As with commercial poultry production, infectious diseases in backyard poultry flocks are common and costly problems. Although the same infectious agents affect all poultry, in a backyard setting some diseases are more common or particularly concerning because of predominant management styles. Furthermore, certain management considerations are especially important for backyard poultry, given that the scale, economics, and goals of production are vastly different from those of commercial flocks.
Parasitism in Backyard Poultry
As with other bird species, the common parasites in poultry are mites, lice, ticks, worms, and protozoa.
Two common mites of poultry are the northern fowl mite (Ornithonyssus sylviarum) and the red mite (Dermanyssus gallinae; see northern fowl and poultry red mites image). The northern fowl mite is usually found around the vent, tail, and breast (see Ornithonysuss sylviarum mites and northern fowl mites in vent region images). These mites are easily observed as small, reddish-brown flecks.
Red mites feed only at night, making daytime diagnosis difficult (see poultry red mite and northern fowl and poultry red mites image images). They can be found in cracks and seams near bedding areas and look 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 observed at the base of feathers (see nit image; also see poultry louse species image). In severe infestations, growth and egg production can be affected. Insecticides are available for treatment.
Courtesy of Dr. Yuko Sato.
Fowl ticks comprise a group of soft ticks that parasitize many species of poultry and wild birds. Ticks in poultry are easily missed, because they spend relatively little time on the bird. Heavy infestations can result in anemia or tick paralysis, and ticks can be vectors for Borrelia anserina (the bacterium that causes spirochetosis).
Application of pesticides to affected buildings is the treatment of choice. After houses are cleaned, appropriate pesticides should be applied using a high-pressure sprayer to thoroughly treat walls, ceilings, cracks, and crevices. After treatment, cracks and crevices should be filled in.
Roundworms and tapeworms are the most common internal poultry parasites (see images in Helminthiasis in Poultry) and are generally the result of soil contamination and poor management. Unless infestations are heavy, clinical signs are usually not evident. Because most domestic poultry have some internal parasitism, a fecal examination should be performed before treatment to assess the extent of infestation (and to provide a benchmark against which to monitor the effectiveness of treatment).
Treatment of internal parasite infestations in poultry is discussed elsewhere (see Helminthiasis in Poultry).
Proper litter management decreases parasite loads and reinfection.
As in commercial poultry production, in backyard poultry flocks the control of coccidia is one of the more common and costly problems. Coccidia are found primarily in the intestinal tract of most poultry; in geese they are also found in the kidney.
Coccidiosis most often occurs in birds 1–4 months old. Birds are not susceptible to infection until 10–14 days of age.
Clinical signs of coccidiosis in poultry include diarrhea that is often bloody and that frequently leads to loss in production, general malaise, and death.
Coccidia thrive in moist, heavily soiled litter, and disease often results because the density of birds is too high. Coccidiosis can be prevented by coccidiostats added to feed, which can be given to birds as early as in their starter diet. Outbreaks can be treated with selected coccidiostats and extralabel 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 poultry flocks.
Vaccination against coccidiosis is available for mail-order day-old chicks from certain hatcheries. The vaccine is administered at the hatchery; care must be taken to provide ideal brooding conditions to confer protective immunity. Chickens vaccinated against coccidiosis should not be given feed medicated with coccidiostats, because coccidiostats can negate the vaccine's effectiveness.
Consult the label before using any insecticides or antiparasitics to ensure that the product is up-to-date, labeled by the EPA, and approved for use in poultry and on 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. Good resources include VetPestX, a database of registered pesticides for animals; and the Food Animal Residue Avoidance Databank (FARAD) Medications Labelled for Layers web page, which also includes information about labeled antimicrobials.
Viral Diseases in Backyard Poultry
Avian Encephalomyelitis
Avian encephalomyelitis occurs in chickens, turkeys, pheasants, and quail; it affects primarily chicks 1–3 weeks old (see clinical signs video and brain lesion image). Nearly all commercial poultry flocks are infected; however, morbidity is low because of maternal antibodies.
Avian encephalomyelitis can be transmitted vertically (from parent to offspring during pregnancy or the birth process) in eggs laid between 5 and 13 days after infection and is an enteric infection under natural conditions. The disease is transmitted more rapidly in floor-raised birds than in cage-raised birds.
