MICE AND RATS (LABORATORY AND FERAL) ARE NOT A RESERVOIR FOR PRRS VIRUS

Porcine reproductive and respiratory syndrome (PRRS) is caused by an u nclassified arterivirus. The syndrome was first reported in the USA in 1987 as epizootics of reproductive failure in sows and respiratory di sease in nursery, growing, and fattening pigs. An enzootic form of the disease has now emerged, characterized by interstitial pneumonia and an increased incidence of secondary infections. Because the disease ha s now become enzootic on many farms, rodents were investigated as a po ssible reservoir for the infection. Wild rodents from an endemically i nfected farm were trapped, and virus isolation for PRRS virus (PRRSV) was attempted using porcine primary alveolar macrophage cultures. PRRS V was not isolated from serum and selected pooled tissues (thymus, lun g, and spleen) of 14 feral mice and 2 feral rats. Also, transmission e xperiments were carried out on 3-week-old Balb/c mice and 12-week-old Fischer-344 rats to determine if these species were susceptible to inf ection. The rodents were inoculated intranasally, orally, and intraper itoneally with a virus proven to transmit PRRS to pigs. Virus isolatio ns from selected pooled tissues (lung, spleen, thymus, and kidney) and from serum were negative, and there were neither gross nor microscopi c lesions. Weight gains and white blood cell counts were not significa ntly different between treated and control groups. These results indic ate that rodents are not susceptible to infection with PRRSV and there fore are probably not a reservoir for the disease.