, roofers, pavers, construction workers, laborers,
mechanics, and other outdoor workers. Many mosquitoes are most active
from dusk to dawn. However, some mosquitoes are active during the day.
When possible, avoid working outdoors during mosquitoes’ peak activity
times.
Is a Woman's Pregnancy at Risk if She is Infected With WNV?
There is one documented case of transplacental (mother-to-fetus) transmission
of WNV in humans. The newborn in this case was infected with WNV at birth
and had severe medical problems. It is unknown whether the WNV infection
itself caused these problems. More research is needed to understand the
possible effects of WNV on pregnancy.
Pregnant women should take precautions to reduce their risk for WNV
infection by avoiding mosquitoes, wearing protective clothing and using
repellents containing DEET according to manufacturers' directions. Pregnant
women who become ill should see their health care provider.
Where Are Mosquitoes Most Commonly Found?
Mosquitoes develop in any standing body of water that persists for more
than four days. Stagnant pools, ponds, watering troughs, irrigation ditches,
rain barrels, manure lagoons, and other stagnant bodies of water increase
mosquito populations. Weedy, bushy, and wooded work environments may
also have large mosquito populations. Workers in these environments should
protect themselves from mosquito bites.
When Are Mosquitoes Most Active?
Many mosquitoes are most active from dusk to dawn. However, some mosquitoes
are also active during the day. When possible, avoid working outdoors
during mosquitoes’ peak activity times. When this is unavoidable, use
personal protection such as protective clothing and insect repellent
to reduce the potential for exposure.
How Can I Be Protected From WNV Exposure?
Recommendations for Employers
Whether controls such as local mosquito control programs are in place,
employers should protect their workers by implementing the following
controls:
- Avoid having workers outdoors when mosquitoes are most active and biting,
most often from dusk to dawn.
- Make insect repellents available to workers.
- Recommend that outdoor workers wear long-sleeved shirts, long pants, and
socks when possible.
- If employee uniforms are provided include long-sleeved shirts
and long pants among uniform options.
- Eliminate as many sources of standing water as possible to decrease
mosquito populations. Water that persists for more than four days provides
a site for mosquitoes to develop.
- Change the water twice a week in animal drinking troughs, birdbaths,
and other water containers.
- Add an aerator to ponds and water gardens to keep the water circulating
or add fish that will eat the mosquito larvae or adults.
- Remove discarded tires from the worksite.
- Turn over, cover, or remove equipment such as tarps, buckets,
barrels, wheel barrows, and containers to avoid water accumulation.
- Place drain holes in containers that collect water and cannot
be discarded.
- Clean out rain gutters.
- Remove debris—leaves, twigs, trash—from ditches frequently.
- Fill in or drain ruts and other areas that accumulate water.
Recommendations for Workers
Outdoor workers can reduce their risk of WNV exposure by taking the
following action steps:
- Insect Repellent
- Apply insect repellent to exposed skin.
- Carefully follow label directions for repellent use.
- Do not apply pump or aerosol products directly to the face. These
products should be sprayed onto the hands and then carefully rubbed
over the face, avoiding the eyes and mouth.
- Use repellents at the lowest effective concentrations.
- The most effective insect repellents contain DEET (N,N-diethyl-m-toluamide
or N,N-diethyl-3-methylbenzamide).
- The more DEET a repellent contains the longer it will protect
against mosquito bites.
- DEET concentrations higher than 50% do not increase its length
of protection.
- Wash skin treated with insect repellent with soap and water after
returning indoors.
- Clothing
- Wear long-sleeved shirts, long pants, and socks when working
outdoors.
- Spray clothing with products containing DEET or permethrin, as
mosquitoes may penetrate thin clothing.
- Permethrin should only be used on clothing; do not apply
it directly to skin.
- Wash clothing treated with insect repellent before wearing it
again.
- Do not apply repellent to skin that is under clothing.
What Should I Do If I Have To Handle Dead Animals?
Anyone handling dead animals should wear gloves. Appropriate gloves
provide a protective barrier that prevents blood and other body fluids
from passing through them. Medical examination gloves are recommended.
Cotton, leather, and other absorbent glove materials are not protective.
If latex gloves are used they should be reduced protein, powder-free
gloves to reduce workers' exposure to allergy-causing proteins.
What Should I Do If I Develop Symptoms Of WNV?
