Pathogenesis of Aujeszky's disease virus infection in swine tracheal organ culture

Immunology of the porcine respiratory disease complex

PRDC is a multifactorial respiratory syndrome that includes several respiratory pathogens. As can be observed in this article, although the pathogenesis of some of the respiratory pathogens of pigs is fairly well defined, the host response and the immune response necessary to control the pathogen often remain unclear. As our ability to evaluate the porcine immune system and its ability to respond to disease improves, the knowledge of how each of these respiratory pathogens alter and evade the immune system will increase. The pathogens most commonly isolated from pigs with clinical signs of PRDC either infect the cells of the immune system or induce significant immunopathology. Thus, PRRSV and M. hyopneumoniae, the two most common pathogens associated with PRDC, alter the ability of the respiratory immune system to respond to their presence and the presence of other pathogens. By changing the respiratory immune system, these two common pathogens increase the susceptibility to the many other pathogens associated with PRDC. As we learn more about the pathogens of the respiratory system, their interactions with each other, and the mechanisms by which they modulate the immune system, our ability to develop effective control measures will improve.

Experimental dual infection of cesarean-derived, colostrum-deprived pigs with Mycoplasma hyopneumoniae and pseudorabies virus

To determine whether pseudorabies virus (PRV) infection increases the severity of pneumonia by Mycoplasma hyopneumoniae, 18, 10-week-old Cesarean-derived, colostrum-deprived pigs were randomly assigned to 3 groups of 6 pigs each. Pigs in groups A and C were inoculated intranasally with M. hyopneumoniae at 10-week-old. At 11-week-old, pigs in groups B and C were inoculated intranasally with PRV. All pigs were initially seronegative for M. hyopneumoniae and PRV. Three pigs of each group were euthanized at 12-week-old, and remaining pigs at 14-week-old. At necropsy, gross lesions in the lung were observed in the pigs of groups A and C. On post-inoculation-week (PIW) 2 with M. hyopneumoniae (at 12-week-old), lung lesions were recognized in one of the 3 pigs in group A and all the pigs in group C. The mean percentage of the lung lesions were 0.1% in group A and 9.8% in group C. M. hyopneumoniae was isolated from broncho-alveolar lavage fluids (BALF) of pigs in group A with titer of 10(2) to 10(3) CCU/0.2 ml and in group C with titer of 10(5) to 10(6) CCU/0.2 ml. On PIW 4 (at 14-week-old), lung lesions were observed in all the pigs in groups A and C, and the mean percentage of the lung lesions were 8.3% in group A and 17.2% in group C. M. hyopneumoniae was isolated from BALF in group A with titer of 10(4) to 10(7) CCU/0.2 ml and in group C with titer of 10(6) to 10(7) CCU/0.2 ml. PRVs were isolated from nasal swab and tissue samples in groups B and C. After inoculation, antibody against M. hyopneumoniae was detected in groups A and C, and against PRV in groups B and C. Under the present experimental conditions, PRV infection appear to have effect on the severity of experimentally induced acute mycoplasmal pneumonia in young pigs.

Enteric lesions induced by different pseudorabies (Aujeszky's disease) virus strains inoculated into closed intestinal loops of pigs

Three different strains of pseudorabies (Aujeszky's disease) virus were inoculated into ligated closed loops in the jejunum and ileum of five specific-pathogen-free pigs. Infected areas were compared with respect to distribution of histologic lesions and pseudorabies virus antigen. Two wild-type strains of pseudorabies virus produced enteric lesions consisting of necrosis of the subepithelial macrophages in the basilar crypt epithelium, necrosis of the lymphoid follicles in the Peyer's patches, degeneration of the epithelial cells in the crypt and villi, degeneration of the neuronal cells in the myenteric plexuses, and formation of intranuclear inclusion bodies on postinoculation days 2-4. Pseudorabies virus antigen was initially detected in subepithelial macrophages of the dome of Peyer's patches on postinoculation day 2 and subsequently extended to superficial epithelium and deeper into the lymphoid follicles and myenteric plexuses on postinoculation days 3-4. Many pseudorabies virus particles were also detected in the center of their necrotic foci. However, 1 mutant strain (ara-T-resistant) of pseudorabies virus did not produce enteric lesions. The results suggest that the primary target of infection by wild-type strains of pseudorabies virus might be the macrophages distributed in the subepithelial area of the dome Peyer's patches.

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

Nine pigs were inoculated endobronchially with Actinobacillus pleuropneumoniae serotype 1 (App-1) 6 days after infection with Aujeszky's disease virus (ADV); four died within 3 days and the remainder were killed after 1-6 days. Immunohistopathologically, there were two types of pneumonic lesion: pleuropneumonia, characterized by coagulative necrosis, oedema and fibrinous thrombosis; and necrotizing interstitial pneumonia, characterized by bronchitis, bronchiolitis and alveolitis. The former type of lesion was associated with App-1 antigen, and the latter with ADV antigen. These results indicated that a combined ADV and App-1 infection produced severe haemorrhagic pleuropneumonia; and that ADV and App-1 each produced a characteristic pneumonic lesion.

Pneumonia in pigs inoculated with pseudorabies virus by means of a bronchoscope

Pigs inoculated endobronchially (EB) with 2 ml of virus suspension containing 10(4) TCID50 per ml of the YS-81 strain of pseudorabies virus (PRV), by means of a bronchoscope, all developed viral pneumonia. No pneumonic lesions were observed in intranasally inoculated pigs. Macroscopical and microscopical lesions were localized to the middle to caudal parts of the right caudal lobe and were closely associated with the site at which the inoculum was deposited. PRV became attached to all types of cells and caused destruction of epithelial cells, and viral antigen persisted in the alveolar macrophages. After PRV infection, the total cell number in broncho-alveolar lavage (BAL) fluid was slightly increased and a high titre of PRV was found in the cells of BAL fluid in EB infected pigs. The findings suggest that PRV infection leads to dysfunction of alveolar macrophages before cell death is produced by virus replication.