Babesiosis is a parasitic infection of red blood cells caused by Babesia species. It's primarily transmitted by ticks and can cause a malaria-like illness, particularly in immunocompromised individuals, the elderly, and those without a spleen. It is most common in the Northeastern and Upper Midwestern United States.
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Babesiosis was first described in 1888 by Victor Babes, who identified the parasite in cattle. The first human case was reported in 1957 in Yugoslavia, followed by the first recognized human case in the United States in 1969 on Nantucket Island. Its discovery marked one of the first recognized tick-borne parasitic diseases affecting humans.
Babesiosis is primarily transmitted to humans through the bite of infected *Ixodes* (deer) ticks, most commonly during their nymphal stage. Less common routes of transmission include contaminated blood transfusions and, rarely, congenital transmission from an infected mother to her baby. It is not spread directly from person to person.
Contagious Period: Varies by disease
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View WHO Resources →Disease information on Virus Watcher is reviewed by our Chief Epidemiologist, a former CDC lead analyst for FluSight forecasting. Outbreak data is aggregated from verified sources including BEACON, ProMED, WHO, CDC, and 50+ national health agencies. This information is for educational purposes and should not replace professional medical advice.
Last reviewed: 2026-07-18
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