Protozoal diseases are parasitic infectious diseases caused by single-celled Protozoa. These diseases are quite widespread, especially in the warmer climates. Some require intermediate hosts, such as mosquitoes, for transmission. Most of the diseases are associated with poor socioeconomic conditions.
A variety of protozoal diseases commonly affect humans. African forms of trypanosomiasis are caused by the parasitic flagellates Trypanosoma brucei gambiense and Trypanosoma brucei rhodesiense, which invade the central nervous system, leading to behavioral changes, coma, and ultimately, if left untreated, death. The organisms are transmitted to humans by the bite of tsetse flies (genus Glossina). Chagas' disease, or South American trypanosomiasis, is caused by Trypanosoma cruzi and occurs primarily in young children. The intermediate host is a blood-sucking insect (triatome), which bites the victim and contaminates the wound with infected feces.
Leishmaniasis is a group of diseases caused by several different species of Leishmania, which are related to trypanosomes and are transmitted by sandflies. In one form of the disease, the parasites are found in the skin, causing sores that are slow to heal.
Another form causes disfigurement by destroying the nasopharyngeal (nose-pharynx) area of the face. In a third form the parasites enter the deeper organs and cause serious infection.
Giardiasis is an infection of the human intestinal tract caused by the flagellated protozoan Giardia lamblia. It is transmitted directly from person to person by fecal contamination, especially of water. Symptoms include diarrhea and abdominal pain. Amebiasis, also known as amoebic dysentery, is caused by an amoeba, Entamoeba histolytica. It is also transmitted by fecal contamination of food and water.
Malaria is a protozoan infection characterized by chills, fever, sweating, and anemia, sometimes with chronic relapses. Malarial parasites Plasmodium vivax, P. falciparum, P. malariae, and P. ovale are transmitted to humans by the bite of the anopheles mosquito.