PMWS Study - First Results
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Results of PMWS StudyClick on the links below or scroll down the page to view the first results of our study of PMWS between 2003 and 2004. We will publish results of how levels of mortality were affected by different management practices in our 116 farms in a future update. How many farms did we visit and how much PMWS was there? How many farms did we visit and how much PMWS was there?We visited 116 farms between August 2003 and July 2004. At the visit 83% of farmers said that they had PMWS on their farm. All the vets agreed with these farmers and two more farms were identified as PMWS positive by their vet. There were two peaks of breakdown with PMWS reported, one in late 2000 and one in late 2001; at least one farm broke down each month between 2000 and 2003. The average percentage of deaths in growers at the peak of disease was 18%. This lasted for 3 – 5 months. Most farmers considered that their unit was still affected by PMWS. Only 9 farmers considered that their unit had recovered. These farmers estimated that they had PMWS for an average of two years and some still had post weaning mortality of 4 – 5%. What influenced when a unit got PMWS?The first set of analysis we did was to consider which management factors affected when a unit broke down with PMWS. For this analysis we used the management practices that were occurring in the six months before a farmer said the herd got PMWS for all affected farms and for farms that had not broken down with PMWS we used the management of the unit in the six months before our visit. You will remember that foot and mouth disease (FMD) occurred in 2001 and that this changed quite a lot of management practices on farms – particularly those related to animal movements. Because of this we analysed the risks of breakdown with PMWS before, during and after the FMD epidemic of 2001. The main findings from this analysis were that Before FMD farms most likely to break down
During FMD farms most likely to break down
After FMD farms most likely to break down
Where were the herds that broke down?We have plotted the timing of herd breakdowns on a map. What does this tell us?These results indicate that
These results give average effects. We cannot be sure how any one farm got PMWS. We can only test the common reasons for introduction of PMWS and there will always be unexplainable breakdowns. What is causing PMWS?What these results tell us is that the infectious agent (probably a virus) has spread slowly through Britain and spreads slowly once on a farm. The agent can spread by pig to pig contact and can survive in the environment to be spread by humans and / or wildlife. No other known infectious agent in pigs has been associated with this spread, so we are looking at a new disease. Is PMWS caused by PCV2?We detected PCV2 antibody on every farm in our study and actual PCV2 virus in about 80% of the pigs we took for post mortem examination. The presence of virus was not linked to units with PMWS. However, pigs which were sick, which we took for post mortem examination, did have large amounts of PCV2 virus. This suggests that PCV2 virus is associated with the disease PMWS but is probably not the cause. Why do we still not know the cause of PMWS?To date no new virus has been identified. Detection of the SARS virus in humans cost millions of pounds. Identifying new infectious agents is very expensive and quite a chance process. Groups around the world are still testing samples from pigs with PMWS for new viruses. The role of other diseases on the farmPMWS occurred sooner on farms with PRRS, Salmonella and / or E. coli disease. This suggests that certain farms are more likely to get any new disease. Farmers who reported other diseases on their farm were also more likely to have higher levels of mortality. In particular, farms with PRRS reported nearly twice the levels of death from PMWS compared with farms without PRRS. Deaths were also higher on farms with parasuis disease. What can farmers do now?The results from this first analysis indicate that good biosecurity is definitely worthwhile.
These practices apply to all diseases. PMWS is a timely reminder of this. Reducing the level of disease from known infections will reduce the impact of PMWS on your farm. This may include vaccination and new approaches to management to reduce cycling of disease on farms. Other countries have varied their approaches to reduce disease. In the USA, segregation by age is used. In Sweden, a weaning age of six weeks is thought to have an important role in reducing a young pig’s susceptibility to disease. Clearly what we do depends on many local factors and we may have to look for new approaches in Britain.
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