Serologic evidence for Rickettsia typhi and an ehrlichial agent in Norway rats from Baltimore, Maryland, USA.

We screened serum from 90 Norway rats trapped in East Baltimore, Maryland, USA, from April to November 2005 for antibodies against Rickettsia typhi and Ehrlichia chaffeensis. Six rats had positive titers of > or = 1:64 against R. typhi and did not react with R. akari. In addition, four rats had cross-reactive antibodies with titers of > or = 1:64 against Ehrlichia chaffeensis. Sera from these rats also cross-reacted with Anaplasma phagocytophilum or Ehrlichia muris. Our data indicate that the agent of murine typhus and ehrlichial agents are circulating in the Norway rat population in Baltimore.