What is malaria?
Malaria is a serious tropical disease affecting people in Africa, South and Central America, parts of the Middle East and Asia (Fig 1). It is transmitted by the bite of a female anopheles mosquito that has been infected with a malaria parasite. The mosquito usually bites between sunset and sunrise, but in Asia and Latin America the peak of transmission is around midnight (Kassianos, 2001). Humans contract malaria when sporozoites present in the saliva of an infected mosquito are injected into their bloodstream by a mosquito biting to take a blood meal. The sporozoites infect the liver cells (hepatocytes) and develop in them over the next six to 11 days, becoming schizonts. When they are mature, the schizonts burst and release merozoites into the circulation, which multiply by asexual fission, some of which then invade the red blood cells. Each release coincides with fever. After entering the red blood cells, the merozoites feed on the contents of the cells and some develop into male and female gametocytes. The life cycle is completed when a mosquito takes a blood meal from an infected person who has both male and female gametocytes in the bloodstream, which initiates sexual reproduction of the parasites in the mosquito’s gut (Steffan and DuPont, 2001) (Fig 2).
The cause of malaria
Malaria is caused by parasitic plasmodium species that are carried by the female of an anopheles mosquito and introduced into the bloodstream of humans by an infected mosquito:
- Plasmodium falciparum;
- Plasmodium malariae;
- Plasmodium ovale;
- Plasmodium vivax.
Plasmodium Falciparum (P.falciparum)
Plasmodium falciparum is the most common strain of malaria and also the deadliest. Found in Asia, Africa, the Middle East, the Pacific and South America, it is responsible for 60% of malarial infections and 90% of malarial deaths, worldwide. The incubation of P. falciparum is 6 – 21 days. The fever cycle is usually 48 hours although it maybe sometimes difficult to pick these spikes. Although limited immunity develops with repeated infection of the same P. falciparum strain; it rarely develops in adults. Unlike the other strains of malaria if adequately treated it should not recur. If prompt treatment is not given, the progression of the disease to a more severe form can be as rapid as a few hours. It is one of the few diseases where an individual can be relatively well in the morning, have a high fever by afternoon and be dead by evening. As the parasite multiplies the smaller blood vessels tend to get blocked, significantly reducing the blood flow to the major organs. This can happen in the vessels supplying the brain (cerebral malaria), the liver (malarial hepatitis) or the kidney causing renal failure. Over time P. falciparum have developed wide resistance to anti-malarial medication. Newer drugs or drug combinations maybe suggested in these cases. Plasmodium Vivax (P. vivax)
Found in Asia and Central America, with small outbreaks in West and Eastern Africa, categorized as a benign form of the disease, P. vivax is in fact the second most deadly strain of malaria. P. vivax parasites have a preference for younger red blood cells. For patients who suffer traumatic rupture of the spleen, it can be fatal, as also in cases of severe anaemia, especially among malnourished and debilitated patients. The incubation period is 12 – 17 days; with fever cycles of 48 hours. Recurrence of infection is common with P. vivax. In some cases of the disease, immunity to some strains have been noted; probably because the mosquitoes live close to their larvae development site, recurrent victims of the disease continually receive infections of the same strain of P. vivax allowing the body to build up some immunity to that one strain. This is a limited immunity; if another strain of P. vivax infects the individual, the immunity is ineffective. In some areas, resistance to anti-malarial medication has been described....
Please join StudyMode to read the full document