Neonatal multifocal encephalomalacia and other lesions in the brains of Georgia chicks: 1991-95

Outbreaks of neonatal multifocal encephalomalacia with sepsis have been reported among flocks of very young chicks in Belgium, Scotland, and the United States. The purposes of the present study were to describe intralesional bacterial cocci in chicks with this type of encephalomalacia and to determine its incidence during 1991-95, and to determine the importance of this lesion with respect to the frequency of all other brain lesions/diseases during the same time period. All laboratory records of broiler chickens examined at the Georgia Poultry Laboratory from Jan. 1, 1991, through Dec. 31, 1995, where the histopathologic diagnoses included the letter string *encephal* were retrieved for further study. The leading etiology for brain disease was nutritional encephalomalacia (57%), followed by neonatal encephalomalacia (22%), septic meningoencephalitis (16%), and Marek's disease (14%), in turn followed by nonpurulent encephalitis (7%), avian encephalomyelitis (3%), and mycotic meningoencephalitis (3%). Diagnosis of neonatal multifocal encephalomalacia with sepsis in the brains of Georgia chicks is a perennial one. Microscopically, the condition is characterized by mild to maximal multifocal locally extensive fibrin thrombosis of blood capillaries, and necrosis (encephalomalacia, malacia) of surrounding zones of brain stem and/or cerebral hemisphere neuropile. In 44% of cases of neonatal encephalomalacia, fibrin thrombosis of blood capillaries was accompanied by intralesional gram-positive coccoid bacteria that were most abundant in medium- and small-sized arterioles or venules. Only gram-positive coccoid bacteria are found in cases of neonatal encephalomalacia (P < 0.05), and only gram-negative rod-shaped bacteria are found in cases of septic meningoencephalitis (P < 0.05). Therefore, bacterial culture and routine light microscopic histopathology are sufficient for diagnosing the condition when the differential diagnosis for neurologic disease in chicks includes neonatal encephalomalacia.