Any worker who develops mild symptoms of WNV such as fever, fatigue,
headache, and muscle or joint pain or severe symptoms such as high fever,
stiff neck, disorientation, tremors, muscle weakness, and paralysis should
contact their health care provider immediately. If the worker is at risk
of WNV infection, a biological sample may be tested for infection. The
period from the infected bite to developing symptoms is reported to be
3 to 14 days.
Is There Treatment Available If I Am Infected With WNV?
No specific treatment exists for WNV infection. Treatment consists of
supportive care to treat the symptoms. Currently, no approved vaccine
exists to prevent WNV infection in humans.
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Plague, caused by a bacterium called Yersinia pestis, is transmitted
from rodent to rodent by infected fleas.
Plague is characterized by periodic disease outbreaks in rodent populations,
some of which have a high death rate. During these outbreaks, hungry
infected fleas that have lost their normal hosts seek other sources of
blood, thus increasing the increased risk to humans and other animals
frequenting the area.
Epidemics of plague in humans usually involve house rats and their fleas.
Rat-borne epidemics continue to occur in some developing countries, particularly
in rural areas. The last rat-borne epidemic in the United States occurred
in Los Angeles in 1924-25. Since then, all human plague cases in the
U.S. have been sporadic cases acquired from wild rodents or their fleas
or from direct contact with plague-infected animals.
Rock squirrels and their fleas are the most frequent sources of human
infection in the southwestern states. For the Pacific states, the California
ground squirrel and its fleas are the most common source. Many other
rodent species, for instance, prairie dogs, wood rats, chipmunks, and
other ground squirrels and their fleas, suffer plague outbreaks and some
of these occasionally serve as sources of human infection. Deer mice
and voles are thought to maintain the disease in animal populations but
are less important as sources of human infection. Other less frequent
sources of infection include wild rabbits, and wild carnivores that pick
up their infections from wild rodent outbreaks. Domestic cats (and sometimes
dogs) are readily infected by fleas or from eating infected wild rodents.
Cats may serve as a source of infection to persons exposed to them. Pets
may also bring plague-infected fleas into the home.
Between outbreaks, the plague bacterium is believed to circulate within
populations of certain species of rodents without causing excessive mortality.
Such groups of infected animals serve as silent, long-term reservoirs
of infection.
Geographic Distribution of Plague
In the United States during the 1980s plague cases averaged about 18
per year. Most of the cases occurred in persons under 20 years of age.
About 1 in 7 persons with plague died.
Worldwide, there are 1,000 to 2,000 cases each year. During the 1980s
epidemic plague occurred each year in Africa, Asia, or South America.
Epidemic plague is generally associated with domestic rats. Almost all
of the cases reported during the decade were rural and occurred among
people living in small towns and villages or agricultural areas rather
than in larger, more developed, towns and cities.
The following information provides a worldwide distribution pattern:
- There is no plague in Australia.
- There is no plague in Europe; the last reported cases occurred after
World War II.
- In Asia and extreme southeastern Europe, plague is distributed from
the Caucasus Mountains in Russia, through much of the Middle East,
eastward through China, and then southward to Southwest and Southeast
Asia, where it occurs in scattered, localized foci. Within these plague
foci, there are isolated human cases and occasional outbreaks. Plague
regularly occurs in Madagascar, off the southeastern coast of Africa.
- In Africa, plague foci are distributed from Uganda south on the eastern
side of the continent, and in southern Africa. Severe outbreaks have
occurred in recent years in Kenya, Tanzania, Zaire, Mozambique, and
Botswana, with smaller outbreaks in other East African countries. Plague
also has been reported in scattered foci in western and northern Africa.
- In North America, plague is found from the Pacific Coast eastward
to the western Great Plains and from British Columbia and Alberta,
Canada southward to Mexico. Most of the human cases occur in two regions;
one in northern New Mexico, northern Arizona, and southern Colorado,
another in California, southern Oregon, and far western Nevada.
- In South America, active plague foci exist in two regions; the Andean
mountain region (including parts of Bolivia, Peru, and Ecuador) and
in Brazil.
How Is Plague Transmitted?
Plague is transmitted from animal to animal and from animal to human
by the bites of infective fleas. Less frequently, the organism enters
through a break in the skin by direct contact with tissue or body fluids
of a plague-infected animal, for instance, in the process of skinning
a rabbit or other animal. Plague is also transmitted by inhaling infected
droplets expelled by coughing, by a person or animal, especially domestic
cats, with pneumonic plague. Transmission of plague from person to person
is uncommon and has not been observed in the United States since 1924
but does occur as an important factor in plague epidemics in some developing
countries.
