Evaluation of 4 intervention strategies to prevent the mechanical transmission of porcine reproductive and respiratory syndrome virus.

Four intervention strategies were tested for their ability to prevent the mechanical transmission of porcine reproductive and respiratory syndrome virus (PRRSV): the use of disposable plastic boots to prevent contamination of personal footwear, the use of boot baths to disinfect PRRSV-contaminated plastic boots, the use of plastic slatted (Polygrate) flooring in the anteroom to prevent PRRSV contamination of incoming personal footwear, and the use of bag-in-a-box shipping methods to prevent PRRSV contamination of the contents of a container destined for a swine farm. Ten PRRSV-positive replicates and 10 PRRSV-negative (sham-inoculated) replicates were used for each strategy. Swabs were collected from selected sites and tested by TaqMan polymerase chain reaction for PRRSV RNA and by swine bioassay to confirm the presence of infectious PRRSV. Results indicated that the use of disposable boots, bleach boot baths or bag-in-a-box shipping methods was highly efficacious in preventing mechanical transmission of PRRSV. In contrast, the use of Polygrate flooring in the anteroom did not prevent contamination of personal footwear. The numbers of PRRSV-positive samples from the Polygrate surface and the soles of incoming footwear placed directly on the Polygrate surface were not significantly different (P = 0.24) from those of footwear that directly contacted the floor of the contaminated anteroom. Although these results are promising, this study should be considered a pilot project and the intervention strategies not considered biosecurity protocols. The model used may or may not represent field conditions. Therefore, the information should be used to develop larger experimental studies, with sufficient statistical power, in combination with field-based epidemiologic studies to better assess the role of mechanical transmission of PRRSV under field conditions.