Babesia

Babesia is a genus of protozoan parasites in the phylum Apicomplexa that infect red blood cells of humans and other mammals. In humans, babesiosis is caused by several Babesia species and is transmitted primarily by ixodid ticks. The clinical presentation ranges from asymptomatic infection to a febrile hemolytic illness, and disease severity is influenced by immune status and splenic function.

Human-infecting Babesia species include Babesia microti and Babesia divergens, with others such as Babesia duncani and Babesia venatorum described in various regions. Babesia spp. also cause disease in cattle and other animals, which has economic significance in agriculture.

Life cycle: The parasite is transmitted to humans by the bite of an infected tick, and rarely via blood transfusion. Sporozoites enter red blood cells and develop into trophozoites, which replicate and divide into merozoites. Infected ticks acquire the parasite from vertebrate hosts and undergo sexual development, enabling transmission to new hosts.

Clinical features: Many infections are mild or asymptomatic. When symptoms occur, they typically include fever, chills, sweats, fatigue, and muscle pains. Hemolytic anemia, thrombocytopenia, and jaundice can occur. Severe disease may affect older adults, asplenic individuals, or immunocompromised patients and can involve organ dysfunction.

Diagnosis and treatment: Diagnosis relies on identification of intraerythrocytic parasites on stained blood smears or by molecular methods such as PCR; serology is also used. Mild to moderate babesiosis due to B. microti is commonly treated with atovaquone and azithromycin; alternatives include clindamycin plus quinine. Severe babesiosis may require clindamycin plus quinine and, in cases with high parasitemia, exchange transfusion.

Prevention: Preventing tick bites is the primary strategy, including protective clothing, repellents, and prompt tick removal. Blood donor screening helps prevent transfusion-transmitted babesiosis, particularly in endemic areas.