COMPARISON OF PORCINE HIGH FEVER DISEASE ISOLATES OF PRRSV TO US ISOLATES FOR THEIR ABILITY TO CAUSE SECONDARY BACTERIAL INFECTION IN SWINE
Location: Virus and Prion Research Unit
Title: Comparison of the pathogenesis of Asian highly-pathogenic PRRSV isolates to U.S. isolates and their ability to cause secondary bacterial infection in swine
Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: October 5, 2012
Publication Date: November 29, 2012
Citation: Brockmeier, S.L., Loving, C.L., Palmer, M.V., Spear, A.R., Faaberg, K.S., Nicholson, T.L. 2012. Comparison of the pathogenesis of Asian highly-pathogenic PRRSV isolates to U.S. isolates and their ability to cause secondary bacterial infection in swine. International PRRS Symposium 2012. Poster No. 64.
The appearance of highly-pathogenic porcine reproductive and respiratory syndrome virus (PRRSV) isolates in Asia necessitates investigation into the clinical repercussions of these viruses if the strains were to appear in the United States. Epidemiologic data from Asian outbreaks suggest that disease severity was associated with both the PRRSV isolates from these cases and secondary bacterial infections. Previous reports have indicated that U.S. isolates of PRRSV predispose to secondary bacterial infections as well, but outbreaks like the ones described in Asia have not been reported in the United States. The objectives of this research were to compare the pathogenesis of Asian and U.S. PRRSV isolates of varying virulence with regard to their ability to cause disease and predispose to secondary bacterial infections in swine. The experiment consisted of 10 groups of 9-10 pigs each. At 6 weeks of age, half the groups were inoculated with a bacterial cocktail of Streptococcus suis, Haemophilus parasuis, and Actinobacillus suis and 1 week later 4 bacterial colonized groups and 4 non-bacterial colonized groups were inoculated with 1 of 2 Asian HP-PRRSV strains (JXwn06 or SRV07) or 1 of 2 U.S. PRRSV strains (SDSU73 or VR2332). The pigs infected with JXwn06 were clinically the most severely affected (based on clinical signs, febrile response, and weight gain) while the pigs infected with SRV07 and SDSU73 were moderately affected, and pigs infected with VR2332 showed minimal clinical signs. One pig coinfected with JXwn06 and bacteria became moribund and was euthanized. An increase in the levels of proinflammatory cytokines in the sera occurred, in general, around day 6-8 post viral infection with the magnitude of increase generally correlating with the severity of clinical disease. The highest viral titers were detected in pigs challenged with JXwn06. A. suis and/or H. parasuis was cultured from the lungs of 3/9 pigs from groups challenged with the bacteria alone, VR2332/bacteria, and SDSU73/bacteria, and from 6/9 pigs challenged with SVR07/bacteria and JXwn06/bacteria, respectively. These bacteria were not isolated from the non-challenged control pigs or pigs challenged with virus alone. Lesions consistent with bacterial pneumonia, including abscesses, were seen in the groups coinfected with PRRSV and bacteria. The levels of proinflammatory cytokines in the serum were often lower for pigs coinfected with virus and bacteria compared to pigs only infected with PRRSV. There was a range of virulence among the PRRSV isolates and differences in their ability to predispose to secondary bacterial infection.