What is Bluetongue Disease?

Bluetongue (BT, BLU) is an infectious disease mainly caused by sheep caused by bluetongue virus

Bluetongue virus

Bluetongue

Bluetongue is a serious infectious disease caused by bluetongue virus in ruminants. It is characterized by ulcerative inflammation in the oral, nasal and gastrointestinal mucosa. It mainly affects sheep. OIE lists it as a Class A disease.

About Bluetongue

Bluetongue (BT, BLU) is an infectious disease mainly caused by sheep caused by bluetongue virus

Bluetongue virus . The disease is characterized by fever, severe catarrhal inflammation of the buccal mucosa and gastrointestinal tract mucosa. Diseases often occur in the breasts and hooves of sick sheep, and lameness often occurs due to invasion of the dermis. The bluetongue virus has strong resistance, has multiple serotypes, and has poor cross-immunity between the various types. Therefore, only by making a multivalent vaccine can reliable protection be obtained.

Blue Tongue Pathogen

Bluetongue virus belongs to the genus Reoviridae of the family Reoviridae and is an arbovirus.

Bluetongue The virus is resistant to ether, chloroform, and 0.1% sodium deoxycholate, and is sensitive to pancreatic enzymes; it can be inactivated by peroxyacetic acid and 3% sodium hydroxide, and is stable between pH5.6 to 8.O. It is rapidly inactivated below pH 3.0 and killed at 60 ° C for 30 minutes. It can survive long-term in dried blood, serum and putrefied meat and sewage. The virus has 24 serotypes, and there is no cross-immunity between different serotypes. The virus can multiply in chicken embryos, newborn lactating mice and hamsters.

Cattle and sheep bluetongue is caused by a virus with symptoms such as high fever, mucosal edema, ulcers, and erosions. It is mainly transmitted by blood-sucking insects. The average mortality rate of bluetongue disease in ruminants is 30%, and the mortality rate among sheep is as high 80%. At present, bluetongue disease has been listed by the International Epidemiological Society as one of 15 class A animal epidemics, but no effective treatment has been found. Belgian veterinarians believe that bluetongue disease is mainly transmitted by a mosquito with a length of 3 or 4 millimeters. According to the characteristics of this type of mosquito, they recommend that farmers should spray insects on the back of cattle and sheep based on thorough deworming measures on the farm. And the animals are raised indoors from one hour before the sun sets to one hour after the sun rises.

Bluetongue epidemiology

Bluetongue

Blue tongue virus capsid protein It first occurred in South Africa in the late 19th century and was formally reported in 1905. It is generally believed that blue tongue disease may exist from 35 degrees south latitude to 40 degrees north latitude.

Diseased and poisoned animals are the source of the disease. The virus can survive and proliferate in long-term in some species of Cucurbitalis, and it can overwinter, which is undoubtedly an important source of infection.

It can only be transmitted by the bites of Kluy and Aedes. Direct contact between sick and healthy animals is not contagious, but the fetus can be directly infected in the womb of the female animal. The virus is mainly found in the red blood cells of animals and can detoxify from semen.

Sheep are most susceptible and show unique symptoms. Purebred Merino sheep are more sensitive. Sick sheep and poisoned sheep are the source of infection. Cattle are susceptible, but are mostly dominated by recessive infections. Goats and wild ruminants such as deer, elk, antelope, and desert bighorn sheep can also be infected, but generally show no symptoms.

The disease has strict seasonality. It is mainly transmitted by the bite of the vector insect Kupffer. The disease can also be infected vertically through the placenta; its occurrence and distribution are closely related to the distribution, habits, and life history of Kuyu. Generally occurs from May to October, mostly in hot and humid summer and autumn, especially in low-lying areas with many ponds and rivers.

Pathogenesis of bluetongue

After the virus infects the animal body, it first replicates in local lymph nodes and then enters other lymph nodes

Bluetongue Nodes, lymphatic reticulum and capillaries, the endothelium of arterioles, venules, peripheral endothelial cells and epithelial cells cause cytoplasmic vacuoles, nucleus and cytoplasmic hypertrophy, shrinkage and nucleus lysis. Endothelial necrosis and regenerative proliferation and hypertrophy lead to vascular occlusion and stasis. The cause of the disease is bluetongue virus. Viral particles can multiply in the cytoplasm of host cells. The virus is very stable. Sick sheep are the main source of infection and are transmitted through Kuyu. Sheep infections, regardless of breed, sex and age, are most susceptible to sheep around one year old, and lambs during lactation have some resistance. The occurrence of this disease has a strict seasonality, which is mainly related to the activities of various Kuyu.

