Malaria parasites have been with us since the dawn of time. They probably originated in Africa (along with mankind) and fossils of mosquitoes up to 30 million years old show that the vector for malaria was present well before the earliest history. The Plasmodium parasites are highly specific, with man as the only vertebrate host and Anopheles mosquitoes as the vectors. This specificity of the parasites also points towards a long and adaptive relationship with our species.
At present, at least 300,000,000 people are affected by malaria globally, and there are between 1,000,000 and 1,500,000 malaria deaths per year . Malaria is generally endemic in the tropics, with extensions into the subtropics. Malaria in travellers arriving by air is now an important cause of death in non-malarious areas, and this is not helped by the common ignorance or indifference of travellers to prophylaxis. Distribution varies greatly from country to country, and within the counties themselves, as the flight range of the vector from a suitable habitat is fortunately limited to a maximum of 2 miles, not taking account of prevailing wind etc. The map indicates current distribution of indigenous malaria according to WHO:
In 1990, 80% of cases were in Africa, with the remainder clustered in nine countries: India, Brazil, Afghanistan, Sri-Lanka, Thailand, Indonesia, Vietnam, Cambodia and China. Current data for Africa is unavailable. The disease is endemic in 91 countries currently, with small pockets of transmission in a further eight. Plasmodium falciparum is the predominant species, with 120,000,000 new cases and up to 1,000,000 deaths per year globally. It is the Plasmodium falciparum species which has given rise to the formidable drug resistant strains emerging in Asia. In 1989, WHO declared malaria control to be a global priority due to the worsening situation, and in 1993, the World Health Assembly urged member states and WHO to increase control efforts.
As well as control measures, such as spraying with DDT, coating marshes with paraffin (to block Anopheles mosquito larvae spiracles), draining stagnant water, and the widespread use of nets, research into the biology and microbiology of malaria enables a methodical search for better vaccines and a possible cure in the fight against malaria.
The Plasmodium genus of protozoal parasites (mainly P.falciparum, P.vivax, P.ovale, and P.malariae) have a life cycle which is split between a vertebrate host and an insect vector. The Plasmodium species, with the exception of P.malariae (which may affect the higher primates) are exclusively parasites of man. The mosquito is always the vector, and is always an Anopheline mosquito, although, out of the 380 species of Anopheline mosquito, only 60 can transmit malaria. Only female mosquitos are involved as the males do not feed on blood. The basic life cycle of the parasite is shown below:
The spozozoites from the mosquito salivary gland are injected into the human as the mosquito must inject anticoagulant saliva to ensure an even flowing meal. Once in the human bloodstream, the sporozoites arrive in the liver and penetrate hepatocytes, where they remain for 9-16 days, multiplying within the cells. Next they return to the blood and penetrate red blood cells, in which they produce either merozoites, which reinfect the liver, or micro- and macrogametocytes, which have no further activity within the human host. Another mosquito arriving to feed on the blood may suck up these gametocytes into its gut, where exflagellation of microgametocytes occurs, and the macrogametocytes are fertilized. The resulting ookinete penetrates the wall of a cell in the midgut, where it develops into an oocyst. Sporogeny within the oocyst produce many sporozoites and, when the oocyst ruptures, the sporozoites migrate to the salivary gland, for injection into another host.
The Walter and Eliza Hall Institute(WEHI) is involved in the microbiological analysis of the malaria species. The DNA mapping of the 14 chromosomes and the discovery of genes, antigens, and their functionality provide vital clues to help us find a means to combat the spread of malaria. A species' genome is all the genetic material in the species' chromosomes. A genome project is the collecting and collating of such information, and a genome database is the storage of the information with searching for sequences, clones, isolates, papers, etc., facilities.
The malaria genome project at the Walter and Eliza Hall Institute
(WEHI) has been going since 1983, and the developement of a Malaria
database (MalDB) using the stucture of the A. C. elegans database(ACeDB) has been underway since
Information concerning the Malaria genome project can be found from
the Malaria Database home page.
Also, from the home page, can be found links to other databases such
Links to a Malaria discusion group, other malaria and parasitology sites, and other miscellaneos information can can be found from the home page.