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Infection with malaria parasites may result in a wide variety of
symptoms, ranging from absent or very mild symptoms to severe
disease and even death. Malaria disease can be categorized as uncomplicated
(complicated) . In general, malaria is a curable disease if
diagnosed and treated promptly and correctly.
Following the infective bite by the Anopheles
mosquito, a period of time (the "incubation period") goes by
before the first symptoms appear. The incubation period in most
cases varies from 7 to 30 days. The shorter periods are observed
most frequently with P. falciparum and the longer ones with
Antimalarial drugs taken for prophylaxis by travelers can delay
the appearance of malaria symptoms by weeks or months, long after
the traveler has left the malaria-endemic area. (This can happen
particularly with P. vivax and P. ovale, both of
which can produce dormant liver stage parasites; the liver stages
may reactivate and cause disease months after the infective mosquito
Such long delays between exposure and development of symptoms can
result in misdiagnosis or delayed diagnosis because of reduced
clinical suspicion by the health-care provider. Returned travelers
should always remind their health-care providers of any travel in
malaria-risk areas during the past 12 months.
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The classical (but rarely observed) malaria attack lasts 6-10
hours. It consists of:
- a cold stage (sensation of cold, shivering)
- a hot stage (fever, headaches, vomiting; seizures in young
- and finally a sweating stage (sweats, return to normal
Classically (but infrequently observed) the attacks occur every
second day with the "tertian" parasites (P. falciparum,
P. vivax, and P. ovale) and every third day with
the "quartan" parasite (P. malariae).
More commonly, the patient presents with a combination of the
- Nausea and vomiting
- Body aches
- General malaise.
In countries where cases of malaria are infrequent, these
symptoms may be attributed to influenza, a cold, or other common
infections, especially if malaria is not suspected. Conversely, in
countries where malaria is frequent, residents often recognize the
symptoms as malaria and treat themselves without seeking diagnostic
confirmation ("presumptive treatment").
Physical findings may include:
- Elevated temperature
- Enlarged spleen.
In P. falciparum malaria, additional findings may
- Mild jaundice
- Enlargement of the liver
- Increased respiratory rate.
of malaria depends on the demonstration of parasites on a blood
smear examined under a microscope. In P. falciparum
malaria, additional laboratory findings may include mild anemia,
mild decrease in blood platelets (thrombocytopenia), elevation of
bilirubin, elevation of aminotransferases, albuminuria, and the
presence of abnormal bodies in the urine (urinary "casts").
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Severe malaria occurs when P. falciparum infections are
complicated by serious organ failures or abnormalities in the
patient's blood or metabolism. The manifestations of severe malaria
- Cerebral malaria, with abnormal behavior, impairment of
consciousness, seizures, coma, or other neurologic abnormalities
- Severe anemia due to hemolysis (destruction of the red blood
- Hemoglobinuria (hemoglobin in the urine) due to hemolysis
- Pulmonary edema (fluid buildup in the lungs) or acute
respiratory distress syndrome (ARDS), which may occur even after
the parasite counts have decreased in response to treatment
- Abnormalities in blood coagulation and thrombocytopenia
(decrease in blood platelets)
- Cardiovascular collapse and shock
Other manifestations that should raise concern are:
- Acute kidney failure
- Hyperparasitemia, where more than 5% of the red blood cells
are infected by malaria parasites
- Metabolic acidosis (excessive acidity in the blood and tissue
fluids), often in association with hypoglycemia
- Hypoglycemia (low blood glucose). Hypoglycaemia may also occur
in pregnant women with uncomplicated malaria, or after treatment
Severe malaria occurs most often in persons who have no immunity
to malaria or whose immunity has decreased. These include all
residents of areas with low or no malaria transmission, and young
children and pregnant women in areas with high transmission.
In all areas, severe malaria is a medical emergency and should be
treated urgently and aggressively.
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In P. vivax and P. ovale infections, patients
having recovered from the first episode of illness may suffer
several additional attacks ("relapses") after months or even years
without symptoms. Relapses occur because P. vivax and have
dormant liver stage parasites ("hypnozoites")
that may reactivate. Treatment to reduce the chance of such relapses
is available and should follow treatment of the first attack.
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- Neurologic defects may occasionally persist following cerebral
malaria, especially in children. Such defects include troubles
with movements (ataxia), palsies, speech difficulties, deafness,
- Recurrent infections with P. falciparum may result in
severe anemia. This occurs especially in young children in
tropical Africa with frequent infections that are inadequately
during pregnancy (especially P. falciparum) may cause
severe disease in the mother, and may lead to premature delivery
or delivery of a low-birth-weigh baby.
- On rare occasions, P. vivax malaria can cause rupture
of the spleen or acute respiratory distress syndrome (ARDS).
- Nephrotic syndrome (a chronic, severe kidney disease) can
result from chronic or repeated infections with P.
- Hyperreactive malarial splenomegaly (also called "tropical
splenomegaly syndrome") occurs infrequently and is attributed to
an abnormal immune response to repeated malarial infections. The
disease is marked by a very enlarged spleen and liver, abnormal
immunologic findings, anemia, and a susceptibility to other
infections (such as skin or respiratory infections).
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