Transmission of porcine reproductive and respiratory syndrome virus by houseflies (Musca domestica).

Three hundred houseflies were allowed to feed on donor pigs viraemic with porcine reproductive and respiratory syndrome virus (PRRSV) on the fifth, sixth and seventh days after the pigs had been inoculated with the virus. After 60 seconds, the flies' feeding was interrupted, and they were transferred manually to feed to repletion on a naive recipient pig housed in a separate room. To enhance the chance of the flies obtaining the pigs' blood, the back of each pig was scarified with sandpaper until a slight haemorrhage was visible. The PRRSV was transmitted from the donor to the recipient pigs, and PRRSV RNA was detected by reverse transcriptase-PCR from homogenates of the flies. In a second experiment, 210 houseflies were allowed to feed to repletion on a PRRSV-infected pig on the sixth day after it had been inoculated, and were then maintained under laboratory conditions. Groups of 30 flies were collected immediately after they had fed and six, 12, 24, 48, 72 and 96 hours later, and were tested for PRRSV. Homogenates of the flies collected up to six hours after feeding were PCR- and pig bioassay-positive, but the others were negative by both tests.