Diagnosis
The pathognomic sign of plague is a very painful, usually swollen, and
often hot-to-the touch lymph node, called a bubo. This finding, accompanied
with fever, extreme exhaustion, and a history of possible exposure to
rodents, rodent fleas, wild rabbits, or sick or dead carnivores should
lead to suspicion of plague.
Onset of bubonic plague is usually 2 to 6 days after a person is exposed.
Initial manifestations include fever, headache, and general illness,
followed by the development of painful, swollen regional lymph nodes.
Occasionally, buboes cannot be detected for a day or so after the onset
of other symptoms. The disease progresses rapidly and the bacteria can
invade the bloodstream, producing severe illness, called plague septicemia.
Once a human is infected, a progressive and potentially fatal illness
generally results unless specific antibiotic therapy is given. Progression
leads to blood infection and, finally, to lung infection. The infection
of the lung is termed plague pneumonia, and it can be transmitted
to others through the expulsion of infective respiratory droplets by
coughing.
The incubation period of primary pneumonic plague is 1 to 3 days and
is characterized by development of an overwhelming pneumonia with high
fever, cough, bloody sputum, and chills. For plague pneumonia patients,
the death rate is over 50%.
Treatment Information
As soon as a diagnosis of suspected plague is made, the patient should
be isolated, and local and state health departments should be notified.
Confirmatory laboratory work should be initiated, including blood cultures
and examination of lymph node specimens if possible. Drug therapy should
begin as soon as possible after the laboratory specimens are taken. The
drugs of choice are streptomycin or gentamycin, but a number of other
antibiotics are also effective.
Those individuals closely associated with the patient, particularly
in cases with pneumonia, should be traced, identified, and evaluated.
Contacts of pneumonic plague patients should be placed under observation
or given preventive antibiotic therapy, depending on the degree and timing
of contact.
It is a U.S. Public Health Service requirement that all suspected plague
cases be reported to local and state health departments and the diagnosis
confirmed by the CDC. As required by the International Health Regulations,
CDC reports all U.S. plague cases to the World Health Organization.
Prevention
Plague will probably continue to exist in its many localized geographic
areas around the world, and plague outbreaks in wild rodent hosts will
continue to occur. Attempts to eliminate wild rodent plague are costly
and futile. Therefore, primary preventive measures are directed toward
reducing the threat of infection in humans in high risk areas through
three techniques -- environmental management, public health education,
and preventive drug therapy.
Environmental Management
Epidemic plague is best prevented by controlling rat populations in
both urban and rural areas. This goal has been reached in the cities,
towns, and villages of most developed countries. It has not been achieved
in either the rural or urban areas of many developing countries where
the threat of epidemic plague continues to exist. Control of plague in
such situations requires two things: 1) close surveillance for human
plague cases, and for plague in rodents, and 2) the use of an effective
insecticide to control rodent fleas when human plague cases and rodent
outbreaks occur.
Public Health Education
In regions such as the American West where plague is widespread in wild
rodents, the greatest threat is to people living, working, or playing
in areas where the infection is active. Public health education of citizens
and the medical community should include information on the following
plague prevention measures:
- Eliminating food and shelter for rodents in and around homes, work places,
and recreation areas by making buildings rodent-proof, and by removing brush,
rock piles, junk, and food sources (such as pet food), from properties.
- Surveillance for plague activity in rodent populations by public health
workers or by citizens reporting rodents found sick or dead to local health
departments.
- Use of appropriate and licensed insecticides to kill fleas during wild
animal plague outbreaks to reduce the risk to humans.
- Treatment of pets (dogs and cats) for flea control once each week.
Preventive Drug Therapy
Antibiotics may be taken in the event of exposure to the bites of wild
rodent fleas during an outbreak or to the tissues or fluids of a plague-infected
animal. Preventive therapy is also recommended in the event of close
exposure to another person or to a pet animal with suspected plague pneumonia.
For preventive drug therapy, the preferred antibiotics are the tetracyclines,
chloramphenicol, or one of the effective sulfonamides.
Vaccines
The plague vaccine is no longer commercially available in the United
States.
