Common Diseases in Backyard Chickens — A Complete Reference Guide
By Happy Heart Farms | Live Oak, Florida
One of the most important things you can do as a backyard flock owner is learn to recognize the signs of common poultry diseases before they become emergencies. Early detection is almost always the difference between a manageable situation and a flock-wide crisis. This guide covers the most common diseases affecting backyard chickens — what they are, what to watch for, how they spread, and where to find reliable, in-depth information for each one.
Bookmark this page. It is designed to be a resource you return to whenever something seems off with one of your birds.
A Note Before You Diagnose
The single most important thing to understand about chicken diseases is that many of them share overlapping symptoms. Respiratory distress, lethargy, reduced egg production, and neurological symptoms can all point to dozens of different conditions — some viral, some bacterial, some parasitic, and some nutritional. Jumping to a diagnosis based on one symptom is one of the most common and costly mistakes backyard chicken keepers make.
Use this guide as a starting point, not a final answer. When in doubt, consult a poultry-experienced veterinarian and consider laboratory testing for a definitive diagnosis. Many conditions that look identical are treated very differently — and treating the wrong disease wastes time while the real problem progresses.
Viral Diseases
1. Marek’s Disease
What it is: A highly contagious herpesvirus that spreads through feather dander and persists in the environment for months. It is one of the most frequently discussed diseases in backyard chicken keeping — and one of the most frequently misdiagnosed.
Symptoms: Progressive paralysis of legs and wings, weight loss despite eating, vision changes, internal tumors, and the characteristic posture of one leg extended forward and one backward.
Important: Many conditions mimic Marek’s symptoms exactly — including Vitamin E deficiency, leg injuries, bumblefoot, and Lymphoid Leukosis. Vaccinated birds can also test positive for Marek’s antibodies without being sick. See our full article on Marek’s Disease for a detailed breakdown of why Marek’s is so often misdiagnosed and what to consider instead.
Prevention: Vaccination in the first days of life. All pullets from Happy Heart Farms are vaccinated before leaving our farm.
Treatment: None. Supportive care only.
Learn more:
- Marek’s Disease — Merck Veterinary Manual
- Common Viral Diseases of Backyard Chickens — VCA Animal Hospitals
2. Newcastle Disease
What it is: A highly contagious viral disease that affects the respiratory, nervous, and digestive systems simultaneously. It is one of the most serious poultry diseases worldwide and is a reportable disease in the United States — meaning suspected cases must be reported to state or federal animal health authorities.
Symptoms: Difficulty breathing, nasal discharge, murky or watery eyes, twisted neck, loss of coordination, paralysis of legs and wings, green or yellow diarrhea, and sudden drops in egg production. The presence of both respiratory AND neurological symptoms together is a strong indicator of Newcastle rather than Marek’s.
Spread: Highly contagious — spreads through direct contact with infected birds, contaminated equipment, clothing, and wild birds.
Prevention: Vaccination is available. Strong biosecurity practices are essential. Limit contact with wild birds and visiting flocks.
Treatment: No specific treatment. Antibiotics may help prevent secondary bacterial infections. Survivability is generally low in severely affected birds.
Learn more:
- Common Poultry Diseases — University of Florida IFAS Extension
- Common Infectious Diseases in Backyard Poultry — Merck Veterinary Manual
3. Infectious Bronchitis
What it is: A highly contagious viral respiratory disease caused by an avian coronavirus. It affects chickens of all ages and spreads rapidly through a flock. Infectious bronchitis is particularly damaging to laying hens because it can permanently affect the reproductive tract, leading to reduced egg production that never fully recovers.
Symptoms: Coughing, sneezing, rattling breathing sounds, watery eyes and nostrils, reduced appetite, sharp drops in egg production, thin or misshapen eggshells, and watery egg whites. In young pullets, infection can cause permanent oviduct damage resulting in hens that never lay normally.
Spread: Spreads through the air via respiratory droplets, direct bird contact, contaminated equipment, and potentially through wild birds.
Prevention: Vaccination is available. Biosecurity practices are critical because the virus spreads so rapidly.
Treatment: No specific treatment. Antibiotics for three to five days may help control secondary bacterial infections. Raise temperature slightly for young chicks while symptoms persist.
Learn more:
- Infectious Bronchitis in Backyard Flocks — Mississippi State University Extension
- Infectious Bronchitis in Chickens — Penn State Extension
- Infectious Bronchitis Virus — University of Florida IFAS Extension
4. Fowl Pox
What it is: A slow-spreading viral disease transmitted primarily by mosquitoes and direct contact between birds. In Florida, where mosquitoes are a year-round presence, Fowl Pox is a genuine and ongoing concern for backyard flocks.
Symptoms: Two forms exist. The dry form produces raised, wart-like lesions on unfeathered areas — comb, wattles, face, and legs. Lesions heal in approximately two weeks. The wet form produces canker-like lesions inside the mouth, throat, and trachea, which can obstruct breathing and is more serious. Affected hens show a temporary drop in egg production.
