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Incubation Period | Uncomplicated
Malaria | Severe Malaria | Malaria
Relapses | Other
Manifestations of Malaria
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
or severe (complicated) . In general, malaria is
a curable disease if diagnosed and treated promptly and correctly.
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Patient with symptoms of malaria seen at the Moronacocha Health Center in the outskirts of Iquitos, on the Peruvian Amazon. A blood smear confirmed that he had malaria. (Image contributed by Dr. Jaime Chang, USAID/Peru)
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Incubation
Period
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 P.
malariae.
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
bite.)
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.
Uncomplicated
Malaria
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 children)
- and
finally a sweating stage (sweats, return to normal temperature, tiredness)
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 following symptoms:
-
Fever
- Chills
- Sweats
- Headaches
- 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
- Perspiration
- Weakness
- Enlarged
spleen.
In P. falciparum malaria, additional findings may include:
-
Mild jaundice
- Enlargement
of the liver
- Increased
respiratory rate.
Diagnosis
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").
Severe
Malaria
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 include:
- Cerebral
malaria, with abnormal behavior, impairment of consciousness, seizures,
coma, or other neurologic abnormalities
- Severe
anemia due to hemolysis (destruction of the red blood cells)
- 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 with quinine.
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.
Malaria
Relapses
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 P. ovale 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.
Other
Manifestations of Malaria
- Neurologic
defects may occasionally persist following cerebral malaria, especially
in children. Such defects include troubles with movements (ataxia),
palsies, speech difficulties, deafness, and blindness.
- 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 treated.
- Malaria
during pregnancy (especially P. falciparum) may cause
severe disease in the mother, and may lead to premature delivery or
delivery of a low-birth-weight 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. malariae.
- 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).
See
also: Diagnosis
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Page last modified : September 21, 2006
Content source: Division of Parasitic Diseases
National Center for Zoonotic, Vector-Borne, and Enteric Diseases (ZVED)
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