[Serologic studies of domestic cats for potential human pathogenic virus infections from wild rodents]

For several viral infections a reservoir in wild rodents has been demonstrated. Some of the agents are known or suspected to be pathogenic for humans. Because improvements in hygiene have reduced direct human contact with rodents, domestic cats could be acting as active transmitters of these viruses from rodents to man. We selected 4 such pathogens--ortho- and parapox-, hanta- and encephalomyocarditis viruses--which, in different ways, may lead to serious human illness: Ortho- and parapoxvirus infections may cause localized pox lesions following direct skin contact. In general, the lesions heal without complications; in immunosuppressed or -deficient individuals, however, infection may generalize and take a dramatic course. Hantaviruses exist in various serotypes with different pathogenicity for human beings, varying from asymptomatic infection to highly fatal disease. In central and northern Europe the Puumala serotype is predominant causing influenza-like symptoms and renal dysfunction. Human infections arise from inhalation of aerosolized excreta of persistently infected rodents. Infections of man associated with encephalomyocarditis virus were demonstrated sporadically in cases of encephalitis and meningitis. In the present study, we investigated in 200 feline serum samples the prevalence of antibodies to ortho- and parapox-, hanta- and encephalomyocarditis virus. All serum samples were from cats that had been allowed to roam outside and to hunt. They were submitted from all parts of Austria for routine diagnosis in 1993. Four per cent of cats showed antibodies to orthopoxviruses with haemagglutination inhibition (HI) titres of 16-512; because of extensive cross-reactivity, positive samples reacted with all investigated orthopoxviruses (a feline orthopoxvirus recently isolated in Vienna, the reference strain of cowpox virus, Brighton, and vaccinia virus, strain IHD), only varying in titre. The specificity of the results was confirmed by virus neutralisation (VN) test, in which the same sera showed titres of 4-32. These data imply that, at least in Austria, unrecognized or subclinical orthopoxvirus infection in cats is more common than previously thought. In contrast to orthopoxviruses, all serum samples proved negative to parapoxvirus (parapoxvirus bovis 1) in VN test. In the same 200 samples, a seroprevalence of 5% was found to hantavirus (immunofluorescence antibody assay), indicating that domestic cats are susceptible to this virus and that infection is not uncommon in cat populations. Because higher titres were obtained against the Puumala serotype compared to the more pathogenic serotype Hantaan, it is most likely that the cats had experienced Puumala infections. Using HI test, antibodies to encephalomyocarditis virus (EMCV) were demonstrated in only 1.5% of the feline serum samples; although the antibody titres were low (16 and 32, respectively) we consider them specific, because these sera proved positive in VN test as well. Nevertheless, EMCV infection in domestic cats seems to be of low importance. The serological results presented in this paper, together with virological and epidemiological data, indicate that the domestic cat plays an important role only in the transmission of orthopoxviruses to human beings, but not in the case of parapox-, hanta-, and encephalomyocarditis virus.