Common Chicken Diseases: Symptoms, Causes and Treatment

Understanding common chicken diseases is one of the most valuable things you can do as a flock keeper. Chickens are hardy animals, but they are also prey species that instinctively hide signs of illness until a disease has progressed significantly. Catching problems early gives your birds a much better chance of recovery and protects the rest of your flock from exposure.

This guide covers the diseases most likely to affect backyard flocks, their symptoms, what causes them, and what you can do about them. It is not a substitute for veterinary care, but it will help you recognize trouble early and ask the right questions when you call a vet.

How to Tell if Your Chicken is Sick

Before diving into specific diseases, it helps to understand the general warning signs that something is wrong. A healthy chicken is alert, active, and responsive. It eats and drinks regularly, produces consistent droppings, and holds its feathers flat against its body.

Signs that should prompt a closer look include:

• Lethargy or sitting apart from the flock
• Ruffled, puffed-up feathers
• Watery, green, or blood-tinged droppings
• Labored breathing, wheezing, or gurgling sounds
• Discharge from eyes or nostrils
• Significant drop in egg production
• Weight loss or a sunken keel bone
• Pale comb and wattles
• Lameness or loss of coordination

For a deeper look at reading your birds’ health signals, visit our guide on how to tell if your chicken is sick before it’s too late.

Marek’s Disease

What it is: Marek’s Disease is a highly contagious viral disease caused by a herpesvirus. It is one of the most widespread diseases in domestic poultry worldwide.

Symptoms: Paralysis of the legs, wings, or neck is the hallmark sign. Affected birds may lie on their side with one leg forward and one stretched backward. Other signs include irregular pupils, gray iris (ocular Marek’s), weight loss, and tumors affecting internal organs in chronic cases.

Cause: The Marek’s Disease Virus (MDV) spreads through feather follicle dander. It is shed in the environment and can persist in dust and litter for months. New birds introduced without vaccination are at serious risk in a flock that has had previous exposure.

Treatment: There is no cure. Supportive care — good nutrition, hydration, and comfortable housing — can help affected birds survive, but most will not fully recover from paralysis.

Prevention: Vaccination at hatch is highly effective at preventing the disease and is standard practice for most commercial hatcheries. Birds vaccinated as chicks are significantly protected, though vaccinated birds can still carry the virus. Read our full breakdown of Marek’s Disease in chickens for detailed guidance on vaccination schedules and management.

Coccidiosis

What it is: Coccidiosis is an intestinal disease caused by single-celled parasites called Coccidia. It is one of the leading killers of young chicks and is extremely common in backyard flocks.

Symptoms: Bloody or watery droppings are the most distinctive sign. Chicks will look puffed up, stop eating, and huddle together. Rapid weight loss and high mortality in young birds are common without treatment.

Cause: Coccidia oocysts are present in almost all soil. They spread through fecal contamination of feed and water. Wet bedding, overcrowding, and stress accelerate outbreaks. Young chicks have not yet developed immunity and are most vulnerable in the first 6 to 8 weeks of life.

Treatment: Amprolium (sold under brand names like Corid) is the standard treatment and is added to the drinking water. Start treatment immediately if you suspect an outbreak — delays increase mortality significantly.

Prevention: Medicated chick starter feed contains Amprolium as a preventive measure. Keeping brooders and coops clean and dry is essential. Many keepers allow chicks gradual exposure to small amounts of soil to help them build natural immunity before moving to the coop.

Infectious Bronchitis (IB)

What it is: Infectious Bronchitis is a highly contagious respiratory disease caused by a coronavirus specific to chickens. It spreads rapidly through flocks via airborne transmission.

Symptoms: Gasping, coughing, sneezing, and nasal discharge are the primary signs. In laying hens, you will often see a dramatic drop in egg production, and eggs laid may have wrinkled, soft, or rough shells. Some strains affect the kidneys.

Cause: The Infectious Bronchitis Virus (IBV) spreads through respiratory secretions and contaminated equipment. It can survive on surfaces for days and travel significant distances through the air. New birds and cold, damp conditions often trigger outbreaks.

Treatment: There is no specific antiviral treatment. Supportive care — warmth, good ventilation, and fresh water — helps birds fight through the infection. Secondary bacterial infections (particularly Mycoplasma) often follow IB and may require antibiotics prescribed by a vet.

Prevention: Vaccination is available and widely used in commercial settings. Good biosecurity, including quarantining new birds for 30 days, is the most practical prevention for backyard keepers.

Chronic Respiratory Disease (Mycoplasma gallisepticum)

What it is: Commonly called CRD, Chronic Respiratory Disease is caused by the bacterium Mycoplasma gallisepticum. It is one of the most persistent and economically damaging diseases in poultry worldwide.

Symptoms: Rattling or bubbling sounds when breathing, nasal discharge, foamy or swollen eyes, reduced egg production, and gradual weight loss. Birds rarely die outright but become chronically ill and act as carriers for life.

Cause: Mycoplasma spreads through direct contact, contaminated equipment, and vertically through eggs from infected hens. Stress, poor ventilation, and concurrent infections accelerate disease progression.

