30 Chicken Diseases You Absolutely Must Know

If you are interested in raising chickens, you likely have made this decision because chickens are one of the easiest kinds of livestock you can raise. While there’s not much you need to do in order to help them thrive, it is possible for your backyard flock to be infected with one of many different diseases.

Chickens can be affected by viruses, parasites, and bacteria just like we, as humans, can. Therefore, it’s important to understand the symptoms and methods of treatment for the most common chicken diseases.

We’ve outlined the 30 most common types here, as well as the best methods for addressing and preventing them.

What Does a Healthy Chick Look Like?

In order to rule out and treat any potential diseases in your flock of chickens, you first need to understand what exactly a healthy bird looks like. A healthy chicken will have the following characteristics:

  • Weight that is typical for its age and breed
  • Legs and feet that are covered in clean, waxy-looking scales
  • Skin color that is characteristic of the breed
  • Bright red wattles and comb
  • Erect posture
  • Engaged behavior and age-appropriate reactions to stimuli like sound and noise
  • Bright, alert eyes
  • Clear nostrils
  • Smooth, clean feathers and joints

While there are some natural variations between individuals in a flock, getting to know your chickens and understanding what behavior and outward characteristics are normal – and those which are not – can help you identify a disease before it becomes a problem.

While nobody ever wants to have to deal with the outbreak of disease in a chicken flock, it’s important to know the symptoms of certain illnesses so that you can be prepared to deal with them if they do arise. Pay attention to the signs of these most common chicken diseases.

egg possibly infected with bronchitis
Egg possibly infected with bronchitis. Photo by L. Mahin – Own work, CC BY-SA 3.0, Link

Infectious Bronchitis

This disease is perhaps one of the most common in backyard flocks of chicken. It causes visible signs of distress in your flock, such as sneezing, coughing, and snoring. You will also notice a mucus-like drainage coming out of your chickens’ nose and eyes. They will also stop laying.

Luckily, you can invest in a shot to prevent infectious bronchitis from taking hold. If you do not give your birds their shots, you will need to act quickly to quarantine your infected hens. Move them to a warm, dry place to recover and to prevent them from spreading the disease to your other birds.

Learn more about infectious bronchitis here.

Avian Influenza

Avian influenza, or bird flu, is the disease on this list that has received perhaps the largest amount of press coverage. Humans can contract bird flu from their chickens, but it is very uncommon. However, it can completely decimate a flock.

The first symptom of avian influenza that you will notice in your birds is a significant difficulty breathing. They may also stop laying and develop diarrhea. Your hens’ faces may swell and their wattles or combs may change color.

There is no vaccine available for avian influenza, and infected chickens will carry the disease for life. This illness can spread from bird to bird and once a chicken is infected, you will need to have it put down and destroy the carcass. Because this disease can also make humans sick, it is one of the most feared illnesses in a backyard chicken flock.

Learn more about avian influenza here.


YOu may have heard of botulism in humans. This disease is typically contracted by eating spoiled canned goods, and it is caused by a bacterium. This bacteria causes progressing tremors in your chickens, and can lead to full paralysis if left untreated. If you do not treat your chickens at all, they can die.

Prevent botulism by keeping the food and water supply clean. Botulism is easily avoidable and is typically caused by the presence of spoiled meat near a food or water supply. If your chickens do contact botulism, purchase an antitoxin from your local veterinarian.

Learn more about botulism in chickens here.

Infectious Sinusitis

Yes, your chickens can get sinusitis just like you! This disease, known formally as mycoplasmosis or mycoplasma gallisepticu, can affect all kinds of homestead poultry. It causes a number of symptoms, including sneezing, watery discharge form the nose and eyes, coughing, trouble breathing, and swollen eyes.

You can treat infectious sinusitis with a range of antibiotics that you can purchase from your veterinarian. In addition, good preventative care (such as preventing overcrowding and maintaining a clean, sanitary coop) can help reduce the spread of this illness in your flock.

