At some point or another most agricultural enterprises need to perform a quarantine to halt pest or disease problems. It is one of the simplest and best forms of control. In the case of livestock parasites can quickly spread from one animal to the next both through physical contact or through digesting food infected via the faecal oral cycle. Diseases can be transmitted between animals and even from hen to egg as is the case for infectious synovitus.
Commonly, bringing new chickens into the flock has the high potential to spread disease and pests. This is why the quarantine of new animals is vital. Keeping new birds in a separate area for anywhere up to 2 months will allow you to observe the new animals for pests and diseases and allow you to treat them if possible. The quarantine area should be at least 10 metres away from the existing area and in a larger scale operation, it would be best if workers entering the quarantine area were then kept away from the main flock.
Be aware also that any time an animal moves through new environments it can pick up pests and diseases. Transport or housing that isn't cleared in between transfers can retain pests and disease which can then be spread amongst any new birds they are exposed to. Any animals brought into a new environment should, as mentioned, be quarantined and observed for a period of time to halt any spread to the existing flock.