Bluetongue virus has a strong selectivity for endothelial cells. The capillary endothelium under the stratified flat epithelium of the skin around the mouth and the hoof crown often has a higher virus concentration. After the virus replicates in target cells, it quickly spreads throughout the body through the bloodstream, so that most organs and tissues contain a certain amount of virus. The virus neutralizing antibody titer began to increase 6-8 days after infection. At this time, the body temperature rose and the initial histological lesions also appeared.

Bluetongue is a relatively rare animal disease. It is an infectious disease caused mainly by sheep caused by the bluetongue virus, but other ruminant animals may also be infected. The disease is characterized by fever, severe catarrhal inflammation of the buccal mucosa and gastrointestinal tract mucosa. Diseases often occur in the breasts and hooves of sick sheep, and lameness often occurs due to invasion of the dermis. It is mainly transmitted by insect bites, and sheep can easily die after being infected, but will not be transmitted to humans. People will not endanger their health by eating lamb or goat milk with the virus. The bluetongue virus has strong resistance, has multiple serotypes, and has poor cross-immunity between the various types. Therefore, only by making a multivalent vaccine can reliable protection be obtained.

Clinical symptoms of bluetongue

Bluetongue Sheep Bluetongue Symptoms

Sheep bluetongue

Bluetongue The typical symptoms begin with an increase in body temperature and a significant decrease in white blood cells. The temperature of the sick animal rose as high as 40 to 42 ° C, and it remained for 2 to 6 days, and some as long as 11 days. At the same time, white blood cells were also significantly reduced. After the high temperature stayed, the body temperature dropped to normal, and the white blood cells gradually rose back to the normal physiological range. After some sick sheep are cured, hair loss occurs. The incubation period is 3-8 days. At the beginning of the disease, the body temperature rises as high as 40.5 -41.5 , and stays for 2-3 days. Shortly after the temperature rose, she showed anorexia, depression, and gregariousness. Swelling and edema of the upper lip can extend to the face and ears, salivation, oral mucosa congestion, blue-purple, and then the lips, gums, cheeks, and tongue mucous membranes can be eroded, making swallowing difficult. The oral mucosa was damaged by ulcers, local exudation of blood, and saliva was red. Secondary infection can cause local tissue necrosis and oral malodor. Nasal purulent discharge, which blocks air circulation after scabbing, can cause difficulty breathing and nasal snore. The hoof crown and hoof leaves are inflamed with lameness, knees, and motionless. Sick sheep are thin, weak, constipated or have diarrhea, sometimes with blood in the chin. Leukopenia occurs early. The course of disease is usually 6-14 days, and the lesions of the hoof can be recovered after 6-8 weeks. The morbidity is 30% -40%, the fatality rate is 2% -30%, and the highest is 90%. Many died of pneumonia and gastroenteritis. About 4 to 8 weeks of pregnancy, if the ewe is infected with live vaccine or immunization, about 20% of the lambs born will develop abnormalities, such as hydrocephalus, insufficient development of the cerebellum, and excessive brain gyrus.

The sick sheep was mentally stupefied, anorexia, salivation, edema of the lips, and spread to the face, eyelids, ears, and neck and underarms. Oral mucosa, tongue congestion, erosion, severe cases of tongue hair, ulcers, erosion, resulting in difficulty swallowing (halitosis when secondary infection); showing the symptoms of blue tongue disease. Nasal secretions are initially serous and mucopurulent, often bloody, crusting around the nostrils, causing breathing difficulties, bleeding from nasal mucosa and nasal erosions. Some hoof crowns and hoof leaves are inflamed and limp. Pregnant women can have abortions, fetal hydrocephalus, or congenital malformations. The course of disease is 6 to 14 days, the incidence is 30% to 40%, and the mortality is 20% to 30%. Mostly caused by complications of pneumonia and gastroenteritis.