There is no treatment for avian encephalomyelitis, and vaccination of breeders (both chickens and turkeys) is critical to prevention because it ensures passive transfer of maternal antibodies to protect the young during early life. Because many specialty breeders, particularly those who sell birds to an intermediate supplier, do not vaccinate, the disease is fairly common in backyard poultry. Birds should be vaccinated at > 8 weeks old and by ≤ 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-pathogenicity avian influenza (LPAI), which typically causes few to no clinical signs in poultry; and high-pathogenicity avian influenza (HPAI), which typically causes high mortality rates (see subcutaneous hemorrhage and ischemic necrosis images). 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 clinical signs of illness.
Backyard poultry are just as susceptible as other poultry to AI infection, if not at higher risk. Many backyard flocks are kept outdoors, are free-ranging, have multiple ages and sources of birds, and have less strict standards for biosecurity compared with commercial flocks. There is also a higher risk of contact with wild waterfowl, creating favorable conditions for the transmission of disease within and between flocks.
Many studies show that backyard flocks with multiple types of poultry and poor sanitary conditions have higher incidences of AI. Since the start of the H5N1 2.3.4.4b A/goose/Guangdong/1/1996 outbreak in 2022, > 100 million birds have been affected with HPAI in the US. Of 1,177 flocks affected, > 50% (668 flocks) have been backyard flocks (1).
Clinical signs of AI vary greatly between different poultry species. Generally, however, poultry show a combination of neurological, respiratory, and/or digestive signs, including incoordination or lethargy; oronasal discharge; coughing or sneezing; purple discoloration or swelling of the head, wattles, combs, and legs; greenish-white diarrhea; decrease in or cessation of egg laying; decreased drinking; or sudden death.
If a poultry flock has sudden high death rates (ie, death rates approaching 50% or greater within a period of < 48 hours) 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; many offer free or low-cost yearly testing for AI in backyard poultry. Birds in flocks showing a sudden increase in death rates should not be moved off premises until the flock is tested.
There is no approved vaccine against AI or treatment for the disease in the US. Good management and biosecurity practices are the only way to protect against AI infection in backyard poultry. USDA recommends that backyard flock owners follow six tips to protect flocks from HPAI infection:
Keep your distance (restrict access to your flock).
Keep it clean (clean and disinfect your clothes, shoes, equipment, and hands).
Don't haul disease home.
Don't risk disease from your neighbor.
Know the warning signs.
Report sick birds.
Fowlpox
Fowlpox virus causes crusty and nodular lesions primarily on the unfeathered portions of the bird (see images of scablike lesions in a male broiler breeder, a turkey, and a laying hen). Occasionally, poxvirus can produce lesions in the mouth and trachea, causing death due to suffocation (the "wet form" of pox). If the bird recovers, immunity is generally lifelong.
Not all pox outbreaks are caused by fowlpox virus; they can also be caused by related virus strains, such as turkey pox, psittacine pox, or quail pox (see Poxviral Infections in Birds Other Than Chickens and Turkeys). Strains are usually species specific (eg, pigeon pox); occasionally, however, they affect more than one species. One strain might not cross-protect with another.
Vaccines against fowlpox are available and should be administered to poultry flocks on premises that have a previous history of pox or that are near other birds with the disease (see Vaccination of Backyard Poultry). Poxvirus is transmitted via contact of infected lesions with open wounds and via insect bites (mosquitoes); insect control is key to preventing spread of the disease.
Infectious Bronchitis
Infectious bronchitis virus (IBV) causes a rapidly spreading respiratory disease in young chicks (see airsacculitis and tracheal mucus images). Production is decreased, and eggshell abnormalities occur in laying hens (see wrinkled eggshell image). Certain strains of IBV also cause kidney disease.
Chicks infected early in life can sustain permanent damage to the oviduct, such that they do not produce eggs or they become false layers. IBV is highly transmissible; however, most birds recover with supportive care. Antimicrobials can be administered in drinking water to prevent secondary infection.
Vaccines against infectious bronchitis are available; however, backyard chickens are generally not vaccinated unless they come in contact with other chickens.
Marek's Disease
Marek's disease is a common viral disease in both commercial production and backyard chicken flocks. The primary lesions are tumors of the viscera, muscle, skin, and peripheral nerves (see skin involvement and peripheral nerve enlargement images).
