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.

Genome sequencing shows that European isolates of Francisella tularensis subspecies tularensis are almost identical to US laboratory strain Schu S4.

BACKGROUND: Francisella tularensis causes tularaemia, a life-threatening zoonosis, and has potential as a biowarfare agent. F. tularensis subsp. tularensis, which causes the most severe form of tularaemia, is usually confined to North America. However, a handful of isolates from this subspecies was obtained in the 1980s from ticks and mites from Slovakia and Austria. Our aim was to uncover the origins of these enigmatic European isolates. METHODOLOGY/PRINCIPAL FINDINGS: We determined the complete genome sequence of FSC198, a European isolate of F. tularensis subsp. tularensis, by whole-genome shotgun sequencing and compared it to that of the North American laboratory strain Schu S4. Apparent differences between the two genomes were resolved by re-sequencing discrepant loci in both strains. We found that the genome of FSC198 is almost identical to that of Schu S4, with only eight SNPs and three VNTR differences between the two sequences. Sequencing of these loci in two other European isolates of F. tularensis subsp. tularensis confirmed that all three European isolates are also closely related to, but distinct from Schu S4. CONCLUSIONS/SIGNIFICANCE: The data presented here suggest that the Schu S4 laboratory strain is the most likely source of the European isolates of F. tularensis subsp. tularensis and indicate that anthropogenic activities, such as movement of strains or animal vectors, account for the presence of these isolates in Europe. Given the highly pathogenic nature of this subspecies, the possibility that it has become established wild in the heartland of Europe carries significant public health implications.