Prevention and treatment of viral arthritis and encephalitis in farmed goats

Goat viral arthritis-encephalitis is a viral infectious disease. The clinical features of adult sheep are chronic polyarthritis, occasionally associated with interstitial pneumonia or interstitial mastitis, and lambs often show symptoms of encephalomyelitis.

The disease is distributed all over the world and has a high infection rate in many countries, the incubation period is long, infected goats carry virus all their lives, there is no specific treatment, and eventually die, which has a great impact on the productivity of the herd and can cause serious economic losses.

First, the pathogen. Goat arthritis-Encephalitis virus is a member of the family Retroviridae and lentivirus. The morphological structure and biological characteristics of the virus are similar to those of Medi-Wiesner virus, with 20% homology in the genome and serological cross-reaction. It contains a single strand of RNA, with a diameter of 80-100nm, a floating density of 1.15g / cm 3 and a molecular weight of 5.5x106. it is composed of 64s and 4S fragments.

Experimental animals such as chicken embryos, mice, guinea pigs, hamsters and rabbits were not infected. Single cells were prepared from diseased sheep joint synovium and cultured in vitro, and syncytial cells appeared after 2-4 weeks. Goat fetal synovial cells are often used for virus isolation and identification. Inoculation materials include synovial fluid, milk and blood white blood cells, of which the former two have the highest virus isolation rate. After inoculating goat fetal synovial cells with domesticated virus for 15-20 hours, the virus began to proliferate, reached the peak at 96 hours, the cells began to fuse at 24 hours after inoculation, and the cell layer was covered with multinucleated giant cells of different sizes at 5-6 days. Experiments have shown that the formation of syncytia is a symbol of virus replication. Therefore, it can be used for infectious titration.

Second, popular characteristics. Diseased goats and latent sheep are the main sources of infection of the disease, and goats are the susceptible animals of the disease. The main mode of transmission of the disease is horizontal transmission, and intrauterine infection occurs occasionally. The main route of infection was digestive tract. The virus infects lambs through breast milk, and contaminated forage, feed and drinking water can be transmitted. Under natural conditions, only goats are infected with each other, but sheep are not infected. There are no differences in age, sex and strain, but most of the adult sheep are infected, and the infection rate is 15-81%. The incidence of lambs born to infected ewes is 16-19% in that year, and the case fatality rate is as high as 100%. Horizontal transmission cohabited and grazed for at least 12 months, and contact between infected rams and healthy ewes for 1-5 days did not cause infection. The possibility of transmission of the disease by respiratory tract infection and medical device vaccination cannot be ruled out. Sheep infected with this disease often do not show symptoms or symptoms are not obvious under good feeding and management conditions. It can only be found through serological examination. Once the stimulation of stress factors such as feeding and management conditions, environment or long-distance transportation is changed, clinical symptoms will appear.

Third, clinical symptoms. They can be divided into three types according to their clinical manifestations. Encephalomyelitis type, articular type and interstitial pneumonia type. Most of them occurred independently, and a few crossed each other. However, at the time of autopsy, most cases had pathological changes of two or three types.

1. Encephalomyelitis type: the incubation period is 53-131 days. It mainly occurred in 2-4-month-old lambs, with obvious seasonality. More than 80% of the cases occurred between March and August, obviously related to late winter and spring lambs. At the beginning of the disease, the sheep were depressed and crippled, leading to ankylosis or ataxia. One or several limbs paralysis, recumbent, limbs stroke, some cases of nystagmus, panic, angle arch dilatation, head and neck askew or circle movement. Sometimes facial paralysis, dysphagia or blindness. The course of the disease ranged from half a month to one year. A few tolerated cases have sequelae. A few cases had symptoms of pneumonia or arthritis.