Lear more about sinus infections in chickens here.

Fowl Pox

Fowl pox causes white spots on the skin and combs of chicken. You might also notice white ulcers in the trachea or mouth for your birds or scabby sores on their combs. This disease can cause a serious decline in laying, but it’s luckily relatively easy to treat.

Feed your chickens soft food for a while and provide them with a warm, dry place away from the rest of the flock to recover. As long as you treat your birds, they will likely recover

However, this disease can spread quickly between infected chickens and mosquitoes – it’s a virus, so it can easily spread through the air.

Learn more about fowl pox prevention here.

Fowl Cholera

Fowl cholera is an incredibly common disease, particularly in crowded flocks. This bacterial disease is spread by contact with infected wild animals, or through exposure to water or food that has been contaminated by the bacteria.

This disease can cause your birds to have a green or yellow diarrhea as well as joint pain, respiratory difficulties, ad a darkened wattle or head.

Unfortunately, there is no real treatment for this disease. If your chicken happens to survive, it will always have the disease and can spread it to your other birds. Euthanasia is typically the only option when your chickens contract this devastating disease. That being said, there is a readily available vaccine that you can give your chickens to prevent the disease from taking hold.

More on fowl cholera here.

Marek’s Disease

Marek’s disease is most common in young chickens that are younger than twenty weeks of age. Chicks that are purchased from a large hatchery are usually vaccinated against this disease, which is a good thing because it can be quite devastating.

Marek’s causes tumors that develop either internally or externally on your chick. The bird will develop greying irises and will eventually become completely paralyzed.

Marek’s is extremely contagious and is transmitted between young birds. As a virus, it is difficult to detect and eliminate. It’s caused by breathing in pieces of infected skin and feathers from infected chicks – just as you might inhale pet dander.

There is no cure for Marek’s, and since infected birds will be carriers for life, the only way to get rid of it is to put your bird down.

Learn more about Marke’s disease here.


Also known as simply trach and laryngo, this disease most commonly affects chickens and pheasants. Birds who are older than 14 weeks of age are more likely to be infected with this disease, as are hens as compared to roosters.

It can cause severe respiratory problems during the colder months of the year, and can be spread between flocks by contaminated clothing or shoes.

Laryngo causes a range of symptoms, including repository problems and watery eyes. It can also cause blood clots and culminates in asphyxiation and the untimely death of your flock.

Birds who are infected with this disease are infected for life. You should dispose of any sick or dead birds, and make sure you give antibiotics to your flock to remove any secondary infections. There are vaccinations available for this illness, but they aren’t as successful as eliminating laryngotracheitis as they are for other diseases.

Learn more about Laryngotracheitis in chickens from this very comprehensive article.


Aspergillosis is also known as brooder pneumonia. It often originates in hatcheries, and can occur as an acute disease in young birds and a chronic disease in mature ones.

This will cause respiratory problems and reduced feed consumption. It can sometimes cause your birds’ skin to turn blue. It can even cause nervous disorders, like twisted necks, and paralysis.

This disease is caused by a fungus. It grows exceptionally well at room temperature or warmer, and is found in litter materials like sawdust, peat, bark, and straw.

While there is no cure for this disease, improving ventilation and adding a fungistat like mycostatin to the feed can help reduce the impact of this disease.

You should also clean your brooder thoroughly between broods. Use only clean litter, like soft wood shavings, and remove any shavings that become wet.

You can read more about Aspergillosis here.


Pullorum can impact both young chicks and adult birds, but it does so in different manners. Young chicks will act lethargic and have white paste on their bottoms.

They may also exhibit respiratory problems. Some birds die before they exhibit any symptoms at all because their immune systems are so weak.

Older birds can also be affected by pullorum, but they will usually only sneeze and cough. They may also experience a decline in laying. This viral disease is spread through contaminated surfaces as well as through other birds.

There is sadly no vaccine for the disease and all birds that are believed to have pullorum should be euthanized so that they do not infect the rest of the flock.