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Rocky Mountain spotted fever (RMSF) is the most severe tick-borne rickettsial
illness in the United States. This disease is caused by infection with
the bacterial organism Rickettsia rickettsii.
How do people get Rocky Mountain spotted fever?
The organism that causes Rocky Mountain spotted fever is transmitted
by the bite of an infected tick. The American dog tick (Dermacentor
variabilis) and Rocky Mountain wood tick (Dermacentor andersoni)
are the primary vectors of Rocky Mountain spotted fever bacteria in the
United States.
What are the symptoms of Rocky Mountain spotted fever?
Patients infected with R. rickettsii usually visit a physician
in their first week of illness, following an incubation period of about
5-10 days after a tick bite. The early clinical presentation of Rocky
Mountain spotted fever is often nonspecific and may resemble many other
infectious and non-infectious diseases. Initial symptoms may include
fever, nausea, vomiting, muscle pain, lack of appetite and severe headache. Later
signs and symptoms include rash, abdominal pain, joint pain, and diarrhea.
Three important components of the clinical presentation are fever, rash,
and a previous tick bite, although one or more of these components may
not be present when the patient is first seen for medical care. Rocky
Mountain spotted fever can be a severe illness, and the majority of patients
are hospitalized.
In the United States, where do most cases of Rocky Mountain spotted fever
occur?
Rocky Mountain spotted fever is a seasonal disease and occurs throughout
the United States during the months of April through September. Over
half of the cases occur in the south-Atlantic region of the United States
(Delaware, Maryland, Washington D.C., Virginia, West Virginia, North
Carolina, South Carolina, Georgia, and Florida). The highest incidence
rates have been found in North Carolina and Oklahoma. Although this disease
was reported most frequently in the Rocky Mountain area early after its
discovery, relatively few cases are reported from that area today.
How is Rocky Mountain spotted fever diagnosed?
A diagnosis of Rocky Mountain spotted fever is based on a combination
of clinical signs and symptoms and specialized confirmatory laboratory
tests. Other common laboratory findings suggestive of Rocky Mountain
spotted fever include thrombocytopenia, hyponatremia, and elevated liver
enzyme levels.
How is Rocky Mountain spotted fever treated?
Rocky Mountain spotted fever is best treated by using a tetracycline
antibiotic, usually doxycycline. This medication should be given in doses
of 100 mg every 12 hours for adults or 4 mg/kg body weight per
day in two divided doses for children under 45 kg (100 lbs). Patients
are treated for at least 3 days after the fever subsides and until there
is unequivocal evidence of clinical improvement. Standard duration
of treatment is 5 to 10 days.
Can a person get Rocky Mountain spotted fever more than once?
Infection with R. rickettsii is thought to provide long lasting
immunity against re-infection. However, prior illness with Rocky
Mountain spotted fever should not deter persons from practicing good
tick-preventive measures or visiting a physician if signs and symptoms
consistent with Rocky Mountain spotted fever occur, especially following
a tick bite.
How can Rocky Mountain spotted fever be prevented?
Limiting exposure to ticks reduces the likelihood of Rocky Mountain
spotted fever infection. In persons exposed to tick-infested habitats,
prompt careful inspection and removal of crawling or attached ticks is
an important method of preventing disease. It may take several hours
of attachment before organisms are transmitted from the tick to the host.
It is unreasonable to assume that a person can completely eliminate
activities that may result in tick exposure. Therefore, prevention measures
should be aimed at personal protection:
- Wear light-colored clothing to allow you to see ticks that are crawling
on your clothing.
- Tuck your pants legs into your socks so that ticks cannot crawl up
the inside of your pants legs.
- Apply repellants to discourage tick attachment. Repellents containing
permethrin can be sprayed on boots and clothing, and will last for
several days. Repellents containing DEET (n, n-diethyl-m-toluamide)
can be applied to the skin, but will last only a few hours before reapplication
is necessary. Use DEET with caution on children. Application
of large amounts of DEET on children has been associated with adverse
reactions.
- Conduct a body check upon return from potentially tick-infested areas
by searching your entire body for ticks. Use a hand-held or full-length
mirror to view all parts of your body. Remove any tick you find on
your body.
- Parents should check their children for ticks, especially in the
hair, when returning from potentially tick-infested areas. Additionally,
ticks may be carried into the household on clothing and pets. Both
should be examined carefully.
