Presentations

The common hamster (Cricetus cricetus) is considered a pest in Eastern Europe, and believed to be a source of human tularemia infections, caused by Francisella tularensis. The aim of our study was to investigate the role of hamsters in the natural cycle of F. tularensis by collecting samples from a subpopulation of common hamsters in an 80-km2 enzootic agricultural area in eastern Hungary during an interepizootic period and to examine clinical signs, pathology and histopathology of acute tularemia resembling natural infection with F. tularensis ssp. holarctica.

Retrospective data about the tularemia situation of the region were obtained from the local veterinary authority and human health service. Estimation of hamster population size in the study area was based on the number of active burrows/hectare. Overall 900 hamsters were trapped with kill traps in the study area: 250 in May 2008, 500 in May 2009, and 150 in October 2009. Hamsters were screened with F. tularensis specific slide and tube (with 1/10 titer) agglutination tests. Lung, liver, spleen, and kidney tissue pools were collected from 50 individuals trapped in May and from 50 animals trapped in October 2009 and tissue pools were analyzed by using a F. tularensis specific real-time TaqMan polymerase chain reaction (PCR) system. We collected 374 Ixodes acuminatus ticks from the hamsters and tested them by real-time TaqMan PCR. To examine clinical signs, pathology, histopatology and immunohistochemistry of acute tularemia infection similar to the natural infection, two hamsters were infected with a large dose of a wild strain of F. tularensis spp. holarctica.

The study area was considered a tularemia-enzootic region based on the infection rate in the local European brown hare (Lepus europaeus) and human population and we suspected that our study was conducted in an interepizootic period based on our results. The estimated population size in the study area was 400,000 hamsters in 2008 and 80,000 in 2009. Thus, at an assumed 0.5% antibody prevalence the probability of diagnosing at least one positive animal was 100% from the 250 screened hamsters in 2008 and 96.2% from the 650 animals in 2009. The serologic testing of all 900 hamsters yielded negative results both with slide and tube agglutination tests. F. tularensis was not detected in any of the tick or organ pools of the 100 hamsters tested. After a short period of apathy, the infected animals died on the eighth and ninth days postinoculation. The pathologic, histopathologic, and immunohistochemical examination contributed to the diagnosis of septicemia in both cases.

Our results confirmed previous findings that common hamsters are highly sensitive to F. tularensis. We conclude that altough septicemic hamsters may pose substantial risk to humans during tularemia outbreaks, hamsters in interepizootic periods do not act as a main reservoir of F. tularensis.