Abstract: Bovine blue tongue disease is an insect-borne viral infectious disease. After infection, sick cattle manifest as elevated body temperature, constant emaciation, ulceration of the mucous membranes of the mouth and nasal cavity, and even limping of cattle. Infection of cows in pregnancy can cause miscarriage and fetal malformations. Calves infected with the disease can lead to growth dysplasia, and severe illness can lead to the death of sick cattle. The occurrence of the disease can cause serious economic losses on farms. This paper provides a reference for the prevention and treatment of this disease through a comprehensive summary of bovine blue tongue disease and the study of prevention and control.
Bovine blue tongue disease is an acute, febrile infectious disease in ruminants caused by blue tongue virus. The disease is mainly transmitted by the blood-sucking insect kushi midge, and the main objects of transmission of this disease are sheep and cattle. The OIE includes this disease in the category of Infectious Diseases of Category A. In the aquaculture industry, the disease is more common, easy to cause large-scale and large-scale transmission, and the harm to farms is greater.
1. Introduction to pathogens
The pathogen of the disease is bovine blue tongue virus. Bluetongue virus belongs to the reoviridae family, cyclovirus genus, and the viral genome contains 10 double-stranded RNA fragments of varying sizes. The virus is symmetrical in 20-sided, with no capsule membrane on the outside, but a layer of fine villous structure wrapped around. The diameter of the viral nucleocapsid is between 53 and 60 nm. This virus is not heat-resistant, usually inactivated after 30 minutes at a temperature of 60 ° C, and when the temperature is raised to 75 ° C, the virus is instantaneously inactivated. However, it has a strong resistance to the environment, especially in the carrion or some blood residues can survive for a long time. The outermost layer of the virus is usually the VB2 protein. This protein causes the virus to coagulate against human O-shaped red blood cells or sheep's red blood cells. This virus can be cultured in chicken embryos or propagated in cells, and can also be propagated and cultured in sheep. The lesion cells are rounded in shape and refractively enhanced. Usually, chicken embryos are used for culture after isolation of this virus. The virus has a certain tolerance to disinfectants, such as ether, chloroform, etc., but it is sensitive to peracetic acid, sodium hydroxide and pancreatin. The virus is also sensitive to formalin, 70% alcohol, and can be used to disinfect it. When the pH of the environment drops below 3.0, the virus loses its activity in a very short period of time. However, it can be stored for a long time in 50% normal saline. The virus has 24 serotypes, and there is no cross-immunity between the different serotypes.
2. Epidemiology
The source of infection of the disease is the pathogenic animal and infected with the animal with the virus, especially the male animal with the poison, its semen contains pathogens, if the semen is not strictly sterilized, the semen is transported to the cow by artificial insemination, it is very easy to cause the spread of the pathogen. The route of transmission of the disease is mainly through the blood sucking of insects. The main blood-sucking insects are Cyborg midge and Aedes mosquitoes. The source of the disease can also be transmitted to cows through semen through artificial insemination, and the disease can also be transmitted vertically. When a pregnant cow is infected with the disease, the fetus in her womb can be infected and cause miscarriage or fetal malformations. The susceptible animals for this disease are ruminants, mainly sheep with the highest susceptibility, followed by cattle and goats. In addition, deer and antelope in wild animals are also highly susceptible to the disease. The occurrence of this disease has a certain seasonality, usually in the summer and autumn of mosquito life. The occurrence of the disease is also of a certain regional nature, mostly occurring in ponds, rivers and low-lying areas. The disease occurs mainly because mosquitoes can transmit the virus to healthy animals when they suck the blood of other non-diseased animals after sucking the blood of the sick animals. Usually, adult midges suck blood and lay eggs in cow dung or moist soil, and these eggs can develop into larvae within 3 days, and then after 10 to 16 days of larval stage, they can develop into adult worms. Adults can mate with males and females after another 24 h. Females need to suck blood every 3 to 4 days. Its life cycle is about 2 months. Midges usually live in dark, damp corners and can migrate with the flow of air. In particular, the ability to migrate to a longer range of areas in the event of stronger air currents has led to an epidemic of the disease, resulting in an expanding incidence. Therefore, wind direction is an uncertain factor in the occurrence of the disease, often resulting in sudden large-scale onset and epidemics on farms. This is mainly due to the role of the cymbals in the wind.
3. Clinical symptoms
Typical clinical symptoms appear after an incubation period of 3 to 8 days. Initially, the body temperature of sick cattle is elevated, usually to more than 40 ° C or even as high as 41.5 ° C, showing a residual heat type, and the body temperature lasts for 5 to 6 days. Then the sick cattle appeared mentally weak, loss of appetite, different degrees of edema in the lips and nasal mucosa, and salivating symptoms could be seen. After opening the mouth, the visible mucosa has varying degrees of hyperemia and cyanosis. With the prolongation of the course of the disease, different degrees of erosion and ulceration appear in the gums, tongue mucosa and cheeks of the sick cattle, causing difficulty in swallowing in the diseased cattle. These ulcer sites then bleed, causing the mouth of the sick cow to turn red or reddish, as well as red saliva. The nasal cavity of the sick cow emits sticky purulent secretions, and then scabs form around the nostrils, resulting in poor breathing and even difficulty breathing in the sick cow, and the sick cow snoring continuously while sleeping. Some sick cattle will also have different degrees of inflammatory changes in the hoof crown and hoof lobes, resulting in limping of the sick cattle due to pain, these inflammatory sites are more sensitive, there is pain when touching, and the course of the disease is less than 2 weeks. If the lesion appears on the tongue, it can cause paralysis of the tongue. Lesions of the throat and esophagus can cause paralysis of the throat, esophagus, etc. It is also easy for sick cattle to regurgitate water or food through the mouth and nasal cavity when drinking water or eating with their heads down. This reflux can easily cause the sick cow to inhale the foreign body into the lungs, causing the foreign body pneumonia of the sick cow.
