NEONATAL MULTIFOCAL ENCEPHALOMALACIA AND OTHER LESIONS IN THE BRAINS OF GEORGIA CHICKS - 1991-95

Outbreaks of neonatal multifocal encephalomalacia with sepsis have bee n reported among flocks of very young chicks in Belgium, Scotland, and the United Stares. The purposes of the present study were to describe intralesional bacterial cocci in chicks with this type of encephaloma lacia and to determine its incidence during 1991-95, and to determine the importance of this lesion with respect to the frequency of all oth er 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 d iagnoses included the letter string encephal* were retrieved for furt her study. The leading etiology for brain disease was nutritional ence phalomalacia (57%), followed by neonatal encephalomalacia (22%), septi c meningoencephalitis (16%), and Marek's disease (14%), in turn follow ed by nonpurulent encephalitis (7%), avian encephalomyelitis (3%), and mycotic meningoencephalitis (3%). Diagnosis of neonatal multifocal en cephalomalacia with sepsis in the brains of Georgia chicks is a perenn ial one. Microscopically, the condition is characterized by mild to ma ximal multifocal locally extensive fibrin thrombosis of blood capillar ies, and necrosis (encephalomalacia, malacia) of surrounding zones of brain stem and/or cerebral hemisphere neuropile. In 44% of cases of ne onatal encephalomalacia, fibrin thrombosis of blood capillaries was ac companied by intralesional gram-positive coccoid bacteria that were mo st abundant in medium- and small-sized arterioles or venules. Only gra m-positive coccoid bacteria are found in cases of neonatal encephaloma lacia (P < 0.05), and only gram-negative rod-shaped bacteria are found in cases of septic meningoencephalitis (P < 0.05). Therefore, bacteri al culture and routine light microscopic histopathology are sufficient for diagnosing the condition when the differential diagnosis for neur ologic disease in chicks includes neonatal encephalomalacia.