Some common ways infectious diseases are introduced into and spread within herds or flocks are:
01. Introduction of diseased animals.
2. Introduction of healthy animals that have recovered from disease but are still carriers or can still transmit the disease to other animals.
03. Contact with inanimate objects that are contaminated with disease organisms (trucks and trailers, feeders, waterers, etc.).
04. Contact with carcasses of dead animals that have not been disposed of properly.
05. Impure water, such as surface drainage water.
06. Rodents and free-flying birds.
07. Mosquitoes. Insects-fowl pox and encephalitis are commonly transmitted by mosquitoes.
08. Shoes and clothing of persons who move from farm to farm.
09. Contaminated feed and feed bags.
10. Contaminated premises through soil, old litter, or bedding.
11. Airborne organisms, which do not spread far through the air, but this source of infection can be a strong factor in heavily populated livestock areas.