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Chapter 7 : Feathered Friends
Infectious diseases can be transmitted to humans from birds by one of several mechanisms. In group 1 infections, birds are the natural reservoirs for the infectious agent, which causes illness among them. Examples of such infections include psittacosis, Newcastle disease, avian influenza, and yersiniosis. In group 2 and 3 infections, birds are the natural reservoirs for the infectious agent but do not become ill themselves. The infectious agents of group 2 infections (for example, salmonellosis and mite infections) disseminate from the colonized birds into the environment directly, and the agents of group 3 infections (for example, eastern equine encephalitis [EEE], western equine encephalitis [WEE], St. Louis encephalitis [SLE], and Japanese B encephalitis [JE]) disseminate by means of arthropod vectors and involve humans as accidental hosts. Psittacosis is mainly an occupational disease among workers in turkey-processing plants, duck or goose pluckers, pigeon breeders, and pet store employees. Mites that infest wild and domestic birds have four stages (egg, larva, nymph, and adult) in their life cycles, which can be completed within 1 week under favorable circumstances. Gastrointestinal defenses may be compromised by antacids, gastrectomy, agents that slow intestinal motility, and antibiotics. Some diseases, such as cirrhosis, lymphoma, and human immunodeficiency virus (HIV) infection, which impair systemic host defenses, also increase susceptibility to salmonellosis. Acute pulmonary histoplasmosis resembles atypical pneumonia, the severity of which depends on the number of infectious particles inhaled.