Questions & Answers
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Here are answers to some of the questions we have been asked by visitors to this site. If you have a question about PMWS, email it to us at pmwsinpigs@warwick.ac.uk. QuestionsWhat about the classical swine fever (CSF) epidemic, or purchasing semen or associations with certain breeds? AnswersQ. What about the classical swine fever (CSF) epidemic, or purchasing semen or associations with certain breeds?A. There are two reasons why we may not have detected an association between PMWS and any given factor that was in our study. One is that there is no association; the other is that this study was not powerful enough to detect a statistical association. So e.g. it would be wrong to say that there was no risk from purchasing semen, it is correct to say that this study did not detect a significant risk from purchasing semen. The power of the study is determined by the number of farms who agreed to provide data. Q. Where did PMWS come from when high health herds that were geographically isolated broke down?A. We do not know from our study. This is probably because there were very few of this type of farm in our study and so we did not have data that would assist in answering this question. Q. What proof is there that three days pig freedom is necessary?A. Epidemiology cannot prove anything. What it can do is provide a statistical strength of association between a practice (e.g. 3 days pig free) and the outcome (breakdown with PMWS). In this study, the practice of not asking visitors to avoid pigs for three days before visiting the farm was strongly associated with PMWS breakdown. This could be a direct association, i.e. avoiding pigs was protective, or indirect, i.e. avoiding pigs was associated with something that we did not measure and it was this ‘something’ that was the true risk. We can never be certain; we do know that the 3 day pig free rule was not explained away by proximity to other farms, quarantine practices or any other biosecurity action that we measured (and there were lots!). Q. Are outdoor farms more affected than indoor farms?A. From our study, larger herds were more strongly associated with PMWS breakdown and outdoor farms tended to be larger. It was the size of the breeding herd rather than its location indoors or outdoors that was the strongest association. |