What is the best way to remove a tick?
To remove attached ticks, use the following procedure:
- Use fine-tipped tweezers or shield your fingers with a tissue, paper towel,
or rubber gloves . When possible, persons should avoid removing ticks
with bare hands.
- Grasp the tick as close to the skin surface as possible and pull upward
with steady, even pressure . Do not twist or jerk the tick; this may cause
the mouthparts to break off and remain in the skin. (If this happens,
remove mouthparts with tweezers. Consult your health care provider
if infection occurs.)
- Do not squeeze, crush, or puncture the body of the tick because its fluids
(saliva, body fluids, gut contents) may contain infectious organisms.
- After removing the tick, thoroughly disinfect the bite site and wash your
hands with soap and water.
- Save the tick for identification in case you become ill. This may help
your doctor make an accurate diagnosis. Place the tick in a plastic bag
and put it in your freezer. Write the date of the bite on a piece of paper
with a pencil and place it in the bag.
Folklore Remedies Don't Work!
Folklore remedies, such as the use of petroleum jelly or hot matches,
do little to encourage a tick to detach from skin. In fact, they may
make matters worse by irritating the tick and stimulating it to release
additional saliva or regurgitate gut contents, increasing the chances
of transmitting the pathogen. These methods of tick removal should be
avoided. A number of tick removal devices have been marketed, but
none are better than a plain set of fine tipped tweezers.
How can ticks be controlled?
Strategies to reduce vector tick densities through area-wide application
of acaricides (chemicals that will kill ticks and mites) and control
of tick habitats (e.g., leaf litter and brush) have been effective in
small-scale trials. New methods being developed include applying acaricides
to rodents by using baited tubes, boxes, and feeding stations in areas
where these pathogens are endemic. Biological control with fungi, parasitic
nematodes, and parasitic wasps may play alternate roles in integrated
tick control efforts. Community-based integrated tick management strategies
may prove to be an effective public health response to reduce the incidence
of tick-borne infections. However, limiting exposure to ticks is presently
the most effective method of prevention.
Return to top
Ehrlichiosis is the general name used to describe several bacterial diseases
that affect animals and humans. These diseases are caused by the organisms
in the genus
Ehrlichia. Worldwide, there are currently four ehrlichial
species that are known to cause disease in humans.
How do people get ehrlichiosis?
In the United States, ehrlichiae are transmitted by the bite
of an infected tick. The lone star tick (Amblyomma americanum),
the blacklegged tick (Ixodes scapularis), and the western blacklegged
tick (Ixodes pacificus) are known vectors of ehrlichiosis in
the United States. Ixodes ricinus is the primary vector in Europe.
What are the symptoms of ehrlichiosis?
The symptoms of ehrlichiosis may resemble symptoms of various
other infectious and non-infectious diseases. These clinical features
generally include fever, headache, fatigue, and muscle aches. Other signs
and symptoms may include nausea, vomiting, diarrhea, cough, joint pains,
confusion, and occasionally rash. Symptoms typically appear after an
incubation period of 5-10 days following the tick bite. It is possible
that many individuals who become infected with ehrlichiae do not become
ill or they develop only very mild symptoms.
In the United States, where do most cases of ehrlichiosis occur?
Most cases of ehrlichiosis are reported within the geographic
distribution of the vector ticks. Occasionally, cases are reported from
areas outside the distribution of the tick vector. In most instances,
these cases have involved persons who traveled to areas where the diseases
are endemic, and who had been bitten by an infected tick and developed
symptoms after returning home. Therefore, if you traveled to an ehrlichiosis-endemic
area 2 weeks prior to becoming ill, you should tell your doctor where
you traveled.
How is ehrlichiosis diagnosed?
A diagnosis of ehrlichiosis is based on a combination of clinical
signs and symptoms and confirmatory laboratory tests. Your doctor can
send your blood sample to a reference laboratory for testing. However,
the availability of the different types of laboratory tests varies considerably.
Other laboratory findings indicative of ehrlichiosis include low white
blood cell count, low platelet count, and elevated liver enzymes.
How is ehrlichiosis treated?
Ehrlichiosis is treated with a tetracycline antibiotic, usually
doxycycline.
Can a person get ehrlichiosis more than once?
Very little is known about immunity to ehrlichial infections.
