Synergism between porcine reproductive and respiratory syndrome virus (PRRSV) and Salmonella choleraesuis in swine

Porcine reproductive and respiratory syndrome virus (PRRSV) and Salmonella choleraesuis are two leading causes of economic loss in the swine industry. While respiratory disease is common in both S. choleraesuis and PRRSV infe ctions, the factors that contribute to its development remain largely undef ined. We investigated the interaction of PRRSV, S. choleraesuis, and stress in 5-week-old swine. All combinations of three factors (inoculation with S . choleraesuis on Day 0, PRRSV on Day 3, and treatment with dexamethasone o n Days 3-7) were used to produce eight treatment groups in two independent trials. Fecal samples, tonsil and nasal swabs, serum samples and postmortem tissues were collected for bacteriologic and virologic examinations. No cl inical signs were observed in pigs inoculated with only PRRSV or only S, ch oleraesuis. In contrast, pigs which were dually infected with S, choleraesu is and PRRSV exhibited unthriftiness, rough hair coats, dyspnea, and diarrh ea, The pigs which received all three treatment factors were the most sever ely affected and 43% (three of seven) of the animals in this group died. In dividuals in this group shed significantly higher quantities of S. cholerae suis in feces and had significantly higher serum PRRSV titers compared to o ther treatments (p less than or equal to 0.05). In addition, S. choleraesui s and PRRSV were shed longer and by more pigs in this group than other grou ps and S. choleraesuis was recovered from more tissues in this group on Day 21 post inoculation. These results suggested that PRRSV, S. choleraesuis, and dexamethasone acted synergistically to produce a syndrome similar to th at observed in the field. (C) 2000 Elsevier Science B.V. All rights reserve d.