Clint Lichty from South West Ontario Veterinary Services, Nurse Sows: The Smoking Gun on IAV and PRRS Virus Transmission

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When McRebel is used as part of an Influenza Type A (IAV) or Porcine Reproductive and Respiratory Syndrome (PRRS) elimination program the goal is to reduce the internal transmission of the virus that sustains the infection of the herd. The McRebel Concept, developed by Dr. Monte McCaw  is well accepted and understood but few studies have examined the exact mechanisms for transmission from pig to pig during the pre-weaning period. These University of Minnesota researchers developed a novel nurse sow model to evaluate the transmission of IAV and PRRSV from infected piglets to lactating sows and further examined transmission from the lactating sow to a litter of adopted naive piglets. There were two studies. In one study piglets were infected with either IAV or PRRSV and then these infected piglets contaminated the udder skin of lactating dams with their nasal and oral secretions while suckling. Once the skin was confirmed virus positive for IAV and PRRSV, the sows were moved to separate empty clean rooms to adopt IAV and PRRSV negative suckling piglets.

The researchers found the following:

  • Infected piglets contaminated the skin of the sows udder with infectious virus
  • In the case of IAV 1 out of eight (12.5%) adopted piglets tested IAV positive 1-day post-adoption (dpa) and the entire litter (8 out of 8) became positive by 4 dpa.
  • In the case of PRRSV, 3 out of 11 (27.3%) pigs tested rRT-PCR positive 2 dpa and there were 7 out of 11 (63.6%) pigs positive at the termination of the study at 7 dpa.

Take Home Message:

  • IAV and PRRSV transmission can occur from a litter of infected piglets to the skin of a sows udder.
  • IAV and PRRSV transmission can occur from the contaminated skin of a sow’s udder to previously naive adopted piglets .
  • The use of nurse sows in pig farms is a technique that is useful in reducing pre-weaning mortality but the practice does facilitate the transmission of IAV and PRRSV to piglets prior to weaning and helps in keeping the virus in an endemic state
  • Sometimes it takes a while for the science to “catch up” with the experience.

Ref: Garrido-Mantilla J, Culhane MR, Torremorell M.  Transmission of influenza A virus and porcine reproductive and respiratory syndrome virus using a novel nurse sow model: a proof of concept.  Vet Res. 2020 Mar 14;51(1):42. doi: 10.1186/s13567-020-00765-1.

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