Detection of the Rocky Mountain spotted fever agent, Rickettsia rickettsii, in dead ticks, Dermacentor andersoni.

Rickettsia rickettsii remained viable and retained chromophilic properties for not more than 24 h after Dermacentor andersoni were killed by freezing. Antigenic reactivity was detected for at least 71 days by direct immunofluorescence. However, rickettsiae in ticks suffocated with mineral oil remained pathogenic for at least 14 days. Accordingly, ticks removed from a host by mineral oil or dying from desiccation in transit are still suitable for rickettsial examination.