Blood parasites in humans are responsible for malaraia, African sleeping sickness, babesiosis, and schistosomiasis. Blood parasites are different from other types of human parasites, because they directly infest the bloodstream, rather than the organs or digestive tract. Most of these parasites are found in tropical and subtropical regions. They are most likely to affect people living in or traveling to less developed regions. There are believed to be four main types of blood parasites that can infest and sicken humans.
Parasites of the Plasmodium species are generally responsible for the tropical disease known as malaria. There are four species of Plasmodium parasites considered capable of infesting humans, P. falciparum, P. vivax, P. ovale, and P. malariae. These parasites typically begin their life cycle within the body of an Anopheles mosquito. When the mosquito feeds on a human, it can infect that human with Plasmodium sporozoites, which generally grow inside the body and cause the symptoms of malaria. The disease can spread when uninfected Anopheles mosquitoes feed on humans infested with Plasmodium blood parasites.
African sleeping sickness is another type of disease generally attributed to human blood parasites. There are believed to be two types of African sleeping sickness, West African sleeping sickness and East African sleeping sickness. Two subspecies of the parasite Trypanosoma brucei are considered responsible for these diseases. T. brucei rhodesiense most often causes East African sleeping sickness, while T. brucei gambiense is considered responsible for most cases of West African sleeping sickness. These disease are typically spread by the bite of the tsetse fly.
Blood parasites of the Schistosoma species can cause the disease known as schistosomiasis. Three species of Schistosoma parasites, S. haematobium, S. japonicum, and S. mansoni, are believed capable of causing this disease in humans. They are generally able to infect the human host via skin contact alone, and may be most commonly transmitted through direct contact with contaminated water. They are most often found in Asia, the Middle East, Africa, and South America.
The disease known as babesiosis generally occurs after infestation with blood parasites of the Babesia species. B. microti and B. divergens are considered the only Babesia species capable of infecting humans. Babesiosis typically spreads to humans via tick bites.
Unlike malaria, babesiosis cannot normally spread from an infected human to an uninfected tick who has bitten that person. Babesiosis may be the most geographically widespread of the illnesses caused by human blood parasites. It can be found in Africa, Asia, Europe, Australia, and North America.