Nerve lesions can be an early indicator of the disease and result in a condition termed "range paralysis" (see leg paresis image).
In birds with visceral tumors, often cachexia is the only clinical sign.
Tumors of the muscles and skin are frequently palpable.
Tumors that affect the eyes (ocular Marek's) can be identified by a grayish color change in the iris or by irregular margins of the pupils (see irregular pupil margins image), with lack of proper pupillary light reflex.
Marek's disease cannot be treated; however, it can be prevented by vaccination at hatch. When backyard poultry are acquired or hatched on-site, every attempt should be made to vaccinate against Marek's disease. Vaccinations might not be effective if administered to birds > 1–2 weeks old. Clinical signs generally occur in birds 4–14 weeks old; however, Marek's disease is not uncommon in older birds, and loss due to death 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 Marek's disease and avian leukosis, another common lymphoid tumor disease caused by a virus. Although the tumors in avian leukosis are similar to those of Marek's disease, avian leukosis typically occurs in slightly older birds, > 14 weeks old. There is no treatment for or vaccination against avian leukosis.
Newcastle Disease
Newcastle disease virus (NDV) affects numerous species of birds and is the reason birds entering the US are quarantined. Exotic NDV is highly fatal and not currently present in the US. Past outbreaks have led to the slaughter of thousands of birds.
Milder forms of NDV are present in the US and are characterized primarily by respiratory disease and a drop in egg production. Mortality rates vary, depending on the virus strain involved. As with IBV, vaccines are available; however, they are generally administered to backyard poultry only in cases of exposure to other birds.
Bacterial Infections in Backyard Poultry
Colibacillosis
Colibacillosis is caused by infection with Escherichia coli and is usually secondary in backyard poultry to other infections, such as infectious bronchitis and mycoplasmosis. E coli infection occurs in most species and age groups of poultry. A wide variety of clinical signs of colibacillosis affect the respiratory, reproductive, and intestinal systems.
Vigorous adherence to biosecurity and sanitation programs can effectively prevent E coli from causing colibacillosis in backyard poultry. Many antimicrobials (eg, tetracyclines and macrolides) can be used for treatment; however, the emergence of antimicrobial resistance and restrictions on antimicrobial use in food-producing poultry have resulted in limited options. Antimicrobial susceptibility should be tested, and regulations for use in food-producing animals should be followed. Treatment is usually successful if the disease is in the early stages.
Mycoplasmosis (Chronic Respiratory Disease)
Chronic respiratory disease in poultry (primarily chickens and turkeys), or mycoplasmosis, is generally caused by Mycoplasma gallisepticum. Mycoplasmosis is a reportable disease in turkeys in select states in the US. Pathogenicity of M gallisepticum is enhanced by infection with other organisms.
Clinical signs of respiratory disease develop slowly in infected flocks, and feed consumption drops. Infection of the sinuses with purulent exudate (swollen face) is common in turkeys (see M gallisepticum turkey image). Serological testing, along with isolation and identification of the organism, can aid diagnosis.
As with salmonellosis (discussed below), prevention depends on the establishment of a clean flock by eliminating the infected flock, completely sanitizing the premises, and obtaining clean birds. 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 backyard poultry include Mycoplasma synoviae (see Mycoplasma synoviae Infection) and Mycoplasma meleagridis (venereal infection and airsacculitis; see Mycoplasma meleagridis Infection).
Salmonellosis
In general, the Salmonella enterica serotypes Pullorum (see Pullorum Disease in Poultry) and Gallinarum (see Fowl Typhoid) cause the greatest problems for backyard poultry. The S enterica serotypes Typhimurium, Enteritidis, Heidelberg, and Kentucky are important in terms of public health.
S Pullorum is transmitted via the egg, causes a diarrheal disease in young chicks and poults, and results in high mortality rates. Adult birds are subclinical carriers. Diagnosis is based on disease history and isolation of the bacteria. Prevention is achieved by purchasing birds from a breeder flock that is certified by the National Poultry Improvement Plan to be clean of S Pullorum and typhoid. Treatment of S Pullorum infection is not recommended, because birds can become carriers as a result.
