Even taking all these precautions, sometimes disease occurs anyway, perhaps carried by wild birds such as sparrows or starlings, or on the wind or even on your own shoes. Diseases are broken down into groups. These groups are classified by the various infective agents and we shall look now at the more common and important ones. Newcastle Disease is an extremely virulent disease which causes high mortality in flocks. It is spread primarily on chicken carcases and chicken meat products, however it can also be carried on clothing, by wild birds and be wind-borne.
Affected birds tend to gape and salivate heavily, but without apparent respiratory distress.
They usually have a fetid diarrhea of yellowish-white colour, sometimes tinged with blood. Other symptoms are twisted necks, paralysis, loss of balance and circling movements of the head. Vaccines are available, however many countries insist upon a complete slaughter of birds in affected yards to control any further outbreak. Newcastle Disease is particularly dangerous as it can affect nearly all kinds of birds. Mareks Disease affects young birds between the ages of 9 to 16 weeks.