Oropharyngeal tularemia was identified as the cause of a die-off in captured wild prairie dogs at a commercial exotic animal facility in Texas. From this point source, Francisella tularensis–infected prairie dogs were traced to animals distributed to the Czech Republic and to a Texas pet shop. F. tularensis culture isolates were recovered tissue specimens from 63 prairie dogs, including one each from the secondary distribution sites. Molecular and biochemical subtyping indicated that all isolates were F. tularensis subsp. holarctica (Type B). Microagglutination assays detected antibodies against F. tularensis, with titers as great as 1:4,096 in some live animals. All seropositive animals remained culture positive, suggesting that prairie dogs may act as chronic carriers of F. tularensis. These findings demonstrate the need for additional studies of tularemia in prairie dogs, given the seriousness of the resulting disease, the fact that prairie dogs are sold commercially as pets, and the risk for pet-to-human transmission.

Due to concern that Francisella tularensis, the causative agent of tularemia, may be used as a bioterrorist weapon, the Clinical and Laboratory Standards Institute recently provided a susceptibility testing method with breakpoints. Here, 169 isolates (92 type A and 77 type B) from North America were tested against seven antimicrobial agents (streptomycin, gentamicin, tetracycline, doxycycline, ciprofloxacin, levofloxacin, and chloramphenicol) used for the treatment of tularemia. The MICs for all of the isolates fell within the susceptible range. In addition, all isolates had MICs for erythromycin of 0.5 to 4 g/ml, in contrast to an MIC of >256 g/ml for the common laboratory strain LVS (live vaccine strain).

Francisella tularensis is a potent pathogen and a possible bioterrorism agent, for which quinolones offer promising new therapeutic options. There are, however, no data on the susceptibility to quinolones of natural isolates of F. tularensis tularensis, the highly virulent North American subspecies. In the present study, 8 isolates of F. tularensis tularensis, originating from 8 different states of the USA, and 16 US isolates of F. tularensis holarctica were tested. All 24 isolates showed MIC values < or = 0.125 mg/l to 6 different quinolones. Against ciprofloxacin, the predominant quinolone used to date in therapy against subspecies holarctica, MIC values were consistently < or = 0.064 mg/l. Thus quinolones seem to be promising options for the treatment of tularemia, including cases caused by the highly virulent subspecies F. tularensis tularensis.