Last edited 08/2020 and last reviewed 06/2022

This is due to a red-cell protozoal parasite of the genus Babesia. It is usually transmitted by the Ixodes tick (less commonly through blood transfusion or transplacentally).

Babesia microti is the main aetiologic agent of human babesiosis and is endemic in the northeastern and the upper Midwestern United States.

  • geographic expansion of babesiosis has followed that of Lyme disease (but has remained more restricted)
  • fever is the prominent feature of babesiosis
    • often is accompanied by a series of non-specific symptoms

  • diagnosis is confirmed by:
    • identification of babesia organisms on Giemsa stained blood smears
    • detection of babesia DNA by PCR, or
    • a four-fold rise in anti-babesia antibody titres in acute and convalescent sera

  • disease may be severe or fatal in particular groups:
    • patients older than 50 years of age
    • immunocompromised patients regardless of age

The majority of patients will have a complete recovery following a standard 7 to 10 day course of antimicrobial therapy (seek expert advice regarding antimicrobial therapy).

Cases of human babesiosis have been reported throughout the world (1)

  • B. divergens is the most common cause of babesiosis in Europe where a few cases of B. microti and B. venatorum infections also have been described
  • Human cases have been reported in Africa, Asia, Australia and South America
  • the first case of babesiosis was reported in the UK on 31/7/2020 (3)