The first recognised case of PWCS was in a 100-sow farrow-finish barn experiencing illness in nursery piglets shortly after weaning resulting in increased nursery mortality from baseline (about two per cent) to about seven per cent. The farm is well managed with excellent stockmanship skills, and of high health status in a reasonably isolated location. Replacement gilts and boars are purchased from one genetic company although the source farm was changed in 2006. Feed is manufactured on farm using mostly grains grown on the farming operation. Routine vaccinations including a piglet PCV2 vaccine are administered at weaning.

Piglets are robust and appear healthy at weaning. Within one to two weeks of weaning, affected pigs demonstrate lethargy, anorexia and become thin and hairy. Within three to four weeks of weaning, these pigs become emaciated and most are euthanised. Many have diarrhoea for a short period of time but this was not a consistent finding. The affected pigs are not runts in that skeletal growth indicates they are normal-sized pigs before becoming anorexic. A few less severely affected pigs may start to eat in the later stages of the disease but these remain smaller than pen-mates and are slow growers in the finisher barn.

Many management and medical interventions involving the farm’s diets, ventilation, sanitation and medication and vaccination programmes have been attempted but all interventions have been ineffective with the exception of disinfecting nursery flooring with hydrated lime. Although this supports that PWCS may be caused by an infectious agent, hydrated lime is harmful if swallowed or inhaled, and causes burns to skin and eyes. Thus, its long-term use as a disinfectant in affected farms is not practical.

The cause of PWCS is unknown. On necropsy, the affected pigs had severe thymic atrophy and little to no gastrointestinal contents. Microscopically, the small intestinal villi are atrophic in all sick pigs, and some had mild to severe colitis. However, colitis was also found in clinically healthy penmates of the sick pigs in the index farm. Thus, we are at present uncertain if these lesions are a direct result of PWCS, or a consequence of weaning, reduced feed intake and/or other farm-related factors. Extensive diagnostic testing has been performed for PRRS, PCV2 and other common swine pathogens. Calicivirus has been ruled out. Calicivirus, which can cause similar intestinal lesions in germfree pigs, was detected in both healthy and sick pigs from this farm by PCR.

The disease is currently affecting or has affected several herds in Saskatchewan (Gauvreau and Harding, 2008; M. Jacobson, 2009, personal communication), up to 20 farms in Manitoba (P. Provis, 2009, personal communication), one farm in Ontario (Br. Jones, 2009, personal communication) and numerous farms in Kansas (S. Henry, 2009, personal communication). Clinically, PWCS waxes and wanes in affected farms, and is not predictable. The majority of pigs with PWCS die, increasing mortality in three- to nine-week-old pigs from one or two per cent to betwen six and 10 per cent on most affected farms.

Future Plans

Having ruled out the common pig diseases, attention has turned to discovering the potentially unusual agents associated with PWCS.

Using advanced microbiologic techniques, screening has begun of affected pigs for all known animal and human viruses and bacteria. Dr Yanyun Huang, a PhD student at WCVM, has begun a pathological review of suspect cases from Manitoba and Ontario to determine similarities in terms of the distribution and severity of lesions.

The researchers have received research funding from the Saskatchewan Agriculture Development Fund, which allows them to continue research, with the ultimate goal of finding the cause and developing diagnostic test(s) which will lead to improved control strategies. To help with this research, the author invited producers to contact the University if they observe clinical signs indicative of PWCS (Table 1).

Acknowledgements

The authors wish to acknowledge the many people who have contributed their expertise to help solve these cases. This includes the colleagues and technicians at Prairie Diagnostic Services, Warman Veterinary Services and Western College of Veterinary Medicine, including Drs. B. O’Connor, J. Hill, H. Gauvreau, and colleagues from out of province including J. Delay, B. Jones, S. Henry, P. Provis, and M. Swendrowski. Funding for this project has been provided by the Saskatchewan Agriculture Development Fund, the Saskatchewan Agriculture and Food (WCVM Disease Investigation Program), and the Saskatchewan Pork Development Board. A special note of thanks is offered to the producers for their patience and continued cooperation. They will remain anonymous for reasons of confidentiality.

Note: This abstract is partially reprinted with slight modifications from Harding, J. “Swine Health Challenges and Emerging Diseases in Western Canada”, Proceedings of the Saskatchewan Pork Industry Symposium, Nov. 17-18, 2009, Saskatoon Inn, Saskatoon, Saskatchewan, 19-20.

Further Reading

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You can view the other papers presented at the Manitoba Swine Seminar 2010 by clicking here.