Biosecurity is still the most important way of keeping disease out. It is critical for staying disease free or maintaining your current health status and must be a part of any eradication programme; otherwise the chances of long-term success are severely limited. On many farm visits, one finds biosecurity is minimal and surprisingly, when you ask “how did the disease come in?” the farmer knows but has not really done anything to stop further infections coming in – too much trouble? Or if they have carried out eradication before they expect it to break down within 6-12 months “like it did the last time.” I frequently say “think of the farm as a fortress and how best you can defend it and keep infections outside.”
More specific pathogens and prevention
If we look at prevention of disease we have been fortunate to have usually an array of vaccines, therapeutic drugs etc to control the effects of the disease. Improvements in management, housing, heating and ventilation, nutrition all have played a part. It is when we have got one infection, then another, then another, the effects of disease complexes can make a major impact on a farm's productivity and profitability and then the farmer usually considers the eradication option.
A combination of PRRSv, which is immunosuppressive, Enzootic Pneumonia (EP), which can also be immunosuppressive and a pathogenic strain of Actinobacillus pleuropneumoniae (App), leading to the porcine respiratory disease complex (PRDC) is a classic example. If the App isolate has developed resistance to the cheaper antibiotics like tetracyclines or trimethoprim/sulphas it is almost a necessity to go for the eradication option. Breaking down with swine dysentery is also a common reason to go for eradication because of its severity.
Most eradication programmes are focused on eliminating infections from the breeding herd. There they usually have some immunity, a low level shedding of the virus or bacteria and a good chance of getting rid of the bug. Trying to eradicate infections from growing pigs is very difficult and also costly, so partial depopulation of the growing/finishing herd is important.
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