Although it has been proposed that infection with ehrlichiae confers
long-term protection against reinfection, there have been occassional
reports of laboratory-confirmed reinfection. Short-term protection has
been described in animals infected with some Ehrlichia species
and this protection wanes after about 1 year. Clearly, more studies are
needed to determine the extent and duration of protection against reinfection
in humans.
How can ehrlichiosis be prevented?
Limiting exposure to ticks reduces the likelihood of infection in persons exposed
to tick-infested habitats. Prompt careful inspection of your body and
removal of crawling or attached ticks is an important method of preventing
disease. It may take 24–48 hours of attachment before microorganisms are
transmitted from the tick to you.
It is unreasonable to assume that a person can completely eliminate
activities that may result in tick exposure. Therefore, prevention measures
should be aimed at personal protection:
- Wear light-colored clothing-- this will allow you to see ticks that are
crawling on your clothing.
- Tuck your pants legs into your socks so that ticks cannot crawl up
the inside of your pants legs.
- Apply repellants to discourage tick attachment. Repellents containing
permethrin can be sprayed on boots and clothing, and will last for
several days. Repellents containing DEET (n, n-diethyl-m-toluamide)
can be applied to the skin, but will last only a few hours before reapplication
is necessary. Use DEET with caution on children because adverse reactions
have been reported.
- Conduct a body check upon return from potentially tick-infested areas
by searching your entire body for ticks. Use a hand-held or full-length
mirror to view all parts of your body. Promptly, remove any tick you
find on your body.
What is the best way to remove a tick?
To remove attached ticks, use the following procedure:
- Use fine-tipped tweezers or shield your fingers with a tissue, paper towel,
or rubber gloves.
- Grasp the tick as close to the skin surface as possible and pull upward
with steady, even pressure. Do not twist or jerk the tick; this may cause
the mouthparts to break off and remain in the skin. (If this happens,
remove mouthparts with tweezers. Consult your healthcare provider
if infection occurs.)
- Do not squeeze, crush, or puncture the body of the tick because its fluids
(saliva, hemolymph, gut contents) may contain infectious organisms.
- Do not handle the tick with bare hands because infectious agents may
enter through mucous membranes or breaks in the skin. This precaution is
particularly directed to individuals who remove ticks from domestic animals
with unprotected fingers. Children, the elderly, and immunocompromised persons
may be at greater risk of infection and should avoid this procedure.
- After removing the tick, thoroughly disinfect the bite site and wash your
hands with soap and water.
- You may wish to save the tick for identification in case you become ill
within 2 to 3 weeks. Your doctor can use the information to assist in making
an accurate diagnosis. Place the tick in a plastic bag and put it in your
freezer. Write the date of the bite on on a piece of paper with a pencil
and place it in the bag.
Note: Folklore remedies such as petroleum jelly or hot
matches do little to encourage a tick to detach from skin. In fact,
they may make matters worse by irritating the tick and stimulating
it to release additional saliva, increasing the chances of transmitting
the pathogen. These methods of tick removal should be avoided. In addition,
a number of tick removal devices have been marketed, but none are better
than a plain set of fine tipped tweezers.
How can ticks be controlled?
Strategies to reduce vector tick densities through area-wide application of
acaricides (chemicals that will kill ticks and mites) and control of tick
habitats (e.g., leaf litter and brush) have been effective in small-scale
trials. New methods under development include applying acaricides to rodents
and deer by using baited tubes, boxes, and deer feeding stations in areas
where these pathogens are endemic. Biological control with fungi, parasitic
nematodes, and parasitic wasps may play important roles in integrated tick
control efforts. Community-based integrated tick management strategies
may prove to be an effective public health response to reduce the incidence
of tick-borne infections. However, limiting exposure to ticks is presently
the most effective method of prevention.
Return to top
Babesiosis is caused by hemoprotozoan parasites of the genus Babesia. While
more than 100 species have been reported, only a few have been identified
as causing human infections. Babesia microti and Babesia
divergens have been identified in most human cases, but variants
(considered different species) have been recently identified. Little
is known about the occurrence of Babesia species in malaria-endemic
areas where Babesia can easily be misdiagnosed as Plasmodium.
