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.

摘要：本研究阐述了巴西东北部地区商品蛋鸡群暴发禽脑脊髓炎（avian encephalomyelitis, AE）的流行病学、临床症状及病理学特征。此次疫情波及23409只1日龄至100周龄的商品蛋鸡，鸡群死亡率达16.5%（5049/30600）。对20只蛋鸡进行临床检查，采集血液样本并通过酶联免疫吸附试验（Enzyme-Linked Immunosorbent Assay, ELISA）开展检测。对5只表现神经症状的蛋鸡进行剖检，采集大脑、小脑、脊髓、坐骨神经、心脏、盲肠扁桃体、腺胃及肝脏样本，经福尔马林缓冲液固定后，按照常规方法开展组织病理学检查。约60%的鸡群出现临床症状，具体表现为精神沉郁、共济失调、头颈震颤、头颈偏斜、运动失调以及角膜与晶状体浑浊。所有受试蛋鸡均发生禽脑脊髓炎血清阳转，几何平均滴度（geometric mean titer, GMT）为6854，变异系数（CV）为9.6%。剖检可见双侧角膜与晶状体浑浊，大脑皮层血管充血。中枢神经系统的主要显微病变表现为大脑皮层、小脑及脊髓内神经元固缩红染。大脑皮层及小脑分子层可见显著的神经胶质增生灶。腺胃淋巴组织与盲肠扁桃体可见不同程度的增生。巴西东北部此前尚无商品蛋鸡暴发禽脑脊髓炎的相关报道，此次疫情可能源于种源供应企业对蛋用种鸡的免疫接种不到位。