Porcine reproductive and respiratory syndrome virus (PRRSV) and Mycoplasma hyopneumoniae (M hyo) are economically significant pathogens of the respiratory tract of the pig. While elimination of these pathogens from individual farms is possible, re-infection via the airborne route is a frequent and frustrating event.

Pigs housed in filtered buildings remained free of both PRRSV and M.hyo infection, according to Dr Dee.

Airborne transmission of both agents was regularly observed in the non-filtered facility.

Meteorological conditions associated with airborne spread of both pathogens included a shedding source population and prevailing winds from the source to neighboring facilities. Cool temperatures, high relative humidly and low sunlight also were associated with airborne PRRSV spread.

The objectives were to:

1. evaluate the efficacy of mechanical filtration (MERV 16, MERV 14 and antimicrobial filtration) and
2. improve the understanding of the meteorological risk factors associated with airborne spread of PRRSV and M.hyo.

The study used a model of a swine-dense production region, with pigs experimentally inoculated with PRRSV and M.hyo.

The model contained three other facilities located 120 miles downwind. Two contained air filtration systems, the third served as a non-filtered control. On-site meteorological data were collected to determine conditions associated with airborne spread of either agent.

Over a two-year period, a variety of samples were collected to determine whether the various filtration systems (MERV 16, MERV 14 and antimicrobial filters) could prevent airborne spread of PRRSV and M.hyo.

The results validate air filtration as a method to reduce the risk of the airborne spread of these two pathogens as well as identify associated risk factors.

In conclusion, under the conditions of this study, we provided new knowledge on the aerobiology and biosecurity of two economically significant diseases of pigs that has already provided immediate impact to the industry.

Currently, the meteorological descriptions of 'positive air days' are being used to forecast PRRSV or M.hyo aerosol risk, heightening on-farm biosecurity and influencing decisions to delay certain events, such as the transport of animals between sites, delivery of breeding stock and repair of air filtration systems.

Furthermore, air filtration is rapidly being applied to AI centres and large breeding herds located in swine-dense regions and promising results have been observed.

September 2014