Avian Encephalomyelitis in Turkeys: Tremors, Ataxia, and Paralysis

Avian encephalomyelitis, sometimes called epidemic tremor, is a viral disease that affects the central nervous system of poultry. In turkeys, it is most important in young poults, where it can cause fine tremors, poor coordination, weakness, and in more serious cases, paralysis and recumbency. The virus involved is avian encephalomyelitis virus, a picornavirus in the genus Tremovirus.

Turkeys can develop this infection naturally, although they are generally considered less susceptible than chickens and often show milder signs. Even so, a flock problem can still be significant because affected poults may struggle to reach feed and water, fall behind in growth, or die from complications related to weakness.

This condition matters at both the individual bird and flock level. A single shaky poult may be the first sign of a larger breeder or hatchery-linked issue, especially when multiple young birds from the same source are affected. Because the disease can move through eggs from infected breeders and also spread between hatchmates through droppings, early veterinary guidance is important.

Avian encephalomyelitis in turkeys is caused by avian encephalomyelitis virus (AEV), a nonenveloped RNA virus in the family Picornaviridae. Field strains are enterotropic, meaning they multiply in the intestinal tract. Infected birds shed virus in feces for days to weeks, which allows spread to hatchmates and other susceptible young birds.

There are two main routes of transmission. Vertical transmission happens when breeder birds become infected during egg production and pass the virus into eggs. This route is especially important because it can lead to outbreaks in newly hatched poults. Horizontal transmission happens after hatch, usually by the fecal-oral route when poults contact contaminated droppings, equipment, or housing.

Age matters. Young birds are the ones most likely to show neurologic disease, while older birds may become infected without obvious signs. In poultry generally, birds become more resistant to clinical disease as they age, even though infection can still occur. In turkeys, natural infection is recognized, but clinical disease is often milder than in chickens.

From a flock-management standpoint, the real cause is often not only the virus itself but also the way it entered the system. Your vet may look closely at breeder vaccination history, hatch timing, source flock health, sanitation, and movement patterns between age groups.

Diagnosis starts with the history and flock pattern. Your vet will want to know the poults' age, hatch source, how many birds are affected, when signs started, and whether the problem is spreading through one group or appearing in several related flocks. Fine tremors, ataxia, leg weakness, and progression to paralysis in young poults raise concern for avian encephalomyelitis, but these signs are not enough to confirm it on their own.

A physical exam and flock assessment are usually followed by diagnostic testing. Merck Veterinary Manual notes that diagnosis is based on history, clinical signs, and characteristic histopathologic lesions, with useful tests including virus isolation, RT-PCR, and ELISA. In practice, your vet may recommend necropsy of freshly affected birds, tissue submission to a poultry diagnostic laboratory, and PCR testing to look for the virus genome.

Because several poultry diseases can cause weakness, tremors, or poor mobility, your vet may also work through a differential list rather than assuming one cause. That can include nutritional problems, toxin exposure, hatchery issues, traumatic injury, and other infectious neurologic diseases. Confirming the cause helps guide realistic next steps for the flock, including isolation, culling decisions, breeder review, and prevention planning.

Prevention is centered on vaccination and flock biosecurity. Merck Veterinary Manual states that no treatment is available and control relies on vaccination. MSD Veterinary Manual's poultry vaccination guidance includes encephalomyelitis vaccination for turkey breeders at about 28 weeks of age by drinking water in areas where the disease is a concern. The goal is to protect breeder birds before egg production so they do not pass virus to offspring and so poults receive maternal immunity.

For pet parents and small flock keepers, prevention also means paying attention to source quality. Ask where poults came from, whether breeder vaccination programs are in place, and whether there have been recent neurologic problems in related flocks. Avoid mixing age groups when possible, because younger birds are more vulnerable and fecal contamination is an important route of spread.

Daily management matters too. Keep brooders clean and dry, remove manure promptly, clean feeders and waterers regularly, and limit traffic of boots, crates, and equipment between groups. USDA APHIS continues to emphasize that strong biosecurity is the key to protecting poultry flocks from contagious disease. While that guidance is often discussed in the context of avian influenza, the same core habits help reduce spread of many poultry pathogens.

If you have had a suspected or confirmed case, work with your vet before bringing in new poults. Your vet can help you decide on downtime, cleaning and disinfection priorities, sourcing changes, and whether breeder-level prevention is the most important long-term fix for your setup.