Environmental samples from trailers in which pigs had been transported uncovered porcine epidemic diarrhea (PED) virus in 5.2 percent of trailers not contaminated at arrival, suggesting that the transport process is a source of transmission if adequate hygiene measures are not implemented, according to a recent university study.

The objective of the study was to assess the risks that harvest facilities and transport vehicles engendered in promoting the initial outbreak of a novel disease organism by estimating the incidence of trailer contamination with the PED virus during the unloading process at harvest facilities. Environmental samples were collected from 575 livestock trailers before and after the pigs were unloaded into holding pens at six harvest facilities (83-102 trailers per facility) located in the central U.S. Samples were collected during a period of 2-3 days at each facility.

Contamination during unloading

According to the study, before unloading, 38 (6.6 percent) of the 575 trailers were contaminated with the PED virus. The proportion of contaminated trailers ranged from 2 percent to 14.6 percent among the 6 harvest facilities; the facility level median was 5.0 percent. Of the remaining 537, 28 (5.2 percent) that were not contaminated at arrival were contaminated in the unloading process. Of the 38 trailers that were contaminated on arrival, environmental samples from 13 (34.2 percent) were negative for the PED virus after unloading.


Contamination during unloading occurred at a higher rate if harvest facility staff entered the trailer or if unloading occurred immediately after unloading another trailer that was found to be contaminated.

Control measures

The results of this study suggest that proactive disease control measures should include improved sanitation, hygiene and segregation practices at collection points to limit the spread of the agent early in the outbreak. Simple measures such as limiting contact between drivers and the collection point and requiring drivers to remain on trucks and out of the collection point during the unloading process may have a dramatic effect on limiting the transmission of novel agents.