Chicken viral arthritis

Chicken viral arthritis, also known as viral tenosynovitis, is a meat- or meat-egg-type poultry infectious disease caused by reovirus. Its main feature is synovitis. Injury of the tendon sheath and the myocardium, swelling of the tendon above the ankle and the ankle. Diseased chickens crouching and squat, do not want to walk, growth stagnation, weight loss, feed utilization of chickens decreased, elimination rate increased, particularly serious damage to broilers.
The disease was first reported in 1957. Since then, the United States, Britain, Italy, the Netherlands, Japan, Hungary and other countries have reported cases of viral arthritis. Since the mid-1980s, China has discovered the disease in Sichuan, Hebei, Beijing, Heilongjiang, Shanghai, Guangdong, Jilin, Yunnan, Guizhou, Henan, Shandong, and Hubei, and isolated reovirus from some cases. Chicken viral arthritis is one of the infectious diseases that cannot be ignored in the chicken industry in China.

1 Popular features

The chicken reovirus (Reo) is widely found in nature and can be isolated from many species of birds. But chickens and turkeys are currently the only animals known to cause arthritis by Reov. The spread of the virus in chickens is spread horizontally and vertically. Although there is information that Reov can be transmitted vertically through eggs, horizontal transmission is the main route of transmission of the disease. After the virus infects chickens, it first enters the bloodstream after replication in the respiratory tract and digestive tract, occurs 24 to 48 hours later, and then spreads to various tissues and organs. However, the toxic content of the tendon sheath and digestive tract is high. The main route of detoxification is the digestive tract.

Tests have shown that adults infected with oral SPE from the mouth can be isolated from the respiratory tract, digestive tract, genital tract, and femoral joints 4 days later. After 14 to 15 days, the amount of toxicants is significantly reduced. After infection, Reov was present in the femoral joint for 3 weeks. After 14 to 16 weeks, the virus was still found in the cloaca of infected chickens. Therefore, poisoned chickens are an important source of infection.

The prevalence and incidence of chicken viral arthritis vary according to the age of the chicken. The older the chicken, the lower the sensitivity. After 10 weeks of age decreased significantly. It is generally believed that the susceptibility of a chick may be completely related to the undeveloped immune system of the chick.

The incidence of natural infections is more common in 4 to 7 weeks old chickens, and there are also reports of arthritis occurring in older chickens. The incidence rate can be as high as 100%, and the mortality rate is usually less than 6%.

2 clinical symptoms

Most field cases that are affected by the virus are latently or chronically infected and must be determined by serological tests and virus isolation. In the case of acute infection, the chicken showed claudication and some chickens were hindered from growing. The claudication during chronic infection was more pronounced, and a few chickens could not exercise. The appetite and vigor of the diseased chickens were not willing to move. They sat on the joints and moved or barely moved, but the gait was unstable, and limp or single-legged jumps followed.

Because of the lack of sufficient water and feed, diseased chickens are gradually losing weight, anemia, and developmental delay. A few chickens gradually die and die. Examination of chickens showed unilateral or bilateral ankle swelling. In large-bodied broilers, tendon rupture can be observed to result in stubborn lameness. Breeding of breeder flocks or laying hens can reduce egg production by 10% to 15%.

3 necropsy changes

Swelling around the upper and lower parts of the chicken's ankle joints, edema of the gastrocnemius muscles on the joints, and hyperemia or spotting in the synovium. The joint cavity contains pale yellow or blood-like exudates. In a few cases, the exudate is pus. Sex, similar to infectious synovitis, may be associated with secondary infections with certain bacteria. Other joints have a reddish color and synovial fluid increases. According to the duration of the disease, it is sometimes seen that the surrounding tissue is detached from the periosteum. Big chicks or adult chickens are prone to rupture of gastrocnemius tendons. When arthritis occurs during moulting, it can be seen in the subcutaneous tissue outside the skin of the chicken. In chronic cases, there is less exudate in the joint cavity, hardening and adhesion of the tendon sheath, soft joints at the distal end of the sacroiliac joint, and a depression in the form of punctate ulcerations. Then it becomes larger and fused, extending to the bone below, and the hyperplasia of the fibrocartilage membrane on the articular surface. In some cases, incomplete rupture and adhesion of surrounding tissues can be seen on the cross-section of the muscles and tendons, and there are pus-like and caseous exudates in the joint cavity. Sometimes epicarditis can be seen, and the liver, spleen, and myocardium have small necrotic lesions.

4 Diagnosis

The initial diagnosis of viral arthritis is more difficult, joint swelling and symptoms of mycoplasma, Syndrome Salmonella, Escherichia coli, and Staphylococcus diseases are not easily distinguishable, and it is easy to co-infect with these pathogens. Therefore, the diagnosis of this disease is generally based on symptoms and epidemiological characteristics of the initial diagnosis, and then diagnosed according to etiology and serological methods.

