Common diseases of poultry include avian influenza, fowl pox, cholera, Newcastle disease and egg-drop disease in ducks, geese and chickens. Other common poultry diseases include colds and swollen-head syndrome. Chickens, turkeys, ducks, geese and other types of poultry also can be infected with botulism, ulcerative enteritis, encephalitis, cholera and staphylococcus infections. Because of high concentrations of fowl populations in modern poultry management, disease may spread quickly.
Poultry can also become infected with two kinds of leukosis, infectious laryngotracheitis, turkey rhinotracheitis, chlamdyiosis and various mycoplasma infections. Some other diseases affecting poultry include avian encephalomyelitis, aspergillosis and infectious bursal disease.
A University of Florida Institute of Food and Agricultural Sciences Extension service article divides poultry diseases into three main categories. They are the 16 viral and bacterial respiratory diseases, eight non-respiratory viral diseases and seven non-respiratory bacterial diseases. Some of these diseases have sub-types, and some affect only certain types of fowl. The turkey vulture, for example, is the only species not subject to infection by botulism. On the other hand, the two types of bronchitis affect only chickens and bobwhite quail.
The University of Florida IFAS Extension page gives clinical signs of the diseases, treatment if any is available and prevention measures. The page also lists which diseases can infect which species of poultry.
It is most often found in chickens and turkeys, and less frequently in ducks, geese, pigeons, canaries and other wild or pet birds. Aspergillosis may cause acute and chronic infection and usually appears in birds that are 7 to 40 days old. It is believed to be caused by impaired immunity and the inhalation of large numbers of spores that have been contaminated.
Avian influenza, or bird flu, is spread through the secretions of infected birds and is caused by the H5N1 virus. Mosquitoes and ticks may also transmit avian flu, with outbreaks often coinciding with the rainy season where mosquitoes are abundant. Avian flu is transmittable to people, and as of 2004, all known cases have appeared in Southeast Asia, contracted by people who handle chickens. Infected birds shed the virus in their saliva, droppings and nasal secretions. As of 2015, the Centers for Disease Control considers the risk of transmission to people as low.
Botulism occurs in poultry as a result of ingesting the toxin Clostridium botulinum, a bacteria that is widespread in soil. Decomposing vegetation, coupled with warm temperatures, provides an ideal environment for botulism to occur. Botulism often causes death in waterfowl, with ducks most often affected.