Human Health and Implications
Malaria is found primarily in the human circulatory system. The circulatory system, then, is especially relevant to malaria as it is one of the three locations the parasite occurs and reproduces in humans. Each of us has roughly 60,000 miles of blood vessels, all tied together in a web of different sized tubes, that transport blood in a constantly flowing loop. There are three main types of blood vessels; arteries that carry blood away from the heart, veins that carry blood back to the heart and capillaries, the smallest vessels, which carry blood in close proximity to cells within the body tissues.
When an infected mosquito bites a person, the parasite is transmitted to the bloodstream, which is the starting point of a new malarial infection. This stage is the sporozoites, which migrate to the liver. In the liver they reproduce and are eventually re-released into the bloodstream as merozoites where they infect red blood cells. Reproducing again in red blood cells, they eventually rupture the cell causing a reaction in the blood from the toxic byproducts of cellular lysis. Lysis is the destruction of the cellular membrane precipitating death of the cell. Antibodies respond to this infection causing the symptoms of malaria.
Though some types of malaria are more resistant, cases that are diagnosed and treated early can be cured. Some statistics measure the lethality of this disease at 50% of all the people that have ever lived. Some 50 billion people have died from malaria over the course of our species’ existence.10
With such a long interrelationship it is not surprising that humans have evolved some defense mechanisms against this plague. Sickle cell anemia is a recessive inherited disease that affects hemoglobin production and leaves cells a quarter-moon shaped sickle. Those afflicted with the condition suffer from a variety of conditions due to reduced oxygen carrying ability and difficulty of the oddly shaped blood cells’ movement through the circulatory system. Lifespan is generally decades shorter, especially without ongoing medical treatment. So what is the connection with malaria? A heterozygous individual, that is one that has two different alleles for the sickle cell trait, has a slightly different hemoglobin molecules, not enough to affect their health, but when infected by Plasmodium their blood cells rupture before the parasite is able to reproduce. This effectively provides them with immunity to malaria and a survival advantage.
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