Malaria is caused in humans by five species of single-cell, eukaryotic Plasmodium parasites (mainly Plasmodium falciparum and Plasmodium vivax) that are transmitted by the bite of Anopheles mosquitoes.

In humans, malaria parasites grow and multiply first in the liver cells and then exponentially in the red blood cells. It is the blood stage of the parasite lifecycle that causes the symptoms of malaria in humans.

Malaria is usually classified as asymptomatic, uncomplicated or severe.

Asymptomatic malaria can be caused by all Plasmodium species; the patient has circulating parasites but no symptoms.

Uncomplicated malaria can be caused by all Plasmodium species. Symptoms generally occur 7-10 days after the initial mosquito bite. Symptoms are non-specific and can include fever, moderate to severe shaking chills, profuse sweating, headache, nausea, vomiting, diarrhoea and anaemia, with no clinical or laboratory findings of severe organ dysfunction.

Severe malaria is usually caused by infection with Plasmodium falciparum, though less frequently can also be caused by Plasmodium vivax or Plasmodium knowlesi. Complications include severe anaemia and end-organ damage, including coma (cerebral malaria), pulmonary complications (for example, oedema and hyperpnoeic syndrome) and hypoglycaemia or acute kidney injury. Severe malaria is often associated with hyperparasitaemia and is associated with increased mortality. 

→Learn more about the epidemiological definition of severe malaria on the Severe Malaria Observatory.

→Learn more about Plasmodium vivax malaria on the Vivax information hub. 

→Go to an online course on malaria by Harvard University. 

Source: Philips et al, “Malaria,” Nature Reviews Disease Primers, 2017.