Plasmodium falciparum: The Causative Agent of Malaria :: Essays Papers

Plasmodium falciparum: The Causative Agent of Malaria Introduction The protozoan Plasmodium falciparum is responsible for causing 500 million cases of malaria per year as well as 100-200 million deaths per year worldwide (Kuby, p438). The majority of these deaths occur in sub-Saharan Africa, especially among malnourished children. Malaria is endemic in 92 countries, where 40% of the world’s population is at risk of the disease (WHO). Documentation of malaria occurs as far back as 4000BC, with mentions of the disease on clay tablets. The name of the disease originates from the late 1800’s and is derived from ‘mal aria,’ meaning bad air. There are four members of Plasmodium that cause malaria along with P. falciparum, with P. vivax, P. ovale, P. malariae (Schaechter, p450). P. falciparum is considered the most important as it is by far the most deadly species. The primary vector of P. falciparum is the female anopheline mosquito, which uses humans as a host for blood meals. The male anopheline feeds only on plant juices, and is not a competent vector for the disease. Humans compromise the only suitable reservoir in the enzootic cycle of the protozoa (Schaechter, p450). Both the P. falciparum and Anopheles gambiae genomic sequences have been recently published (Gardner et al. Holt et al. 2002), thus giving rise to invaluable tools in the development of new and much needed anti-malarial drugs and vaccines, as well as new targets in mosquito control. Encounter and Entry The female Anopheles interacts with the human host by piercing the host’s epithelium and releasing Plasmodium falciparum from its salivary glands into the human bloodstream while obtaining a blood meal. The form of P. falciparum injected into the human host is the sporozoite stage in the pathogen's life cycle (Kuby, Schaechter). As humans compromise the only competent reservoir for P. falciparum, the female Anopheles must have acquired the protozoan via blood meal from another infected human 9 to 17 days prior to being able to infect a new human host. Spread and Multiplication The sporozoites enter the human host and then travel via the bloodstream to the liver, where they enter liver cells and mature into schizonts after a period of 8-14 days. Sporozoites are covered with a 45-kDa protein called circumsporozoite which mediates adhesion to hepatocytes (Kuby, p439). Schizonts are released into the bloodstream as merozoites after a week, and are capable of entering and lysing erythrocytes and thus causing disease.