Prevalence of coinfection with Francisella tularensis in reservoir animals of Borrelia burgdorferi sensu lato.

INTRODUCTION AND PURPOSE: Studies on Lyme borreliosis and other tick-borne zoonoses in the Austrian and Slovakian borderland, a region endemic for tularemia, revealed a relatively high prevalence of infection with Borrelia burgdorferi s.l. and Francisella tularensis in small terrestrial mammals, as well as in the ticks, during a one-year survey. The occurrence of coinfection with the agents of Lyme borreliosis and tularemia was assessed in different species of rodents.

METHODS

Organs of small mammals, live-trapped mostly in six-week intervals from May 1994 to April 1995, were cultured on appropriate media in order to grow borreliae and F. tularensis.

RESULTS

Infection with B. burgdorferi s.l. and also with F. tularensis was found in all the most abundant rodent species. A significant difference was observed in the time period of isolation of these agents. Borrelia was cultured from May to January (PCR detected borrelia up to April), while F. tularensis was isolated from August to December. Coinfection was seen in two species of voles, Clethrionomys glareolus trapped in August and Microtus arvalis in October. The Borrelia strains isolated from these animals were identified as B. garinii. Isolates of F. tularensis belonged to the subspecies holarctica, biovar II.

CONCLUSIONS

Results obtained indicate that in endemic regions for tularemia the prevalence of infection with borreliae could be modified in different animal species mainly during epizootic outbreaks of tularemia.