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.

Malaria Symptoms

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QUESTION

How does the virus cause the symptoms?

ANSWER

Malaria is actually not caused by a virus—it is caused by a microscopic single-celled parasite called Plasmodium. Several different species cause malaria in humans, the most common of which are P. vivax and P. falciparum.

To describe the process in a very oversimplified way, the malaria parasites cause disease by infecting red blood cells, multiplying inside them, then simultaneously bursting out again, destroying then red blood cell in the process. The sudden destruction of lots of red blood cells, plus the debris and waste products left behind by the malaria parasites, stimulate a rapid immune reaction, which itself causes the rapid spike of fever. The characteristic cycles of fever sometimes seen with malaria sufferers occurs because the malaria parasites synchronise their emergence from the red blood cells. The destruction of red blood cells, together with concurrent physiological changes associated with immune response and inflammation, can also lead to decreased haemoglobin levels and anaemia.

More severe clinical symptoms are often seen with P. falciparum malaria infection, particularly if not promptly diagnosed and treated. This is because the P. falciparum parasite infects a red blood cell, it changes the surface of the cell and makes it “sticky”; when the red blood cell then tries to pass through the small blood vessels that lead into the body’s organs, it becomes stuck. This process is known as “sequestration”. If enough red blood cells become sequestered in the organs, it can reduce blood flow to the organ, resulting in oxygen deprivation. When this happens in the blood vessels in the brain, the patient may experience impaired consciousness, confusion and even coma and death—this manifestation is known as “cerebral malaria.”

Malaria in Mosquitoes

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QUESTION

Why can’t mosquitoes become sick of malaria? What do they have in their system that prevent them from becoming sick yet they transmit the disease to humans?

ANSWER

First of all, mosquitoes do get “sick” when infected with malaria, though not in the same way as humans. This is due to the major differences between human and mosquito physiology and also differences in the life stage of the malaria parasite between the different hosts.

Humans get sick from malaria because the malaria parasite, when inside the human host, sequentially infects red blood cells, multiplying inside them and then destroying them. This process of destruction and the resultant debris in the blood results fever and other symptoms (some of which are exacerbated by the body’s immune response).

Mosquitoes are insects, and do not have blood in the same way as humans. Instead, in the mosquito, the malaria parasites differentiate into male and female life stages (called gametocytes) which fuse into the mosquitoes gut. After further reproduction, they eventually produce sporozoites that rupture out of the mosquito gut wall and migrate to the salivary glands, where they can be infected into a new human host.  

Mosquitoes also have a very different immune system to humans, and so the concept of “sick” is not the same for them as for humans. However, there is a lot of evidence that infection with malaria results in reduced reproductive success for the mosquito, as well as lower survival. This could be due to protective responses on the part of the mosquito, but also could be mediated by the malaria parasite, by diverted resources towards its own development that could have been used for mosquito reproduction or survival.

Malaria and Renal Failure

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QUESTION

Explain how malaria can cause renal failure?

ANSWER

There are several mechanisms by which malaria can contribute to renal failure, which vary due to the type of malaria. The exact way in which these various effects combine to cause acute renal failure is not known.

The most common type of malaria to cause renal failure is Plasmodium falciparum, generally the most severe and deadly form of the disease. P. falciparum infected red blood cells are known to sequester in tiny red blood cells deep within major organs, including the kidney; it is thought that reduced blood flow and resulting lack of oxygen may contribute to renal failure. Exaggerated immune response to infection may also be a major contributor to renal failure—this is most likely to cause of renal complications seen in other forms of malaria infection, such as Plasmodium malariae infection.

Moreover, acute renal failure is more usually observed in non-immune adults to malaria (such as those who did not grow up in malaria areas) or older children, again suggesting an involvement of the immune response. Finally, dehydration, associated with a lack of sufficient fluid intake during illness with malaria, may compound these other issues, and contribute to renal failure. Perhaps counterintuitively, administration of intravenous fluids may actually worsen the system, due to the body’s shock-like response to the sudden increase in fluids.