Common Chicken Diseases and How to Spot Them

Keeping backyard chickens is largely uneventful. Most flocks go weeks or months without anything worse than a scraped comb or a soft-shelled egg. But illness does happen, and the earlier you catch it the better your odds of keeping it from spreading. The tricky part is that chickens are prey animals by instinct, which means they hide discomfort until they can't anymore. By the time a bird looks obviously sick, she has usually been struggling for a day or two already.

This guide covers the diseases backyard keepers run into most often: what causes them, what the birds look like when they have them, how they spread, and what you can reasonably do at home versus when you need a poultry vet or your county extension office. It is general guidance, not a diagnosis or a treatment plan. For any bird that is deteriorating fast, for outbreaks affecting several birds at once, or any time you are thinking about prescription antibiotics, a professional is the right call.

Before you dig into specific diseases, it is worth bookmarking signs of a sick chicken and what to do, which covers the baseline health checks that help you spot trouble early, regardless of the cause.

Respiratory Diseases

Chicken respiratory disease is one of the most common complaints in backyard flocks, and it covers a wide range of pathogens. The two you will hear about most often are Mycoplasma gallisepticum (commonly called MG or chronic respiratory disease) and Infectious Bronchitis (IB), a coronavirus specific to poultry.

What it looks like. Both show up as rattling or gurgling breath, coughing, sneezing, nasal discharge, and swollen sinuses or face. Infectious Bronchitis often comes on suddenly and moves fast through a flock, with birds showing symptoms within a day or two of each other. MG tends to build more slowly, can smolder in a flock for weeks, and is often triggered or worsened by stress, poor ventilation, or crowding.

How it spreads. Respiratory diseases spread primarily through direct bird-to-bird contact and through the air, which is why they travel so quickly in a closed coop. MG can also pass through hatching eggs, so if you are buying chicks or hatching eggs, sourcing from NPIP-certified flocks matters.

What you can do. Good ventilation is the single most effective prevention. Coops that trap ammonia and moisture are ideal environments for respiratory pathogens. If one or two birds are mildly symptomatic, isolate them immediately, improve airflow in the main coop, and monitor the rest. Infectious Bronchitis has no treatment; supportive care (warmth, food, fresh water) is all you can offer, and most birds recover on their own. MG can be managed with antibiotics, but prescription access and appropriate drug choice are decisions for a vet. Birds that recover from MG often remain carriers for life, which is something to factor in if you plan to expand your flock.

When to call a vet. Any bird with labored breathing or a swollen face that is not improving within 48 to 72 hours warrants professional assessment. If multiple birds are showing symptoms at the same time, get help sooner rather than later.

Marek's Disease

Marek's disease is caused by a herpesvirus and is present on virtually every property where chickens have been kept. The virus survives in feather dander for months or years, which means new birds are almost always exposed at some point. The good news is that vaccination is effective and widely available; most hatchery chicks receive it at hatch.

What it looks like. There are several forms of Marek's, and they present differently depending on which tissues the virus attacks. The classic sign is partial or full paralysis of one or both legs, often with one leg stretched forward and one back (sometimes called the "splits"). Affected birds may also show a drooping wing, head tremors, or dilated or irregularly shaped pupils. A third form causes internal tumors that produce weight loss and a generally wasting bird with no obvious external sign until late in the disease. Birds usually show clinical signs between 6 weeks and 30 weeks of age.

How it spreads. Marek's spreads through feather follicle dander, which drifts on air and is nearly impossible to fully contain. Infected birds shed the virus indefinitely. The vaccine prevents disease but does not prevent infection or shedding, which is why vaccinated birds can still expose unvaccinated ones.

What you can do. Vaccination is the most important step, and it needs to happen before any exposure, which means at hatch. If you are hatching your own eggs or buying day-old chicks from small breeders, ask about vaccination status. There is no treatment for Marek's disease once a bird shows symptoms. For a bird with mild neurological signs that is still eating and drinking, many keepers provide supportive care, a low-sided waterer and feeder, and a safe, padded space while monitoring closely. Birds with full paralysis or those that cannot reach food and water face a welfare question that you will need to answer based on what you can observe.

When to call a vet. A confirmed or strongly suspected Marek's diagnosis is worth discussing with a vet, partly to rule out other causes of neurological signs (thiamine deficiency and certain toxins can look similar) and partly for guidance on how to manage the rest of the flock.

Coccidiosis

Coccidiosis in chickens is caused by Eimeria, a protozoan parasite that lives in the intestinal lining. It is extremely common in young birds between three and eight weeks old, though older unmedicated birds can get it too. Chicks raised on medicated starter feed receive amprolium, which limits Eimeria replication while still allowing gradual immunity to build.

What it looks like. The hallmark sign is bloody or very watery droppings, sometimes with a brownish-red tinge. Affected chicks look fluffed up, lethargic, and stop eating. They may have a soiled vent area and will often huddle together even in warm conditions. In severe cases birds deteriorate quickly, and mortality in untreated young chicks can be high.

