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Mycoplasma Gallisepticum Infection

Bulgy Eye, Mycoplasmosis, MG, CRD, Chronic Respiratory Disease (CRD)

Mycoplasma gallisepticum (MG) infection is a significant disease in poultry, causing chronic respiratory disease in chickens, infectious sinusitis in turkeys, and conjunctivitis in finches. MG develops as a slow-spreading infection. All flock members will become infected with MG; however, not all of the birds will show signs of disease. Mycoplasma infections are known to be associated with oxidative damage of the host cells and tissues, resulting from reactive oxygen species generated by both the immune system of the host and the bacterium as its primary virulence factor. MG infection generally causes the most severe clinical signs in young birds, between 4 to 8 week old and/or when birds are concurrently infected with Escherichia coli, M. meleagridis, M. synoviae, Ornithobacterium rhinotracheale (ORT), Infectious Bursal Disease Virus (IBDV), and Newcastle Disease Virus (NDV). When chickens are co-infected with multiple pathogens, it often increases the severity of the clinical signs and makes it more difficult to diagnose.

Birds with MG infection often show clinical signs associated with the respiratory system, which include mild tracheitis (coughing, abnormal respiratory noses, difficulty breathing), sinusitis (facial swelling, nasal discharge), airsacculitis and conjunctivitis (eye discharge, swelling around the eyes). The facial swelling is primarily concentrated around and just below the bird's eyes. The swelling is the result of pus accumulation in the bird's sinuses located in the area under the eyes. They can sometimes be so severe, that the chicken is unable to open their eyes and see. If left without treatment, the bird can permanently lose their eyesight as a result.

Transmission and Incubation Period

MG is transmitted vertically, from breeding birds to chicks through eggs, and horizontally from inhaling contaminated dust particles or droplets and consuming contaminated feed or water. Other animals such as rodents and wild birds serve as carriers of MG and are capable of transmitting the organism into the flock's environment. Humans are also able to transmit MG to their flocks, if they have been exposed to other birds or equipment contaminated with MG. The incubation period typically ranges from 6 to 21 days.

How MG Infection is Diagnosed

There are several different tests offered by veterinary diagnostic laboratories, used for detection of MG infection in chickens:
  • Mycoplasma gallisepticum culture: Swabs are taken of the chicken's ocular or nasal discharge and mailed off to diagnostic laboratories to be cultured in order to identify the bacterium.
  • Serological tests: These tests are used to detect the presence of antibodies in the chicken's serum (obtained from taking their blood). Serum is the straw-colored liquid fraction of blood plasma from which clotting factors have been removed. There are several serological tests available that are used to detect MG, however due to variations in specificity and sensitivity, they are typically recommended primarily for flock screening, rather than for testing individual birds. Some of the more commonly used tests are the hemagglutination-inhibition (HI) assay, plate agglutination assay, enzyme labeled immunosorbent assay (ELISA), and the rapid serum agglutination (RSA) test.
  • Polymerase chain reaction (PCR) assay: The PCR assay is a molecular based technique which has become increasingly popular. It works by targeting and detecting specific nucleic acid sequences, and is able to provide results in less than 24 hours.

Treatment and Control

Since Mycoplasma species lack cell walls, it makes many types of antibiotics, such as penicillin, useless in treatment. Tylosin and tetracycline have been used successfully.

Documented cases of MG infection

Causative agentAffectedHistoryClinical signsDiagnostic FindingsRef
M. gallisepticumA flock of adult grey partridges kept at a game bird farm in Czech Republic.The infection developed slowly with a 100% morbidity rate and 60% mortality, where the birds died within 3 to 4 weeks after initial appearance of clinical signs.Nasal and eye discharge, open-mouth breathing, eyelid and infraorbital sinus swelling, poor feed intake, weight loss, drop in egg production, and lethargy.M. gallisepticum was identified in a culture taken from tracheal swabs taken from the bird and PCR. E. coli was found in the lungs, infraorbital sinuses and air sacs. Serological tests for other diseases were negative. Necropsy revealed tracheitis, pneumonia and airsacculitis.F Vitula et al., 2011
M. gallisepticum, ORT, and NDV.Adult commercial egg laying hens from multiple flocks in BrazilAssociated with an average mortality rate of 15%Significant swelling of the face and eyelidsSevere catarrhal sinusitis, tracheitis, bronchitis, and pneumonic changes of congestion and consolidation of the lungs.Unknown
M. gallisepticum and E. coliAdult commercial egg laying hens from multiple flocks in BrazilAssociated with a 14.8% mortality rate.Respiratory disease Severe airsacculitis and egg peritonitis.S Sivaseelan et al., 2013
M. gallisepticumBackyard chicken flockUnknownSeverely underweight, gasping, nasal discharge, and deathSevere airsacculitis, tracheitis, and pneumonia.CAHFS Connection, March 2016
M. gallisepticumTwo flocks of adult chickens of the Babcock and Dekalb breedAll of the birds were previously vaccinated against Marek's disease, NDV, and IBV. The first signs appeared when the chickens were about 30 days of age, after giving the IBV vaccine. The disease gradually spread through the flock, despite treatment with antibiotics and additional vitamins. There was a 27.8% morbidity and 10% mortality.Unilateral or bilateral swelling of the eyelids and facial skin, corneal opacity, excessive tearing of the eyes, conjunctivitis, closed or partially closed eyes, depression, respiratory rales, and deathHigh positive ELISA titers against IBDV, all the sera were positive for IBV, and six sera showed positive HI titers for NDV, apparently due to the vaccination. Laryngitis and tryophy of the thymus and bursa of Fabricius. Unknown


Nasal discharge
Facial swelling
Cyanosis (blue/purple coloring of comb/wattles)
Reduced egg production
Decreased feed intake
Ruffled feathers
Weight loss


  • History
  • Clinical signs
  • Mycoplasma culture
  • FA test
  • PCR
  • qPCR
  • RAPD


Supportive careIsolate the bird from the flock and place in a safe, comfortable, warm location (your own chicken "intensive care unit") with easy access to water and food. Limit stress. Call your veterinarian.
Tiamulin hydrogen fumarate (hf)A pleuromutilin antibiotic drug that either on it's own or combined with chlortetracycline hydrochloride (hcl)A Garmyn et al., 2017
Tylosin10-15 mg/kg (administered IM, twice a day) or 0.5 g/L (added to drinking water, once a day)K Marx
Colloidal silver2 drops/kg administered orally, once daily.K Marx
Apple cider vinegarMay help clear mucus from mouth and throat. Add 1 tablespoon of apple cider vinegar to each gallon of water (double dose if using hard water)G Damerow; K Marx


  • Cover feed and water to prevent contamination from wild birds
  • Try not to attract rodents: Discard any uneaten feed at the end of the day and pick up any spilled feed. Remove waterers at night and replace with fresh water for birds in the morning. Seal up any possible entry points into the coop (mice can fit anything larger than a quarter inch diameter). Store feed in a sealed plastic or metal container that is not accessible by rodents.
  • Purchase chickens from NPIP-certified breeders
  • Do not share any tools, cages, or other equipment with other bird owners without disinfecting it first
  • Quarantine any new flock members for 30 days prior to adding them to your flock.

Scientific References

Good Overviews

Age Range

Younger birds are affected more severely then adult birds.

Risk Factors

  • Purchasing or obtaining chickens from reputable breeders, especially NPIP-certified flocks
  • High populations of rodents on the premises