General features
Clinical manifestations of malaria may greatly vary depending on a number of factors summarized in the table below.

Table1. Factors affecting clinical manifestation
Factors Comments
Species & strain
Geographic origin
Size of inoculum
P.falciparum - "malignant" malaria
Endemic zones (Africa, South-East Asia etc.)
Immune status
Nutritional status
Children and elderly are more susceptible
Immune-naive individuals have most severe infection Pregnant women are more susceptible to severe infection Very effective if used correctly
Transmission mode
Bloodborne(transfusion etc.)
Classical - all phases present
No hepatic phase (bloodborne, transplacental, niddlestick, transplant etc.)

The incubation period for malaria may vary from days to months and even years. However, on average, it is 9-14 dys for P. falciparum, 12-17 days to 6-12 months for P. vivax, 16-18 days or more for P. ovale, and 18-40 days or more for P.malariae. Some patients can get prodrome 2-3 days before the febrile paroxysm, which is the best known clinical feature of malaria. The prodrome may include malaise, fever, fatigue, muscle pain, nausea, anorexia etc. Because of these non-specific symptoms, malaria may be easily mistaken for influenza or gastrointestinal infection.

Cardinal clinical symptoms
Back pain
"Flu-like" symptoms
Occasional symptoms

Whenever we are talking about the clinical presentation of malaria, it is very important to remember that:

  1. symptoms may greatly vary or even be absent
  2. malaria is a great "actor" that can mimic many diseases
The following information must be always requested whenever a potential case of malaria is evaluated (Table2).

Table2. Key information on suspected malaria case
» Age » Blood transmission?
» Sex » Past history of malaria?
» Pregnancy status » Malaria prophylaxis?
» Travel history » Drug allergies
» Clinical status » Lab results
» Exposure to mosquito  

Below, we will try to summarize some general clinical features.
Malaria febrile paroxysm starts with the cold stage accompanied by rigors. Usually shivering stops after 15-60 min, followed by the hot stage. Massive peripheral vasodilatation makes patient extremely hot. Temperature rises up to 40-41 0C. Headache, palpitations, tachycardia, vomiting etc. are usually present. The skin is dry, flushed and burning. The splenomegaly may be detected. Lasting on average 2-6 hours, the hot stage changes to the sweating stage, which is accompanied by profuse, drenching sweat. The fever goes down during the next 2-4 hrs, symptoms subside and exhausted patient sleeps. The typical malaria attack usually lasts 8-12 hrs, starting between midnight and midday.
Periodicity of the malarial paroxysm depends upon the length of asexual erythrocytic stage and also on how synchronized is the merozoite release by erythrocytes. The attack is classically strikes at day 1 and 3 (48 hrs) for so called tertian malarias (P. vivax, P. ovale and P. falciparum), and at day 1 and 4 (72 hrs) for P. malariae. However, it is important to know that irregular, persistent daily fever is more usual for P. falciparum.
General manifestations of malaria (malaria clinical syndromes) may vary in the ptresentation and severity (Fig1).

Fig1. Clinical syndromes of malaria (adopted from J. MacArthur, CDC)

P. vivax malaria (benign, uncomplicated malaria)
The incubation period may extend to months (5-10% of cases) and years (e.g. northern latitudes of Russia).
The primary attack may include headache, pain in the back, general malaise, dizziness, vague abdominal pain, anorexia, nausea, and vomiting. Fever is usually irregular for the first 2-4 days, but soon may become intermittent (morning - evening). Jaundice and tender hepatosplenomegaly may be detected. Anemia may vary between mild and severe. Thrombocytopenia is common. Overall, complications are low with extremely low mortality. However, it is important to remember that splenic rupture, although rare, may happen. Splenic rupture is a very serious and specific complication of P.vivax, which carries high mortality.
Relapse (reactivation of hypnozoite forms of parasite in liver) is very common in untreated or inadequately treated patients (up to 60%). This necessitates the terminal treatment of hypnozoite forms along with blood stages.

P. falciparum malaria (pernicious, complicated)
The incubation period may be prolonged by immunity, chemoprophylaxis, and partial treatment. The signs and symptoms as well as physical findings are non-specific. One third of patients are afebrile when first examined. However, the classical febrile paroxysm followed by an afebrile asymptomatic interval is very unusual with P.falciparum infection.
This form of malaria is a principle killer of almost 2 million people world wide annually.
P.falciparum is a potentially fatal disease for non-immune individuals. On the other hand people in the endemic areas usually mount some degree of protective immunity against life threatening complications of P. falciparum. In non-immunes the disease can progress very rapidly to severe malaria causing high mortality (sometimes despite treatment). Patients may sometimes die within 24 hrs of their first symptom. Specifically for P.falciparum, parasites can become sequestered in tissue and therefore not detected in peripheral blood smear. This would imply that patient may develop severe malaria even with low parasitemia or after parasites clear peripherally. Prompt use of appropriate anti-malaria drugs along with careful monitoring of clinical and parasitological improvement is essential in management of falciparum malaria.


© 2002. Malaria in Armenia.
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