Emerging diseases and diseases of complex or unknown etiology

The emergence of new diseases and the re-emergence of recognized diseases are familiar events in the annals of poultry medicine. Some of these emerging diseases could have been present earlier but were not recognized because of low prevalence, mild signs and lesions, lack of diagnostic techniques, or misdiagnosis. This chapter presents information on the complexity of respiratory and enteric diseases. In addition, it presents information on four emerging conditions: white chick syndrome, focal duodenal necrosis in table egg layers, wooden breast and other muscle abnormalities, and idiopathic egg production drops in brown layers. Definitive diagnosis of white chick syndrome involves taking isolates from the affected birds or embryos and putting them back into specific pathogen free embryos to recreate the lesions. Because of the sporadic nature of this syndrome, and relatively short duration of the problem, concern for prevention and control are moderate when compared with more serious threats.