Spread: Primarily through mosquito bites. Also spreads through direct contact between infected and healthy birds and through wounds.
Prevention: Vaccination is available and highly recommended in Florida given the year-round mosquito pressure. Mosquito control measures around the coop help reduce transmission.
Treatment: No specific treatment — the disease runs its course in two to four weeks in the dry form. Supportive care and prevention of secondary infection are the priorities. Wet form cases may require veterinary attention.
Learn more:
- Common Poultry Diseases — University of Florida IFAS Extension
- Backyard Poultry Disease Resources — Merck Veterinary Manual
5. Avian Influenza (Bird Flu)
What it is: A group of influenza viruses that affect birds. Low pathogenicity strains cause mild illness. Highly pathogenic avian influenza — HPAI — is a serious, rapidly fatal disease that is also a reportable illness requiring immediate notification of animal health authorities. HPAI outbreaks have affected backyard flocks across the United States in recent years.
Symptoms: Sudden death with little warning, swelling of the head and comb, respiratory distress, purple discoloration of wattles and comb, dramatic drop in egg production, and neurological symptoms.
Spread: Wild birds — particularly waterfowl — are the primary reservoir. Spreads through direct contact with infected birds, contaminated water, feed, equipment, and clothing.
Prevention: Limit contact with wild birds. Cover feed and water to prevent contamination by wild birds. Maintain strict biosecurity. Report any sudden unexplained deaths to your state veterinarian immediately.
Treatment: None. HPAI-affected flocks are typically depopulated under government authority to prevent further spread.
Learn more:
Bacterial Diseases
6. Mycoplasma Gallisepticum — Chronic Respiratory Disease
What it is: One of the most common bacterial respiratory infections in backyard flocks, caused by Mycoplasma gallisepticum. It is chronic, meaning it persists in the flock indefinitely once established, and infected birds remain carriers for life.
Symptoms: Rattling or gurgling breathing, nasal and eye discharge, facial swelling particularly around the sinuses, reduced appetite, and gradual decline in egg production. Symptoms often worsen when birds are stressed.
Spread: Direct contact between birds, airborne transmission, contaminated equipment, and from infected hens to chicks through eggs. Highly contagious.
Prevention: Purchase birds from Mycoplasma-free flocks. Quarantine all new birds for a minimum of thirty days before introducing them to your flock. Maintain excellent ventilation — poor air quality dramatically worsens MG.
Treatment: Antibiotics can suppress symptoms but do not eliminate the infection. Affected flocks remain carriers permanently.
Learn more:
7. Infectious Coryza
What it is: A bacterial respiratory disease caused by Avibacterium paragallinarum. It spreads rapidly through flocks and causes significant drops in egg production.
Symptoms: Foul-smelling nasal discharge, facial swelling — particularly under the eyes — swollen wattles, watery eyes, and labored breathing. The distinctive foul odor of the discharge is a strong indicator of Coryza over other respiratory diseases.
Spread: Direct contact with infected birds, contaminated water and equipment. Carrier birds that show no symptoms are a major source of flock-to-flock transmission.
Prevention: Vaccination is available. Purchase birds from reputable sources. Never mix birds from different sources without proper quarantine.
Treatment: Antibiotics — particularly sulfonamides and tetracyclines — can reduce symptoms but do not eliminate carrier status.
Learn more:
8. Salmonella
What it is: A bacterial infection that is particularly important because it can be transmitted to humans. Adult chickens often carry Salmonella without showing any symptoms, making it a biosecurity concern for the entire family rather than just the flock.
Symptoms: In adult birds — often none. In chicks — diarrhea, weakness, and failure to thrive. In humans — nausea, vomiting, diarrhea, and fever following contact with infected birds or their environment.
Spread: Through contaminated droppings, eggs, soil, and equipment. Humans become infected through contact with birds or their environment and then touching their mouths without washing hands.
Prevention: Wash hands thoroughly with soap and water after every contact with chickens or their environment. Do not allow young children, elderly individuals, or immunocompromised people to handle birds without supervision. Do not bring chickens inside the home.
Treatment: Antibiotics in severe cases in birds. Human cases may require medical treatment.
Learn more:
Parasitic Diseases
9. Coccidiosis
What it is: An intestinal disease caused by microscopic parasites called coccidia. It is one of the most common and serious diseases in young chickens and is closely tied to coop hygiene and moisture management.
Symptoms: Bloody or watery diarrhea, lethargy, ruffled feathers, pale comb, weight loss, and huddling. In severe cases, rapid death. Symptoms are most severe in young birds.
Spread: Through contaminated droppings — birds ingest oocysts from the environment. Wet, dirty conditions dramatically accelerate the spread and severity of coccidiosis.
Prevention: Keep the coop clean and dry. This is one of the strongest arguments against deep bedding, which traps moisture and creates ideal conditions for coccidia to thrive. Medicated chick feed containing coccidiostats helps prevent infection in young birds.
Treatment: Anti-coccidial medications — most commonly Amprolium — prescribed by a veterinarian. Early treatment is critical.
