Mycoplasma gallisepticum

Bird infected with Mycoplasma gallisepticum, also known as Bulgy eye.
Bird infected with Mycoplasma gallisepticum, also known as Bulgy eye.

One of the causes of chronic respiratory infections in chickens and infraorbital sinusitis in turkeys and gamebirds.


“Bulgy eye”, frequently referred to as Mg.


Mycoplasma gallispecticum


Chickens, Turkeys, Pheasants, Partridge, Peafowl, Guinea Fowl, Quail, Racing pigeons, Amazon parrot, Ducks, Geese. Also recorded in Tree sparrows (Japan), House sparrows (India), Chough (Scotland), Finches (North America


Vertical transmission – infection can be spread in or on the egg. The ability to survive for long periods in yolk mean that hatchery and nest infection are important.

Horizontal transmission – aerosol spread directly from bird to bird when they cough or sneeze. This can be from infected chicks or following the introduction of new stock.

Indirect spread – possible routes include contaminated dust or manure that is blown in or on feathers, clothing or hair that is walked into the flock.

Clinical signs

Swelling associated with the head which makes the bird look like “ET” also known as “Bulgy eye” in gamebirds. Affected birds will lose weight, be depressed, eyes closed, and lethargic. Respiratory singns include open mouthed breathing, uni- or bilateral infraorbital sinusitis. Froth in the inner canthus of the eye, excessive lachrymation, conjunctivitis, rhinitis and loss of skin colour. Rubbing of the sore and itchy eye on the wing will discolour the feathers. Marked dyspnoea if an airsacculitis is involved. Reduced egg output and pale eggs., increased feed conversion, depressed hatchability, lameness may be seen in chickens with swollen hocks or ataxia in turkeys and if complicated a more severe colibacillosis. The severity of the disease will vary with the presence of secondary complications.


The severity of the clinical signs depends on the exacerbating factors that may be present e.g. concomitant viral, bacterial and fungal infections and atmospheric contaminants.


Turkeys seem to be more susceptible than chickens. In the latter there may be no clinical signs.


There are many causes of infraorbital sinusitis in turkeys. Whilst this may look like infection due to Mg, it was not possible to prove this. I believe that this is the result of a combined Mm and Ms infection exacerbated by secondary bacterial infection.
There are many causes of infraorbital sinusitis in turkeys. Whilst this may look like infection due to Mg, it was not possible to prove this. I believe that this is the result of a combined Mm and Ms infection exacerbated by secondary bacterial infection.

Respiratory lesions
can be mild with only a little clear mucus being present in the nose, sinuses, trachea, lungs and cloudiness of the air sacs. This can progress to a more marked inflammation with thicker white to yellow pus in the sinuses and air sacs (sinusitis, tracheitis, air sacculitis).The severity of the lesions increases with the presence of secondary infections.


Swollen head. Initially, a conjunctivitis may be accompanied by excessive lachrymation and froth in the eye. If accompanied by a caseous sinusitis can result in subcutaneous infection and closure of one or both eyes.


Ataxia in turkeys. This can be the result of an encephalopathy, demonstrated by histopathology. No other gross lesions are seen.


Infection of the oviduct in laying hens will present as a caseous salpingitis.


Tenosynovitis and arthritis may be seen in chickens looking similar to that caused by M.synoviae.


Diagnosis can be confirmed by culture of the mycoplasma, PCR or blood samples from live birds (RSA, HI and ELISA tests)

Differential diagnoses

Most likely: Mycoplasma gallisepticum, Avian Pneumovirus, Pasteurella multocida, Ornithobacterium rhinotracheale, Pseudomonas aeruginosa, Mycoplasma synoviae Mycoplasma synoviae and Mycoplasma meleagridis combined. Possibly: Avibacterium gallinarum, Reimerella anatipestifer, Bordetella avium, Chlamydophila psittaci, Moraxella osloensis, Vitamin A deficiency, Avian Influenza


Mycoplasma infections are often part of a multi-factorial complex. Infection can be controlled but not eliminated by a variety of antibiotics – Aivlosin, Baytril, Linco-spectin, Pulmotil, Tetracyclines and Tylan. Vaccinating for other respiratory infections e.g. IB and ART, may activate subclinical mycoplasma infections.


Mg and Ms had been eradicated from primary breeding stock when I joined in the poultry industry in the late 1970’s. This was achieved by a combination of treatment and monitoring. This included:


  • – Heat treating hatching eggs – internal temperatures of 46oC for 11 to 14 hours
  • – Antimicrobials:
  • – By injection
  • – By pressure dipping
  • – By temperature dipping
  • – Combined with strict monitoring of hatched progeny in small groups and culling all positives


Mg has been eradicated from commercial poultry and good hygiene precautions, which includes not visiting other farms for 48 to 72 hours previously, are employed to prevent the introduction of infection along with regular blood testing and slaughter of infected flocks. Mg can now be controlled by live vaccine or by importing under an SIC a dead vaccine. Antibiotic treatment of multi-age flocks has limited success with infection reappearing shortly after medication stops. However, in single age flocks it can stop the development of clinical disease.

Mycoplasma gallisepticum is the 22nd commonest diagnosis made by my local AHVLA labs. Details of species affected, clinical signs and post mortem lesions observed can be found by clicking here.

About David Parsons 19 Articles
David Parsons began his veterinary career in mixed practice which triggered his 39-year passion for poultry. Following positions as a veterinary research officer in the Poultry Department at the government’s Central Veterinary Laboratory and then as a poultry company veterinarian, he set up his own poultry veterinary practice in the southwest of England in 1985. He obtained his MSc in Applied Immunology in 1981, Certificate in Poultry Medicine and Production in 1989 and a Nuffield Farming Scholarship Trust to study the“Status of diseases specific to poultry and their control in Europe” in 1991.

He has been an Honorary External Lecturer at the University of Bristol Veterinary School on poultry medicine and production since 1999,a lecturer on the Institute of Animal Health’s poultry disease course since 2000 and is a regular monthly contributor of veterinary articles for backyard poultry keepers in the Practical Poultry magazine.