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Common Infectious Diseases in Backyard Poultry


Yuko Sato

, DVM, DACPV, Veterinary Diagnostic and Production Animal Medicine, College of Veterinary Medicine, Iowa State University;

Patricia S. Wakenell

, DVM, PhD, DACPV, Department of Comparative Pathobiology, College of Veterinary Medicine, Purdue University

Reviewed/Revised May 2020 | Modified Oct 2022
Topic Resources

The following list includes some of the more common conditions encountered in backyard poultry practice.


As in other species, the common parasites in poultry are mites, lice, ticks, worms, and protozoa.

Two common mites of poultry Mites of Poultry The most economically important of the many external parasites of poultry are mites of the families Dermanyssidae and Macronyssidae (poultry red mite, northern fowl mite, and tropical fowl mite)... read more Mites of Poultry are the Northern fowl mite (Ornithonyssus sylviarum) and the red mite . The Northern fowl mite is most commonly found around the vent, tail, and breast. These mites are easily observed as small, reddish-brown flecks. Red mites (Dermanyssus gallinae) feed only at night, making daytime diagnosis difficult. They can be found in cracks and seams near bedding areas and appear like flea dust or salt and pepper–like deposits. Red mites cause feather loss, irritation, and anemia.

Several types of lice live on poultry, and lice or nits (egg packets of lice) can be seen at the base of the feathers. In severe infestations, growth and egg production can be affected. Insecticides are available for treatment.

Fowl ticks Fowl Ticks The fowl tick, Argas persicus, is found worldwide in tropical and subtropical countries and is the vector of Borrelia anserina ( avian spirochetosis) and the rickettsia Aegyptianella... read more comprise a group of soft ticks that parasitize many species of poultry and wild birds. Ticks are easily missed, because they spend relatively little time on the bird. Heavy infestations can cause anemia or tick paralysis, and ticks can be vectors for Borrelia anserina (spirochetosis). Spraying of buildings with insecticide is the treatment of choice.

Roundworms and tapeworms are the most common internal poultry parasites and are generally the result of soil contamination and poor management. Unless infestations are heavy, clinical disease is usually not evident. A fecal examination should be performed before treatment to assess levels of infestation (and monitor effectiveness of treatment), because most domestic poultry will have some degree of internal parasitism. Piperazine can be used for roundworms, although its effectiveness can be minimal and drug resistance is a problem; off-label fenbendazole or levamisole can be used for tapeworms. These compounds should not be used in laying hens. Proper litter management will reduce parasite loads and reinfection.

As in commercial poultry production, control of coccidia Coccidiosis in Poultry is one of the more common and costly problems in raising backyard poultry. Coccidia are found primarily in the intestinal tract of most poultry but are also found in the kidney in geese. Coccidiosis is generally seen in young birds (1–4 months old), although it can be seen in any bird >10–14 days old. Signs include diarrhea that is often bloody and frequently leads to loss in production, general malaise, and death. Coccidia thrive in moist, heavily soiled litter, and disease is often a result of too high a density of birds. Prevention is by supplying coccidiostats in the feed, which can be given to birds as early as in their starter diet. Outbreaks can be treated with treatment dose of selected coccidiostats and extra-label sulfa drugs. Sulfa drugs have a long withdrawal period and should not be used in laying hens. Routine yearly fecal examinations are recommended for all backyard flocks. Coccidiosis vaccination is available in mail-order day-old chicks from certain hatcheries, but care must be taken to have ideal brooding conditions to confer protective immunity.

Consult the product label before use of any insecticides or antiparasitics to ensure the product is up-to-date and labeled by the EPA and approved for use in poultry and poultry premises. Topical products approved for use in dogs and cats, such as fipronil and selamectin, are strictly forbidden for use in all food animals, including backyard poultry. Some good resources include VetPestX, a database of registered pesticides for animals, and the FARAD poultry page, which also includes information about labeled antimicrobials.

Viral Diseases

Avian Encephalomyelitis 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 in Backyard Poultry

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.

Backyard 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 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 in Backyard Poultry

Infectious bronchitis virus Infectious Bronchitis (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 False Laying in Poultry False layer hens look normal and ovulate normally but do not produce eggs. Typically, hens appear healthy, with fully developed secondary sex characteristics and an active ovary but a nonfunctioning... read more False Laying in Poultry . 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 Vaccination of Backyard Poultry For the small flock owner, vaccination is generally necessary only if the birds have had disease problems in the past, may possibly be exposed to other birds (eg, at poultry shows, meat swaps... read more unless they come in contact with other chickens.

Marek's Disease in Backyard Poultry

Marek's disease Marek's Disease in Poultry Marek's disease is a highly contagious viral disease of poultry characterized by T-cell lymphomas and peripheral nerve enlargement. Standard criteria used for diagnosis include history, clinical... read more Marek's Disease in Poultry (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's) 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 Lymphoid Leukosis in Poultry Lymphoid leukosis is a neoplastic disease of poultry caused by avian leukosis virus. The disease is characterized by B-cell lymphoma, occurring in chickens approximately 16 weeks of age and... read more Lymphoid Leukosis in Poultry , 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 in Backyard Poultry

Newcastle disease virus Newcastle Disease and Other ParamyxovirusInfections (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 Vaccination of Backyard Poultry For the small flock owner, vaccination is generally necessary only if the birds have had disease problems in the past, may possibly be exposed to other birds (eg, at poultry shows, meat swaps... read more is available but is generally given to backyard poultry only if exposed to other birds.

