Common Viral Diseases in Backyard Poultry
Avian Encephalomyelitis
Avian encephalomyelitis (AE) is seen in chickens, turkeys, pheasants, and quail. It primarily affects chicks 1–3 weeks old. Nearly all commercial flocks are infected, but clinical disease is low because of maternal antibodies. AE can be transmitted vertically in eggs laid between 5 and 13 days after infection and is an enteric infection under natural conditions. The spread is more rapid in floor-raised birds than in cage-raised birds. There is no treatment, and vaccination of breeders (both chicken and turkey) for maternal antibodies to protect the young during early life is critical to prevention. Because many specialty breeders, particularly those that sell stock to an intermediate supplier, do not vaccinate, AE is a fairly common viral disease in backyard poultry. Vaccination should be given after 8 weeks of age but by at least 4 weeks before production.
Avian Influenza
Avian influenza (AI) is a highly contagious respiratory viral disease that affects both domestic and wild birds. AI viruses are classified into two pathotypes: low pathogenic avian influenza (LPAI), which typically causes few to no clinical signs in poultry, and highly pathogenic avian influenza (HPAI), which typically causes high mortality. Waterfowl and shorebirds, such as ducks and geese, are natural hosts for the AI virus, and these birds can shed the virus, often without showing any signs of illness or deaths.
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Learn MoreBackyard poultry are just as susceptible to AI infection, if not at higher risk. Many backyard flocks are kept outdoors, free-ranging, have multiple ages and sources of birds, and have less strict standards for biosecurity compared with commercial flocks. This results in mixing with other poultry within the flock and higher risk of contact with wild waterfowl, creating favorable conditions for disease spread within and between flocks. Many studies show that the backyard flocks with more types of poultry and the worst sanitary conditions have higher incidences of AI.
If a flock has sudden (less than 24-48 hours), high death rates (close to or over 50%) or many birds with respiratory signs, owners should contact a veterinarian or the state animal health emergency number to test for AI infection. A state poultry association can also be contacted, as many offer free or reduced cost yearly testing for AI in backyard poultry. There is no approved vaccine in the US nor treatment for AI. Good management and biosecurity practices are the only way to protect against AI infection in backyard poultry.
Fowlpox
Fowlpox virus causes crusty and nodular lesions primarily on the unfeathered portions of the bird. Occasionally, poxvirus can cause lesions in the mouth and trachea, causing death due to suffocation (wet form). If the bird recovers, immunity is generally lifelong. Not all pox outbreaks are caused by fowlpox virus but can be caused by related strains such as turkey pox, psittacine pox, quail pox, etc. Strains are usually species specific but can occasionally affect other species (eg, pigeon pox). One strain may not cross-protect with another. Vaccination is available and should be given to flocks on premises with a previous history of pox or with presence of pox in nearby birds. Poxvirus is transmitted through contact of infected lesions with open wounds and by insect bites (mosquitoes), and insect control is key to prevent spread.
Infectious Bronchitis
Infectious bronchitis virus (IBV) causes a rapidly spreading respiratory disease in young chicks. Production is reduced and egg shell abnormalities are seen in laying hens. Certain strains of IBV also cause kidney disease. Chicks infected early in life may have permanent damage to the oviduct, so they do not produce eggs or become false layers. IBV is highly transmissible, but most birds recover with supportive treatment. Antibiotics can be administered in the water to prevent secondary infection. Vaccines are available; however, backyard chickens are usually not vaccinated unless they come in contact with other chickens.
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Marek Disease
Marek disease (MD) is a common viral disease of chickens, both in commercial production and backyard flocks. The primary lesions are tumors of the viscera, muscle, skin, and peripheral nerves. Nerve lesions can be an early indicator of the disease and result in a condition termed “range paralysis.” Birds with visceral tumors often have cachexia as the only clinical sign. Tumors of the muscles and skin are frequently palpable.
Tumors that affect the eyes (ocular Marek) could be seen as a grayish color change in the pupils or irregular margins of the pupils, with lack of proper pupillary light reflex. MD cannot be treated but can be prevented by vaccination at hatch. When backyard poultry are acquired or hatched onsite, every attempt should be made to vaccinate for MD. Vaccinations may not be effective if administered to birds >1–2 weeks old. Clinical MD generally affects birds 4–14 weeks old; however, it is not uncommon in older birds, and death loss is often sporadic rather than explosive. If tumors are found in the viscera of deceased birds, carcasses should be submitted to a diagnostic laboratory for differential diagnosis between MD and avian leukosis, another common lymphoid tumor disease. Avian leukosis is seen in birds >14 weeks old, and tumors are similar to those found with MD. Avian leukosis has no treatment or vaccination.
Newcastle Disease
Newcastle disease virus (NDV) affects numerous species of birds and is the reason for quarantine regulations for birds entering the USA. Exotic NDV is highly fatal and is not present in the USA at this time. Past outbreaks have resulted in the slaughter of thousands of birds. Milder forms of NDV are present in the USA and are primarily characterized by respiratory disease and a drop in egg production. Mortality is variable and depends on the strain of the virus. As with infectious bronchitis virus, vaccination is available but is generally given to backyard poultry only if exposed to other birds.
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