Updated: May 27
Malaria is a disease carried by mosquitoes. Malaria in human is cause by the following parasites: Plasmodium falciparum, Plasmodium malariae, Plasmodium ovale, Plasmodium vivax and Plasmodium knowlesi. Amongst these P.falciparum is the most common and can be the most aggressive. The host, a female mosquito will transmit a sporozoite (infective form of malaria) into a host (eg human). The sporozoite travels through the blood vessels to the liver. Once in the hepatocytes it reproduces asexually producing thousands of merozoites, this takes 8-30 days in which the patient is usually asymptomatic, dormant period. Until the amount of merozoites causes the hepatocytes to burst, allowing them to escape into the blood stream. These parasites can escape the liver undetected as they coat themselves in the hepatocyte membrane and therefore aren’t detected by the immune system at this point. These can then infect new red blood cells and initiate a series of asexual multiplication cycles, when around 20 new infective merozoites are produced the cells burst open and the infective cycle begins again. This rupturing of red blood cells correlates with waves of fever that occurs before the merozoites infect more red blood cells. P.falciparum parasite to stop destruction of infected red blood cells by the spleen, produces an adhesive protein on the surface of the blood cells so they stick to the walls of small blood vessels stopping them travelling around the circulatory system and through the spleen, this can cause blockage of the microvasculature.
There are a few genetic conditions that cause malarial immunity, such as sickle cell anaemia. This is a condition that affects the chains in the haemoglobin molecule (protein that carries oxygen within the red blood cells) causing the blood cell to form and abnormal sickle shape. Once infected these change shape and therefore are removed from the circulation system before the parasite gets to the liver.
Initially malaria can present as flu like symptoms, which usually occur 8-25 days after infection. The classic symptom of malaria is paroxysm, cyclical occurrence of sudden coldness followed by shivering and then fever and sweating. This occurs every day to every 3 days, the length of time between attacks can indicate which specific parasite is causing the infection. For example P.falciparum infection can cause recurrent fever ever 36-48hrs. Cerebral malaria can be caused as sequestered parasite can cross the blood brain barrier, resulting in encephalopathy.
Due to the nonspecific nature of presentation a high degree of suspicion, usually based on patient history, is needed for diagnosis in non-endemic areas. Malaria is usually confirmed by blood film or antigen based rapid diagnostic tests.
Treatment is through antimalarial medication; the medication used is based on the severity and type of infection and supportive care.