Sunday, December 10, 2023

Diagnosing poultry diseases

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By Katie Keiger

Poultry Times staff

GAINESVILLE, Ga. — The most dangerous predators to modern chickens are not foxes or wolves, but microorganisms which cause illnesses, some of which can be deadly. A producer who can diagnose different diseases can often save themselves and their chickens a lot of unnecessary grief.

Mississippi State University (MSU) explains how these organisms infect birds and the problems they can cause to chickens’ health.

Respiratory diseases

Some organisms may infect the respiratory tract and although some may produce different symptoms or none at all, but the typical symptoms of respiratory illness include coughing, sneezing and labored breathing.


Organisms of the genus mycoplasma are the cause of three major diseases in turkeys and chickens. Mycoplasma synoviae is responsible for infectious synovitis, also known as sinusitis, in poultry, according the MSU.

Sinusitis comes in an “upper” and “lower” form. The “upper” form of the disease only symptom is swelling under the eyes. The “lower” form creates the more typical symptoms of respiratory diseases because it causes air sacs to become cloudy and full of liquid.

MSU says that both forms are often both present at the same time with both sets of symptoms. The University of Florida’s Extension Service added that infected birds are lethargic and can have green diarrhea in later stages. Treatment is possible with antibiotics but recovery is slow and often producers chose instead to eradicate the flocks. Flocks that have recovered should not be used for breeding as the disease can still be spread and is deadly to young chickens and turkeys.

Air sac syndrome

Airsacculitis, also known as air sac syndrome, is caused by Mycoplasma meleagridis. In addition to respiratory distress, air sac syndrome can be identified by low egg production and hatching rates, deformity in legs, necks and upper vertebrate.

Birds that survive tend to have stunted growth and are considered unfit for consumption when processed. Though, if the farmer choses to still treat the disease, antibiotics are the way to go. MSU said that younger birds are harmed the most by air sac syndrome, often having a high mortality rate. Like sinusitis, breeding flocks that have been exposed to the disease is not recommended as it can carry into new eggs.

Chronic respiratory disease (CRD)

Like sinusitis and air sac syndrome, chronic respiratory disease (CRD) is caused by an organism in the genus mycoplasma called Mycoplasma gallisepticum (MG). However, MG can also cause sinusitis and, if combined with E. coli, air sac syndrome. Birds that have been exposed to Newcastle disease and infectious bronchitis are more likely to trigger MG’s infections.

CRD causes all the normal respiratory symptoms as well a decrease in feed consumption and a rapid weight loss in birds.

MSU states that to solve MG and the problems it creates, producers must depopulate the flock. Treatment varies and is overall considered unsuccessful.

Infectious coryza

Hamophilus gallinarum is responsible for infectious coryza and the symptoms that come with it. Symptoms include typical lung problems like labored breathing, but also swelling around the face and thick, smelly discharge from eyes and nostrils.

The organism is hard to isolate, according to MSU, and even recovered birds are carriers for a long time. The symptoms can be treated with drugs like sulfadimethoxine added to the water, but the disease can never truly eliminated.

It is spread through direct contact with other birds, so if one bird has it, the entire flock has it. The only way to prevent it is to isolate flocks from other flocks because sometimes it is not apparent in birds that are still carriers.

Newcastle disease

Though Newcastle disease causes nervous disorders, it is still considered as a respiratory disease. It causes both respiratory symptoms such as nasal discharge and difficulty breathing, as well as neurological symptoms like tremors and paralysis in legs and wings.

The virus is transmitted can be transmitted through the air, contaminated equipment and other objects entering the facility where birds live, and through direct contact with infected birds. It is highly contagious and is taken very seriously in the U.S. MSU said that strict quarantine procedures are used to ensure that the disease does not spread.

There are several vaccines which are commonly implemented and biosecurity is always recommended. For farmers who chose to keep their infected chickens alive, the disease normally does not live more than 30 days and the recovered birds are not considered carriers.

Infectious bronchitis

Like the bronchitis that infects humans, the poultry version is extremely contagious and causes all the typical lung problems such as difficulty breathing and gasping in chickens.

According to MSU, infectious bronchitis is considered the most contagious poultry disease, though it only affects chickens.

In young chicks, the disease can be deadly, killing more than 40 percent of birds in some cases. Chicks that do survive can experience stunted growth, partially due to their loss in appetite. It can be very difficult to diagnose because the symptoms are so typical of all other respiratory diseases. Laboratory tests are usually required to identify infectious bronchitis. The tests are worth it because most adult birds recover in a few weeks. Laying birds return to normal production normally within a month.

Biosecurity measures do not always work to prevent infectious bronchitis because it is so contagious. Vaccines are recommended and sometimes antibiotics are used to fight secondary bacterial infections.

Nonrespiratory diseases

Nonrespiratory diseases can still include respiratory symptoms but the organisms responsible infect other parts of the body. Bacterial and viral infections are responsible for nonrespiratory diseases, but they do not include parasites such as ticks and worms.

Marek’s disease

Believe it or not, the herpes virus is what causes Marek’s disease, according to The Chicken Vet. The virus can survive on farms for at least a year in dander and feather dust and can infect birds as early as one day old. The Chicken Vet said that it takes seven days for the virus to infect the white blood cells and kills B Lymphocytes.

“Marek’s disease may produce a variety of clinical responses, all lymphoid in character.” MSU said. However, if there are no lesions present there are other ways for farmers to tell if the disease is present. Additional symptoms include loss of weight, anemia, labored breathing and diarrhea.

MSU adds that diagnosing the disease is based on disease manifestations and flock history. Most cases of Marek’s disease sees no survivors, but sometimes the lesions do go away and birds recover. However, if birds do survive, their immune systems can be severely compromised and more susceptible to other diseases.

Vaccinating birds are very effective, but young chickens can still become infected if they are under stress.


Infectious bursal disease, also known as gumboro disease, is a highly infectious disease that mostly affects young chickens. It causes high mortality rates in flocks, but for chickens that do not experience sudden death; they have ruffled feathers and slight tremors, no appetite and are often dehydrated, according to MSU.

It is transmitted through direct contact with other birds, and contaminated equipment, feed and even air. It is very contagious.

There are mixed results for vaccinating chickens against gumboro, but increasing heat and ensuring chickens have lots of water can help them recover.

Coliform infections

E. coli is the most common coliform infections associated with chickens. Coliform infections can range from mild to severe. In severe cases, there are high mortality rates in poultry.

Symptoms vary with different infections, but infected chickens can experience ruffled feathers, diarrhea, labored breathing and coughing, lesions, swollen organs, and excess mucus.

MSU says that diagnosis can be difficult because isolating the organism responsible is not always enough. Laboratory tests are highly recommended for properly diagnosing coliform infections.

Proper diagnosis is necessary because specific medications are needed to treat infections. MSU recommends that poultry should be moved to a different facility while they are being treated because outbreaks can reoccur because the disease is very contagious.

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