Pathogenicity of emerging Japanese type 1 porcine reproductive and respiratory syndrome virus in experimentally infected pigs

To clarify the pathogenicity of Japanese type 1 porcine reproductive and respiratorysyndrome virus (PRRSV) isolate in experimentally infected pigs, we evaluated clinicalsigns and monitored viremia for 21 days post-inoculation (dpi). Lungs were mottled, tannedand reddish in appearance; had lesions predominantly in the cranial, middle and accessorylobes; and failed to collapse at 10 dpi. Although microscopic lesions of lungs werereproduced using the Japanese emerging type 1 PRRSV isolate under experimental conditions,no significant differences were noted between the challenge and control groups regardingmean rectal temperature and daily weight gain. These results provide useful insights intothe limited pathogenicity of single infection with the Japanese type 1 PRRSV isolate inpiglets, which differ from findings in reported field cases.