Jose A. Linares, DVM
January 18, 2016

Common Chicken Diseases – Urban Farm OnlineCommon Chicken DiseasesChicken problems can cause grief for chicken owners. Take these cues from a veterinarian on how to prevent disease in your flock.Chicken problems can cause grief for chicken owners. Take these cues from a veterinarian on how to prevent disease in your flock.Chicken problems can cause grief for chicken owners. Take these cues from a veterinarian on how to prevent disease in your flock.By Jose A. Linares, DVM, and John El-Attrache, PhD

It’s often difficult to recognize or to differentiate signs of a disease in chickens. For example, most respiratory diseases start with some degree of sneezing, but as they progress, death or recovery will vary depending on the disease. Even more important than recognizing the signs of disease (and probably more difficult) is the ability to prevent disease from occurring in your chicken flock.

Getting to know how your chickens interact every day  is key to observing signs of disease. Read about these five common chicken illnesses to know how to identify an unhealthy chicken. As always, if you notice a member of your flock acting ill, be sure to consult your veterinarian.



Coccidiosis is a disease caused by the parasite Eimeria. Chickens are susceptible to five different species of Eimeria—all of which target various portions of the chicken’s intestines.

Symptoms and Causes

Coccidiosis is characterized by diarrhea, weight loss and sometimes death. Mild infections result in weight loss and pigmentation loss. Severe infections cause bloody diarrhea and could be fatal to chickens without treatment.

Can it spread?

Yes. Coccidia are passed through chicken feces in the form of oocysts, or tiny eggs. Chickens will ingest these eggs, which resist most environmental extremes and disinfectants, when pecking the ground. The oocysts remain dormant until temperature and humidity conditions are right. Warm and humid areas rich in feces are the main source of infection. These conditions are most common around waterers and feeders.

Coccidiosis is often a problem in floor pens, which have dirt floors where oocysts build up in the soil over time. Exposure to high levels of oocysts over time results in severe disease, while exposure to low to moderate numbers of oocysts over time can result in immunity. Young chickens and poorly fed chickens are most susceptible.


Improve drainage, rotate water and change the topsoil in a floor pen yearly. Coccidiosis can also be prevented with medicated starter and growth chicken feeds.


Treat coccidiosis with amprolium or sulfa drugs administered in the drinking water.



Mycoplasmosis is a chicken respiratory disease caused by a bacterial infection.

Symptoms and Causes

The symptoms, which are slow to develop, resemble a standard respiratory infection: watery eyes, dirty nostrils, coughing and sneezing. It also causes decreased egg production, lowered fertility and decreased hatchability.

There are various species of Mycoplasma that can infect chickens, but the most common in small flocks is Mycoplasma gallisepticum (MG). The disease can have a long course of infection and can lead to the accumulation of a “cheesy” material in the eyelids and sinuses, and can cause noticeable outward swelling.

Can it spread?

Chickens that recover from MG remain asymptomatic carriers for life. Therefore, introduction of seemingly healthy chickens to an uninfected flock can become a source of infection. Infected breeders can transmit the disease through the egg to the chicks.


Purchase MG-free chickens. A simple and inexpensive blood test performed by most veterinary diagnostic laboratories can detect previous exposure to MG



Sick chickens benefit from lowered stress, reduced dust, clean coops, proper nutrition and antibiotic treatment. Tylosin and tetracycline antibiotics can reduce symptoms, but cannot eliminate the infection or cure a carrier chicken. Antibiotics are best administered through drinking water at the dosage indicated on the label and used no longer than seven days.

Vaccines are available, but are only practical for large flocks of laying chickens to protect egg production. The use of live vaccines is regulated by most states and should be used with care.

Avian Influenza (HPAI) and Exotic Newcastle Disease (END)


Although not commonly diagnosed in small flocks, these highly contagious viruses can spread rapidly and cause up to 100 percent fatality in a chicken flock.

Symptoms and Causes

Signs and symptoms include severe depression, purplish discoloration of the comb and the face, respiratory stress, reddish shanks and diarrhea. If your chicken flock experiences sudden deaths, report it immediately to your veterinarian or state animal-health official. HPAI and END can strike so fast that chickens die before developing symptoms.

Can it spread?

These are highly contagious viruses.


Prevent contact with wild or migratory birds (ducks and geese), eliminate the introduction of new chickens to an existing flock, and adhere to strict biosecurity practices.


There is currently no effective treatment for HPAI or END. Eradication is the preferred control method. Infected chickens must be culled from the rest of the flock to limit spread of the disease. Vaccination has been used in widespread outbreaks as a control tool, but mass vaccination of backyard flocks is not economically practical.

About the Authors: Jose A. Linares, DVM, ACPV, is the resident director of the Texas Veterinary Medical Diagnostic Laboratory, Poultry Diagnostic Laboratory in Gonzales, Texas. John El-Attrache, PhD, is an assistant professor in the Department of Veterinary Pathobiology in the College of Veterinary Medicine at Texas A&M University.

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