Infectivity of Swine Manure from Pits at Varying Lengths of Time Post Infection with Porcine Epidemic Diarrhea (PED) Virus

October 8, 2014 — 

Preliminary data from work conducted at the University of Minnesota indicates when PED virus is experimentally inoculated into manure, it is capable of surviving at least 14 days at 25 degrees Celsius, and greater than 28 days when stored at 20 and 4 degrees Celsius (Goyal #13-215: University of Minnesota Environmental stability of PED (porcine epidemic diarrhea) virus. National Pork Board). With this in mind, little is known about the duration of which manure from field settings is able to retain viable PED and therefore making informed decisions regarding how to sequence pumping crews and risks of applying infective manure is challenging. [Source: Swine Vet Center; Steve Tousignant, DVM]

The objectives of this pilot project are:

1. Improve our understanding of the risks posed by manure in pits transported and applied to fields, as well as risks to negative pigs entering potentially contaminated grow finish sites using samples from field infections rather than spiked samples from the lab.
2. Additionally, by sampling a large cross section of farms at 6 and 4 months post infection, it may be possible to detect associations between bio assay positive (or negative) pit status and variables we intend to measure for each barn and pit.

Methods: In this project manure was sampled from barns that were either filled with known PEDV positive pigs or that had confirmed lateral infection during the nursery (through contaminated feed, transport, etc.). 15 barns approximately 6 months post infection and 15 barns approximately 4 months post infection were selected for the study. Manure was sampled through pit pump out using a 10 foot length of PVC pipe angled into the pit under the pigs as far as collection personnel could reach.

Samples were first tested by PCR at the U of MN veterinary diagnostic laboratory. Samples that tested positive by PCR were then tested by swine bio assay. 21 day old weaned pigs were used for the bio assay. Each pig was assigned to a manure sample and housed individually. 20 mL of the manure sample was administered to each pig via a stomach tube. Pigs were observed for a period of 3.5 days, and then delivered to the U of MN for diagnostic work up. Negative control pigs received manure from a known negative barn. Positive control pigs received feedback material from a known positive sow farm.

Results:

• 6 month post infection barns – Of the 15 barns sampled, 14 tested positive by PCR (93%). Of these positive samples, 0 tested positive for live virus by swine bio assay.
• 4 month post infection barns – Of the 15 barns sampled, 13 tested positive by PCR (86%). Of these positive samples, 2 tested positive for live virus by swine bio assay (2/13 = 15%).

Discussion and preliminary conclusions: The findings of this study provide the first insight into the survivability of PEDV in the pits of swine barns. These data suggest there could potentially be less live virus in manure pits than originally suspected. That said, 15% of the barns tested by bio assay were positive for live virus. An important limitation, however, of this study is that we tested only 20 mL of manure from pits that contain upwards of 1 million gallons. Additionally, we sampled only around the outside of the barn through the pump outs.

In conclusion, it is still prudent to be careful when sequencing pit pumping crews in the fall of 2014. As before (with diseases such as PRRS), clean sites should be pumped first, followed by barns that have had the longest amounts of time post PEDV infection and then working towards the barns that have had less amount of time post infection. Communication with neighboring swine farms is crucial, especially when manure has to be applied near to their sites. This communication may allow for the development of alternative arrangements to be made, allowing negative manure to be applied where positive was originally planned to be applied.

Additional work is ongoing to try to understand factors that favored the survivability of the 2 positive samples in the 4 month post infection barns. Results will be made available as soon as the analysis is complete.