Pseudorabies virus infection in piglets accompanying with the lesion of bilateral encephalomalacia

Encephalomalacic lesions in pigs dually infected with porcine reproductive and respiratory syndrome virus and pseudorabies virus

Four pigs (group 1) were infected with an aerosol containing porcine reproductive and respiratory syndrome virus (PRRSV) followed 7 days later by pseudorabies virus (PRV). Three further pigs (group 2) received PRRSV alone, two (group 3) received PRV alone, and two (group 4) remained as uninfected controls. Despite the admittedly small numbers of animals, the experiment appeared to throw light on aspects of synergy. Thus, the group 1 pigs showed severe neurological signs characterized by ataxia and muscular tremors. Total cell numbers in the bronchoalveolar lavage fluid were increased in all PRRSV-infected pigs, and PRRSV antigen was detected in the alveolar macrophages. Total cell numbers in the cerebrospinal fluid of group 1 pigs were considerably greater than those demonstrated in group 3, but no PRV antigen was found. Pigs of groups 1 and 2 showed pulmonary lesions, characterized by interstitial pneumonia and PRRSV antigen immunolabelling. Non-suppurative encephalitis was found in five of the six pigs of groups 1 and 3. In particular, one group 1 animal had severe necrotizing encephalitis with intranuclear inclusion bodies and associated immunolabelling of PRV antigen. The other three group 1 pigs had prominent malacic lesions, with macrophages. These neuropathological findings strongly suggested that PRRSV infection in pigs enhances the severity of brain lesions caused PRV.

Invasion and spread of equine herpesvirus 9 in the olfactory pathway of pigs after intranasal inoculation

The neuropathogenesis of equine herpesvirus 9 (EHV-9) in pigs was investigated by intranasal inoculation of the virus together with intramuscular administration of dexamethasone (DM). All infected pigs developed characteristic meningo-encephalitis, accompanied by basophilic intranuclear inclusion bodies in the neuronal cells. One non-DM-treated and two DM-treated pigs had prominent malacic lesions in the rhinencephalon. Associated with the encephalitic lesions, there was invariably an increase in the number of nucleated cells in the cerebrospinal fluid (CSF). EHV-9 antigen was first detected in the nasal and olfactory epithelial cells in the nasal cavity, and in the neuroglial cells in the olfactory bulb. Subsequently it was demonstrated in the amygdaloid and caudate nuclei, and putamen. The virus was not isolated from the CSF. These results suggest that, after intranasal inoculation, EHV-9 replicates in the olfactory epithelial cells, spreading to the central nervous system via the olfactory pathway.

Bilateral encephalomalacia in a pig related to latent Aujeszky's disease virus infection

A case of bilateral encephalomalacia in a pig related to latent Aujeszky's disease virus infection is reported. The pig was experimentally inoculated with the NIA-3 strain and survived the infection after showing intense central nervous system disease. Abnormal behaviour was observed up to the date of death. The pig was demonstrated to be latently infected with the virus by polymerase chain reaction (PCR). The main microscopic lesion was a bilateral encephalomalacia which involved structures related to the limbic system. A complete description of lesions observed and their relation to abnormalities shown by the pig are exposed.

Immunohistological study of encephalomalacia in pigs infected with Aujeszky's disease virus

Seven hysterectomy-derived colostrum-deprived pigs aged 4 weeks were inoculated intranasally with 10(3) plaque-forming units (1 ml) of the Yamagata YS-81 strain of Aujeszky's disease virus. One pig died and five developed encephalomyelitis and trigeminal ganglionitis. Three pigs killed on days 12-16 showed prominent malacic degeneration. Associated with the malacic foci were many lysosome-positive cells. IgG- and IgM-containing cells in the perivascular cuffs and glial nodules were first detected on day 7, after which they increased in number. They were thought to be closely associated with the presence of neutralizing antibody. These findings suggest that inflammatory cells in the brain are of haematogenous origin.

Immunopathology in Aujeszky's disease virus-infected pigs exposed to fluctuating temperatures

Pigs exposed to fluctuating temperatures (high, 30 +/- 2 degrees C; low, 4 +/- 1 degrees C) were intranasally inoculated with Aujeszky's disease virus (ADV). ADV-infected pigs, exposed to the fluctuating temperatures, showed severe clinical signs and ADV in the nasal secretions persisted longer than in the ADV-infected control pigs kept at the normal temperature (20 +/- 2 degrees C). High concentrations of ADV were isolated from nasal secretions on the 1st day after inoculation of the virus. Pathologically, all ADV-infected pigs had non-suppurative encephalitis and trigeminal ganglionitis. The lesions were more widely distributed in pigs exposed to fluctuating temperatures than in infected control pigs. Two infected pigs given the stress had severe malacic foci in the frontal lobe and four of them had prominent interstitial pneumonia. In the pigs exposed to fluctuating temperatures, a significant number of immunoglobulin-containing cells, especially IgM-containing cells, did not respond to ADV infection. A significant (P < 0.01) difference in the number of IgG- and IgM-containing cells was observed between the ADV-infected pigs exposed to the fluctuating temperature and ADV-infected control pigs, respectively. These results demonstrated that the stress of fluctuating temperatures enhanced the susceptibility to ADV infection.

A necrotizing meningoencephalitis of pug dogs

Clinical and pathologic features of a sporadic, necrotizing meningoencephalitis affecting adolescent and mature pug dogs are described. Many of the affected animals were closely related. Acute and chronic forms occur, with clinical signs reflecting the pathologic affinity of the disease for the cerebral hemispheres. No etiologic agent has been identified. The extensive necrosis and affinity for the cerebral hemispheres are similar to alphatype herpesvirus encephalitides of other species.