Effects of intranasal inoculation of porcine reproductive and respiratory syndrome virus, Bordetella bronchiseptica, or a combination of both organisms in pigs

Objective - To examine effects of co-infection with porcine reproductive an d respiratory syndrome virus (PRRSV) and Bordetella bronchiseptica in pigs. Animals - Forty 3-week-old pigs. Procedure - 30 pigs (10 pigs/group) were inoculated with PRRSV, B bronchise ptica, or both. Ten noninoculated pigs were control animals. Results-Clinical signs, febrile response, and decreased weight gain were mo st severe in the group inoculated with both organisms. The PRRSV was isolat ed from all pigs in both groups inoculated with virus. All pigs in both gro ups that received PRRSV had gross and microscopic lesions consistent with i nterstitial pneumonia. Bordetella bronchiseptica was cultured from all pigs in both groups inoculated with that bacterium. Colonization of anatomic si tes by B bronchiseptica was comparable between both groups. Pigs in the gro up that received only B bronchiseptica lacked gross or microscopic lung les ions, and B bronchiseptica was not isolated from lung tissue. In the group inoculated with B bronchiseptica and PRRSV, 3 of 5 pigs 10 days after inocu lation and 5 of 5 pigs 21 days after inoculation had gross and microscopic lesions consistent with bacterial bronchopneumonia, and B bronchiseptica wa s isolated from the lungs of 7 of those 10 pigs. Conclusions and Clinical Relevance - Clinical disease was exacerbated in co -infected pigs, including an increased febrile response, decreased weight g ain, and B bronchiseptica-induced pneumonia. Bordetella bronchiseptica and PRRSV may circulate in a herd and cause subclinical infections. Therefore, co-infection with these organisms may cause clinical respiratory tract dise ase and leave pigs more susceptible to subsequent infection with opportunis tic bacteria.