A Sequential Study of Experimental Porcine Paramyxovirus (LPMV) Infection of Pigs: Immunostaining of Cryostat Sections and Virus Isolation

Abstract

Abstract. La Piedad Michoacan Paramyxovirus (LPMV) is a recently recognized paramyxovirus infecting pigs throughout Mexico. Disease syndromes observed in field cases associated with LPMV infection include neurologic, respiratory, and reproductive disorders. Clinical signs and the distribution of LPMV virus and antigen in tissue samples from pigs experimentally infected with LPMV by natural routes were studied. Severe neurologic 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 the pigs inoculated at 17 days of age were affected. Virus was consistently recovered from or demonstrated in tissues from the respiratory tract of both groups of pigs. LPMV and antigen were also demonstrated in central nervous system (CNS) tissues from these pigs; however, differences in virus distribution within the CNS were demonstrated in the 2 groups. In the pigs inoculated at 17 days of age, isolation of LPMV was restricted to the olfactory bulb and midbrain. In contrast, in the pigs 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. Comparatively large quantities of infectious LPMV were consistently recovered from urine samples of experimentally infected pigs.

A Comparative Study on the use of Virus and Antibody Detection Techniques for the Diagnosis of La Piedad Michoacan Paramyxovirus (LPMV) Infection in Pigs

“…1 The results for virus isolation reported here are generally in agreement with those of this earlier study. Virus was recovered consistently from tonsil (days 1-9 PI), lung (days 3-9 PI, with the exception of day 5), and olfactory bulb (days 4-9 PI).…”

“…Under these circumstances, to maximize the efficiency of virus isolation procedures for diagnosis, the results reported here and supported by the results a pig infected at 3 days of age of an earlier study 1 indicate that selective sampling of olfactory bulb and/or midbrain is required.…”

“…Two pigs were euthanized on each of days 1, 2, 3, 4, 5, 7, 8, 9, 11, and 14 after inoculation, and samples of trachea, lung, tonsil, olfactory bulb, midbrain, parotid lymph node, and pancreas were taken. These tissues were selected on the basis of an earlier study 1 as organs from which virus was most consistently recovered. Exact 10% suspensions were prepared by grinding 1 g of tissue with sterile sand and 9 ml of minimal essential medium a containing Earle's salts and 100 µg/ml of gentamycin (MEMG) in a mortar with a pestle.…”

“…Tissues were collected from 3-day-old pigs as previously described. 1 The 3-day-old colostrum-fed pigs were housed in animal accommodation under negative air pressure and fed a mixture of equal volumes of 1% dextrose in water and fullcream evaporated milk.…”

“…Tissues were collected from pigs inoculated at 17 days of age as described previous1y. 1 Each pig was inoculated by intranasal and intraconjunctival routes with 10 7 . 00 TCID 50 of LPMV.…”