Infectious synovitis in chickens, also known as infectious mycoplasmosis in chickens, is an infectious disease of chickens caused by Mycoplasma synoviae. Its main features are synovitis and tenosynovitis.

　　I. Etiology

　　Mycoplasma synoviae is similar to Mycoplasma gallisepticum in many respects. Mycoplasma synoviae is slightly smaller than Mycoplasma gallisepticum, with a diameter of approximately 0.2 micrometers. Its colonies are characterized by a round, raised shape, somewhat resembling a lattice, with or without a raised center. Its resistance is also similar to that of Mycoplasma gallisepticum.

　　II. Prevalence characteristics

　　The disease mainly infects poultry, particularly chickens aged 4–6 weeks, and is occasionally seen in adult chickens. It is transmitted mainly vertically, but can also spread through the respiratory tract and direct contact.

　　III. Symptoms and necropsy findings

　　The pathogen mainly affects the joints of chickens. Early signs include lameness, a tendency to lie down, swelling and deformity of the hocks and toe joints, pale combs, and stunted growth. In severe cases, the combs become atrophied and cyanotic; the feathers all over the body are ruffled; the birds are lethargic, have poor appetites, and become emaciated; and they pass blue-green feces containing large amounts of urates. Mild respiratory symptoms may sometimes be observed. Egg production in adult chickens decreases by 20%–30%, and the mortality rate is generally below 10%.

　　At necropsy, swelling of the joints and footpads can be observed. Large amounts of inflammatory exudate are present in the synovium, synovial bursae, and tendon sheaths. In the early stages, the exudate is viscous and grayish-white or yellow; in the later stages of chronic cases, it becomes caseous. The liver and spleen are enlarged, and the kidneys are enlarged with a pale, mottled appearance. The respiratory tract generally shows no obvious changes.

　　Four. Diagnosis

　　A preliminary diagnosis can be made based on the characteristics of the disease. Laboratory diagnosis uses the same methods as those for diagnosing Mycoplasma gallisepticum.

　　Five. Prevention and control

　　Refer to the prevention and treatment methods for Mycoplasma gallisepticum disease. However, the vaccine used is a Mycoplasma synoviae vaccine.