A recent study that I conducted as veterinarian and infectious disease researcher with the Swine Vet Center in St. Peter, MN, found manure in deep pits still had live porcine epidemic diarrhea virus (PEDV) four months after positive pigs were placed on the site. This finding continues to raise concerns about the 2014 manure pit pumping season, and what it means for the potential to spread the disease.
Since the introduction of PEDV into the United States’ swine herd in 2013, the disease has spread rapidly across many states causing devastating losses in suckling pigs. The Swine Health Monitoring Project, which is an ongoing study sponsored by the National Pork Board (NPB), U.S. Department of Agriculture, National Pork Producers Council and the American Association of Swine Veterinarians showed that during the fall and winter of 2013-14, the rate of new infections reported in sow herds across the United States surpassed epidemic levels (www.cvm.umn.edu/sdec/SwineDiseases/pedv).
Since the end of June, the virus has remained relatively quiet. Early studies funded by the NPB at the University of Minnesota showed that the virus could survive at least 28 days at very cold or frozen temperatures, and at room temperature the virus appeared to be able to survive for at least 14 days (NPB project number 13-215). That said, very little was known about how long the virus could survive in the manure pits under swine barns.
Recent Research Results
In this study, manure was sampled from pump-outs of 30 wean-to-finish swine barns across southern Minnesota and northern Iowa in late-August and early September. Fifteen sites had PEDV-positive pigs placed approximately six months prior to sampling. The other 15 sites had PEDV-positive pigs placed about four months prior to sampling. At each site, samples of manure were drawn from the pit using a 10-ft. section of PVC pipe angled underneath the animal space as far as possible.
Of the 15 sites sampled at six months after having PEDV-positive pigs on them, 14 tested positive for the presence of PEDV using polymerase chain reaction (PCR), whereas 13 of 15 of the barns at the four-month mark tested positive. On average, all barns had a reported cycle time (CT) value of about 30, indicating a fairly high concentration of viral genetic material.
Since the PCR is not able to discern if the virus is alive or dead, swine bioassay was conducted. In this test, 20 mL of manure from one site was carefully administered to one 21-day old pig through a stomach tube. If the virus was alive, this pig develops a PEDV infection, which was confirmed at the diagnostic laboratory. If the virus was dead, the pig does not develop a PEDV infection.
None of the barns six months after having PEDV-positive pigs resulted in the bioassay pigs developing infection. Surprisingly, two of the barns that were sampled four months after having PEDV-positive pigs resulted in the bioassay pigs developing infection.
This study suggests a few barns will still have live PEDV; however, there are a few limitations that should be considered. In this study, manure was sampled only from the outside perimeter of the barn, through pit pump-outs. Additionally, a very small amount of manure (20 mL) was tested for live virus. It is possible that these conditions may have affected the ability to detect live virus in very large pits.
With this in mind, it is prudent to remain extremely cautious during the 2014 pit pumping season. As with previous recommendations, it is advised to always start by pumping disease-free sites, and finish by doing sites with disease last, especially those most recently infected with PEDV. Practicing good biosecurity is imperative. Any people, vehicles, tools or equipment that comes in contact with the facility should be cleaned, disinfected and allowed as much “down-time” as possible to help prevent the transmission of disease. Routing manure trucks over roads less frequently traveled by animal transport trucks might help minimize the risk of spreading PEDV.
Communication with neighbors is essential. This will be especially true if potentially infectious manure needs to be applied near negative farms. Communication may allow for alternative arrangements to be made where potentially infectious manure could be exchanged with manure from disease-free farms. Your herd veterinarian can be a source to help facilitate these discussions. Additionally, many regional projects are now monitoring for PEDV, and they can be another way to open up lines of communication.
Additional studies are being designed to test for live virus on sow farms in farrowing, gestation and gilt development units. Because of the presence of animals of different ages on these sites, the patterns of PEDV infections are very different from wean-to-finish sites. This could influence how many months the virus remains infective, and how much live PEDV is present in these pits.
Use Caution During Pit Pumping
In conclusion, it appears that some barns will still have live PEDV in them during the pit pumping season this fall. It is recommended to be very careful about sequencing of equipment when possible and practice good biosecurity measures. It is hopeful that careful planning and good communication may help minimize the spread of PEDV during this time. Additional studies will be conducted to better understand the risk of manure coming from sow barns where the infection patterns are likely to be very different.
Steve Tousignant and the Swine Vet Center of St Peter, MN, would like to thank the NPB and the USDA for the quick response in providing funding to get this study completed.