Laboratory Analysis of Tularemia in Wild-Trapped, Commercially Traded Prairie Dogs, Texas, 2002

Abstract

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.

Susceptibility of selected murine and microtine species to infection by a wild strain of Francisella tularensis subsp. holoarctica

“…This finding corresponds with reports on chronic shedding tularemia nephritis in Microtus pennsylvanicus (Bell and Stewart, 1975). Common voles (Microtus arvalis), like prairie dogs (Petersen et al, 2004), are part of the terrestrial cycle of tularemia due to their selection of grassland habitats (Delattre et al, 1996). Interestingly, the epizootics of tularemia among wild rodents have mainly been reported during autumn months (Gurycova et al, 2001;Vyrostekova et al, 2002).…”

“…Quantification of bacteria in the tissues of this animal killed on Day 37 post exposure revealed low numbers of F. tularensis CFU. Nevertheless, the total numbers of bacteria in the tissues of this survivor still amounted to levels sufficient for the spread of infection by, for example, cannibalism (Bell and Stewart, 1975;Petersen et al, 2004;Petersen and Schriefer, 2005) in an overcrowded population. Generally, tissue bacterial burdens in common voles start to develop later post exposure and amount to lower levels than in laboratory mice with the only exception of the higher F. tularensis burden in kidneys of common voles during terminal stages of infection.…”

“…On the other hand, there are reports of chronic shedding of tularemia nephritis in rodents (Bell and Stewart, 1975), seropositive animals remaining culture positive for F. tularensis (Petersen et al, 2004) and chronic infection in species highly sensitive to tularemia (Dunaeva and Olsufyev, 1958;Shlygina et al, 1987;Shlygina et al, 1989).…”

Tularemia: emergence/re-emergence

“…Tularemia is a recognized disease of the United States, yet in 2002 it emerged in a rather unusual and unexpected setting [6,15,56]. The site of the outbreak was a Texas exotic pet facility where a variety of animal species were housed together and sold to domestic and international distributors.…”

“…PCR subtyping assays have been developed that allow for discriminating F. tularensis subsp., Type A and Type B, in the absence of a culture [46,56]. These assays are gel-based and center on the detection of differences in amplified product sizes.…”