The incubation period differs depending on the pathogen. After 7 to 40 days, the first uncharacteristic symptoms appear, such as fever, headache, aching limbs, and a general “feeling of being sick.” These unspecific symptoms are often misinterpreted as a flu-like infection or gastroenteritis. The time lag between a tropical visit and the onset of malaria may favor misdiagnosis in our latitudes.
Forms of malaria
The intensity of the symptoms depends on the degree of immunity of the infected person. Persons infected multiple times acquire what is known as semi-immunity, which prevents particularly severe disease. Non-immune individuals are most at risk – especially young children and the elderly.
Plasmodium ovale and vivax cause malaria tertiana. In this form, a regular rhythm of fever attacks sets in after a few days, which then occur every 48 hours. In this case, chills occur in the late afternoon, and the fever rises rapidly to levels around 40°C. After three to four hours, the fever drops back to normal, accompanied by profuse sweating.
Malaria quartana is the rarest form of malaria and is caused by Plasmodium malariae. The fever attacks occur in a rhythm of 72 hours. Both forms usually heal within 8 weeks even without treatment.
Malaria tropica is the most dangerous form of malaria; in non-immune patients it is fatal in 20% of cases if left untreated. Unlike the other types of malaria, there is no rhythmic alternating fever, which makes diagnosis difficult. In more than half of those affected, there is a drop in blood platelets, which can lead to clotting disorders; there is also enlargement of the spleen or liver and diarrhea. If the nervous system is affected, seizures and clouding of consciousness occur. Complications also include acute renal failure and circulatory collapse.
The prognosis of malaria tertiana and quartana is good; this also applies to malaria tropica treated early. The mortality from malaria in Germany is only 2%. However, malarial pathogens have the ability to form dormant forms that lead to relapses after two or five years (Plasmodium vivax and ovale) or even after 40 years (Plasmodium malariae)
Diagnosis of malaria
The most important examination for suspected malaria is microscopic examination of the blood. This usually involves examining the so-called “thick drop,” an air-dried drop of blood, or sometimes a thin blood smear for pathogens. An experienced physician can even distinguish the different malaria pathogens under the microscope on the basis of their appearance. The number of pathogens in the blood drop reflects the severity of the disease. The detection of pathogens in the blood is proof of the presence of malaria.
On the other hand, a negative test result does not exclude malaria – possibly the number of parasites in the blood is still too low and only when the test is repeated can the pathogens be seen. In addition, there are malaria rapid tests. They can be used by any traveler on site for self-diagnosis. Unfortunately, they sometimes give false test results because they do not detect every pathogen and their implementation is not very simple.