Necrotizing enteritis in piglets associated with Aujeszky's disease virus infection.

Abstract

Aujeszky's disease is a naturally occurring disease of young pigs caused by a herpesvirus. The virus commonly affects the central nervous system, producing a non-suppurative meningoen~ephalomyelitis.~.~.~.~-~~ Lesions of Aujeszky's disease outside the central nervous system of piglets have been reported4; however, there is no description of lesions of the small intestine. This paper describes necrotizing enteritis in piglets induced by Aujeszky's disease virus infection. Seed virus was obtained from a piglet affected with Aujeszky's disease in Japan. An approximately 10% homogeneous suspension of brain and tonsil was prepared in Earle's balanced salt solution. No viruses other than Aujeszky's disease virus were detected in the suspension by electron microscopic and virological examination^.^ This suspension was titrated in pig kidney cell culture and contained approximately lo3 median tissue culture infective doses (TCID50) of the virus.5 Ten five-day-old piglets, free of neutralizing antibody to this virus, were inoculated intranasally with a 1-ml suspension of infected tissues. Two piglets were killed daily from one to three days after inoculation, and one piglet was killed daily from one to seven days after inoculation. Each piglet was necropsied systematically and tissues were fixed in 10% neutral buffered formalin, embedded in paraffin, sectioned, and stained with hematoxylin and eosin (HE). The formalin-fixed tissues of the jejunum and ileum were fixed in I% osmium tetroxide in 0.1 M phosphate buffered solution at pH 7.3 for one hour, dehydrated in alcohol, embedded in epon, and then cut and stained with uranyl acetate and lead citrate. All inoculated piglets developed pyrexia, ataxia, muscular tremors and vomition. A yellow, watery fluid was present in all parts of the small intestine in three piglets killed at five to seven days after inoculation. The major findings were necrosis in the central nervous system, trigeminal ganglion, tonsil, lung, submaxillary lymph node, and adrenal gland. Affected cell nuclei were pyknotic, and eosinophilic intranuclear inclusion bodies often were found in the cells in the peripheral necrotic regions. Necrotizing enteritis was observed in the lower part of the jejunum and ileum in three piglets killed at five to seven days after inoculation. There were numerous foci of epithelial necrosis with a minimal inflammatory reaction (fig. 1). Intranuclear inclusion bodies were present in a few degenerating crypt epithelial cells (fig. 2). The necrotic areas frequently developed into the underlying muscularis mucosa and tunica muscularis (fig. 3). Coincident with these muscular changes, neuronal necrosis was detected in Meissner's and Auerbach's plexuses in the jejunum and ileum. The nuclei of the degenerating neurons usually were weakly basophilic and contained a few inclusion bodies (fig. 4). Electron microscopically, great numbers of virions, morphologically indistinguishable from herpesvirus, were scattered throughout the nuclei and cytoplasm. Immature virus particles (capsids) often were arranged in clusters near the nuclear membrane, and enveloped virus particles were distributed in cytoplasmic vesicles and/or extracellular spaces of the epithelial, muscular and neuronal cells (figs. 5, 6). Except for the lesions found in the small intestine, the histological changes and the distribution of lesions were similar to those previously described in pigs naturally and experimentally infected with Aujeszky's disease viru~.~~~.~-~* Other investigators isolated Aujeszky's disease virus from the feces of infected piglets, but no intestinal lesions were dete~ted.'.~.' In the present study, although we did not isolate the virus from feces, the presence of necrotizing enteritis was demonstrated clearly. Therefore, the small intestine, in addition to the respiratory route, plays at least a minor role in the excretion of Aujeszky's disease virus.