PRRS is generally passed into a herd via other pigs and semen. Researchers are working to analyze other routes of infection. It was found that needles transmit PRRS from PRRS positive pigs to PRRS negative pigs. Contaminated coveralls, boots and hands of people can transmit PRRS to non-infected pigs following the direct contact with infected pigs. Therefore it is good practice to change clothing and clean up after contact with PRRS positive pigs. Results have shown that with “real” conditions (meaning not an experimental set of conditions), PRRS may be transmitted over short distances with infected animal air space, but transmission of PRRS through the air between farms seems to be an infrequent event.

Houseflies and mosquitoes believe it or not serve as a mechanical method of PRRS transmission. The PRRS virus can survive in the fly for 12 hours and the mosquito for 6 hours following feeding on an infected pig, and as little as 1 fly is capable of transmission.