Bacterial Infections

Colibacillosis in Backyard Poultry

Colibacillosis Colibacillosis is caused by Escherichia coli and is usually secondary to other infections such as infectious bronchitis virus and mycoplasmosis. E coli is seen in most species and age groups. A wide variety of clinical signs affecting the respiratory, reproductive, and intestinal systems can be seen. Vigorous adherence to biosecurity and sanitation programs can effectively prevent the organism from causing disease. Many antibiotics can be used for treatment, and sensitivity to the antibiotic should be tested. Treatment is usually successful if the disease is in the early stages.

Mycoplasmosis (Chronic Respiratory Disease) in Backyard Poultry

Chronic respiratory disease in poultry (primarily chickens and turkeys), or mycoplasmosis Mycoplasmosis , is generally caused by Mycoplasma gallisepticum infection. M gallisepticum is a reportable disease in turkeys in select states in the USA. Pathogenicity of M gallisepticum is enhanced by infection with other organisms. Clinical signs of respiratory disease develop slowly in a flock, and feed consumption drops. Infection of the sinuses with purulent exudate (swollen face) is common in turkeys. Serology and isolation and identification of the organism can be used for diagnosis. Prevention, as with the salmonellae, rests with establishment of a clean flock by eliminating the infected flock, completely sanitizing the premises, and obtaining clean stock. Vaccination is available on a state-by-state basis. Treatment is expensive, and the disease often recurs after treatment is stopped. Other important mycoplasmas in poultry include M synoviae (infectious synovitis Mycoplasma synoviae Infection in Poultry Mycoplasma synoviae most commonly causes subclinical upper respiratory infections in chickens, turkeys, and other avian species. It can also cause exudative tendinitis and synovitis,... read more <i >Mycoplasma synoviae</i> Infection in Poultry ) and M meleagridis (venereal infection and airsacculitis).

Salmonellosis in Backyard Poultry

S Pullorum is egg transmitted, causes a diarrheal disease in young chicks and poults, and results in high mortality. Adult birds are asymptomatic carriers. Diagnosis is based on disease history and isolation of the bacteria. Prevention is achieved by purchasing birds from a breeder flock that is National Poultry Improvement Plan certified clean of S Pullorum and typhoid. Treatment is not recommended, because it can cause birds to become carriers. Fowl typhoid is seen in chickens, turkeys, and many other game and wild birds. Fowl typhoid is similar in disease presentation and diagnosis to S Pullorum, although mature birds can show clinical signs of fowl typhoid. Clinical signs are infrequently observed in poultry infected with S Enteritidis and S Typhimurium, although most paratyphoid Salmonella infections are asymptomatic in most poultry. Flocks can be monitored by obtaining egg samples and environmental samples to culture the organism.

Fungal Diseases

Aspergillosis in Backyard Poultry

Aspergillosis Aspergillosis , or brooder pneumonia, is seen in many poultry and other species of birds. Birds < 3 weeks old are most commonly affected, and infection is obtained from hatchers or brooders contaminated with fungal spores. Morbidity is variable, and mortality can be high in clinically affected birds. Culturing the fungus or demonstrating typical fungal hyphae in fresh preparations from lesions are used for diagnosis. Prevention is accomplished by thoroughly cleaning hatchers, incubators, waterers, feeders, and ventilation fans and by keeping litter clean and dry. Treatment is expensive and may not be effective. Ketoconazole and nystatin have been used.

Favus in Backyard Poultry

Favus, or ringworm, also known as white comb, is a fungal disease caused by Microsporum gallinae, which is of minor importance in all fowl, especially chickens and turkeys. Affected birds have small, white, chalky deposits on the comb, which can enlarge and coalesce to form a dull white, moldy layer that could be several millimeters thick. The disease is self-limiting, and the comb heals after several months. Typically, if the disease is limited to the comb, the health of the bird is not affected, but if feathered portions are involved, the bird may become emaciated and die. Favus is a public health concern.

Antibiotic Usage

Antibiotics are readily available in feed stores and online poultry supply sites; however, use of antibiotics must be carefully considered. Beginning in 2017, livestock and poultry producers were required to have a veterinary feed directive (VFD) in place to buy or use medically important antibiotics in animal feed, and all water medications now require a prescription.

Medications are one of the most difficult aspects of treating backyard poultry because patients are typically both pets and food animals. However, the FDA considers all chickens and poultry to be food animals regardless of an owner’s attachment to a pet bird. Thus, all regulations pertaining to the treatment of food animals must be followed when treating backyard poultry. Even if this is treating one 4-H bird, the veterinarian will still need to have a VFD to dispense a VFD product, so injectable, oral, or water-soluble medications are suggested if dealing with small flocks. Consult with FARAD for FDA-approved medications for use in laying hens, and contact a local poultry health specialist for specific treatment concerns.

Each antibiotic is labeled for different species and the use of the poultry, and administering the correct dosage may be difficult. In some instances, antibiotics are useful to treat and control disease. Certain antibiotics, such as chloramphenicol, glycopeptides, and fluoroquinolones, are prohibited for extra-label use in food animals, including backyard poultry. Judicious use of antibiotics may be recommended after appropriate diagnostic tests. However, vaccination, good biosecurity, good management, proper sanitation practices, and a good plan of nutrition are key to control of disease and are far more effective than antibiotic usage.

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