#06-151

Complete

Date Full Report Received

01/04/2008

Date Abstract Report Received

01/04/2008

Investigation

Institution:
Primary Investigator:

It is not uncommon for swine herds to become infected with PRRS virus with no obvious source of the infection. In such cases, the producer and veterinarian having explored all possible routes of transmission or contamination, conclude that the virus must have been airborne from a neighboring farm. In this study, we were interested in determining how frequently weather conditions might have been suitable for PRRS virus to be transmitted through the air. We selected 8 herds that were presumed to have been infected by airborne virus and 8 others where no PRRS virus was transmitted. We analyzed weather data for a 2 week period in both sets of herds. We found that wind and other weather conditions were suitable for virus to survive and transmit in the air from the presumed source to the newly infected herd in all 8 cases. However, we also found at least one time period where wind and weather were suitable for airborne transmission to the herds where no infection occurred. This study reminds us to be cautious in concluding that a herd must have been infected by airborne transmission. Wind and weather conditions appear to frequently be suitable for PRRS virus transmission and yet transmission does not occur. Other factors such as the strain of the virus, co-infections, population size and density at the presumed source and recipient site, age of the pigs, wind dispersion, ventilation type and direction of fans and inlets, must be playing a role.