List of Human Blood Parasites

There are many parasites that can invade the human body. Some of them are blood borne, meaning they are found in the blood rather than in tissues. These parasites can be transmitted from one person to another through exposure to infected blood (e.g. through blood transfusion or the sharing of a needle). Some are transferred by insect carriers, such as mosquitos. Blood donors are screened for possible parasite exposure, and donations are screened for some blood borne parasites, but some do still get through.

Babesia microti

This parasite is responsible for Babesiosis, which is caused by infected red blood cells being spread by ticks. Tickborne transmission occurs most commonly in the US during particular seasons, usually during warm months, in parts of the Midwest and Northeast. The ticks that transmit this parasite are typically in the nymph stage, which occurs early in development. Diagnosis requires microscopic examination of a blood sample. People infected by this parasite often don’t have symptoms but when they do those symptoms are easily treated.


There are multiple species of this parasite that are responsible for this infection, which often presents as skin ulcers. It can be spread through the bite of certain kinds of sandflies. Aside from being more easily diagnosed, due to visible sores, this parasite is different from the others because it infects white blood cells instead of red. This means that microscopic diagnosis usually requires a sample of bone marrow, which contains the infected white blood cells. Treatment varies depending on the individual species with which the person has been infected.

Plasmodium falciparum

Most cases of malaria result from infection by this species of the Plasmodium parasite. It is spread to both humans and animals through mosquito bites. Early diagnosis is critical, as this disease can spread rapidly through a community, and can usually be based on symptoms, travel history, and physical exam. However, blood test confirmation is required. Some species can be difficult to treat, due to drug resistance, but malaria is rarely fatal.

Toxoplasma gondii

This parasite is responsible for Toxoplasmosis, one of the leading causes of US deaths due to foodborne illness. Although most of the 30 million people infected are protected by their immune systems, those for whom that is compromised can suffer severe consequences, including death. Diagnosis can be accomplished through blood test, and rarely requires treatment.

Trypanosoma brucei

African Trypanosomiasis, or sleeping sickness, occurs due to infection by this parasite. The tsetse fly, which is only found in rural Africa, is responsible for its transmission. This infection is rarely found in the United States, but approximately 10,000 new cases are reported every year in sub-Saharan Africa. Many more cases are believed to go both undiagnosed and unreported. Sleeping sickness must be diagnosed through lab tests because the symptoms are not specific enough for a clinical diagnosis. If treated, sleeping sickness can be cured but, if left untreated, it is fatal.

Trypanosoma cruzi

Spread by insects to both humans and animals, infection with this parasite leads to Chagas disease, which is named after the physician who discovered it in 1909. It is found mainly in rural areas of Latin America, where widespread poverty occurs. Parasitic infection must be acute before this parasite can be detected in a blood smear, so it’s generally diagnosed clinically based on symptoms and the likelihood of exposure. Although treatment is recommended for people who have a suppressed immune system, others don’t usually require it.