Pathogens must be able to survive for a certain amount of time in aerosols in order to be spread by air. Survival of swine pathogens in air is dependent on pathogen numbers, temperature and humidity. Each pathogen will have a set of environmental conditions that allows for their best survival.
Contamination of air is extended in buildings in which infected pigs are continuously shedding organisms. Pathogen transmission by air probably has the greatest chance of occurring when there are a large number of infected pigs, shedding high numbers of pathogens to the air, during environmental conditions ideal for that pathogen's survival. The distance that pathogens can be transmitted by aerosol is widely based on anecdotal evidence and computer modeling. Experimentally, pathogens rarely travel more than 2 miles in the air. Biosecurity practices that could be used to minimize the risk of aerosol transmission/infection:
-Locating in a low pig density area at least 2 miles from other swine or manure spreading locations,
-Dust reduction protocols (adding fat to feed),
-Maintaining relative humidity
-Optimizing ventilation systems,
-Maintaining a suitable tree or shrub barrier surrounding the farm or near ventilation. See Vegetative Environmental Buffers
