A single strain of Staphylococcus aureus was used to study the pathogenesis of osteomyelitis in chickens. The disease was consistently reproduced in 6-week-old broiler chickens when 1 X 10(5) or more organisms were given intravenously. Severe feed restriction, debeaking, and single or multiple injections of corticosteroids delayed the appearance and decreased the severity of lesions due to staphylococcal infection. This increased resistance was associated with increased numbers of circulating heterophils and monocytes. No correlation between the presence of tibial dyschondroplasia and osteomyelitis was found.

Erysipelas was diagnosed in 2 succeeding caged layer flocks housed in the same building and was characterized clinically by sudden death. At necropsy, lesions comprised generalized congestion, hemorrhages in the skeletal muscles and visceral organs, and swelling of liver, spleen, and kidney with or without large irregular zones of necrosis. Focal to massive hepatic necrosis was seen histologically with minimal or no inflammatory reaction. Erysipelothrix rhusiopathiae was cultured from internal organs of affected birds in both outbreaks. Medication with penicillin in the feed controlled the mortality, but relapse occurred after cessation of medication. Two attendants who handled the dead birds in this building developed a painful localized infection of the fingers that later spread to the regional lymph node. The infection responded when antibiotic therapy for erysipeloid was initiated.

Sarcocystis-associated encephalitis was diagnosed in a backyard chicken flock that had nervous manifestations. The main histopathologic lesion was necrotizing encephalitis characterized by a large focal area of necrosis infiltrated and surrounded by mononuclear cells, heterophils, and multinucleated giant cells. Schizonts and merozoites were observed in the lesion. Immunohistochemical staining of the brain lesion revealed positive reaction to Sarcocystis antiserum. The ultrastructural characteristics of the parasite were typical of Sarcocystis, including the presence of a nucleus, a conoid, numerous micronemes, and lack of rhoptries. Medication with amprolium and sulfamethazine or with chlortetracycline was not effective in controlling the mortality. Trapping of opossums on the farm and relocating the chickens to clean, new premises seemed to reduce mortality from this infection.

Erysipelas was diagnosed in two commercial breeder flocks of Coturnix quail and was characterized clinically by sudden mortality. At necropsy, lesions comprised generalized congestion, hemorrhages in the thigh and breast muscles, swelling of liver, spleen, and kidney, and dark red edematous lungs. Erysipelothrix rhusiopathiae was cultured from visceral organs of affected birds. Medication with penicillin in the drinking water controlled the mortality. A possible source of infection was fish raised on the premises. Seven people at the quail processing plant developed localized inflammation of the fingers, which responded when antibiotic therapy for erysipeloid was initiated.