Fowl typhoid occurs in chickens, turkeys, and many other game and wild birds. The disease is similar in clinical signs and diagnosis to S Pullorum infection, except that mature birds can show clinical signs of fowl typhoid.
Clinical signs are infrequently observed in poultry infected with S Enteritidis and S Typhimurium; however, most paratyphoid Salmonella infections are subclinical in most poultry. Flocks can be monitored by obtaining egg samples and environmental samples to culture the organism.
Fungal Diseases in Backyard Poultry
Aspergillosis
Aspergillosis, or brooder pneumonia, occurs in many species of poultry and other birds (see granulomatous fungal pneumonia, granulomatous fungal airsacculitis, and fungal plaque and nodules gross lesion images). Birds < 3 weeks old are most commonly affected, and infection is acquired from hatchers or brooders contaminated with fungal spores. Morbidity rates vary, and mortality rates can be high in clinically affected birds.
Diagnosis of aspergillosis is based on culturing the causative fungus or demonstrating typical fungal hyphae in fresh cytological preparations from lesions. Aspergillosis can be prevented by thoroughly cleaning hatchers, incubators, waterers, feeders, and ventilation fans and by keeping litter clean and dry. Treatment is expensive and can be ineffective. Antifungal agents such as itraconazole, amphotericin, and terbinafine have been used with limited success.
Favus (Avian Ringworm)
Favus (also known as avian ringworm or "white comb") is a fungal disease that is caused by Microsporum gallinae and is of minor importance in all fowl, especially chickens and turkeys. In rare instances, Microsporum gypseum and Trichophyton gallinae have also been isolated as causative agents.
Affected birds have small, white, chalky deposits on the comb (see favus infection image) that can enlarge and coalesce to form a dull white, moldy layer up to several millimeters thick.
Courtesy of Dr. Patricia Wakenell.
Favus 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; however, if feathered portions of skin are involved, the bird can become emaciated and die.
Favus is a public health concern. Microsporum gallinae is a rare cause of dermatophytosis in humans.
Antimicrobial Use in Backyard Poultry
Antimicrobials are readily available in feed stores and online poultry supply sites; however, the use of antimicrobials in poultry must be carefully considered.
Medications are one of the most difficult aspects of treating backyard poultry, because the birds are typically both pets and food animals. In the US, 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.
Since 2017, keepers of production animals in the US, including backyard poultry, have been required to have a veterinary feed directive (VFD; written authorization from a veterinarian) in place to buy or use medically important antimicrobials in animal feed, and all medications administered in drinking water now require a prescription.
Even if treating a single 4-H bird, veterinarians in the US must have a VFD to dispense a VFD medication. Therefore, injectable, oral, or water-soluble medications are suggested for treating small flocks. FARAD should be consulted for FDA-approved medications to use in laying hens, and a local poultry health specialist should be contacted for specific treatment concerns.
Each antimicrobial is labeled for different species and uses in poultry, and administering the correct dosage can be difficult. Sometimes antimicrobials are useful to treat and control disease. Certain antimicrobials, such as chloramphenicol, glycopeptides, and fluoroquinolones, are prohibited for extralabel use in food animals, including backyard poultry.
Judicious use of antimicrobials might be recommended after appropriate diagnostic tests. However, vaccination, good biosecurity, good management, proper sanitation practices, and a good plane of nutrition are key to the control of disease and are far more effective than antimicrobial use.
Key Points
Some diseases, such as Marek's disease and avian encephalomyelitis, can be prevented by vaccination. Others, depending on the cause, are controlled by antimicrobials.
Each antimicrobial is labeled for different species and uses in poultry, and certain drugs are prohibited for use in food animals, including backyard poultry. The label should be consulted before administration of any medication to backyard poultry.
Vaccination, good biosecurity, good management, proper sanitation practices, and appropriate nutrition are key to the prevention and control of disease.
For More Information
USDA Animal and Plant Health Inspection Service: Confirmations of Highly Pathogenic Avian Influenza in Commercial and Backyard Flocks
USDA Questions and Answers: Protecting Birds From Avian Influenza. April 2015.
University of Minnesota Extension: Diseases of Small Poultry Flocks
References
USDA Animal and Plant Health Inspection Service. Detections of Highly Pathogenic Avian Influenza. Updated August 14, 2024. Accessed September 19, 2024.
