6 May 2009
A Protozoan Parasite
Malaria parasites have been around since the beginning of time, and fossils of mosquitoes that are up to five-thousand years old show that malaria's vector has existed for just as long. The parasites causing malaria are highly specific, with man as the only host and mosquitoes as the only vector. Every year, 300,000,000 people are affected by malaria, and while less than one percent of these people die, there are still an estimated 1,500,000 deaths per year. While Malaria was one of the first infectious diseases to be treated successfully with a drug, scientists are still looking for a cure or at least a vaccination today (Cann, 1996). Though many people are aware that malaria is a disease, they are unaware that it is life threatening, killing over a million people each year, and is a very elusive target for antimalarial drugs (Treatment of Malaria, 1996). Being a very specific disease, malaria is caused by only four protozoan parasites: Plasmodium falciparum (this is the only parasite that causes malignant malaria, and it causes the most severe symptoms and results in the most fatalities), Plasmodium vivax (this causes benign malaria with less severe symptoms than P. falciparum. P. vivax can stay in the liver for up to three years and can lead to a relapse), Plasmodium ovale (this causes benign malaria and can stay in the blood and liver for many years without causing symptoms), and Plasmodium malariae (this causes benign malaria and is relatively rare). Not only is the disease specific, but the parasites are too, with only sixty of three hundred eighty species of female Anopheles mosquitoes as vectors. With the exception of Plasmodia malariae, which may affect other primates, all parasites of malaria have only one host, Homo sapiens. Because some mosquitoes contain substances toxic to Plasmodium in their cells, not all species of mosquitoes are vectors of Plasmodium. Although very specific, malaria still causes disruption of over three hundred million people worldwide each year (Cann, 1996). The life cycle of the parasite causing malaria exists between two organisms, humans and the Anopheles mosquito. When a female mosquito bites a human, she injects anticoagulant saliva, which keeps the human bleeding and ensures an even flowing meal for her. When the vector injects her saliva into the human, it also injects ten percent of her sporozoite load. Sporozoites are cells that develop in the mosquito's salivary glands and leave the mosquito during a blood meal. Once in the bloodstream, the Plasmodium travels to the liver where they continue to grow and multiply by asexual reproduction. This can happen so quickly that they clog blood vessels and rupture blood cells. Once the liver cells burst, they release the parasites back into the bloodstream in another form called merozoites, where they then enter red blood cells. Here, the Plasmodium feed on hemoglobin, which is the iron-containing oxygen-transport metalloproteinase in the red blood cells. In humans, the protein makes up about ninety-seven percent of the red blood cell’s dry content, and around thirty-five percent of the total content (including water). Hemoglobin transports oxygen from the lungs to the rest of the body where it releases the oxygen for cell use. After feeding on hemoglobin, the Plasmodium reproduces again by asexual reproduction. Thereafter, the red blood cells burst and release the parasites. Some of the parasites released from red blood cells may be able to replicate by sexual reproduction. When a mosquito has bitten the host again, infected blood inters the mosquito. Here, sexual forms of the parasite develop in the stomach of the Anopheles mosquito completing the parasites life cycle (Herman, 1996). People infected with malaria have several flu-like symptoms including fever, chills, headaches, weakness, and an enlarged...
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