There are 4 types of malaria that infect humans:
  1. Plasmodium vivax, abbreviated as P.v. - 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. However, it can still cause significant illness. In addition, some strains of P. vivax have the ability to incubate in the liver for 6 – 10 months or longer, thereby delaying the appearance of initial symptoms until long after the actual exposure and
    infection occurred. In these cases, malaria may initially be overlooked as a diagnosis, resulting in delayed treatment. In other instances, the parasites can remain dormant in the liver and reactivate (“relapse”) months to years later. In addition, P. vivax is becoming increasingly resistant to anti-malarial drugs in some areas. Plasmodium vivax accounts for approximately 70-80 million cases annually (or 20%
    of the global burden of 350-500 million total cases of all human malarias). While P. falciparum predominates in warmer regions close to the equator (where transmission is intense because it occurs year-round), P. vivax predominates in more temperate regions. Since P. vivax can tolerate cooler temperatures, it is more geographically widespread than P. falciparum, although transmission is usually low because it is season-dependent.
  2. Plasmodium malariae, abbreviated as P.m - 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. This is a quartan malaria since its cyclic paroxysms occur every 72 hours. Plasmodium malariae ranks third in prevalence, but has a widespread distribution. It is not usually life-threatening. Plasmodium malariae is also known to cause malaria in dogs.
  3. Plasmodium ovale, abbreviated as P.o. - . is the rarest of the four species, and is mostly confined to tropical West Africa including countries such as Ghana, Liberia, and Nigeria. In highly endemic areas, the patient may become infected with one, two or even more species of the malarial parasite. In India, 4-8% of infections are due to mixed infection. P. ovale, can relapse; some parasites can rest in the liver for several months up to 4 years after a person is bitten by an infected mosquito. When these parasites come out of hibernation and begin invading red blood cells, the person will become sick.
  4. Plasmodium falciparum, abbreviated as P.f. - is wide spread and found in tropical and subtropical areas of Central and South America, Africa, and S.E. Asia. P F Malaria results in the most severe infections and is responsible for nearly 90% of malaria-related deaths in sub Saharan Africa. P. falciparum malaria in Africa is at least tenfold that in similar malaria endemic areas in India and Vanuatu. Reasons for this are unclear but might include better access to prompt treatment. Studies done in 2002 suggest that 2.2 billion people were at risk from the P. falciparum parasite, leading to an estimated 515 million clinical episodes of malaria. Seventy percent of these events took place in the African region and 25% in the South East Asia region.