Life Cycle:
The Babesia microti life cycle involves two hosts, which includes
a rodent, primarily the white-footed mouse, Peromyscus leucopus. During
a blood meal, a Babesia-infected tick introduces sporozoites into
the mouse host (1). Sporozoites enter erythrocytes and undergo
asexual reproduction (budding) (2). In the blood, some parasites
differentiate into male and female gametes although these cannot be distinguished
at the light microscope level (3). The definitive host is a tick,
in this case the deer tick, Ixodes dammini (I. scapularis). Once
ingested by an appropriate tick (4), gametes unite and undergo a sporogonic
cycle resulting in sporozoites (5). Transovarial transmission (also
known as vertical, or hereditary, transmission) has been documented for
“large” Babesia spp. but not for the “small” babesiae, such as B.
microti (A).
Note: Deer are the hosts upon which the adult ticks feed and
are indirectly part of the Babesia cycle as they influence the
tick population. When deer populations increase, the tick population
also increases, thus heightening the potential for transmission.
Geographic Distribution:
Worldwide, but little is known about the prevalence of Babesia in malaria-endemic
countries, where misidentification as Plasmodium probably occurs. In
Europe, most reported cases are due to B. divergens and occur in splenectomized
patients. In the United States, B. microti is the agent most frequently
identified (Northeast and Midwest), and can occur in non-splenectomized individuals. Two
variants, arguably different species, have been reported in the U.S. states
of Washington and California (WA1- type and related parasites) and Missouri
(MO1).
Clinical Features:
Most infections are probably asymptomatic, as indicated by serologic surveys. Manifestations
of disease include fever, chills, sweating, myalgias, fatigue, hepatosplenomegaly,
and hemolytic anemia. Symptoms typically occur after an incubation period
of 1 to 4 weeks, and can last several weeks. The disease is more severe
in patients who are immunosuppressed, splenectomized, and/or elderly. Infections
caused by
B. divergens tend to be more severe (frequently fatal if not
appropriately treated) than those due to
B. microti, where clinical recovery
usually occurs.
Laboratory Diagnosis:
Diagnosis can be made by microscopic examination of thick and thin blood smears
stained with Giemsa. Repeated smears may be needed.
Diagnostic findings
- Microscopy
- Antibody detection by indirect fluorescent antibody (IFA) test is
a complementary diagnostic test.
- Molecular methods
Isolation of the organisms by inoculation of patient blood into hamsters
or gerbils may also assist in diagnosis. Animals inoculated with
infective blood typically develop parasitemia within 1 to 4 weeks.
Treatment:
Treatment with clindamycin* plus quinine or atovaquone* plus azithromycin*
are the options. The Medical Letter notes that exchange transfusion
has been used in severely ill patients with high parasitemias.
* These drugs are approved by the FDA, but considered investigational
for this purpose.
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Perspectives
Arthropod-borne viruses,
i.e., arboviruses, are viruses that are maintained in nature through
biological transmission between susceptible vertebrate hosts by blood
feeding arthropods (mosquitoes, psychodids, ceratopogonids, and ticks).
Vertebrate infection occurs when the infected arthropod takes a blood
meal. The term 'arbovirus' has no taxonomic significance. Arboviruses
that cause human encephalitis are members of three virus families: the Togaviridae (genus
Alphavirus), Flaviviridae, and Bunyaviridae.
All arboviral encephalitides are zoonotic, being maintained in complex
life cycles involving a nonhuman primary vertebrate host and a primary
arthropod vector. These cycles usually remain undetected until humans
encroach on a natural focus, or the virus escapes this focus via a secondary
vector or vertebrate host as the result of some ecologic change. Humans
and domestic animals can develop clinical illness but usually are "dead-end" hosts
because they do not produce significant viremia, and do not contribute
to the transmission cycle. Many arboviruses that cause encephalitis have
a variety of different vertebrate hosts and some are transmitted by more
than one vector. Maintenance of the viruses in nature may be facilitated
by vertical transmission (e.g., the virus is transmitted from the female
through the eggs to the offspring).
Arboviral encephalitides have a global distribution, but there are four
main virus agents of encephalitis in the United States: eastern equine
encephalitis (EEE), western equine encephalitis (WEE), St. Louis encephalitis
(SLE) and La Crosse (LAC) encephalitis, all of which are transmitted
by mosquitoes. Another virus, Powassan, is a minor cause of encephalitis
in the northern United States, and is transmitted by ticks. A new Powassan-like
virus has recently been isolated from deer ticks. Its relatedness to
Powassan virus and its ability to cause disease has not been well documented.
