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Chronic Respiratory Disease (MG Infection)

Other Names: Bulgy Eye, Mycoplasmosis, MG, CRD, Chronic Respiratory Disease (CRD)

Chronic respiratory disease is caused by infection with Mycoplasma gallisepticum (MG). It often resembles many other respiratory diseases that affect poultry, including Newcastle disease, Infectious Bronchitis, and/or Escherichia coli infections. It is also relatively common for chickens to be co-infected with multiple pathogens, such as E. coli, M. meleagridis, M. synoviae, Ornithobacterium rhinotracheale (ORT), Infectious Bursal Disease Virus (IBDV), and/or 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.

Clinical signs of Chronic respiratory disease

Chickens are much less susceptible to MG infections than turkeys and suffer less severe clinical signs than that seen in turkeys. Some chickens infected with MG may show outward signs of infection, until a trigger stressful event. Younger chickens, between 4 to 8 months of age, and male chickens are more likely to develop classic more severe clinical signs of MG infection which includes nasal discharge, coughing, and tracheal rales. Occasionally, chickens can develop more severe clinical signs such as eyelid or facial swelling, conjunctivitis, increased lacrimation, and sinusitis. Conjunctivitis may be present in one or both eyes. The facial swelling is primarily concentrated around and just below the eyes. The swelling is the result of pus accumulation in the 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---directly from bird to bird via respiratory secretions, as well as indirectly, from contaminated dust, feed, water sources, droplets, or feathers. 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. MG is able to live in the environment for days to weeks, depending on the material it's living in and the temperature. It will remain active longer when present in chicken manure or eggs, therefore the cleaner the facility, the less likely MG will survive in the environment. The incubation period typically ranges from 6 to 21 days.

Diagnosis of Chronic Respiratory Disease

There are several different tests offered by veterinary diagnostic laboratories 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.
  • Hemagglutination-inhibition (HI) assay: detects IgG.
  • Serum plate agglutination (SPA) assay: This is a screening test used to detect IgM. It is prone to false positive reactions. Factors associated with false positive plate agglutination reactions include:
    • Administration of inactivated vaccines 2-5 weeks prior
    • When birds are infection with avirulent or atypical strains that are poorly immunogenic
    • Sera that have been frozen and thawed prior to testing
    • Turbid contaminated serum
    • Cross-reaction of MS-infected birds with the MG antigen
    Plate agglutination is not useful for detecting antibodies in egg yolk and maternally derived antibodies that are primarily IgG.
  • Enzyme labeled immunosorbent assay (ELISA):
  • Rapid serum agglutination (RSA) test: detects IgG.
  • 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 for Chronic Respiratory Disease

Several antibiotics can be used to treat mycoplasma infections in chickens: macrolides, lincosamides, aminoglycosides, tetracyclines, floroquinolones, and pleuromutilins.

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

Clinical Signs

Watery eyes
Nasal discharge
Facial swelling
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.
Doxycycline (Vibramycin)25-50 mg/kg PO q12-24h x 21 days
Lincomycin/spectinomycinAdministered orally (50 mg/kg q24h), or in drinking water (528 mg/L for 3-7 days)B Speer
Tiamulin (Denagard)25-50 mg/kg administered orally q24 x 3 daysB Speer
TilmicosinAdministered orally (30 mg/kg q24h) or in drinking water (100-500 mg/L) x 5 daysB Speer
Tylosin (Tylan)Administered IM (15-30 mg/kg q6-12h), or in drinking water (50 mg/L)B Speer



  • Minimize contact with wild birds, and environments contaminated with their feces.
  • Quarantine any new flock members, or any birds taken to a poultry show, swab, county fair, auction, etc. for 30 days prior to adding them to your flock.
  • Minimize stress.

Scientific References

Good Overviews

Age Range

Younger birds are affected more severely then adult birds.

Risk Factors

  • Bringing chickens to or purchasing chickens from poultry auctions, swap meets, shows, county fairs, or other large poultry-associated events.
  • Contact with wild birds or environments contaminated with their feces.