Read more on Pullorum disease here.


Bumblefoot is another common issue in backyard chicken flocks. This disease can occur as a result of injury or illness. Most often, it is caused by your chicken accidentally scratching its foot on something.

When the scratch or cut becomes infected, the chicken’s foot will swell, causing swelling as far as all the way up the leg.

You can perform a simple surgery to rid your chicken of bumblefoot, or you can take it to the veterinarian. Bumblefoot can be a very minor infection if dealt with swiftly, or it can take your chicken’s life if you’re not quick enough in treating it.

Here’s a video of a chicken that had bumblefoot and how it was treated:

Or, if you prefer to read, here’s a nifty article on Bumblefoot.


Thrush in chickens is very similar to the kind of thrush that human babies contract. This disease causes a white substance to ooze inside the crop. Your chickens might be hungrier than normal, yet will appear lethargic. Their vents will appear to be crustry and their feathers will be ruffled.

Thrush is a fungal disease and can be contracted through eating moldy food. It can also be transmitted on contaminated surfaces or water.

There’s no vaccine, since it is a fungus, but you can easily treat it by removing the infected water or food and applying an antifungal medicine that you can acquire from a veterinarian.

More on chicken thrush here.

Air Sac Disease

This disease will usually show first symptoms in the form of poor laying habits and overall lethargy and weakness. As the disease worsens, your chickens might have a hard time breathing.

Chickens may sneeze or cough, occasionally displaying other respiratory problems as well. Infected birds might also have swollen joints. Left untreated, air sac disease can lead to death.

Luckily, there is a modern vaccine for this disease. It can also be treated with an antibiotic from the veterinarian. However, it can be transmitted between other birds, including wild birds, and can even be passed from a mother hen to her chick via the egg.

More on Airsacculitis here.

Infectious Coryza

This disease, also known as cold or croup, is a virus that causes the eyes of your birds to swell shut. It will appear as though the heads of your birds are swollen, and their combs will puff up, too.

They will soon develop a discharge from their noses and eyes and they will stop laying mostly or entirely. Many birds also develop moisture beneath their wings.

There is no vaccine to prevent infectious coryza, and you will sadly need to euthanize your chickens if they happen to contract this disease. Otherwise, they will remain carriers for life, which can harm the rest of your flock. If you must put your infected chicken down, make sure you discard the body carefully so that no other animal can be infected.

You can prevent infectious coryza by making sure the water and foods that your chickens come into contact with are not contaminated with bacteria. Keeping your flock closed (not introducing new birds from other areas) and housing them in a clean area can reduce the likelihood of this disease.

More on Infectious Coryza here.

Newcastle Disease

Newcastle disease is another respiratory illness. This can cause a range of problems, including nasal discharge, a change in the appearance of the eyes, and a cessation of laying. It can even cause paralysis of the legs, wings, and neck.

This disease is carried by most other kinds of birds, including wild ones. In fact, that’s usually how a flock of chickens is introduced to this nasty illness. Keep in mind that you can also be a carrier of the disease, passing the infection to your flock from your shoes, clothes, or other items.

Luckily, this is a disease that is easy for adult birds to recover from. They can bounce back quickly if they are treated by a veterinarian. Unfortunately, young birds usually do not have the immune system necessary to survive.

Learn more on the Newcastle Disease here.

Avian Leukosis

This disease is quite common and is often mistaken for Marek’s disease. While both illnesses cause devastating tumors, this illness is caused by a retrovirus that is similar to bovine leukosis, feline leukosis, and HIV.

Fortunately, this virus cannot spread to any other species and it is relatively weak outside of a bird. Therefore, it is typically spread through mating and biting pests. It can also be transmitted through the egg.

There is no treatment for this disease and its effects are so significant that it usually requires your birds to be put to sleep. Because this disease can be transmitted by biting pests, it is important that you do your best to limit the impact of biting parasites like mites and lice inside your chicken coop. Keeping clean and sanitary conditions can help with this.

