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Infectious Synovitis

Other Names: Mycoplasma Synoviae Infection, MS Infection, Enlarged Hock Disease, Synovitis

Infectious synovitis is an acute to chronic, systemic disease of chickens caused by infection with Mycoplasma synoviae (MS). The chicken is often sub clinically infected, until a stressful event occurs which causes the infection to become systemic, affecting the synovial membrane of joints and tendons.

Clinical Signs

Chickens with infectious synovitis develop swollen, red, and warm hock joints. They are in so much pain it is difficult for them to walk. The synovial membranes of tendon sheaths become thickened, edematous, with fibrinous exudates accumulating within and around the tendon sheaths.


Sources of infection include latently and chronically infected birds (domestic chickens and turkeys or wild birds). It spreads vertically (from breeding parents to offspring) and horizontally both directly from bird to bird and can be indirectly spread by living and inanimate vectors. Within a flock the spread of the pathogen is normally slow. M. synoviae doesn't survive for very long in the environment, and only remains infective for a couple of hours to days.

Icubation Period

The incubation period for infectious synovitis is approximately 11 to 21 days.


Your veterinarian will need to take a culture of the bird's joint fluid. This is done by performing a joint aspiration, where they will remove the fluid from the affected joint using a needle and syringe. Joint aspiration can also relieve pressure due to fluid collecting around the joint. After collecting the sample, your veterinarian will send it to a diagnostic laboratory for testing.

There are several different testing methods offered by diagnostic laboratories, used for detection of MS infection in chickens. The methods recommended by the OIE for MS detection include bacterial isolation, serological assays, and polymerase chain reaction (PCR). MS isolation is considered to be the gold standard method for MS detection. However it is a slow process and can take up to 28 days to confirm. MS is isolated through the use of a culture performed on a tissue sample, such as joint fluid, from the affected chicken. Other methods include:
  • Serological assays: Serological tests are used to detect the presence of antibodies in the chicken's serum. 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 MS, 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.


Treated chickens often have a slow recovery. There are several antibiotics that can be used, however each with varying effectiveness. The injectable forms of antibiotics such as tylosin, erythromycin, spectinomycin, or chlortectracycline have proven to be more effective than those administered in drinking water or feed.

Clinical Signs

Swollen, inflamed (warm and red) footpads, toes and/or hocks
Ruffled feathers
Shriveled, shrunken, pale comb
Red-blue comb
Breast abscess


  • History
  • Clinical signs
  • Physical exam
  • Radiographs
  • Joint fluid culture

Reported Cases

  • Case 1: Infectious synovitis in a Commercial turkeys Mycoplasma synoviae (MS) was isolated from the brains of 22-week-old commercial meat turkeys displaying severe synovitis and infrequent central nervous system signs. Histological examination of the brains revealed mild-to-severe meningeal vasculitis. The vasculitis ranged from fibrinoid necrosis with little inflammation to a marked infiltration of lymphocytes and plasma cells disrupting the architecture of the vessel wall, accumulating as perivascular cuffs, and involving surrounding meninges. Occasional arteries were undergoing thrombosis. Similar lesions were occasionally seen in renal, synovial, and splenic vessels. MS isolates from the brain, trachea, and joint showed similar protein-banding patterns by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. However, the protein profile differed markedly from the standard MS reference strain, WVU 1853. Ref


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.
Lincomycin/spectinomycinAdministered orally (50 mg/kg q24h), or in drinking water (528 mg/L for 3-7 days)B Speer
Tylosin (Tylan)Administered IM (15-30 mg/kg q6-12h)B Speer



  • Minimize contact with wild birds.
  • 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.


Low to moderate morbidity, with mortality of 1-10%.

Scientific References

Good Overviews

Age Range

It is most common in chickens between 4 and 16 weeks of age

Risk Factors

  • Cornish cross breeds and other heavy "meat type" breeds such as the barred rock.
  • Bringing chickens to or purchasing chickens from poultry auctions, swap meets, shows, county fairs, or other large poultry-associated events.
  • Contact with wild birds.