Serosurveillance forFrancisella tularensisAmong Wild Animals in Japan Using a Newly Developed Competitive Enzyme-Linked Immunosorbent Assay

Abstract

Tularemia, a highly infectious zoonotic disease caused by Francisella tularensis, occurs sporadically in Japan. However, little is known about the prevalence of the disease in wild animals. A total of 632 samples obtained from 150 Japanese black bears, 142 Japanese hares, 120 small rodents, 97 rats, 53 raptors, 26 Japanese monkeys, 21 Japanese raccoon dogs, 20 masked palm civets, and three Japanese red foxes between 2002 and 2010 were investigated for the presence of antibodies to F. tularensis by competitive enzyme-linked immunosorbent assay (cELISA) and the commonly used microagglutination (MA) test. Seropositive cELISA and MA results were obtained in 23 and 18 Japanese black bears, three and two Japanese raccoon dogs, and two and one small rodents, respectively. All MA-positive samples (n = 21) were also positive by cELISA. Six of seven samples that were only positive by cELISA were confirmed to be antibody-positive by western blot analysis. These findings suggest that cELISA is a highly sensitive and useful test for serosurveillance of tularemia among various species of wild animals. Because this is the first study to detect F. tularensisseropositive Japanese raccoon dogs, these could join Japanese black bears as sentinel animals for tularemia in the wild in Japan. Further continuous serosurveillance for F. tularensis in various species of wild animals using appropriate methods such as cELISA is important to assess the risks of human exposure and to improve our understanding of the ecology of F. tularensis in the wild.

Francisella tularensisin Swedish predators and scavengers

“…The remnants of the red blood cells obscured the bottom of the wells and made it impossible to read the result at low titres. A cut-off level for a positive serum in these wildlife species that are assumed not to develop disease and to have low titres could presumably be set to 1:10 [13]. Since this titre level was not possible to read for the majority of samples, the results will be useful just for establishing that most of these animals had low titres, if any.…”

Detection of Francisella tularensis and analysis of bacterial growth in ticks in Japan

“…The phylogenetic analysis demonstrated that the F. tularensis strains detected in ticks in this study were closely related to strains distributed throughout Eurasia (Wang et al 2011). Although F. tularensis DNA had not been detected in ticks in Japan since 1991 (Fujita et al 2008), surveys of F. tularensis among wild mammals in Japan have been reported (Hotta et al 2012(Hotta et al , 2015Sharma et al 2014). These reports suggest that F. tularensis is still present in Japan.…”

“…In addition, seropositive Japanese raccoon dogs were detected by serosurveillance of tularaemia among various species of wild animals in Japan (Sharma et al . ). However, F. tularensis had not been detected in ticks in Japan since 1991 (Fujita et al .…”

Survey of <i>Francisella tularensis</i> in Wild Animals in Japan in Areas Where Tularemia is Endemic

“…Although several other animal species have also been implicated as the source of infection (7), the epizootic transmission cycle of F. tularensis is yet to be understood. Our previous studies showed that wild animals that tested positive for antibodies to F. tularensis were exclusively found within an area in Japan where tularemia is endemic (10,11). In order to better understand how this zoonotic pathogen is maintained in nature, identification of wild animals harboring infectious bacteria is necessary.…”

“…Most of the small mammals captured in Aomori prefecture carried ectoparasites other than ticks, such as mites or fleas, but none of them carried F. tularensis DNA (data not shown). The samples from this area were obtained from 3 seropositive rodents (2 Japanese grass voles and a large Japanese field mouse) as previously reported (11). F. tularensis DNA was not detected in the sero-positive rodents, and was only detected in the spleen and liver of a Japanese hare carcass found in Akita prefecture in 2009 ( Table 1).…”