Human babesiosis: an emerging tick-borne disease

Human babesiosis is an important emerging tick-borne disease. Babesia diver gens, a parasite of cattle, has been implicated as the most common agent of human babesiosis in Europe, causing severe disease in splenectomized indiv iduals. In the US, Babesia microti, a babesial parasite of small mammals, h as been the cause of over 300 cases of human babesiosis since 1969, resulti ng in mild to severe disease, even in non-splenectomised patients. Changing ecology has contributed greatly to the increase and expansion of human bab esiosis in the US. A relatively recently described babesial parasite, the W A1-type, has been shown to be the causative agent in seven human cases in t he western US. This parasite is closely related to babesial parasites isola ted from large wild ungulates in California. Like B. microti, WA1-type para sites cause mild to severe disease and the immunopathogenesis of these para sites is distinctly different from each other in experimental infections of hamsters and mice. A B. divergens-like parasite was also identified as the cause of a fatal human babesiosis case in Missouri. Isolated cases of huma n babesisosis have been described in Africa and Mexico, but the causative p arasites were not well characterized. Standard diagnostic techniques for hu man infection, such as examination of Giemsa-stained thin blood smears and serology, have been complemented with molecular techniques, such as PCR. Cu rrent treatment for babesiosis is focused on a regimen of clindamycin and q uinine, although new drugs have shown promise. Prevention of infection reli es on self-monitoring for the presence of ticks and, in some locations, tar geted application of pesticides to decrease tick abundance. Identification of human infection with Babesia spp. will probably increase as physicians a nd the public become more aware of the disease, as people live and recreate in rural tick-infested areas, and as the numbers of immunocompromised indi viduals increase. (C) 2000 Australian Society for Parasitology Inc. Publish ed by Elsevier Science Ltd. All rights reserved.