VMC 311: Systematic Veterinary Bacteriology and Mycology (2+1)

HISTORY AND HABITAT

History

• The name Rickettsiales has been given in honor of American Pathologist Howard Taylor Rickets (1909) who first observed these microorganisms in Rocky Mountain spotted fever.
• Derrick (1935) investigated cases of fever occurring in abattoir workers in Brisbane, Australia.
• As the etiology of the disease was unknown, it was referred to as Querry or Q fever.
• The causative agent was identified by Burnert (Australian) and Cox (American)- so, it named as Coxiella burnetti.

Habitat

• The Rickettsiales are essentially parasites of arthropods, replicating in the cells of gut.
• Some can be passed transovarially, in ticks and mites but others such as Cowdria and Ehrlichia, are passed transtadially.
• They do not survive the outside the living cells (host or vector) with the exception of Coxiella burnetii, which produce endospore like forms, that can survive in dust particles for 50 days or more.
• Several Rickettsiales may persist in the host in a latent form.