How it spreads. Coccidia spread through fecal contamination of food, water, and bedding. Wet, warm litter is the ideal environment. Overcrowding, a leaking waterer, or a brooder that does not dry out between uses are all risk factors. Birds that survive develop immunity to the strains they were exposed to, but that immunity does not extend to all strains, and stress or a new strain can cause a flare-up in older birds.

What you can do. Prevention in chicks is mostly about management: keep litter dry, do not overcrowd the brooder, and let chicks have some access to the ground or run soil early to build exposure. Medicated starter feed handles the rest for most backyard situations. If a chick shows symptoms, treatment with amprolium dissolved in the drinking water is available over the counter and works well if started early. Follow the label, keep sick birds warm, and ensure they are drinking. Coccidiosis can kill quickly in a young flock, so acting on the first day of symptoms is worth it.

When to call a vet. If multiple chicks are affected and treatment is not producing visible improvement within 48 hours, or if you are seeing deaths, get professional guidance. A fecal float can confirm the diagnosis and rule out other causes.

Other Diseases Worth Knowing

A few other conditions show up regularly enough in backyard flocks to mention briefly.

Fowl pox is a slow-moving viral disease with two forms. Dry pox causes wartlike scabs on the comb, wattles, and face. Wet pox produces lesions inside the mouth and throat, which can interfere with eating and breathing and is more serious. There is no treatment; most birds recover from dry pox on their own over several weeks. Wet pox cases that are affecting a bird's ability to breathe need a vet.

Bumblefoot is a staph infection that enters through a cut or abrasion on the footpad, often from a rough roost edge or rough ground. It shows up as a hard, dark scab on the bottom of the foot, sometimes with swelling. Mild cases can be treated at home with a soak, gentle debridement, and bandaging. More advanced cases need a vet because the infection can go deep.

Egg binding and internal laying are reproductive issues rather than infectious diseases, but they are common enough to mention. An egg-bound hen will strain repeatedly without producing an egg, look uncomfortable or lethargic, and may stand in a penguin-like posture. This is a time-sensitive situation. A warm bath and a quiet, warm space may help within an hour or two, but if the egg does not pass, the bird needs veterinary care.

Parasites like mites, lice, and worms are technically separate from the disease list, but they weaken birds enough to make other illnesses worse. If you are dealing with a rundown flock that is not obviously sick but not thriving, it is worth reading how to treat mites and lice on chickens and deworming chickens: when and how before chasing other diagnoses.

Biosecurity Habits That Make a Real Difference

Knowing the diseases is only half the picture. Most outbreaks in backyard flocks come from somewhere: a new bird brought in without quarantine, a tool shared between a sick flock and a healthy one, or wild birds landing in an open run.

A few habits that pay off over time: quarantine any new bird in a separate space for 30 days before introducing her to the flock; wash your hands before and after handling birds or working in the coop; keep wild bird feeders away from your run; and if you visit another flock, change your shoes before you go home. None of this is complicated, but it closes the most common entry points for disease.

Frequently Asked Questions

How do I know if my chicken is sick versus just having a bad day? A single quiet, low-energy bird that is otherwise eating, drinking, and moving around is worth watching but not necessarily a crisis. A bird that is not eating or drinking, has discharge from the eyes or nose, has loose or bloody droppings, or is being avoided by the rest of the flock needs a closer look. The article signs of a sick chicken and what to do walks through the specific checks to run.

Can I treat chicken diseases at home without a vet? Some things, yes. Mild coccidiosis in chicks, bumblefoot in early stages, and basic supportive care for a recovering bird are all manageable at home. But bacterial diseases that need antibiotics, respiratory infections that are spreading, or any bird that is deteriorating fast need professional input. Over-the-counter antibiotics sold without a prescription are not appropriate for all conditions and can contribute to resistance.

Is Marek's disease contagious to other animals or to people? No. Marek's disease is specific to chickens and a few other gallinaceous birds. It poses no risk to humans, dogs, cats, or other livestock.

My hen had bloody droppings once and then it stopped. Should I be concerned? Not necessarily. Cecal droppings, which are produced every 8 to 10 cycles of normal droppings, are naturally dark brown to brownish-red and look alarming to new keepers but are completely normal. Truly bloody droppings are bright red, more liquid, and tend to show up repeatedly. If you see genuinely bloody droppings more than once, especially in young birds, it is worth treating for coccidiosis or having a fecal float done.

How often should I be checking my birds for signs of illness? Briefly, every day. Collect eggs, top up food and water, and spend two minutes actually looking at the birds while you do it. You are not running a full physical exam each time; you are just noticing whether anyone looks off, is standing apart from the flock, or has an unusual posture or discharge. Keepers who do this catch problems in hours rather than days.