Project Title: Analysis of prevalent winds in areas with suspicious cases of PRRSV’s lateral transmission between pig farms

Institution: University of Minnesota

Outcome/Results: Results indicated that PRRS virus spread between herds will not necessarily occur just because wind is blowing from an infected herd towards a negative site.

Summary: This project analyzes prevalent winds in neighboring PRRS virus-infected and PRRS virus-negative pig sites. Eight pairs (1 pair consists of 1 PRRS virus-infected site and 1 PRRS virus-negative site) were selected because airborne transmission was suspected (cases) and 8 pairs were selected because airborne transmission apparently did not occur (controls). To determine the relationship between prevalent wind direction and the potential spread of PRRS virus from infected herds to known-negative herds, information about virus strain, weather conditions and location of herds were analyzed. In all 8 PRRS cases, there was at least one instance where wind was of sufficient speed and duration and in the correct direction during the 2 week period when infection was thought to occur. The distance between sites varied from 1.10 to 12.02 km. However, there was also at least one occasion where wind was of sufficient speed and duration and in the correct direction for all control pairs of herds. The distance varied from 1.48 to 7.01 km. The distances between sites or the wind conditions did not differ significantly between case and control pairs of herds. The results of this study indicate that PRRS virus spread between herds will not necessarily occur just because wind is blowing from an infected herd towards a negative site. More information is necessary to understand why some herds apparently become infected by airborne transmission while others remain un-infected under similar conditions of season and distance between sites.