|The following article is a special report from the 2014 Allen D. Leman Swine Conference|
There were so many good sessions at the 2014 Allen D. Leman Swine Conference that it was difficult to pick highlights for the PED Newsletter. However, research presented by Dr. Andres Perez, associate professor in the College of Veterinary Medicine, University of Minnesota, gave some interesting clues to how and when Porcine Epidemic Diarrhea virus (PEDv) is transmitted.
Perez’s findings showed:
- There were areas and times at highest risk for disease and that disease spread in specific directions
- Cases neighbored other cases (<20thand <4th order of neighborhood in NC and IA, respectively)
- Clustering was maximum within 1 week, high within 2 weeks, and still significant within 3 weeks.
- Clustering increased linearly, up to 1 mile, and then remained stable.
The Data Set
Perez explains most of the data came from farms (>2000) in four counties. About 59 percent of the farms were finishing operations, 21 percent were nurseries and 15 percent were sow farms. There were 614 positive sites, representing 30 percent of the farms (54.6 percent lateral). Reporting began in July 2013 and ended in January 2014.
“There were five significant clusters,” says Perez. “In North Carolina, hog operations are largely clustered, and as a result, there can be a huge concentration of cases in one single location.
“This study illustrates how they relate to each other,” he continues. “We computed the number of cases we found and at the end of the day, the maximum clustering that showed distances in time and space was 2 kilometers.”
In other words, if you have an operation within one mile of an infected farm, you’re in a critical area. Furthermore, your farm is more susceptible to becoming infected within the first 5 or 10 days of the infection on your neighbor’s nearby farm. There appears to be a relationship between time and space.
A particularly interesting finding was a highly significant trend towards NE: 33.8°.
Iowa Study Results
Perez says he also collected data from four Iowa companies, located in several counties. In this study, there were 156 positive sites (37 percent) (73 percent lateral). These cases started in May 2013 and ended in Feb. 2014.
“In one week, something changed and we saw multiple cases,” he reports, “and in Iowa we saw a highly significant trend towards Southeast: 322o.”
There was a cluster at the first levels of the neighborhood (meaning if your farm is within a mile of an infected farm, your herd is likely to become infected).
“Time and space is a similar shape to what we had in North Carolina,” says Perez. “Most of the clustering is within one mile/2 km., and the same approximation can be made for time [the closer you are to the beginning of an infection, the more likely your neighboring herd is to become infected].”
It’s extremely interesting that Perez and the team of researchers identified these common patterns. “We now know there were areas and times at highest risk for disease and that disease spread is more likely from specific directions. The data is compatible with the hypothesis of airborne transmission of PED virus,” he states.