Treatment: Antibiotics such as Tylan (Tylosin) and Oxytetracycline can reduce clinical signs but do not eliminate the infection. Once a flock tests positive, it is considered a Mycoplasma-positive flock permanently.

Prevention: Purchase birds only from Mycoplasma-negative flocks or NPIP-certified hatcheries. Strict quarantine of new birds is essential. Vaccination is available in some countries.

Fowl Pox

What it is: Fowl Pox is a slow-spreading viral disease that appears in two forms: dry pox (skin lesions) and wet pox (lesions inside the mouth and throat).

Symptoms: Dry pox causes wart-like scabs on the comb, wattles, and unfeathered skin. Wet pox causes yellowish-white plaques inside the mouth and trachea, which can interfere with breathing and eating. Wet pox has a significantly higher mortality rate.

Cause: The Fowl Pox virus spreads through mosquito bites (the primary vector), direct contact with infected birds, and contaminated equipment. It can also enter through wounds and skin abrasions.

Treatment: No specific treatment exists. Remove the scabs from dry pox lesions with care and apply iodine to prevent secondary infection. Wet pox cases may require gentle removal of throat plaques by a vet and supportive care. Vitamins A and E support immune function during recovery.

Prevention: Vaccination is effective and available from most poultry supply companies. Reducing mosquito exposure through standing water elimination and mosquito netting in runs helps limit transmission significantly.

Newcastle Disease

What it is: Newcastle Disease is a serious viral disease affecting the respiratory, nervous, and digestive systems of poultry. Virulent strains are reportable diseases in many countries due to their devastating impact on commercial and backyard flocks.

Symptoms: Respiratory distress, greenish watery droppings, sudden drops in egg production, twisted necks or paralysis (torticollis), and in virulent strains, very high mortality within a short window.

Cause: Newcastle Disease Virus (NDV) spreads through respiratory secretions, droppings, and contaminated feed, water, and equipment. Wild birds and waterfowl are common reservoirs.

Treatment: There is no treatment. Birds with virulent strains are typically humanely destroyed to prevent spread. Milder velogenic strains may resolve with supportive care.

Prevention: Vaccination is available and commonly used. Report suspected cases to your state or national poultry authority immediately, as Newcastle Disease is a notifiable disease in many jurisdictions.

Keeping Your Flock Healthy Year-Round

The single most effective disease prevention strategy for backyard flocks is good management. This means maintaining a clean coop, providing quality nutrition, minimizing stress, and observing your birds daily so you catch changes early.

Feeding a complete and balanced diet supports immune function significantly. A quality complete layer feed like Purina Layena provides the protein, vitamins, and minerals laying hens need to stay productive and resilient. Adding crushed oyster shell in a separate dish ensures hens with higher calcium demands can self-regulate their intake.

High-protein treats like dried mealworms are an excellent supplement during molt, when your birds need extra protein to regrow feathers while maintaining immune defenses.

If you are just starting out and want to build good flock management habits from the beginning, our guide for backyard chicken beginners is a great starting point.

Recommended Products for Flock Health

• Purina Layena Complete Layer Feed — formulated with the vitamins and minerals laying hens need for sustained health and egg production.
• Crushed Oyster Shell — an easy calcium supplement that helps hens produce strong-shelled eggs and maintain bone density.
• Dried Mealworms — a high-protein treat ideal for supporting recovery, feather regrowth, and flock enrichment.

Frequently Asked Questions

What is the most common disease in backyard chickens?

Coccidiosis is arguably the most common disease affecting backyard flocks, particularly in young chicks. Marek’s Disease and Mycoplasma (CRD) are also extremely widespread. The diseases you are most likely to encounter depend heavily on your region and your purchasing practices.

Can chickens recover from Marek’s Disease?

Some birds with mild cases survive, but paralysis is generally permanent. Vaccinated birds that become infected tend to have milder symptoms and a better chance of survival than unvaccinated birds. The vaccine does not prevent infection but significantly reduces disease severity and mortality. Read our full article on Marek’s Disease for more detail.

How do I prevent disease from spreading through my flock?

Isolate any sick or new bird immediately, at least 30 feet from your main flock. Wash your hands and change clothes before moving between the sick bird and healthy birds. Disinfect any equipment that has contacted an ill bird. This quarantine principle applies both to sick birds and to new birds being introduced to your flock.

Are chicken diseases contagious to humans?

Most common chicken diseases are not directly transmissible to humans. However, Salmonella and Campylobacter — bacteria found in poultry droppings — are significant human pathogens. Always wash hands after handling birds, eggs, or cleaning the coop. Avoid kissing or allowing children to put chickens near their mouths.

When should I call a vet for a sick chicken?

Call a vet any time you see neurological symptoms (twisted neck, paralysis, loss of coordination), rapid spread of illness through multiple birds, blood in droppings combined with other serious symptoms, or when a bird fails to improve with basic supportive care within 24 to 48 hours.

Related Articles

• Is My Chicken Sick? How to Spot Trouble Before It’s Too Late
• Marek’s Disease in Chickens: What You Need to Know
• Backyard Chickens for Beginners: The Complete Starting Guide

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