QUESTION

Why malaria so dangerous?

ANSWER

Malaria can be dangerous for a number of different reasons, some of which relate to each other. First of all, there are five different types of malaria that infect humans, and each varies in terms of its severity and potential for severe consequences. Even within these types, the severity of the disease caused (termed “virulence” by scientists and doctors), can even vary by strain or geography. Generally, the most dangerous form of malaria is caused by Plasmodium falciparum. One reason why this species of malaria is so dangerous is that is replicates very quickly in the blood. This means that infection levels can build up very quickly; if a person infected with P. falciparum does not get diagnosed and treated within a few days of feeling sick, the infection can progress to a point where the disease becomes very severe. This rapid accumulation of infection is also observed with P. knowlesi, a much rarer form of malaria found in south-east Asia. The parasites of P. knowlesi have a 24-hour reproductive cycle in the blood, the quickest for any type of malaria that infects humans. However, P. falciparum also has other characteristics which make it even more dangerous, and which do not occur with P. knowlesi. For example, when P. falciparum infects red blood cells, it causes their shape to change, and makes them “sticky”. This stickiness causes the red blood cells to become lodged in the blood vessels leading in to major organs, in a process known as sequestration. Sequestration creates blockages of these blood vessels, reducing blood flow and resulting in oxygen deprivation. When this process occurs in the blood vessels in the brain, the outcome is known as cerebral malaria, characterised by impaired consciousness, coma and even death. It is this pathology which is associated with most cases of severe malaria, and causes the most number of deaths.

However, if treated promptly with the correct drugs, even P. falciparum malaria is usually easily controlled. Therefore, one of the additional reasons why malaria is so dangerous is that in many places, and particularly sub-Saharan Africa, people do not have access to medication, or not the right types of medication. Many strains of P. falciparum have become resistant to chloroquine, once the first line treatment for malaria, and so this drugs is now ineffective in many cases. Instead, the World Health Organisation recommends now that artemisinin-based combination therapies (ACTs, such as Coartem) should be given as first-line treatment against all uncomplicated malaria, to prevent additional resistance from developing.