(A) The distribution of human infections caused by F. tularensis subsp. holarctica (type B) (light gray squares) and subsp. tularensis clades A1 (black circles) and A2 (gray circles) in the USA. Human infection data is from Staples et al. . Cases are plotted randomly with the county of infection. Infections represent all routes of exposure (arthropod, animal contact, inhalation, etc.). (B) Approximate geographic distributions of tick species associated with human tularemia in the USA, D. variabilis (light gray diagonal striped shading), A. americanum (black shading) and D. andersoni (gray shading). Tick distributions are from Brown et al. .