More on Avian Leukosis.

Mushy Chick

The name of this disease truly says it all. Impacting only baby chicks, mushy chick appears in newly hatched chicks. It will cause them to have midsections that appear to be blue and swollen. Usually, the chick will smell oddly and exhibit weak, lethargic behaviors.

Unfortunately, there is no vaccination available for this disease. It can be passed between chicks via dirty surfaces and is contracted from bacteria. It affects chicks only because their immune systems are not yet well-developed enough to fight off an infection.

Antibiotics can sometimes work to fight this disease, but because it impacts such young birds, it is very difficult to treat. If one of your chicks has this illness, make sure we separate it immediately so that it does not infect the rest of the flock. Keep in mind that the bacteria that cause this disease can also impact humans.

Lots of good info on the Mushy Chick in this article.

Swollen Head Syndrome

Swollen head syndrome frequently infects chickens and turkeys. You may also find guinea fowl and pheasants who are infected, but other types of poultry, like ducks and geese, are believed to be immune.

Luckily, this disease is not found in the United States, but it is found in just about every other countries around the world. This illness causes sneezing along with reddening and swelling of the tear ducts. It can cause severe facial swelling as well as disorientation and a drop in egg production.

This illness is spread by direct contact with infected birds and while there is no medication for this virus, there is a commercial vaccine available. Since it is considered an exotic disease, the vaccine is not yet approved for use in the United States.

Some good photos of the Swollen Head Syndrome here.


Viral arthritis is a common disease in chickens. It is transmitted through the feces and can cause lameness, poor mobility, slow growth, and swelling. There is no treatment for this disease, but it can be prevented by administering a live vaccine.

More on arthritis in chicks here.


You’re likely familiar with this disease, because it is one that humans can be exposed to as well. Salmonellosis is a bacterial disease that can cause severe health problems and even death in your chickens.

It is typically spread by rodents, so if you have a mouse or rat problem in your chicken coop, you need to be aware of this disease.

Salmonellosis can cause diarrhea, loss of appetite, excessive thirst, and other problems. Keeping your coop clean and rodent-free is the best way to prevent it from rearing its ugly head.

More on salmonella in chickens here.

Rot Gut

Rot gut is a bacterial infection that causes some seriously unpleasant symptoms in chickens but is most common in young chicks. This disease causes your birds to have foul-smelling diarrhea and severe restlessness.

It is common in conditions of overcrowding, so keeping your birds in a properly sized brooder and coop will help reduce the likelihood of this disease. There are also antibiotics that can be administered to infected chicks.

Avian Encephalomyelitis

Also known as epidemic tremor, this disease is the most common in chickens who are younger than six weeks of age. It can cause a range of problems, including dull eye tone, incoordination, and tremors.

It can eventually lead to full paralysis. While this disease is treatable, chicks who survive the disease may develop cataracts and loss of vision later in life.

This virus is transmitted via the egg from an infected hen to her chick. This is why the chick is affected during the first few weeks of life. Interestingly, birds who suffer from this disease are then immune for the rest of their lives and they do not spread the virus.

More on Avian Encephalomyelitis.


Coccidiosis is a parasitic disease that is spread by protozoa that reside in a specific section of your chickens’ gut. This parasite is usually harmless, but when your birds consume an oocyst that has produced spores, it can create an internal infection.

The release of spores serves as a domino effect that creates a major infection inside your chicken’s digestive tract. It can cause serious damage to your bird’s internal organs, causing it to lose its appetite, have diarrhea, and experience rapid weight loss and malnutrition.

More on Coccidiosis here.


Blackhead, also known as histomoniasis, is an illness caused by the protozoan Histomonas meleagridis. This disease causes severe tissue destruction in the liver of your chickens. While it’s more common in pheasants, ducks, turkeys, and geese, chickens can occasionally be impacted by this disease.

More on blackhead here.

