The blood, of life are strongly suggestive of the infection. The blood, other tissues and droppings of such chicks as well as the parents excreta, are rich sources of the organisms. As little as ten per cent of all eggs may hatch, and all of these squabs may die before leaving the nest. The effect of a long established infection, however, may be much less spectacular. It is sometimes thought that a single hen has merely been clumsy when the flattened dead chicks are later found in or thrown out of the nest, but poor hatchability in several nest should point to a more serious cause.
Losses usually start a few days to two weeks after eating contaminated seed or other food.
According to the virulence of the organism and the susceptibility of the species concerned, clinical signs may last only a day or two with occasional losses over several weeks or, within 10 days of the first death, as much as 90 per cent of the growing and adult stock may be dead. The vent feathers become matted with excreta, the eyes begin to close, and immediately before death some birds show apparent blindness, inco-ordination, staggering, tremours, or other nervous signs including convulsions. In addition pigeons sometimes show arthritis, especially of the wings. A really sick bird seldom recovers even with appropriate treatment. Diagnosis Diagnosis cannot be made on the basis of clinical signs alone.