Malaria Effects on the Body

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QUESTION

What are the effects of malaria on the body?

ANSWER

Malaria has a number of effects on the body. The parasite passes from the blood (where it enters via the bite of an infected mosquito) into the liver, where it reproduces and changes form. After a period of 1-4 weeks (usually – it can be longer) in the liver, the malaria parasite re-enters the blood and begins to infect red blood cells, undoing more reproduction inside the cells and then, in synchrony, bursting out once the cycle is complete. This process of reproduction and destroying red blood cells results in a build-up of toxins and debris in the blood; the resultant immune reaction produces side effects which are the common observable symptoms of malaria, such as fever, chills, nausea and aches.

One particular type of malaria, Plasmodium falciparum, is also able to modify the surface of red blood cells it infects. It causes these cells to become “sticky”, so they lodge in the small blood vessels leading up to major organs. This build-up is called sequestration, and results in reduced blood flow and oxygen deprivation in the organs. When sequestration occurs in the blood vessels in the brain, the patient may experience impaired consciousness, psychological disruption, coma and even death – this manifestation is called “cerebral malaria”.

If diagnosed and treated promptly, the malaria parasites in the blood can usually be killed rapidly and the patient will soon enjoy a complete recovery. With two forms of malaria, P. vivax and P. ovale, the parasite can remain dormant in the liver for months or even years, resulting in relapse of disease at a later date. To prevent this from occurring, patients with these types of malaria can sometimes take primaquine, a drug which kills the liver stages of the malaria parasite as well.

Thalassaemia and Malaria

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QUESTION

How can Thalassaemia effect Malaria infection?

ANSWER

Thalassaemia is the name given to a group of inherited genetic blood disorders, which result in reduced or no synthesis of one of the globin protein chains that combine to make haemaglobin. Haemaglobin is used to carry oxygen throughout the body and to its organs.

Thalassaemia can result in anaemia; in some cases, this is severe enough to require periodic blood transfusions. There has long been a hypothesis that thalassaemia might have persisted due to conveying protection against malaria infection; this was suggested due to the geographical distributions of populations with high prevalence of the alleles (gene types) that cause thalassaemia and areas with high levels of malaria transmission. However, scientifically confirming this association has proved challenging.

A recent study from Kenya demonstrated that children with either one copy of the thalassaemia allele or two copies appeared to have a reduced incidence of severe malaria, fewer deaths from malaria and were hospitalized less frequently for malaria. However, they were just as likely as non-thalassaemic children to have mild or sub-clinical malaria, and the same levels of parasitaemia (numbers of parasites in the blood).

A contrasting study from Vanuatu observed higher incidences of severe malaria in children with thalassaemia, though one potential confounding factor in comparing these studies is that the Vanuatu study looked at both P. falciparum and P. vivax, whereas the Kenya study only looked at P. falciparum malaria.

The difference is significant: one of the proposed mechanisms by which thalassaemia protects against malaria is by preventing modification of the surface of red blood cells, which causes the red blood cells to become “sticky” and sequester within the blood vessels that feed major organs, eventually restricting blood flow and causing major complications. This sequestration is only observed to occur during infection with P. falciparum, and so thalassaemia might not be as protective against other forms of malaria. More empirical research from the field is needed to understand the mechanisms relating malaria infection with thalassaemia more fully.