In most swine-producing areas, large groups of pigs are housed under intensive conditions, often in geographical
regions with a dense pig population. High stocking density in a closed environment facilitates transmission
of airborne pathogens within a herd and between herds Worldwide, respiratory diseases continue to cause substantial losses to the swine industry. Financial losses are often due to increased mortality; decreased weight gain; increased feed costs; increased condemnation at slaughter; and increased costs for treatments, vaccination, and labor. Consequently,
respiratory diseases are regarded as some of the most serious disease problems in modern swine
production