Zoonotic Pathogens of Peri-domestic Rodents

Rodents are important vectors of disease as they have the potential, arguably more than any other wildlife species, to move pathogens across geographical distances. Although there is little known of the prevalence of zoonotic pathogens in UK rodents thus it is difficult to determine the public health risk. The aims of this project were to collect a large range of rodent sample from a variety of peri-domestic locations across the UK that could be used as a representation of the British rodent population and screen them for zoonotic pathogens that could be a potential risk to public health. Rodent species were sampled from 2014 to 2016 from peri-domestic locations across Northern England, North Wales and Southern Scotland. A total of 333 rodent specimens were collected from this project which included; brown rats (R. norvegicus, n=68), house mice (Mus musculus, n=105), wood mice (Apodemus sylvaticus, n=48), bank voles (Myodes glareolus, n=56), field voles (Microtus agrestis, n=23), red squirrels (Sciurus vulgaris, n=21) and grey squirrels (Sciurus carolinensis, n=12). Each rodent carcass was examined post mortem and tissue samples were taken. Viral zoonotic pathogens that were screened for in this project were Hantavirus (Seoul virus, SEOV, Puumala virus, PUUV and Tatenale virus, TATV), Lymphocytic choriomeningitis virus (LCMV) and Hepatitis E virus (HEV). RNA was extracted from kidney, lung and liver tissue. Each of the viruses were screened for using published pan RT-PCR assays specific to the viral genus. Positive PCR products were Sanger sequenced and phylogenetically analysed. Additional specific RT-qPCR assays were performed for SEOV and rat HEV. An LCMV ELISA was also performed on house mice serum samples. Histological examinations were performed on a subset of samples. SEOV RNA was detected in 13/68 (19%, 95% CI 0-40%) brown rats and 4/47 brown rats in an RT-qPCR assay. TATV RNA was detected in 7/23 (30.4%, 95% CI, 11.6-49.2%) field voles. No PUUV RNA was detected in this study. The PCR screening results for LCMV revealed an overall prevalence of 8% (26/331, 95% CI 15-36) with LCMV RNA present in 3.2% brown rats, 17.5% house mice, 2% wood mice and 4% bank voles liver tissue. There was no LCMV RNA detected in field voles, red squirrels or grey squirrels. Seroprevalence in house mice was 7% (3/43). No histological changes were observed in the kidney tissue of LCMV infected house mice. In this study, 8/61(13%, 95% CI, 4.6-21.4) of brown rat livers were positive for rat HEV RNA. Lesions and necrosis were observed histologically in 2/3 samples examined, which appears to be indicative of HEV infection based on observations in other HEV infected animals. RT-qPCR results confirmed rat HEV. No HEV RNA of any variant was detected in any other rodent species. This is the first reported detection of rat HEV in a wild rat from the United Kingdom. Bacterial zoonosis Campylobacter in rodents was also investigated in this study. Campylobacter from rodent faecal samples was cultured on Campylobacter specific media and DNA was extracted. An lpx gene PCR was performed to differentiate between C. jejuni and C. coli. In total, 28% (43/152) rodents were Campylobacter positive and of these, 86% (37/43) were shown to be either C. jejuni (20/43, 46%) or C. coli (17/43, 40%) and 14% (6/43) isolates that were lpx negative. House mice were shown to be most commonly infected with C. coli (8/10) and bank voles with C. jejuni (13/17). In brown rats, 50% (13/26) were positive in which 39% C. jejuni (5/13) and 61% C. coli (8/13) positive. Whole genome sequencing was also performed on a subset of isolates and sequence types ST-6561, ST-45 and ST-51were identified in brown rats and host-specific sequence type ST-3704 was present in bank voles. This project has proved that there are multiple zoonotic pathogens circulating in the wild rodent population that could be hazardous to human health. It has also highlighted gaps in our current knowledge, such as the unknown zoonotic potential of some pathogens, such as TATV. In order to comment on the significance of a pathogen to public health the zoonotic potential must be known. The prevalence of known pathogens with known zoonotic potential, such as SEOV, LCMV and rat HEV in people remains unknown. This project has also indicated that there may be possible occupational risks and geographical hot spots for rodent zoonosis. Although further investigation including human surveillance, improved diagnostics and mathematical modeling could be used to determine the risks. This could aid in the prevention of possible outbreaks through improvement of biosecurity, pest control as well as raising public awareness, reduce the risk of exposure and be beneficial for public health in the future.