Babesiosis is an emerging infectious disease caused by protozoa of the genus Babesia that invade and lyse red blood cells. Most cases of human babesiosis are reported from the United States and Europe. The epidemiology of human babesiosis depends on the Babesia species, the density of the tick and vertebrate reservoirs, and the immune status of the infected individuals. In most cases, the parasite is acquired via tick bite; the parasite may also be transmitted via blood transfusion and from mother to fetus.
The epidemiology and the pathogenesis of human babesiosis will be reviewed here. Clinical manifestations, diagnosis, treatment, and prevention of babesiosis are discussed separately. (See "Clinical manifestations, diagnosis, treatment, and prevention of babesiosis".)
Species characteristics — Babesia species have the following life cycle characteristics [1-5]:
- Vertebrate host reservoirs
- Transmission via tick bite
- Lack of a pre-erythrocytic stage
- Sporogony by budding (rather than schizogony)
- Absence of hemozoin deposit in red blood cells
Babesia and Plasmodia are both apicomplexan parasites of red blood cells. Their life cycle characteristics differ in that Plasmodium species are transmitted by mosquitoes, have a pre-erythrocytic (hepatic) stage, multiply by schizogony, and leave hemozoin deposit in red blood cells (due to incomplete digestion of hemoglobin).