Top 5 Chicken Diseases

What You Need to Know

Top 5 Chicken Diseases

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When it comes to keeping chickens, there are 5 top chicken diseases that you need to know about. These diseases can wreak havoc on your flock whether small or large. Some of them are bad enough that you may have to cull your entire flock and start from scratch after disinfecting your coop. With luck and good practice, hopefully, you will never face that decision. Here are those diseases.

Avian Influenza 

Avian influenza is typically carried by wild birds, waterfowl in particular. They are often asymptomatic, so there is little way to tell that they have the disease. Most of the time, the strains of avian flu are mild, termed low pathogenicity. It may cause your chicken to have respiratory symptoms such as coughing, sneezing, eye and nose discharge, and can cause a decrease in egg production or fertility. However, much like the influenzas that infect humans, it has a tendency to mutate and occasionally one of those mutations becomes what is termed high pathogenicity. This is the avian influenza that backyard poultry owners dread. It is highly lethal to the flock and spreads rapidly. In acute cases, symptoms may include cyanosis; edema of the head, wattle, and comb; hemorrhaging of the feet causing discoloration; and blood-tinged nasal discharge. An entire flock may succumb in just a few days, and some may die too quickly to display outward symptoms. Suspected outbreaks must be reported. There is technically a vaccine that may help the severity of the illness, but it requires approval by the state veterinarian to be administered. The best way to prevent avian flu is to practice good biosecurity measures such as isolating new flock members and washing your shoes if you have visited a neighboring coop (Swayne, 2019). While rare mutations do happen which can make this disease able to transfer to other animals including humans, it is extremely uncommon for how prevalent avian influenza is.

Infectious Bronchitis  

Often called the chicken “cold,” infectious bronchitis comes from a type of coronavirus that can only infect chickens and has several subtypes. Symptoms may look much like a human cold with nasal discharge, coughing, rales (rattling in breathing), difficulty breathing, depression, and huddling together. Adult chickens will eat less and have much lower egg production. Eggs may be misshapen, ridged, or thin and soft. If one chicken has a cold, within a couple of days all of your chickens will likely have a cold. This affects chicks under six weeks of age the most, and they have the highest mortality rate. There are vaccines to help prevent infectious bronchitis, but the prevalence of subtypes and mutations makes it difficult to completely prevent. The best prevention is good ventilation in your coop because it is spread via respiratory droplets or contaminated feed/equipment. Birds that recover will continue to be carriers (Duchy College Rural Business School).

Virulent Newcastle Disease

The common name of avian paramyxovirus serotype 1, Newcastle disease has three levels of virulence or severity. The middle and high levels are what is referred to as virulent Newcastle disease. The low level is often used for vaccinations and is not typically reported as the others are. Chickens are the most susceptible out of the domestic poultry species. While Newcastle is endemic in much of the world, the U.S. and Canada have been working to eradicate it with import quarantines and destroying infected flocks. Transmission happens from feces, respiratory discharge, and exhaled air from infected birds even during the latency period. It may also be present in eggs laid while a bird is ill. Symptoms may include tremors, paralyzed wings or legs, twisted necks, circling, or complete paralysis. The most virulent form may display watery greenish diarrhea, respiratory signs, and swelling of the head and neck along with the previously listed symptoms. Vaccinated birds may only have decreased laying, but will still shed the virus to others (Miller, 2014).

Gumboro (Infectious Bursal Disease)  

Infectious bursal disease is often called Gumboro disease in the United States because it was first identified in the town of Gumboro, Delaware in 1962. IBD is caused by a virus that infects the bursal sac in young chickens. Some strains cause more deaths than others, but chicks seem to be most susceptible at three to six weeks of age. At this age, they tend to be visibly ill with watery diarrhea, depression, ruffled feathers, and dehydration. Many chicks younger than three weeks can have the disease but not show symptoms. However, those that are exposed during this time frame often suffer from a suppressed immune system afterward. They will likely be sickly and often succumb to secondary infections. The virus is shed in the chicken poop and can easily spread between farms that way. Maternal antibodies tend to help with very young chicks and can be attained by vaccinating chickens before egg production. Vaccination can also be done via eye drops, in the drinking water, and subcutaneously between one and 21 days of age. There is no treatment once a chicken is ill, but most strains have a low mortality rate. If a chicken is going to recover, it will typically be in less than a week from the onset of illness (Jackwod, 2019).  

Marek’s Disease  

Marek’s disease is a viral disease caused by a type of herpes that is almost always fatal. Because of this, most hatchery chicks are vaccinated against it in their first 24 hours after hatching or even while they are still in the egg. You should consider vaccinating your day-old chicks as they will quickly have less response to the Marek’s disease vaccine as they age. All types of poultry are able to be infected. While most chickens have probably been exposed at some point to Marek’s without becoming ill, becoming stressed can weaken their immune system enough to be susceptible. This disease is transferred through the dander of an infected chicken and can survive in that dander for months. Marek’s has a two-week latency period while still contagious before the chicken becomes visibly ill. In chicks, it typically manifests by weight loss even with a good diet and death within about eight weeks. Older chickens have other symptoms such as cloudy eyes, leg paralysis, and tumors (Dunn, 2019).

Legs splayed forward and back is a common clinical symptom of Marek’s disease.

By knowing what to watch out for, you can keep your flock healthy and safe. Do not discount these top 5 chicken diseases, but rather be proactive against them with good biosecurity and cleanliness practices.


Duchy College Rural Business School. (n.d.). Infectious Bronchitis in Chickens. Retrieved April 21, 2020, from

Dunn, J. (2019, October). Marek Disease in Poultry. Retrieved April 28, 2020, from Merck Manual Veterinary Manual:

Jackwod, D. J. (2019, July). Infectious Bursal Disease in Poultry. Retrieved Aprikl 29, 2020, from Merck Manual Veterinary Manual:

Miller, P. J. (2014, January). Newcastle Disease in Poultry. Retrieved April 29, 2020, from Merck Manual Veterinary Manual:

Swayne, D. E. (2019, Nov). Avian Influenza. Retrieved April 28, 2020, from Merck Manual Veterinary Manual:

Originally published in the Backyard Poultry Special Subscriber 2020 issue  Comb to Tail Health  and regularly vetted for accuracy.

3 thoughts on “Top 5 Chicken Diseases”
  1. One of my 9 hens had paralysis legs, she looked like she was dying, is very hot here, I place here in a cage ( in the house) and bring her frozen corn with water, plus treats ( dried worms), she is much better, after 3 days she stands up for a while, she eats. Last 2 days she was with her sisters, then back to house.. She has open bick ( no cough) and her comb is getting dark on the top. Please help.
    Thank you.

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