Learn more:
10. External Parasites — Mites and Lice
What it is: Mites and lice are among the most common challenges in backyard flocks. Northern fowl mites live directly on the bird and feed continuously. Red mites hide in coop crevices during the day and feed on birds at night. Both cause significant stress, anemia, and reduced production in heavy infestations.
Symptoms: Feather loss particularly around the vent and neck, pale comb indicating anemia, restlessness especially at night, weight loss, and reduced egg production. Visible mites or lice can be seen by parting feathers at the vent and under wings.
Spread: Direct contact between birds, wild birds visiting the property, and introduction of new birds without quarantine.
Prevention: Regular inspection of birds, particularly under wing feathers and around the vent. Quarantine new birds before flock integration. Keep wild bird contact to a minimum.
Treatment: Permethrin-based sprays and dusts applied according to label directions. Food-grade diatomaceous earth in dustbathing areas helps reduce populations naturally.
Learn more:
- Poultry Mites and Lice — Merck Veterinary Manual
- Common Chicken Health Problems — The Old Farmer’s Almanac
11. Internal Parasites — Worms
What it is: Intestinal worms — including roundworms, cecal worms, and capillary worms — are common in free-ranging backyard flocks. Most chickens carry some worm burden without obvious ill effects, but heavy infestations cause significant health decline.
Symptoms: Weight loss despite good appetite, pale comb and wattles, diarrhea, reduced egg production, and general failure to thrive. Symptoms develop gradually, which is why worms are frequently overlooked until the infestation is severe.
Spread: Through contaminated soil, droppings, and intermediate hosts like earthworms and beetles. Free-ranging birds are at significantly higher risk than confined birds.
Prevention: Rotate grazing areas when possible to break the parasite lifecycle. Keep waterers clean. Consider periodic fecal testing through a veterinarian to monitor worm burden.
Treatment: Fenbendazole — sold as Safeguard — is currently the only product approved for roundworm treatment in chickens in the United States. Consult your veterinarian before treating.
Learn more:
Common Non-Infectious Conditions
12. Bumblefoot
What it is: A bacterial infection of the foot pad caused by Staphylococcus bacteria entering through a small cut or abrasion. It is frequently mistaken for a neurological or systemic disease because affected birds are in significant pain and reluctant to move.
Symptoms: Lameness, swelling of the foot pad, a characteristic dark scab on the bottom of the foot, and reluctance to bear weight. In advanced cases the infection can spread up the leg.
Prevention: Avoid rough or sharp surfaces in the coop and run. Keep roost bars smooth and splinter-free. Inspect feet regularly.
Treatment: Clean the wound thoroughly, apply antibiotic cream, and bandage the foot. Separate the affected bird from flock mates to allow healing. Severe cases require veterinary attention to drain the abscess.
Learn more:
13. Wry Neck — Vitamin E and Selenium Deficiency
What it is: A condition caused by Vitamin E and selenium deficiency in which the bird loses the ability to hold its head normally. It is one of the most commonly misdiagnosed conditions in backyard chicken keeping — frequently and incorrectly attributed to Marek’s Disease or Newcastle Disease.
Symptoms: The bird holds its head twisted backward or sideways — called stargazing — loses balance, falls, and cannot right itself. The bird is typically alert and still trying to eat and drink despite the dramatic posture.
Prevention: Ensure feed is fresh and nutritionally complete. Vitamin E deficiency can develop when feed is stored improperly or past its freshness date.
Treatment: Vitamin E oil given orally combined with selenium supplementation. Many birds show significant improvement within days of treatment beginning — a response that strongly distinguishes this condition from the viral diseases it resembles.
Learn more:
When to Call a Veterinarian
Not every health concern requires professional intervention, but some situations demand it. Seek veterinary care when:
- Multiple birds show symptoms simultaneously
- A bird deteriorates rapidly despite supportive care
- You observe neurological symptoms — circling, tremors, inability to stand
- Swelling, wounds, or lesions are severe or worsening
- Sudden unexplained death of one or more birds occurs
- You suspect Avian Influenza — contact your state veterinarian immediately
Finding a poultry-experienced veterinarian before you have an emergency is one of the wisest things you can do as a flock owner. They are less common than small animal vets — locating one in your area in advance means you are not scrambling in a crisis.
The American Association of Avian Pathologists and your state’s Cooperative Extension Service are both excellent resources for finding qualified poultry veterinarians and diagnosticians in your region.
Healthy Birds Start Here
The best defense against disease is starting with healthy, vaccinated birds from a reputable source. At Happy Heart Farms in Live Oak, Florida, every pullet we sell is vaccinated for Marek’s Disease, guaranteed female, and backed by a seven-day health guarantee.
We serve customers across North Florida, South Georgia, and the entire Southeast. Visit happyheartfarmsfl.com to browse available breeds and reserve your flock. Questions about chicken health or disease prevention? Call us at 386-208-0495 — we are always happy to help.
~ Grateful hearts make happy hearts ~