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Avian encephalomyelitis virus (AEV) is a viral disease impacting the central nervous system. It is caused by a virus from the Hepatovirus family that occurs throughout the world in the following birds: Japanese quail, turkeys, chickens, pigeons and pheasants. Chickens of all ages can be impacted by the virus, however the symptoms of encephalitis will only be seen in those under four weeks old. The progression of the disease is similar in chickens and turkeys.
A viral disease that infects the nervous system of Japanese quail, turkeys, chickens, pigeons and pheasants, encephalomyelitis leads to symptoms like tremors, weakness and paralysis.
Should a bird experience encephalomyelitis, you may notice the following:
Should a chick be infected vertically (from his mother prior to hatching) he will often show signs during the first week after he has hatched; in some cases, the symptoms will be seen immediately upon his hatching.
Symptoms may later be seen in hatch mates of the infected chick who have been horizontally infected through the route of feces to mouth; virus in feces can live for over four weeks.
In chickens that lay eggs, when infected with the virus there will be a sudden drop in egg production (by about 5-10%). This will often last for less than two weeks and afterward, production will return to normal. Eggs laid during this period of time will be infected with the virus.
The disease is often milder in turkeys than in chickens.
Infection can be vertical, where the chick is infected by his mother prior to hatching. Horizontal infection can occur in hatch mates through feces. Chicks that experience horizontal infection will usually show symptoms at 2-4 weeks of age. The disease will progress through the flock for the first few weeks after the chicks hatch with the infection period being complete by the time they are four weeks old.
The virus causing the condition is transmitted both through the egg (vertical transmission) and by direct contact. For example, eggs that are laid by a hen who is infected with the virus will carry it. The number of eggs that are laid and then subsequently hatch may decrease by about 5% as a result of embryonic mortality. This will lead to a decrease in the number of eggs that hatch and those chicks that hatch will develop the clinical form of the disease quickly; typically, about 5% of the flock will be impacted by the virus. Those chicks who have the virus will shed it in their feces, which will infect other chicks.
Sometimes older chickens will develop symptoms similar to those of young chicks after being vaccinated with the egg-embryo adapted commercial vaccines.
Diagnosis of encephalomyelitis will be based on the bird’s history, symptoms and lesions on his brain and spinal cord. Should a bird you are caring for be experiencing unusual symptoms, you will want to contact your veterinarian. A physical examination will be conducted; your veterinarian may cup the bird in his hands, which when the is experiencing encephalomyelitis, may lead to a buzzing feeling as a result of the tremors. Your veterinarian will inquire as to what symptoms you have noticed, when you first noticed them and any changes you have observed.
Diagnosis can be made through histopathology and immunofluorescent assay, as well as through isolating the virus. In adults, serologic testing may be used to determine if there is an increase in antibody titers which will confirm the virus is present. Your veterinarian will look to rule out Newcastle disease, vitamin E, A or riboflavin deficiency, Marek’s disease, mycotic encephalitis and brain abscess.
Birds with encephalomyelitis should be isolated from those without the virus. In many cases, euthanasia is preferred as few will recover from the condition. In some cases, supportive care is recommended.
Immunization of breeding chickens aged 10-16 weeks old is recommended. There is a commercial live vaccine that will stop vertical transmission of the virus, as well as offer immunity against the virus to the chicks through their mother. Pheasants can be vaccinated at 5-10 weeks old and bobwhite quail at 6-10 weeks.
Unfortunately, infected birds rarely recover; they will often become paralyzed and die from being unable to eat or drink or by being trampled. This is why euthanasia is often recommended. Some birds do recover and other survive but experience ongoing symptoms.
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