Blood-Borne Parasites in Humans

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Blood-borne parasites are found worldwide and usually spend a certain part of their life-cycle in the blood of the host. Blood-borne parasites may be transmitted in two ways according to the Centers for Disease Control and Prevention: parasites may be spread through infected blood transfer during needle exchange or blood transfusion, or they may also be transmitted by a vector such as an infected insect that bites a host and injects the parasites into the bloodstream. Although rare in the United States, blood-borne parasites are responsible for thousands of deaths annually in developing countries.

Types of Parasites

The most well-known blood-borne parasite is Plasmodium, which causes malaria. Malaria can be fatal and is characterized by high fevers, chills and flu-like symptoms. Trypanosoma cruzi is a parasite that causes Chagas disease. The parasite enters the blood and stays for a prolonged period of time, causing severe heart and digestive problems. Babesia microti parasites cause the condition babesiosis. The parasites destroy red blood cells, causing severe anemia and other blood disorders, blood clotting, organ failure and death. Leishmania parasites cause the disease leishmaniasis. The parasites infect the skin causing ulcers and may also infect the spleen, liver and bone marrow, according to the National Institutes of Health.

Modes of Transmission

According to the Centers for Disease Control and Prevention, parasites are transmitted through different sources called vectors. Malaria is transmitted by the bite of the Anopheles mosquito. The parasites grow and develop in the stomach of the mosquito and are injected into humans where they multiply in red blood cells. Chagas disease is spread through the infected feces of a Triotomine (kissing bug) insect. The insect eats blood and drops feces on the host allowing the parasites to enter the skin. Babesia is spread through the bite of an infected tick. The parasites are present in the saliva of the tick and are transmitted when the tick bites the host. Leishmania is spread through the bite of an infected sand fly. The parasites live in the stomach of the fly and are spread when the fly bites its host for a blood meal.

Diagnosis and Testing

Diagnosis and testing for malaria involves patient travel history as well as blood tests used to observe the malaria parasites. PCR, or DNA, testing is also available and can be done quickly. Chagas disease is diagnosed by observing a blood smear on a slide for presence of the parasite. Babesia is diagnosed by also observing a blood smear on a slide. Serologic, or antibody, or PCR testing is also used as a confirmation. Leishmania parasites from skin ulcers are observed under the microscope, though antibody and PCR testing is also available, according to the Centers for Disease Control and Prevention.


Malaria is treated with chloroquine, mefloquine, quinine and other drugs depending on resistance and type of organism. Chagas disease is treated with benznidazole and nifurtimox while heart and digestive problems are treated depending on symptoms. Babesia is treated with atovaquone with azithromycin or clindamycin with quinine. Patients with severe illness may need additional treatment according to illness. Leishmania is treated with sodium stibogluconate, megulmine antimonate, fluconazole and amphotericin B. Plastic surgery may be needed if disfiguring sores are visible, according to the New York Times health guide.


According to the Centers for Disease Control and Prevention, malaria can be prevented by avoiding endemic areas and using insect repellent, mosquito nets, long-sleeve clothes and malaria medication. Chagas disease can be prevented by eliminating the triotomine insect with insecticides. Proper treatment of infected individuals will also help stop the spread. Babesia can be prevented by using pest control sprays to kill ticks. Careful observation should be done after a walk or run in wooded areas to avoid bringing ticks into the home. Leishmania is treated by preventing sand fly bites. Avoid being out from dusk to dawn. The use of insect repellents and long clothes will also prevent bites.