Babesia are malaria-like protozoans that parasitize and reproduce within mammalian red blood cell. Although primarily transmitted by tick bite, babesiosis can also be acquired via blood transfusion and maternal-fetal transmission.
The first Babesia species was discovered in 1888 by Victor Babes, a Hungarian pathologist in whose honor the organisms were subsequently named. Over 100 distinct species have since been identified within the Babesia genus, despite there being 20+known forms to date known to infect humans, current testing only looks for two of them.
Clinically, babesiosis appears to have a wide spectrum of disease severity. Most patients experience a viral-like illness that can last weeks to months but which usually resolves fully. A significant minority of patients are entirely asymptomatic. In patients with a complicating condition, however – such as underlying immunosuppression – the disease course can be severe and potentially fatal. Some species of Babesia, such as B. divergens, appear to be more virulent than others.
Other symptoms are intermittent fevers accompanied by malaise, chills, and myalgias. Hemolysis, Imbalance without true vertigo and Mild encephalopathy can also be symptoms. A reduction in appetite and depression can also occur. Some patients will develop enlarged livers or spleens. The usual disease course lasts weeks to several months, but some patients take even longer to fully recover. Coinfection with Lyme disease or Anaplasmosis may complicate the clinical presentation and predispose the patient to more severe disease.