Effect of concurrent infections on persistence and shedding of porcine reproductive and respiratory syndrome virus and transmissible gastroenteritis virus

Objective: To determine the duration of persistence and shedding of porcine reproductive and respiratory syndrome virus (PRRSV) and transmissible gastroenteritis virus (TGEV) for pigs inoculated with one or both viruses. Methods: Pigs were allocated to three principal groups (Principal Groups A, B, and C: four pigs per group). They were inoculated with PRRSV (Principal Groups B and C) at 14 +/- 2 days old (Day 0) and with TGEV (Principal Groups A and C) on Day 13. On Day 28 and at or about 14-day intervals (up to and including Day 83), a group of two age-matched, naive pigs were placed in contact with each Principal Group for an interval of 10 days. Samples obtained at selected intervals from both principals and contacts were tested for PRRSV (sera and lung lavage samples) and TGEV (rectal swabs). Sera were also tested for antibody to both viruses. Results: Contact transmission of PRRSV and TGEV was detected for 56 and 15 days, respectively. A longer interval of infectionwith PRRSV (up to 121 days) was detected when samples from principals were tested using a nested-set polymerase chain reaction. Concurrent infection with PRRSV and TGEV did not enhance clinical effects, shedding, or persistence of eithervirus. Implications: Pigs infected with PRRSV and TGEV should be kept isolated for more than 8 and 2 weeks, respectively, to reduce the chance for virus transmission. Concurrent infection with TGEV and PRRSV is likely to have little or no effect on subsequent shedding or persistence of either virus.