Mites and Lice

Mites and lice are parasites that live on the inside or outside of your chickens. There are several kinds of mites and lice that may affect a backyard chicken flock, including northern fowl mites, scaly-leg mites, sticktight fleas, poultry lice, chicken mites, fowl ticks, and even bed bugs.

Mites and lice can cause a range of issues, including itching, anemia, and decreased egg production or growth rate.

You can prevent mites and lice by providing your chickens with plenty of coop and run space. Giving your birds a place to engage in dust baths can also help to prevent parasites from latching on to your birds.

Learn more about chicken mites here.

Egg Peritonitis

Egg peritonitis is one of the most common problems in laying hens. This causes your hens issues in producing a membrane and shell around the egg. Because the egg does not form properly, the yolk is laid internally.

This causes a buildup inside the abdomen of the chicken, which can then cause discomfort and difficulty breathing.

This disease can be caused by a variety of external factors, such as stress and coming into laying at an inopportune time. Every now and then, this condition is not dangerous. However, when a hen has this issue as a chronic occurrence, it can cause oviduct problems and lead to permanent internal laying.

A chicken suffering from this disease will be extremely uncomfortable. It will have prominent breastbones and lose weight, but it can be difficult to witness the weight loss because the abdomen will be so swollen.

Often, a chicken can survive this disease if it is provided with veterinary intervention and a strong antibiotic treatment plan, but sometimes, the bird will need to be put to sleep.

Lots of good pictures on Egg Peritonitis in action here.

Sudden Death Syndrome

This illness is also known as flip-over disease. This one is scary because it shows no clinical symptoms or other signs of illness. It is believed to be a metabolic disease that is tied to high intake of carbohydrates.

You can prevent this disease by controlling the diet of your flock and limiting starchy treats. Unfortunately, as the name implies, there is no other method of treatment for this illness.

More on Sudden Death Syndrome here.

Green Muscle Disease

Green muscle disease is also known scientifically as deep pectoral myopathy. This degenerative muscle disease affects the breast tenderloin. It creates muscle death and can cause discoloration and pain in your bird.

This is common in pasture-raised chickens who grow to sizes that are too large for their breeds. Reducing stress in your flock and avoiding overfeeding can help prevent green muscle disease.

Learn more about Green Muscle Disease here.

Egg Drop Syndrome

Egg drop syndrome originated in ducks and geese, but is now a common problem among chicken flocks in many areas to the world. Chickens of all kinds are susceptible.

There are very few clinical signs of this disease besides those on egg quality and production. Healthy-looking hens will lay thin-shelled or shell-less eggs. They can also have diarrhea.

There is currently no successful treatment for this disease, and it was originally believed to have originated through contaminated vaccines. Interestingly, molting can restore regular egg production.

More on the Egg Drop Syndrome here.

Infectious Tenosynovitis

Infections tenosynovitis impacts turkeys and chickens. This disease is the result of a reovirus that localizes in the joints, respiratory tract, and intestinal tissues of your birds. This can cause eventual lameness and tendon rupture, causing permanent damage.

There are no successful treatments for this disease, and it spreads rapidly through flocks of broiler birds. It is transmitted through the feces, so dirty coops prove to be a risk factor for the spread of this illness. A vaccine is also available.

Check out how it looks like here.

How to Prevent Diseases in Chickens

The best way to treat disease in your backyard flock is to prevent them from becoming a problem in the first place. For starters, make sure your chickens are not crowded (provide at least four square feet of space per bird, with even more being ideal) and supply them with a constant supply of food and water.

You can boost your birds’ immunity by using feed supplements and additives. These will help increase the absorption of nutrients and improve digestive functioning.

Keeping your brooder clean is a great way to prevent disease, as is administering any relevant shots. Keep a close eye on your birds, particularly if you are introducing new members to the flock, so that you are aware of any changes in your chickens.

With any luck and a bit of preventative care, you’ll never have to deal with any of these unpleasant (yet common) chicken diseases.

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