Malaria

Malaria is a life- threatening disease caused by Plasmodium parasites transmitted by mosquitoes. There are five parasite species that can infect humans: 

• Plasmodium falciparum
• Plasmodium vivax
• Plasmodium ovale
• Plasmodium malariae
• Plasmodium knowlesi

Plasmodium falciparum is the deadliest amongst the species and the most prevalent on the African continent. Plasmodium vivax is the dominant malaria parasite in most countries outside of sub-Saharan Africa. Plasmodium malariae is uncommon but is found in most malaria endemic areas. Plasmodium ovale is relatively unusual outside of sub-Saharan Africa and comprises less than one percent of isolates. Plasmodium knowlesi is very rare and has been identified in southeast Asia. It's natural reservoir are macaques. It was initially discovered in Malaysia, but human cases have been reported from several neighbouring countries.

Transmission

Vector

Infectious female Anopheles mosquitoes who only bite in the evening and night. They often go unnoticed because they are small and almost make no sound.

Life cycle

After a bite by an infectious mosquito, people are inoculated with sporozoites. These will enter the hepatocytes within minutes where they start to multiply quickly. After an incubation period of minimally one week, the malaria parasites will appear in the blood, where they will infect the red blood cells and start to multiply (trophozoites). After one (P. knowlesi), two (P. falciparum, P. vivax, P. ovale) or three (P. malariae) days, the reds blood cells start to burst. The released parasites will infect other red blood cells. This cycle will be repeated multiple times. Blood stage parasites are responsible for the clinical manifestations of the disease. After a few cycles, gametocytes (male microgametocytes and female macrogametocytes) will appear. If ingested by an Anopheles mosquito during a blood meal, the parasites can continue its lifecycle in the Anopheles mosquito.

Incubation period

Seven days to months and sometimes more than a year.

Symptoms

Travellers should be aware that malaria is a life-threatening disease that can be fatal within days of onset. They must be informed that medical advice must be sought immediately in the event of fever or other flulike symptoms, until at least 3 months after their return. Malaria can be treated effectively, but without treatment this disease can quickly cause complications and become fatal. The disease appears very similar to influenza - particularly during the first few days - with fever, headache, muscle pain and sometimes diarrhea or a cough.
Plasmodium falciparum is the most common species and results in the most severe symptoms. Plasmodium falciparum-infected erythrocytes adhere to the vascular endothelium of blood vessel walls and do not freely circulate in the blood. When this sequestration of infected erythrocytes occurs in the vessels of the brain, it is believed to be a factor in causing the severe disease syndrome known as cerebral malaria, which is associated with high mortality. 
The other three species (P. vivax, P. ovale, P. malariae) can give significant symptoms but are normally not deadly. If mortality occurs, it is usually due to the rupture of the spleen but in rare cases severe malaria with organ failure can develop. Late-onset P. vivax and P. ovale malaria may occur despite effective prophylaxis because these parasites cause relapses that cannot be prevented with medicines that are currently recommended for chemoprophylaxis.
Plasmodium knowlesi is primarily seen by macaques in forested areas of South East Asia, but can cause severe malaria (similar to P. Falciparum) in humans too.
Still every year a few people die in Belgium due to malaria. These are mainly people who didn’t adhere to preventive malaria medication or where there was a delay in seeking medical attention, establishing a diagnoses or involving expert care. 
The diagnosis of malaria can be established with a simple blood analysis (EDTA- tube) by a reliable laboratory within a few hours.