Iowa State University researchers have investigated time and temperature combinations sufficient to inactivate porcine epidemic diarrhea virus in swine feces on metal surfaces similar to what is found in livestock trailers after fecal and other organic matter has been removed by scraping and sweeping. Combinations of time and temperature evaluated represent possible options for trailer decontamination when washing and disinfecting are not possible.
Seven treatment groups representing different combinations of time and temperature were evaluated. Five ml of undiluted PEDV-positive feces (or negative feces for the negative control group) were spread evenly on the bottom surface of a 6-inch by 6-inch aluminum tray with 1-inch sides, made to replicate a trailer floor. Following treatment as outlined in Table 1, the feces were re-collected from the tray, diluted and passed into PEDV-negative 4-week-old pigs via oral-gastric tube. These pigs served as a bioassay to detect the presence of infectious PEDV. Pigs were monitored for clinical signs consistent with PEDV, and fecal swabs were collected on days 3 and 7 post-challenge. Swabs were tested via PEDV RT-PCR.
Each treatment group contained four replicates of the treatment, with passage into separate pigs for the bioassay. An individual pig was the experimental unit. The seven treatment groups and negative control are described in Table 1.
Preliminary results are summarized in Table 2. These results were analyzed via Fishers Exact test and overall, treatment was found to have a significant effect on PEDV status (p=0.0335). More specifically, the 160F10M and 68F7D groups were each found to be significantly different than the positive control group (p=0.0286). No other group comparisons were found to be significantly different from one another.
Conclusions and implications
These results suggest it may be possible to inactivate PEDV in the presence of feces by heating trailers to 160 degrees F for 10 minutes or by maintaining them at room temperature (68 degrees F) for at least seven days. No other combinations of time and temperature were shown to be effective at inactivating PEDV in a contaminated, unwashed hog trailer.
The investigators do not propose that this is a preferred alternative to thoroughly washing, disinfecting and drying trailers after hauling PEDV-positive animals. Rather, this work demonstrates the value of possible alternatives when proper washing and disinfection absolutely cannot be accomplished as a means to reduce the risk of transmitting PEDV between groups of animals.
This information is not meant to suggest alternatives to thorough washing, disinfecting and drying of hog trailers between loads of pigs — these are the gold standard for trailer biosecurity and should be accomplished whenever possible. This information is meant to serve those producers who absolutely cannot wash, disinfect and dry trailers between loads due to facility or logistical constraints.
Heating to 145 degrees F was ineffective at killing PEDV, while heating to 160 degrees F was effective. There are many trailer-drying facilities operating between these temperatures. Until more information is known, producers are advised to increase drying temperatures (trailer temperatures) to 160 degrees F for at least 10 minutes.
This study showed that proper heating in the absence of washing and disinfecting can be effective at killing the PEDV. If producers meet time constraints that keep them from washing and disinfecting trailers, there is still great value in heating these trailers to 160 degrees F for 10 minutes. The heating process requires less time than washing, and so may be able to be accomplished in these instances.