Exhaust expulsion of the porcine reproductive and respiratory syndrome virus (PRRSV) through ultrasound machines

Objective: Three experiments (EXP) were conducted to investigate if air contaminated with PRRS virus (Ingelvac PRRS MLV vaccine containing the North American strain) can be sucked into ultrasound machines and then expelled back into an infected (EXP-1) or a clean environment (EXP-3) through the action of ventilation fans, and if covering the machines prevents exhaust expulsion of the virus (EXP-2). Materials and methods: The experimental apparatus basically comprised of a plastic chamber, an ultrasound unit HS 1201, a device that allowed for virus aerosolization and a pipe system that allowed the air to return into the chamber (EXP-1) or to be expelled into the atmosphere (EXP-3), or was blocked by using a rubber membrane (EXP-2). In EXP-1, different virus concentrations were tested (i. e. 10(4), 10(5) and 10(6) TCID(50), each concentration in three replicates and two runs). In EXP-2, the highest concentration, i. e. 10(6) TCID(50) was used (three replicates and two runs). EXP-3 immediately followed EXP-2 without introduction of new virus (two runs). Virus exhaust expulsion was monitored by swabbing the pipe system with the swabs being subjected to RT-nPCR and culture. Results: In EXP-1, 10(6) TCID(50) PRRSV, but none of the other concentrations, gave constantly virus-positive results by RT-nPCR. In EXP-2, covering completely prevented virus exhaust expulsion. In EXP-3, two out of eight swabs were positive by RT-nPCR. Cell culture of positive swabs was negative. Conclusion: The study suggests exhaust expulsion of PRRSV through ultrasound machines equipped with a ventilator fan into an infected and a clean environment, but failed to demonstrate infectivity of the expelled virus. Preventing exhaust air expulsion by complete covering prevents the expulsion of the virus.