Effects of intranasal inoculation with Bordetella bronchiseptica, porcine reproductive and respiratory syndrome virus, or a combination of both organisms on subsequent infection with Pasteurella multocida in pigs

Objective-To determine effects of intranasal inoculation with porcine reproductive and respiratory syndrome virus (PRRSV) or Bordetella bronchiseptica on challenge with nontoxigenic Pasteurella multocida in pigs. Animals-Seventy 3-week-old pigs. Procedure-In experiment 1, pigs were not inoculated [n = 10) or were inoculated with PRRSV (10), P multocida (10), or PRRSV followed by challenge with P multocida (10). In experiment 2, pigs were not inoculated (n = 10) or were inoculated with B bronchiseptica (10) or PRRSV and B bronchiseptica (10); all pigs were challenged with P multocida. Five pigs from each group were necropsied 14 and 21 days after initial inoculations. Results-Pasteurella multocida was not isolated from tissue specimens of pigs challenged with P multocida alone or after inoculation with PRRSV. However, in pigs challenged after inoculation with B bronchiseptica, P multocida was isolated from specimens of the nasal cavity and tonsil of the soft palate. Number of bacteria isolated increased in pigs challenged after coinoculation with PRRSV and B bronchiseptica, and all 3 agents were isolated from pneumonic lesions in these pigs. Conclusions and Clinical Relevance-Infection of pigs with B bronchiseptica but not PRRSV prior to challenge with P multocida resulted in colonization of the upper respiratory tract and tonsil of the soft palate with P multocida. Coinfection with PRRSV and B bronchiseptica predisposed pigs to infection of the upper respiratory tract and lung with P multocida. Porcine reproductive and respiratory syndrome virus and B bronchiseptica may interact to adversely affect respiratory tract defense mechanisms, leaving pigs especially vulnerable to infection with secondary agents such as P multocida.