Blue tongue disease

The initial symptoms of this disease are not obvious, and the fever is only about 40 ° C, which is not serious, but nasal cavity, rhinoscopy and oral congestion occur at the same time as loss of appetite, and then turn into congestion. Soon some of these tissues will cause necrosis and gradually form scabs, exfoliating the tissue below the scabs can form a shallower ulcer surface. Conjunctival congestion, swelling, and tears were also seen. Due to the different individuals of cattle, the same lesions appear in the crown of the hoof, so some are often misdiagnosed as foot-and-mouth disease.

The above symptoms are only prodromal symptoms, and generally only those symptoms can be recovered. However, some sick cattle suddenly show "throat paralysis" when these prodromal symptoms are about to disappear, and some cattle often have paralyzed throat before these prodromal symptoms appear. This kind of paralysis is caused by hyaline degeneration of rhabdomyomus Caused. Paralysis can be caused by different parts of cattle. The symptoms of esophageal paralysis appear in the esophagus. The symptoms appear on the tongue, and the symptoms of "dangling tongue" appear. Sometimes the myocardium and skeletal muscle are damaged to varying degrees.

In short, most sick cows have symptoms of difficulty swallowing, and the drinking water of sick cows with paralysis of the throat can often cause swallowing, which is very likely to cause secondary swallowing pneumonia with high mortality. The mortality of the disease is generally around 10%. ^[1]

Pathological changes in bluetongue

Mainly in the oral cavity, rumen, heart, muscles, skin and hooves, there are erosion points, ulcers and necrosis. The inside of the lip, the gums, the lingual side, the tip of the tongue, and the lingual surface fall off. Subcutaneous tissue hyperemia and gel-like infiltration. The epithelium of breasts and hoof crowns is shed but no blisters occur. Hoofs have hoofitis changes and often fester. Severe edema of the alveoli and interstitial lungs and severe congestion of the lungs. Spleen is slightly swollen, bleeding under the capsule, lymph nodes edema, pale appearance. Skeletal muscles are severely degenerate and necrotic, with clear liquid infiltration between the muscles, showing a gel-like appearance.

Erosion and crimson areas appeared in the mouth, and edema of the mucous membranes of the tongue, gums, palate, and cheeks. The sheep's tongue is like a blue tongue. The rumen has dark red areas, and the surface epithelium forms vacuole degeneration and death. Dermal hyperemia, bleeding and edema. Muscle bleeding with serous and jelly-like infiltration between muscles. In severe cases, bleeding around the hair follicles and eczema changes occurred. Red or red silk appears on the crown of the hoof, deep congestion and bleeding. Mucosal hemorrhage of the epicardium, myocardium, respiratory tract and urinary tract. Drainage and slaughtering of pastures should be done well, adhere to medicated baths and deworming of flocks. Strengthen feeding management and improve environmental hygiene. In endemic areas, the vaccine is given annually. The sick sheep can be treated with sulfa drugs or antitoxins.

Blue tongue disease

Bluetongue disease is similar to foot-and-mouth disease, viral diarrhea-mucosal disease, malignant catarrhal fever, infectious rhinotracheitis, and vesicular stomatitis, and should be identified.

Blue tongue disease impact

Bluetongue disease is an animal disease caused by the bluetongue virus, which is regulated by the World Organisation for Animal Health

Bluetongue is common in sheep It is a reported disease and China has classified it as a type of animal disease. Because blue tongue disease has a very important impact on the international trade of animals (including animal products) and the safety of viruses of human-derived biological products, international organizations and governments have listed it as animal disease surveillance and control the key of. With the global warming, blue tongue disease has been outbreak in many countries in Europe, and its distribution has been expanding. In August 2006, Germany, Belgium, France, the Netherlands and other countries first detected cattle infected with bluetongue disease. In July 2007, blue tongue disease broke out in Britain, France and Italy. The World Organisation for Animal Health reported that in March-April 2008, France, Italy and other countries had an outbreak of bluetongue disease. The new situation of the blue tongue disease epidemic has aroused great attention from China's agriculture, entry-exit quarantine and drug supervision departments.