4.1 Preliminary diagnosis

Although the etiology of the disease is difficult to identify, but according to the characteristics of the symptoms and lesions, in the clinic can make a preliminary diagnosis of the disease, mainly from the following symptoms identified.

4.1.1 The diseased chicken limped and the ankles swelled.

4.1.2 There is infiltration of myocytes between myocardial fibers.

4.1.3 In chickens suffering from viral arthritis, some chickens often show a phenomenon of dysplastic syndrome. The diseased chickens are pale, the bones are not calcified, the feathers are abnormal, growth is retarded or growth stops.

4.2 Virus isolation and identification

Isolation and identification of pathogens is the most accurate diagnostic method. The virus can be isolated from swollen tendon sheaths, synovial joint fluid, trachea and bronchi, intestinal contents, and spleen. When virus is isolated from the diseased part, it is necessary to pay attention to the timing of the disease, and the virus can be easily separated within 2 weeks after infection. The treatment of the diseased material before inoculation can refer to the procedure for the isolation of other viruses. The virus was isolated from the field material and finally inoculated with 5 to 7 days old chicken embryo yolk sac. Chicken embryos should be from SPF or breeders without Reov infection. 3 to 5 days after inoculation, the chick embryo died, the embryo body bleeds, and the internal organs were congested and bleeding. The body is lavender. If the egg is seeded with Reov maternal antibodies, or if the disease contains low levels of toxic substances, the time of death of the chick embryo may be delayed, and some chick embryos may be hatched. Chicken embryos that died after inoculation for a long period of time had poor embryo body development, liver, spleen, heart enlargement and small necrotic lesions, and the embryonic body was dark purple. If the virus-containing material is inoculated on CAM, the embryo death and embryo body changes after inoculation are basically the same as the results of yolk sac inoculation. The characteristic change is thickening of the chorioallantoic membrane with white or pale yellow spot-like lesions. Cytoplasmic inclusions were seen in CAM cells.

After the virus is isolated, it can be identified through physical and chemical characteristics of the virus, electron microscopy, viral nucleic acid electrophoresis, serological tests, and animal sensitivity tests.

4.3 Serological diagnosis

There are many methods for serological tests. In addition to the common agar diffusion test (AGP) and enzyme-linked immunosorbent assay (ELISA), there are also indirect fluorescent antibody methods (1FA) and neutralization tests (VN).
4.3.1 Agar diffusion test (AGP)
AGP is the most commonly used diagnostic method for chicken viral arthritis. After 2 to 3 weeks of viral infection, this method can detect specific antibodies of reovirus, and S1133 strain used by Wang Xizheng etc. can inoculate chicken embryo allantoic membrane to prepare reovirus AGP antigen. The antigen was used for AGP detection of chicken serum inoculated on the sole of the paw. The positive rate was 93% at 7 days after inoculation, 100% at 14 to 90 days, 94% at 105 days, 64% at 120 days, and 25% at 150 days. . Although this method is slightly less sensitive and is not suitable for detection of low-titer antibodies, it is easy to operate, easy to popularize, and practical. It can be used for epidemiological surveys of chickens and for the diagnosis of chicken viral arthritis.

4.3.2 Enzyme linked immunosorbent assay (ELISA)

Slaght et al. first established an ELISA method for detection of avian Reo virus antibodies. Using the S1133 strain as an antigen, it was found that it reacted with antibodies against Reo and WVU2939 strains, with the highest homologous antibody titers. Domestic Chen Shiyou et al., Shan Songhua et al. successively established the detection of poultry Reo and ELISA methods. Compared with AGP, this method has the advantages of high sensitivity, rapidness, and automation. At present, the ELISA system has been commercialized and this system is suitable for the analysis of the population Reo antibody level.

4.3.3 Fluorescent Antibody Method (FA)

FA is a comparatively effective, rapid and specific method for detecting chicken Reo virus. The diseased chicken's tendon sheath, liver, spleen, etc. were frozen sectioned and fixed with acetone and stained with anti-Reo virus fluorescent antibody. The bright green clump antigen was seen under the fluorescence microscope, and the disease can be diagnosed accordingly. Xiao Chengrui used FA to detect 8 artificially infected chickens and 18 naturally infected chickens. The detection rate of spleen and liver was 100%. The spleen and liver were considered to be the preferred organs for the detection of Reo virus by FA.

5 Prevention

5.1 Strengthen feeding management, pay attention to the house and the environment. Introduced from chicken farms without viral arthritis.

5.2 Stick to a strict quarantine system and eliminate diseased chickens.

5.3 vulnerable chickens can be vaccinated; 12 weeks of age using avian reovirus vaccine for basic immunization, and then 16 to 20 weeks of age to strengthen the vaccine with inactivated vaccine, immune chicken breeders can get high levels of offspring chicks Maternal antibodies are sufficient to prevent early infection with viral arthritis.

5.4 There is currently no effective treatment for the disease.

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