M synoviae was first recognized as an acute to chronic infection of chickens and turkeys that produced an exudative tendinitis and synovitis; it now occurs most frequently as a subclinical infection of the upper respiratory tract. M synoviae infection is also a complication of airsacculitis in association with Newcastle disease or infectious bronchitis. It is seen primarily in chickens and turkeys, but ducks, geese, guinea fowl, parrots, pheasants, and quail may also be susceptible. Serum (preferably swine serum) and nicotinamide adenine dinucleotide are required for growth on artificial media.

Transmission, Epidemiology, and Pathogenesis

M synoviae is egg- transmitted (transovarian), but the infection rate is low and some hatches of progeny may be free of infection. Egg transmission occurs with greatest frequency during the first 1–2 mo after infection of susceptible breeders. Lateral transmission via the respiratory tract is similar to that of M galli-septicum (see Mycoplasmosis: Mycoplasma gallisepticum Infection in Poultry), but the rate of spread is generally more rapid.

M synoviae isolates vary widely in pathogenicity. Isolates from cases of airsacculitis are more apt to produce air sac lesions than isolates from synovial fluid or membranes. Some strains produce the typical clinical signs of synovitis. The paucity of natural outbreaks of synovitis in chickens in recent years may be related to the adaptation of M synoviae to the respiratory tract; however, clinical synovitis in turkeys is relatively common. The incidence of M synoviae infection in commercial poultry in the USA has decreased due to National Poultry Improvement Plan control programs implemented for chicken and turkey breeders. However, M synoviae infections of multiple-age layer flocks may contribute to decreased productivity.

Clinical Findings

Although slight rales may be present in birds with respiratory infection, usually no signs are noticed. Younger birds, especially those under stress or with concurrent infections, are more likely to be affected. Outbreaks of infectious synovitis occur most commonly in chickens at 4–6 wk and in turkeys at 10–12 wk. Lame birds tend to sit. The more severely affected birds are depressed and are found around the feeders and waterers. Swellings of the hocks and footpads are seen, and occasionally sternal bursitis (breast blisters) are noted. Morbidity is 5–15%, and mortality 1–10%. The effect on egg production is minimal, but instances of egg production losses have occurred.

Lesions

In the respiratory syndrome, airsacculitis occurs when birds are stressed from Newcastle disease, infectious bronchitis, or poor air quality. In many cases, air sac lesions resolve after 1–2 wk. Early in synovitis, the liver is enlarged and sometimes green. The spleen is enlarged, and the kidneys are enlarged and pale. A yellow to gray, viscid exudate is present in almost all synovial structures; it is most commonly seen in the sternal bursa, hock, and wing joints. In chronic cases, this exudate may become inspissated and orange.

Diagnosis

A presumptive diagnosis can be based on the lesions and clinical signs, but laboratory confirmation is necessary. Skeletal abnormalities must be eliminated as the cause of lameness. The disease must be differentiated from viral tenosynovitis and from staphylococcal and other bacterial infections.

Serum plate agglutination or ELISA are used to detect infected flocks, but cross-reactions with M gallisepticum and other nonspecific reactions may occur. Reactors are confirmed as positive by hemagglutination-inhibition or by isolation and identification of the organism. PCR may be used to rapidly detect the organism's DNA from pre- or postmortem specimens. In turkeys, the agglutination test for M synoviae may not be reliable.

Treatment and Control

The National Poultry Improvement Plan coordinates control and serology-based surveillance programs for M synoviae similar to those for M gallisepticum. These programs have resulted in eradication of the infection in most primary breeder flocks of chickens and turkeys in the USA. Antibiotics in the feed may be beneficial in prevention of synovitis but are not very effective in established cases. When airsacculitis is a problem, preventive antibiotic therapy during the time of respiratory reaction to Newcastle disease and infectious bronchitis vaccine may be helpful. Medication of breeder flocks is of little value in preventing egg transmission. A live temperature-sensitive vaccine (MS-H) is commercially available and permitted in some countries.

Last full review/revision March 2012 by David H. Ley, DVM, PhD, DACVM, DACPV