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March 10, 2020
Porcine epidemic diarrhea virus is an enteric pathogen of swine that has been circulating in other continents for quite a few decades before it suddenly emerged in the United States in 2013. The virus spread rapidly throughout the country disrupting the industry's sow herd throughput as hundreds of sow herds were infected in a short period of time, leading to millions of piglets succumbing to the virus generating important losses.
Additionally, the magnitude of the epidemic was such that even hog market prices were affected as prices increased considerably. Producers, practitioners and industry came together and intervened rapidly, leading to a strong decrease in the number of new infections during the following years. This whole scenario certainly raised several questions around national, regional and farm biosecurity.
Currently, this pathogen continues to be present in our industry and unfortunately continues to reach our sow and growing pig barns. After the 2013 epidemic, the number of sow farms becoming infected with PEDV has decreased significantly. However, there continues to be a low-level incidence below 10% based on Morrison Swine Health Monitoring Project data. For instance, PEDV incidence for the current MSHMP 2019-20 year is 2.5%, which is around the same low incidence trend as the 2018-19 MSHMP year. This is certainly good news for the industry; however, MSHMP is only assessing breaks at the breeding herd level and the situation at the growing pig herd is still uncertain.
As we analyze the MSHMP database, most of the farms that reported a PEDV break have had a previous infection in recent years. When assessing the spatial distribution of these breaks between 2013 and 2019, at least one outbreak has been reported in 138 of the 3,141 counties in the United States. In 2013, there were 43 counties that had reported at least one break, whereas in 2014 this number increased to 97 counties.
The rapid intervention and effort by producers and practitioners allowed this number to drop to 31 counties in 2015. In 2016, outbreaks of the virus were reported again in 31 counties, which were not necessarily the same counties as in previous years. However, in 2019 there were breaks reported in only 17 counties in seven states throughout the United States. One important message from the data collected through the MSHMP is that the cases reported in 2019 are scattered through the United States and are not limited to high-dense regions.
In addition, production systems continue to work toward elimination while prevention is in place. Unfortunately, this virus continues to be present in our barns as there are reports of growing pigs becoming infected toward the end of the finishing period, indicating that the risk is still present, and we are continuing to give this virus opportunities to reach naïve populations.
Still, more work needs to be done, especially at the growing pig level to further understand the epidemiology of PEDV in this population together with the role of this population on the occurrence of PEDV at the sow herd level. Presently, the industry has moved to raising pigs in large populations and growing pig sites are not the exception, therefore these populations can become efficient virus generators even if it's for one or two days either at the barn or slaughter plant. The more viral particles being generated, the higher the probability of these particles contaminating surfaces (e.g. fomites) that can travel several miles and reach other pigs.
Overall, the fact that the number of counties and the number of cases per county has decreased over time is an important indicator of how the dynamics of the virus has been influenced through interventions. This is also an indicator of industry success as all worked toward the same objective, to prevent viral introductions, which has had a tremendous impact. As these efforts continue and more time and resources are invested in the growing pig side of the business, very likely this virus may not have hosts where to replicate, bringing risk to an even lower level. Interestingly, those same interventions at the growing pig level may also have an impact on other diseases, making these efforts a win-win situation.
Sources: Cesar A. Corzo, Juan Sanhueza and Mariana Kikuti, who are solely responsible for the information provided, and wholly own the information. Informa Business Media and all its subsidiaries are not responsible for any of the content contained in this information asset.
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