2. Arthritis type: it occurs in adult goats over 1 year old, and the course of disease is 1-3 years. Typical symptoms are enlargement of the wrist or claudication. The knee and accessory joints are also affected. The disease worsens gradually or occurs suddenly. At the beginning, the soft tissue around the joint edema, damp and heat, fluctuations, pain, there are varying degrees of claudication, and then joint swelling such as fist, inconvenience of movement, common kneeling on the front knee. Sometimes the anterior shoulder lymph nodes of diseased sheep are enlarged. Fluoroscopy showed periarticular soft tissue edema in mild cases, tissue necrosis, fibrosis or calcification in severe cases, and synovial fluid was yellow or pink in severe cases.

3. Pneumonia type: relatively rare. There was no age limit and the course of disease was 3-6 months. The sheep had progressive weight loss, cough, dyspnea, dullness in chest percussion and voiced rales in auscultation. In addition to the above three disease types, interstitial mastitis sometimes occurs in lactating ewes.

Fourth, pathological changes. The main lesions were found in the central nervous system, limb joints and lungs, followed by breast.

1. Central nervous system: it mainly occurs in the gray matter of the cerebellum and spinal cord. The left vestibular nucleus transects the cerebellum and medulla oblongata, and there is a brown area in the white matter on one side. Microscopic examination showed that lymphoid cells, monocytes and reticular fibers proliferated around the blood vessels, forming a cannula, surrounded by proliferation of glial cells and oligodendrocytes around the cannula, and demyelination of nerve fibers in varying degrees.

2. The lungs were slightly swollen, hard and gray, with small gray spots on the surface and lobular or patchy consolidation areas on the section. Bronchial and mediastinal lymph nodes were enlarged, bronchi were empty or filled with serous and mucus. Microscopic examination showed infiltration of lymphocytes, monocytes or macrophages around bronchioles and blood vessels, even lymphoid nodules and alveolar epithelial hyperplasia. Alveolar septum hypertrophy, interlobular connective tissue hyperplasia, adjacent cell atrophy or fibrosis.

3. Joint: swelling and fluctuation of soft tissue around joint and exudation of subcutaneous serous fluid. The articular capsule is hypertrophic and the synovium often adheres to the articular cartilage. The joint cavity is dilated and filled with yellow and pink fluid, in which the fibrin cord or blood clot is suspended. The surface of the synovium is smooth, or with nodular proliferation. Calcified spots in the tissue can be seen through the synovium. Microscopic examination showed proliferation and folding of synovial villi, focal aggregation of lymphocytes, plasma cells and monocytes, and fibrin necrosis in severe cases.

4. Breast: in the case of mastitis, microscopic examination showed that there were a large number of lymphocytes, monocytes and giant cells exudation around the blood vessels, milk ducts and glandular lobes, followed by a large number of plasma cells, and focal necrosis often occurred in the stroma.

5. Kidney: in a few cases, there are 1-2 mm gray dots on the surface of the kidney. Microscopic examination showed extensive glomerulonephritis.

Fifth, diagnosis. On-the-spot diagnosis can be made according to medical history, symptoms and pathological changes. The etiological diagnosis can be carried out by preparing milk suspension from the liver of diseased animals in febrile or death-related period and fresh animal corpses for virus isolation test, and mice or hamsters can also be selected for animal experiments. Serological diagnosis mainly used Agar diffusion test or enzyme-linked immunosorbent assay to determine recessive infected animals. The detection of IgM antibody in serum by immunofluorescence antibody technique can be used as an index for judging new diseases.

Sixth, prevention and control. There is no effective treatment or vaccine. Mainly to strengthen feeding management and epidemic prevention and health work. Carry out regular quarantine and eliminate serological positive sheep in time. The introduction of sheep to carry out strict quarantine, especially the introduction of foreign breeds, in addition to the implementation of strict quarantine system, but also separate isolation and observation after entry, regular re-examination, confirmed health, can be transferred to normal breeding or put into use. In disease-free areas, we should also promote self-breeding and strictly prevent the disease from being brought in from other places.