Comparison of three different air sampling systems for the detection of aerosolized type 1 PRRSV MLV

Airborne transmission of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) has been known for a long time. Most experiments were performed using type 2 PRRSV and fairly little information is available on the spread of type 1 PRRSV via aerosols. The aim of this study was to compare 3 different air sampling systems for their ability to detect aerosolized type 1 PRRS modified live vaccine virus.

Three different air sampling systems were tested: Coriolis®μ (flow rate: 3 m3/10 min), Sartorius MD8 Airscan Air Sampler (flow rate: 1 m³/10 min), and IOM Multidust sampler with polycarbonate filters (flow rate: 2.5 l/min; pore size: 0.2 µm). In an experimental chamber (air volume 68.5 m3), one liter of PBS containing 1 x 10⁷ TCID₅₀ (2.6 x 10¹¹ virus copies measured by qRT-PCR) of a type 1 PRRSV MLV (ReproCyc® PRRS EU) was nebulized for 10 minutes with a cold-fogging system (UNIPRO² Igeba). Air sampling with 2 IOM Multidust samplers started simultaneously with nebulisation and continued for a period of 2 hours. Two air samplings of 10 minutes each were performed with Coriolis®μ and Sartorius MD8, the first during nebulisation and the second 1 hour later. Cell culture medium (MEM + 3 % FCS) was used for Coriolis®μ (15 ml) and to dissolve gelatine filters used in the Sartorius MD8 (20 ml) or to wash polycarbonate filters (10 ml). The medium was tested for the presence of PRRSV by qRT-PCR and virus isolation on MARC-145 cells.

Relative humidity in the experimental chamber was 34 % at an air temperature of 22.8°C. The highest concentration of virus particles was measured by qRT-PCR in samples collected with Coriolis®μ (9 x 108 virus copies/m3 air during nebulisation, 2.4 x 10⁸ one hour later). In Sartorius MD8 samples 3.0 x 10⁸ and 1.1 x 10⁸ virus copies/m3 air were measured during and after nebulisation. In samples of the 2 IOM Multidust samplers virus concentrations were 2.1 x 10⁷ and 1.7 x 10⁷ copies/m³ air. PRRSV could successfully be isolated from the sample collected during nebulisation with Coriolis®μ (1.5 x 10 TCID₅₀/ml).

All three systems were able to detect type 1 PRRSV by qRT-PCR under experimental conditions. Virus isolation was only possible from a sample collected with Coriolis®μ. The same air sampling systems were tested in a PRRSV positive farm but failed to detect field virus in nursery and finishing rooms in which pigs were tested positive for PRRSV in oral fluids and blood. Further studies are necessary to investigate air sample collection in the field and to optimize sample collection and processing in order to evaluate the role of aerosols in transmission of type 1 PRRSV isolates.

Disclosure of Interest: None Declared.

      

 Published in the proceedings of the International Pig Veterinary Society Congress – IPVS2016. For information on the event, past and future editions, check out https://www.theipvs.com/future-congresses/.