Severe Outbreak of Avian Encephalomyelitis in Laying Hens in Northeastern Brazil

Abstract

This paper describes the epidemiological, clinical and pathological aspects of an avian encephalomyelitis (AE) outbreak in commercial laying hens in Northeastern Brazil. The disease affected 23,409 layers (from day one until 100 weeks) leading to mortality of 16.5% (5,049/30,600) of the flock. Twenty laying hens were clinically examined, and blood samples were collected and tested by Enzyme-Linked Immunosorbent Assay (ELISA). Five laying hens with neurological signs were necropsied and samples of the brain, cerebellum, spinal cord, sciatic nerve, heart, ceca tonsils, proventriculus and liver were collected, fixed in formalin buffered solution and processed according to routine methods for histological examination. Clinical signs were observed in approximately 60% of the chicken flock and included depression, ataxia, head and neck tremors, head tilt, motor incoordination and corneal opacity and of lens. All laying hens presented seroconversion for AE, with a geometric mean titer (GMT) of 6,854 and CV of 9.6%. At necropsy, there were bilateral opacity of the cornea and lens and the blood vessels of the cerebral cortex were hyperemic. The main microscopic lesions in the central nervous system consisted of red and shrunken neurons in the cerebral cortex, cerebellum and spinal cord. Significant areas of gliosis were observed in the cerebral cortex and in the molecular layer of the cerebellum. Hyperplasia of the proventricular lymphoid tissue and the ceca tonsils were observed with different degrees of intensity. In Northeastern Brazil, there haven't been previous reports of AE in commercial laying hens and this outbreak possibly occurred by inefficient immunization of laying breeders at the genetic supply company.

Diva Molecular Detection of Suspected Case of Newcastle and Encephalomylitis Disease in Layers

“…Experimentally, the virulence of NDV is classified according to pathogenicity: into (velogenic, mesogenic, lentogenic, and asymptomatic) forms, the velogenic NDV (vvNDV) produce neurological signs with hemorrhagic lesions and/ or respiratory signs (12). While(AE) is one of the important viral diseases many avian young species with an economic impact on poultry production (3,7,30). The disease has neurological signs especially, tremors and ataxia is transmitted vertically and horizontally, and also caused 40-60% morbidity and a 25% mortality rate (21,22).…”