Bluetongue virus test

In order to be able to effectively monitor and control bluetongue disease, many scholars at home and abroad have been working on the research of bluetongue diagnosis technology. Among them, the nucleic acid detection technology of bluetongue virus has attracted much attention due to its fast and specific characteristics. Yin Huiqiong, a doctoral student of the Institute of Field Blood Transfusion of the Academy of Military Medical Sciences, under the guidance of his mentor Zhang Jingang, with the support and cooperation of the Academy's Military Veterinary Research Institute and the Henan Academy of Agricultural Sciences Biotechnology Institute, actively carried out the bluetongue virus reverse transcription The development work of the universal polymerase chain reaction nucleic acid universal detection kit and the fluorescent quantitative reverse transcription-polymerase chain reaction nucleic acid universal detection kit have made breakthrough progress after intensive research. These two kits have completed a series of pre-clinical research and pilot-scale assembly such as specificity, sensitivity, repeatability, coincidence rate, stability, and analysis of growth and decline laws.

At present, the core technologies of the two kits have been applied for national invention patents. Zhang Jingang said that if these two kits successfully pass clinical trials, they can achieve rapid, specific and sensitive universal detection of blue tongue virus serotypes, which will not only have important prospects in the field of blue tongue virus detection technology research, More importantly, high-throughput screening of bluetongue disease is made possible, thereby providing reliable technical guarantee for early monitoring and effective control of bluetongue disease, and also for ruminant-derived biological products and biological dressings of bluetongue virus Safety inspection provides powerful technical means and supporting conditions.

Bluetongue diagnosis

A preliminary diagnosis can be made based on typical clinical symptoms and pathological changes, and further laboratory diagnosis is needed to confirm the diagnosis.

1. Sample collection: For virus isolation and identification, whole blood (plus 2 IU heparin anticoagulation per milliliter), liver, spleen, kidney, lymph nodes, and semen in animal viremia stage should be collected (store in a refrigerated container and sent to the laboratory for inspection within 24 hours) Processing) and capture library .

2. Agar gel immunodiffusion test: A dense precipitation line appears between the tested serum well and the antigen well, and is connected to the end of the precipitation line of the standard positive serum to be positive.

3 Immunofluorescence test: (1) direct method (2) indirect method. The blue tongue virus showed cytoplasmic staining under fluorescent microscope, and star-shaped green particles appeared.

4 Enzyme-linked immunosorbent assay: 50% inhibition is used as the judgment value.

Blue tongue disease prevention

There is no effective treatment. Sick sheep should be strengthened in nutrition and carefully cared for. Symptomatic treatment. Rinse the mouth with water, vinegar or 0.1% potassium permanganate solution; then use 1% to 3% copper sulfate, 1% to 2% alum or iodine glycerol to coat the eroded surface; or use boron powder for external treatment . When the hoof is sick, you can wash it with 3% Suer, and then rub it with wood tar vaseline (1: 1), iodine glycerol or oxytetracycline ointment, and bandage it.

In the area where the disease occurs, the diseased animals should be culled, the epidemic source should be eliminated, insect vectors should be eliminated, and preventive immunization should be carried out if necessary. Vaccines used for prevention include live attenuated vaccines and inactivated vaccines. The polymorphism of bluetongue virus and the lack of cross-immunity between different serotypes make immunization difficult. First, the local virus serotype should be determined before immunization, and the corresponding serotype vaccine should be used to obtain satisfactory immune results. Second, when there is more than one serotype in a region, a bivalent or multivalent vaccine should be used. . Otherwise, single immunizations with several monovalent vaccines of different serotypes can only be used one after the other.

In areas without this disease, the introduction of susceptible animals from infected areas is prohibited. Strengthen customs quarantine and transportation quarantine, and strictly prohibit the introduction of cattle and sheep or frozen sperm from countries or regions with the disease. In the vicinity of the affected area, avoid grazing during the time when the vector insects are active, strengthen insect prevention and insecticide measures, prevent the vector insects from invading susceptible animals, and avoid herding and lodging in low-humidity areas.

Once the disease is transmitted, emergency and compulsory control and extinguishing measures shall be adopted in accordance with the provisions of the "Animal Epidemic Prevention Law of the People's Republic of China" to kill all infected animals. Animals in affected and threatened areas are vaccinated urgently.