Most cases of arboviral encephalitis occur from June through September,
when arthropods are most active. In milder (i.e., warmer) parts of the
country, where arthropods are active late into the year, cases can occur
into the winter months.
The majority of human infections are asymptomatic or may result in a
nonspecific flu-like syndrome. Onset may be insidious or sudden with
fever, headache, myalgias, malaise and occasionally prostration. Infection
may, however, lead to encephalitis, with a fatal outcome or permanent
neurologic sequelae. Fortunately, only a small proportion of infected
persons progress to frank encephalitis.
Experimental studies have shown that invasion of the central nervous
system (CNS), generally follows initial virus replication in various
peripheral sites and a period of viremia. Viral transfer from the blood
to the CNS through the olfactory tract has been suggested. Because the
arboviral encephalitides are viral diseases, antibiotics are not effective
for treatment and no effective antiviral drugs have yet been discovered.
Treatment is supportive, attempting to deal with problems such as swelling
of the brain, loss of the automatic breathing activity of the brain and
other treatable complications like bacterial pneumonia.
There are no commercially available human vaccines for these U.S. diseases.
There is a Japanese encephalitis vaccine available in the U.S. A tick-borne
encephalitis vaccine is available in Europe. An equine vaccine is available
for EEE, WEE and Venezuelan equine encephalitis (VEE). Arboviral encephalitis
can be prevented in two major ways: personal protective measures and
public health measures to reduce the population of infected mosquitoes.
Personal measures include reducing time outdoors particularly in early
evening hours, wearing long pants and long sleeved shirts and applying
mosquito repellent to exposed skin areas. Public health measures often
require spraying of insecticides to kill juvenile (larvae) and adult
mosquitoes.
Selection of mosquito control methods depends on what needs to be achieved;
but, in most emergency situations, the preferred method to achieve maximum
results over a wide area is aerial spraying. In many states aerial spraying
may be available in certain locations as a means to control nuisance
mosquitoes. Such resources can be redirected to areas of virus activity.
When aerial spraying is not routinely used, such services are usually
contracted for a given time period.
Financing of aerial spraying costs during large outbreaks is usually
provided by state emergency contingency funds. Federal funding of emergency
spraying is rare and almost always requires a federal disaster declaration.
Such disaster declarations usually occur when the vector-borne disease
has the potential to infect large numbers of people, when a large population
is at risk and when the area requiring treatment is extensive. Special
large planes maintained by the United States Air Force can be called
upon to deliver the insecticide(s) chosen for such emergencies. Federal
disaster declarations have relied heavily on risk assessment by the CDC.
Laboratory diagnosis of human arboviral encephalitis has changed greatly
over the last few years. In the past, identification of antibody relied
on four tests: hemagglutination-inhibition, complement fixation, plaque
reduction neutralization test, and the indirect fluorescent antibody
(IFA) test. Positive identification using these immunoglobulin M (IgM)
- and IgG-based assays requires a four-fold increase in titer between
acute and convalescent serum samples. With the advent of solid-phase
antibody-binding assays, such as enzyme-linked immunosorbent assay (ELISA),
the diagnostic algorithm for identification of viral activity has changed.
Rapid serologic assays such as IgM-capture ELISA (MAC-ELISA) and IgG
ELISA may now be employed soon after infection. Early in infection, IgM
antibody is more specific, while later in infection, IgG antibody is
more reactive. Inclusion of monoclonal antibodies (MAbs) with defined
virus specificities in these solid phase assays has allowed for a level
of standardization that was not previously possible.
Virus isolation and identification have also been useful in defining
viral agents in serum, cerebrospinal fluid and mosquito vectors. While
virus isolation still depends upon growth of an unknown virus in cell
culture or neonatal mice, virus identification has also been greatly
facilitated by the availability of virus-specific MAbs for use in IFA
assays. Similarly, MAbs with avidities sufficiently high to allow for
specific binding to virus antigens in a complex protein mixture (e.g.,
mosquito pool suspensions) have enhanced our ability to rapidly identify
virus agents in situ. While polymerase chain reaction (PCR)
has been developed to identify a number of viral agents, such tests have
not yet been validated for routine rapid identification in the clinical
setting.
Mosquito-borne encephalitis offers a rare opportunity in public health
to detect the risk of a disease before it occurs and to intervene to
reduce that risk substantially. The surveillance required to detect risk
is being increasingly refined by the potential utilization of these
