Porcine Reproductive and Respiratory Syndrome: NEB-1 PRRSV Infection did not Potentiate Bacterial Pathogens

Abstract

Abstract.V. L. Cooper, A. R. Doster, R. A. Hesse, N. B. Harris A 2-phase study was conducted to evaluate the ability of the NEB-1 strain of porcine reproductive and respiratory syndrome virus (PRRSV) to potentiate common bacterial pathogens of swine. In phase I, 25 of 50 4-5-week-old specific-pathogen-free (SPF) pigs were exposed to NEB-1 PRRSV (day 0). Seven days after virus inoculation, 8 groups received 1 of 4 bacterial pathogens: Haemophihs parasuis, Streptococcus suis, Salmonella cholerasuis, and Pasteurella multocida. The ability of NEB-1 PRRSV to produce clinical disease, viremia, neutralizing antibody, gross and microscopic lesions and to potentiate bacterial pathogens was assessed. Response to NEB-1 PRRSV was similar among inoculated pigs; prolonged hyperthermia, lethargy, mild to moderate dyspnea, and cutaneous erythema were consistent clinical signs. No clinical differences were observed in groups after bacterial challenge. Virus was isolated from serum at weekly intervals through the end of the study, and all PRRSV-inoculated pigs had seroconverted by study termination. Two of 5 pigs died in non-PRRSV-inoculated groups challenged with H. parasuis and Streptococcus suis. Mortality in PRRSV-infected pigs was limited to 1 of 5 pigs from the Salmonella cholerasuis-challenged group. Gross lesions were seen in pigs dying after inoculation in H. parasuis-and Streptococcus suis-inoculated groups, in Salmonella cholerasuisand P. multocida-challenged pigs, and in 1 non-PRRSV-inoculated control pig. Microscopic lesions consisted of mild to moderate proliferative interstitial pneumonia, nonsuppurative myocarditis, lymphoid hyperplasia, and nonsuppurative encephalitis in PRRSV-inoculated pigs. Findings in phase I indicated that NEB-1 PRRSV does not potentiate bacterial disease while inducing consistent clinical signs, viremia, seroconversion, and microscopic lesions. Based upon initial findings in phase I, in phase II, 18 of 36 4-6-week-old SPF pigs were exposed to NEB-1 PRRSV (day 0). Two days after virus inoculation, 2 of 4 groups were exposed to either Streptococcus suis or P. multocida. Clinical findings were similar to those of phase I. One of 6 pigs died in each of the Streptococcus suis-challenged groups. Animals succumbed 3 and 5 days after bacterial challenge in the non-PRRSV-inoculated and PRRSV-inoculated groups, respectively. Mild gross and microscopic pulmonary lesions were observed. Phase II findings support the conclusions of phase I that NEB-1 PRRSV does not potentiate certain bacterial infections of swine.

Prior Infection of Nursery-Age Pigs with Porcine Reproductive and Respiratory Syndrome Virus Does not Affect the Outcome of Transmissible Gastroenteritis Virus Challenge

“…21 Mild, prolonged, recurrent fever was reported for 4-6-weekold SPF pigs infected with a Nebraska strain of PRRSV. 2 The prolonged, mild fevers in pigs in that study were similar to the results observed in 2-weekold pigs infected with PRRSV strain NADC-8.…”

“…3 In contrast, other researchers were unable to demonstrate any potentiation caused by PRRSV for Haemophilus parasuis, S. suis, S. cholerasuis, and Pasteurella multocida. 2 Likewise, additional experiments have demonstrated that clinical signs or pathology due to Mycoplasma hyopneumoniae was not increased by prior PRRSV infection. 19 In terms of respiratory viral pathogens, sequential infections with PRRSV and then porcine respiratory coronavirus or with PRRSV followed later by swine influenza virus in both instances produced more severe clinical signs in pigs than when any of the 3 viruses were inoculated individually.…”

A review of evidence for immunosuppression due to Porcine Reproductive and Respiratory Syndrome Virus

“…This ambiguity may be due to a number of factors, including the particular strain of PRRSV and/or the secondary pathogen used, the timing of such challenge and the status and immunological history of the pigs involved. Cooper et al [21] were unable to potentiate infections by challenge of 4-5 week-old specific pathogen-free (SPF) pigs with H. parasuis, S. suis, S. cholerasuis or P. multocida seven days after infection with an American PRRSV strain (AmPRRSV). But Galina et al [28], using the virulent strain of S. suis serotype 2 (DH5) in SPF piglets, observed that only those which had previously been inoculated with EuPRRSV developed clinical signs, a suppurative meningitis and large numbers of the bacteria in tissues, including the brain and meninges.…”

Proinflammatory cytokines and viral respiratory disease in pigs

“…Galina et al [43] 34,116,132]. Variable degrees of respiratory disease and growth retardation may result from infections with PRRSV followed by either PRCV or SIV [141].…”