Babesiosis is the only tick-borne disease in the United States that is caused by a protozoan (Babesia microti). Other well-known protozoal illnesses--none of which are transmitted by ticks--include malaria, toxoplasmosis, giardiasis, and trichomoniasis.
Rodents are the principal natural reservoir for Babesia, and deer ticks (Ixodidae) are the primary vectors of transmission. Ixodes ticks also transmit Lyme disease and some forms of ehrlichiosis; thus, it is possible for one tick to transmit more than one disease with a single bite.
Larval ticks become infected with the Babesia protozoan while feeding on infected rodents. Tick larvae then transform into nymphs and adult ticks that are capable of transmitting the infection to other animals, including humans.
Once Babesia organisms enter a host, they invade red blood cells (much like malaria organisms do), where they mature and replicate. Infected red blood cells (RBCs) eventually rupture and release the protozoa into the bloodstream, where they infect other RBCs.
Babesiosis occurs mainly on the Nantucket Islands and surrounding mainland areas of Massachusetts, in eastern Long Island and Shelter Island in New York, along coastal Connecticut, and in New Jersey, Wisconsin, Georgia and California. Certain regions of Europe have also reported infections, although different species of Babesia and ticks appear to be involved.
Since Babesia is an intracellular parasite of RBCs, this disease can be transmitted by blood transfusion.
Signs and Symptoms of Babesiosis
An unknown number of individuals infected with Babesia—particularly those under the age of 40—remain asymptomatic for months to years. Indeed, the disease may never become clinically apparent. (The Merck Manual, 18th Edition 2006:1571-72)
When symptoms do occur, they usually begin within one to two weeks of inoculation (many people do not recall a tick bite, however) and may last for several weeks. The illness initially resembles many other tick-borne diseases:
- Malaise
- Fatigue
- Chills
- Fever
- Headache
- Muscle pain
- Joint pain
As the disease progresses, liver and spleen enlargement, jaundice, and hemolytic anemia (due to RBC destruction) may occur.
Elderly individuals, asplenic patients, and people with AIDS can develop severe illness. In such cases, babesiosis resembles falciparum malaria, with high fever, severe hemolytic anemia, jaundice, hemoglobinuria (hemoglobin in the urine), and kidney failure. This syndrome may be fatal.
Occasionally, people with previously acquired but asymptomatic babesiosis may develop full-blown disease when their spleen is removed due to trauma or for other medical reasons.
Diagnosis of Babesiosis
Babesiosis should be suspected in any individual who develops a fever and hemolytic anemia in an endemic area or who reports a history of a tick bite.
Diagnosis is most commonly made by finding Babesia in blood smears; classically, a characteristic tetrad, or “Maltese cross,” appears, but this is not a universal finding. Serologic testing and polymerase chain reaction tests are also available. (Bratton R, Corey G. Tick-borne disease. Am Fam Phys 2005;71(12):2323-30)
Treatment of Babesiosis
Asymptomatic individuals don’t require any treatment. For those who develop high fever, significant anemia, or evidence of increasing numbers of protozoa in blood smears, combination therapy with quinine and clindamycin or atovaquone and azithromycin is effective.
Occasionally, exchange transfusion is performed in severely ill patients with high burdens of protozoa.
Prevention of Babesiosis
- When going outdoors, people should wear long-sleeved shirts and long pants. Pants should be tucked into socks in tick-prone areas.
- Hikers should remain on paths and walkways.
- Effective repellants should be used (DEET on clothing and skin, or permethrin on clothing).
- Frequent body searches for crawling or embedded ticks should be performed, and embedded ticks should be removed without delay.
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