Infectious synovitis is an infection of the joint capsule and tendon sheaths of the joints. A disease that affects, among other structures, the synovial membranes, tarsal joints, and tendon sheaths, as well as the synovial bursa at the anterior end of the sternal keel in birds and the toes, causing inflammatory reactions of varying intensity, with local swelling and sometimes death.

The causative agent of this disease is the Mycoplasma synoviae, which tends to affect clinically birds in growth.

The first symptom is usually a small limp, which coincides with a tiny difficulty in the movements, pallor general and later cachexia due to claudication.

The affected bird resent in its development, it being clearly delayed.

Chickens can get sick at a very young age, and turkeys generally start getting sick around the tenth week.

Prevention of the disease is linked to hygiene and the handling of the birds; if the conditions at the facility are proper, the disease may not develop, even in birds that are carriers of Mycoplasma synoviae.

Chickens are the only natural hosts and experimental disease. Attempts to reproduce the disease in the canaries, doves, curieles, rats, mice, hamsters, and rabbits have failed.

In the inoculation to turkeys has not produced arthritis.

The agar gel diffusion test is positive only when turkeys are inoculated intravenously. Reoviruses have been isolated from turkeys suffering from enteritis, but they have not been linked to arthritis.

The chickens of heavy breed are more susceptible, although the breeds of light can have it, but with a higher resistance.

The economic importance of this disease is remarkable. In acute cases are presented lethality is not very high, low conversion in weight gain and increase of the birds of selection and waste.

Morbidity can reach as high as 100%. Economic losses are generally due primarily to increased mortality, which can reach as high as 75%, and low egg fertility, as affected males have difficulty mating with females.

Etiology and contagiousness:

In the origin of the arthritis bacterial involving several agents, such as salmonella, streptococcus, pasteurellas and colibacilos.

Mycoplasmas are most important for your character epizootic.

Infectious synovitis is transmitted through direct contact between infected and healthy hens and via eggs.

Viral arthritis is caused by an RNA virus, classified in the group of reovirus. (Respiratory Enteric Orphan virus) virus orphans enteric breathing.

Reoviruses are widely distributed among chickens and turkeys and are likely present in other bird species as well. Avian reoviruses are antigenically distinct from mammalian reoviruses, including those found in humans. They have a diameter of 75 nm.

The reovirus is isolated frequently from the respiratory tract and apparatus, the digestive tract of chickens and turkeys, with a variety of pathologies.

They have been found to be contaminating the Marek's vaccine.

Although the pathogenesis of this reovirus should be studied more deeply, all the isolates were able to produce arthritis or tenosynovitis in chickens inoculated.

The human types do not grow in the yolk sac of chicken embryos. The avian strains appear to be related antigenically.

There is the horizontal transmission among birds, both direct and indirect, although there is considerable difference between the virus strains in the development of the disease by contact between chickens, verified by neutralization tests and agar gel diffusion.

Vertical transmission has been demonstrated, although the transmission rate is low, at 1–3%.

After inoculation via the tracheal, oral and nasal in breeder hens, the virus was detected in chicks hatched from eggs incubated from 17, 18 and 19 days postinoculación.

The virus was also demonstrated in the reproductive organs. The chickens carriers are important in the transmission, as the virus has been demonstrated in chickens 289 days after you have had the disease.

Clinical manifestations:

The incubation period ranges from 9 to 13 days following intratracheal inoculation and contact among susceptible chickens. The disease can occur as early as 4 weeks of age, although outbreaks are also likely to occur in 14- to 16-week-old birds.

The most common age of onset is between 6 and 7 weeks. In many field cases, the infection is asymptomatic. In acute cases, lameness is the most significant sign, and some chicks show delayed development.

As the disease progresses, lameness becomes more pronounced, and in a small percentage of chickens, the tarsal joint becomes immobile.

Gastrocnemius rupture is associated with the presence of reovirus. The case fatality rate is generally no higher than 5%, although the mortality rate may be higher due to the increased number of birds that must be culled.

Pathologic lesions:

The lesions observed are inflammation of the tendons digital flexor and extensor of the metatarsal. Subsequently, there is an inflammation of the metatarsal, which becomes more apparent when the feathers are removed from the region.

Inflammation of the plantar pad and the elbow is less common. The affected tarsus or elbow exhibits a bloody or yellowish exudate; in a few cases, there is a considerable amount of purulent exudate, similar to that seen in infectious synovitis.

In the early stages of the disease, there is marked swelling of the tendon sheaths of the tarsal and metatarsal tendons. Inflammation of the tendon areas progresses to hardening and fusion of the tendon sheaths.

Histopathologically, in the early stages of the process, edema, coagulative necrosis, an increase in heterophils, and perivascular infiltration are observed.

Subsequently, the tendon sheaths thicken. The synovial cavity becomes filled with heterophils, macrophages, and dead synovial cells. Periostitis is present, accompanied by increased osteoclast formation.

During the chronic phase, which is manifested 15 days after the start of the process, appreciate the nodules of lymphoid. After 30 days, the inflammatory changes are more chronic, and there is an increase in the number of fibers of the connective tissue and infiltration pronounced or proliferation of reticular cells, lymphocytes, macrophages, and plasma cells.

Some tendons are completely replaced by granulation tissue spot.

By day 54, affected chickens exhibit chronic fibrosis of the tendon sheaths and fibrous tissue invading the tendons, leading to ankylosis and immobility.

Heart lesions consist of an infiltration of heterophil cells that appear among the myocardial fibers. In some cases, this is accompanied by a proliferation of mononuclear cells, likely reticular cells. Red blood cell count, hematocrit, and total white blood cell count are within the normal range, although there may occasionally be an increase in heterophils and a decrease in lymphocytes.