Rickettsial infections, and other related conditions such as anaplasmosis and Q fever, are transmitted to humans via the bites of fleas, lice, ticks or mites. The Rickettsiae are an unusual group of bacteria in that they are only able to survive inside the the cells of another organism. The antigenic cross-reactivity between Rickettsia and specific antigen of Proteus have been a long serving method for diagnosing various rickettsial infections.