Immunohistopathological characterization of pig pneumonia caused by a combined Aujeszky's disease virus and Actinobacillus pleuropneumoniae infection

Multifocal granulomatous hepatitis caused by Actinobacillus pleuropneumoniae serotype 2 in slaughter pigs

In a survey of 66 894 slaughter pigs, 11 animals from three farms were found to have multifocal granulomatous lesions in the liver, caused by Actinobacillus pleuropneumoniae serotype 2. The lesions consisted of epithelioid cells and multinucleated giant cells, with asteroid bodies and discernible gram-negative bacteria. Lymph nodes and spleen were occasionally affected. The results suggested that haematogenous spread had occurred from pre-existing pulmonary infections.

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.

Reactivity of anti-Nipah virus monoclonal antibodies to formalin-fixed, paraffin-embedded lung tissues from experimental Nipah and Hendra virus infections

The immunohistochemical reactivity of seven clones of mouse monoclonal antibodies raised to Nipah virus antigens were investigated using formalin-fixed, paraffin embedded porcine and equine lung tissues from experimental Nipah and Hendra virus infection, respectively. Either microwave irradiation or enzymatic digestion effectively unmasked the viral antigens in formalin-fixed, paraffin-embedded tissue sections. Four clones showed positive reaction to both Nipah virus-infected porcine lung tissue and Hendra virus-infected equine lung tissue. Two clones (11F6 and 13A5) reacted with Nipah virus-infected porcine lung tissue, but not with Hendra virus-infected equine lung tissue. These Nipah virus-specific monoclonal antibodies may therefore be useful for immunohistological diagnosis of Nipah virus infection and for further research on Nipah virus pathogenesis.

Immunohistochemical characterization of calf pneumonia produced by the combined endobronchial administration of bovine herpesvirus 1 and Pasteurella haemolytica

Ten calves ("group 4") were inoculated endobronchially with Pasteurella haemolytica 4 days after inoculation with bovine herpesvirus 1 (BHV-1). Four calves (group 3) were similarly inoculated with P. haemolytica alone, and three (group 2) with BHV-1 alone. All group 4 animals showed severe respiratory signs and had bilateral lobar pneumonia; one died 6 days after inoculation with P. haemolytica. Two types of pneumonic lesion were observed. One was characterized by interlobular and interstitial lymphatic thrombosis, fibrinous pleuritis and coagulative necrosis, and the other by necrotizing bronchiolitis with intranuclear inclusion bodies. The former type of lesion was associated with the presence of P. haemolytica antigen and the latter with the presence of BHV-1 antigen. The weight of infection of BHV-1 and P. haemolytica in bronchoalveolar (BAL) fluid was clearly reflected in the immunohistochemical demonstration of the corresponding antigens in BAL fluid cells. Group 4 calves differed from the calves of groups 1-3 in showing 10-1530 times more endotoxin in BAL fluid. These findings suggested that BHV-1 infection partly destroyed the clearance mechanisms of the respiratory tract epithelium and exacerbated the subsequent P. haemolytica infection.

Actinobacillus pleuropneumoniae osteomyelitis in pigs demonstrated by fluorescent in situ hybridization

Necrotizing osteomyelitis and fibrinopurulent arthritis with isolation of Actinobacillus pleuropneumoniae serotype 2 is reported in two pigs from a herd with lameness and mild coughing problems among 8 to 12-week-old pigs. Application of fluorescent in situ hybridization targeting 16S ribosomal RNA of A. pleuropneumoniae in formalin-fixed tissue was performed to verify the association of A. pleuropneumoniae with the bone and joint lesions. By in situ hybridization A. pleuropneumoniae was demonstrated as multiple microcolonies or single cells dispersed in focal fibrinonecrotizing pleuropneumonia, in joints with arthritis, and in bone necroses including lysis of growth plate and suppurative inflammation in the adjacent trabecular metaphysis, thus demonstrating that well-known infections manifest new, unusual lesions.