A SEQUENTIAL STUDY OF EXPERIMENTAL PORCINE PARAMYXOVIRUS (LPMV) INFECTION OF PIGS - IMMUNOSTAINING OF CRYOSTAT SECTIONS AND VIRUS ISOLATION

La Piedad Michoacan Paramyxovirus (LPMV) is a recently recognized para myxovirus infecting pigs throughout Mexico. Disease syndromes observed in field cases associated with LPMV infection include neurologic, res piratory, and reproductive disorders. Clinical signs and the distribut ion of LPMV virus and antigen in tissue samples from pigs experimental ly infected with LPMV by natural routes were studied. Severe neurologi c disease and death occurred following experimental inoculation of 3- and 17-day-old pigs. All of the pigs inoculated at 3 days of age were either dead or moribund by 8 days after inoculation, whereas 30% of th e pigs inoculated at 17 days of age were affected. Virus was consisten tly recovered from or demonstrated in tissues from the respiratory tra ct of both groups of pigs. LPMV and antigen were also demonstrated in central nervous system (CNS) tissues from these pigs; however, differe nces in virus distribution within the CNS were demonstrated in the 2 g roups. In the pigs inoculated at 17 days of age, isolation of LPMV was restricted to the olfactory bulb and midbrain. In contrast, in the pi gs inoculated at 3 days of age, isolation of LPMV was more widespread throughout the CNS tissue examined. Virus excretion studies indicated that nasal spread of LPMV was more important than fecal spread. Compar atively large quantities of infectious LPMV were consistently recovere d from urine samples of experimentally infected pigs.