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Mycoplasma synoviae infection, M.s. Infectious Synovitis

Extracted From:
A Pocket Guide to
Poultry Health
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By Paul McMullin
© 2004
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Infection with Mycoplasma synoviae may be seen in chickens and turkeys in association with synovitis and/or airsacculitis. It occurs in most poultry-producing countries, especially in commercial layer flocks. Infection rates may be very high. Spread is generally rapid within and between houses on a farm, whilst illness is variable and mortality less than 10%.

Infection is via the conjunctiva or upper respiratory tract with a long incubation period, 11-21 days following contact exposure. Transmission may be transovarian, or lateral via respiratory aerosols and direct contact. Survival of the infectious agent outwith the bird is poor but fomite transmission between farms is important. Predisposing factors include stress and viral respiratory infections.


  • There may be no signs.
  • Depression.
  • Inappetance.
  • Ruffled feathers.
  • Lameness.
  • Swelling of hocks, shanks and feet (sometimes severe and bilaterally asymmetrical).
  • Faeces may be green in acute infections.
  • Effects on egg production appear to be minor under good management.

Post-mortem lesions

  • Joints and tendon sheaths have viscid grey to yellow exudate.
  • Some strains can lead to amyloidosis.
  • Swollen liver, spleen and kidney have been seen in the past but are not common now.
  • Green liver.
  • Exudate becomes caseous later.
  • Sternal bursitis.
  • Airsacculitis - usually in heavy broilers and associated with condemnations.


Lesions, serology, isolation (difficult - requires NAD) and identification. Differentiate from viral arthritis, staphylococcal arthritis, Mycoplasma gallisepticum infections, Ornithobacterium rhinotracheale, viral respiratory disease with colibacillosis.

Serology: SAG used routinely, Elisa in some countries - PCR and/or culture used to confirm. False positives post inactivated vaccines are, if anything more common than in the case of M.g.


Tilmicosin, chlortetracycline, oxytetracycline, tylosin.


Eradication of this infection is also possible using similar techniques as described for Mycoplasma gallisepticum. These are based on purchase of uninfected chicks, all-in/all-out production, and biosecurity. Maintenance of Mycoplasma synoviae free status seems to be more difficult than for Mycoplasma gallisepticum. In some circumstances preventative medication of known infected flocks may be of benefit.

Vaccines are not widely used though they are available in some countries. Infected birds do develop some immunity to the effects of repeated inoculation.

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