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Title: Comparison of Asian highly-pathogenic PRRSV isolates to US isolates for their ability to cause secondary bacterial infection in swine

item Brockmeier, Susan
item Loving, Crystal
item Palmer, Mitchell
item Spear, Allyn
item Faaberg, Kay
item Nicholson, Tracy

Submitted to: Research Workers in Animal Diseases Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 10/1/2012
Publication Date: 12/2/2012
Citation: Brockmeier, S.L., Loving, C.L., Palmer, M.V., Spear, A.R., Faaberg, K.S., Nicholson, T.L. 2012. Comparison of Asian highly-pathogenic PRRSV isolates to US isolates for their ability to cause secondary bacterial infection in swine. Conference of Research Workers in Animal Diseases. Paper No. 184.

Interpretive Summary:

Technical Abstract: 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 U.S. 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 U.S. 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 had to be euthanized. 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. There was a range of virulence among the PRRSV isolates and differences in their ability to predispose to secondary bacterial infection.