Topics in Clinical Microbiology:Francisella tularensis

Abstract

In 1911, McCoy discovered an unusual illness among ground squirrels in Tulare County, California. The illness resembled plague but was clearly different because a pathogen could not be isolated on the usual culture media. With the addition of egg yolk to the media, McCoy finally isolated an organism and named itBacterium tularensis. It was soon recognized thatB. tularensiscould cause disease in humans, and many investigators, especially Edward Francis, did much of the early work defining the bacteriology, pathology, and epidemiology of tularemia. The name of the organism was eventually changed toFrancisella tularensisin honor of Francis.UnlikePseudomonas aeruginosaand the Enterobacteriaceae which are relatively non-pathogenic in the normal host,F. tularensiscan easily cause disease in previously healthy persons. In contrast,F. tularensishas not been implicated in nosocomial infections and person to person spread is rare. The organism is, however, extremely hazardous to workers in the clinical microbiology laboratory. Of all common bacterial and fungal pathogens isolated in the clinical laboratory,F. tularensisis second only toCoccidioides immitisin its potential to infect the laboratory worker. Many experienced investigators claim that it is impossible to work with the pathogen for any length of time without becoming infected. Currently it is highly recommended that persons who routinely work with the organism be immunized.