How to prevent and treat avian encephalomyelitis? A full analysis of the key methods

Avian encephalomyelitis (AE) is an infectious disease of chicks caused by the avian encephalomyelitis virus, mainly affecting the nervous system, also known as epidemic tremor. Its main features are that affected chicks show ataxia, tremors of the head and neck muscles, leg paralysis, and paralysis; laying hens show a drop in egg production rate.

I. Symptoms 1. Chicks. In the early stage of the disease, affected chickens are depressed and slow to respond; subsequently, some diseased chickens gradually develop ataxia and are unwilling to move; or they walk with an unsteady gait until they cannot stand; both hock joints rest on the ground, both wings are spread and drooping to the ground, and they barely flap their wings to help themselves move forward, and may even become completely paralyzed; some affected chicks have tremors of the head and neck, and the tremors worsen especially when stimulated. Affected chickens still have appetite during the course of the disease, but often cannot eat or drink because of complete paralysis, and eventually die of exhaustion; the course of the disease is 5 to 7 days. 2. Growing chickens. A small number of chickens are affected; diseased chickens appear dazed and weak in the legs, and may even show central nervous system disorders; affected chickens tilt the head and stretch the neck to walk forward in a straight line, or walk backward, or suddenly and without reason twist the head to the left, right, or other directions. Individual affected chickens may develop unilateral or bilateral cloudiness of the lens of the eye, and may even go blind. 3. Adult breeding chickens. There are no neurological symptoms; the main manifestation is a transient drop in egg production. The drop in egg production rate generally reaches 10% to 20%, and returns to normal after about 14 days. In terms of egg quality, the main issue is a drop in hatchability, and most embryos die around 19 days of age; hens may also lay small eggs, but there is no obvious change in the shape, color, or contents of the eggs.

II. Necropsy Affected chicks have some mottled grayish-white areas on the muscle cross-section of the gizzard. Cloudiness appears in the lens of the eye. On histopathological examination, central chromatolysis of neurons in the gray matter of the medulla oblongata of the brainstem and the spinal cord can be seen, there is a "cuffing" phenomenon around blood vessels in the brain, focal proliferation of glial cells, and a large amount of lymphocyte infiltration in the gizzard and pancreas.

III. Diagnosis Chicks developing the disease at 1 to 2 weeks of age, showing obvious ataxia and tremors of the head and neck muscles, together with a history of a recent drop in egg production in their mother hens, can serve as the key points for clinical diagnosis of this disease; when necessary, examination of the brainstem, spinal cord, gizzard, and pancreas can be performed.

IV. Prevention and treatment To prevent and treat this disease, the policy of "prevention first" must be adhered to. At present, the vaccines used for immunization include two types: the avian encephalomyelitis "canek114 strain" attenuated live vaccine and the avian encephalomyelitis oil-emulsion inactivated vaccine. The basic immunization program is: first vaccination, at 12 weeks of age for replacement breeding chickens, via drinking water immunization with the attenuated live vaccine, 1 to 2 doses per bird; second vaccination, at 16 weeks of age for replacement breeding chickens, via drinking water immunization with the attenuated live vaccine, 2 doses per bird, and at the same time, intramuscular injection of the oil-emulsion inactivated vaccine at 0.5 to 1 ml per bird. Through the above immunization, the immunity period can reach more than 1 year; when necessary, the oil-emulsion inactivated vaccine can be injected intramuscularly once more in the middle of the laying period of breeding chickens, or when breeding chickens develop the disease, the oil-emulsion inactivated vaccine can be used for emergency immunization injection for prevention and treatment.