Malaria is an infectious disease caused by protozoan parasites which are transmitted by female Anopheles mosquitoes only. There are more than 3.500 known species of mosquitoes worldwide. Out of that, only around 30 to 40 species can transmit the infection. Anopheles mosquitoes are crepuscular (active from dusk till dawn) or nocturnal (active at night) and are either indoor- or outdoor-resters (after the blood meal). The protozoan parasites belong to the genus Plasmodium and are widespread in tropical and subtropical regions. The four species that produce human disease are P. falciparum, P. ovale, P. vivax, P. malariae.
Plasmodium falciparum is known to be the most lethal form of the plasmodium parasite, with most malaria infections and deaths being due to falciparum.
Plasmodium ovale is the rarest of the four species, and is mostly confined to tropical West Africa including countries such as Ghana, Liberia, and Nigeria.
Plasmodium vivax has the widest geographic distribution throughout the world and causes much debilitating disease. It is usually found in Central and South America, India and S.E. Asia. In India, about 60% of the infections are due to P. vivax. Malaria caused by Plasmodium vivax is rarely fatal.
Plasmodium malariae has restricted distribution and is said to be responsible for less than 1% of infections in India. It is found in tropical and subtropical areas of Central and South America, Africa, and S.E. Asia.
The species Plasmodium vivax and Plasmodium ovale can persist in the liver in a dormant stage and cause relapses by invading the bloodstream weeks, or even years later.
Once multiplying within red blood cells, the fist symptoms of the disease are fever, chills, nausea and light headedness whereas in severe cases anemia and coma are visible. The incubation period is 7 to 15 days for Plasmodium falciparum, 12 to 18 days for Plasmodium vivax and ovale and 18 to 40 days for Plasmodium malariae.