4. Pathological changes
The diseased cattle are examined by autopsy, and the lesions are mainly manifested as edema and bleeding of the mucosa of the esophagus to varying degrees. Varying degrees of bleeding may also be seen in the rumen mucosa, and the contents of the rumen are dry. The contents of the mesh stomach and flap stomach are also drier. The surrounding area is cut open to reveal that the mucous membrane is also congested and bleeding, accompanied by larger areas of ulcers and erosions. Sick cattle with foreign body pneumonia may also see inflammatory lesions and hemorrhagic gangrene lesions in the trachea and lungs, and limbs and hooves showing defects of the epidermis and appendages to the crust. Severe edema may be seen in the subcutaneous tissue of the neck of the sick cow, which can spread to the throat and around the esophagus. For sick cattle with a longer course of disease, their edema can even extend to the organs in the body. Microscopic examination of the esophagus, throat, and tongue reveals necrosis and degeneration of the striated muscles, and the disappearance of muscle tissue structures is transparent. The appearance of edema around the blood vessels of the central nervous system, as well as congestion of blood vessels. On the skin of cattle. Small punctate bleeding is common, while the subcutaneous tissue is diffusely hyperemic and jelly-like infiltrated. In addition, there are different degrees of punctate bleeding in the myocardium and epicardium, and punctate bleeding can be found even in the respiratory tract and digestive tract. In severely sick cattle, there are obvious ulcers and necrosis of the respiratory and digestive tracts.
5. Diagnostic methods
A preliminary diagnosis can be made by analyzing its epidemiological features and observing clinical symptoms and pathological changes. However, due to the similarity of its incidence and foot-and-mouth diseases, the diagnosis of this disease needs to be confirmed by laboratory techniques, and the laboratory techniques that are usually used more are agar diffusion test and neutralization test. The diagnosis of the disease can also be confirmed by isolation and identification of the virus.
The disease can be diagnosed more conveniently and accurately by agar diffusion test. When the agar diffusion test is performed, the visible precipitation phenomenon between the detected serum pore and the antigen pore, and the end of the precipitation line and the standard positive serum precipitation line can be connected to each other, which can be judged as a positive diseased cattle. In addition, the diagnosis of the disease can be carried out by neutralization experiments. Isolation and identification of pathogens is also a major method of diagnosing the disease. By isolating the pathogen, proliferating culture, and microscopic examination by electron microscopy, the pathogen can be determined to be bovine blue tongue virus, so that the diagnosis can be made. However, the isolation and culture of pathogens is more complex and takes a long time, which is not conducive to timely diagnosis. Molecular biology methods can also be used to diagnose the disease. Molecular biology methods mainly use PCR technology or DNA probe technology, which can efficiently diagnose the disease.
In addition, the diagnosis of this disease should also be carried out with the differential diagnosis of diseases such as bovine foot-and-mouth disease and bovine viral diarrhea.
6. Prevention and control measures
6.1 Preventive measures This disease is mainly prevented by immunization, and the vaccines are the weakening virus vaccine of chicken embryo and the bovine embryo kidney cell implant vaccine. Cows can be immunized before breeding or during pregnancy, which has a good immune effect. In addition, the spread of the disease can be reduced by cutting off the mode of transmission of the pathogen. Since bovine blue tongue disease is caused by the blood sucking of kuya midges, the work of eliminating kushina should be effectively carried out in the daily production management process, which can reduce the spread of the disease and avoid the occurrence and epidemic of the disease. The eradication of coopers can be sprayed with a pyrethroid kerosene solution at a concentration of 0.2%. Sprayed every 2 weeks, it is effective in killing midges in farms. It is also possible to spray 0.05% fly venom phosphorus or 1.25% malathion at a concentration of 1.25% on the surface of cattle. It can also reduce the bite of the midge on the cattle, which has a good effect on preventing the disease.
Prevention of the disease requires avoidance of introduction from endemic areas or susceptible areas of the disease. Artificial insemination is also prohibited from using semen produced by bulls in these areas. If introduction is really necessary, it needs to go through strict quarantine procedures and the introduction of cattle is subject to strict disinfection and isolation before entering the farm. After 1 month, if the sick cattle do not develop clinical symptoms, they can be raised in mixed groups. Once the epidemic situation of the disease occurs in the farm, the epidemic situation should be reported in a timely manner and the principle of culling should be adopted for the sick cattle, culling and harmless treatment should be carried out, and strict disinfection should be carried out. The farm shall formulate a scientific and reasonable disinfection plan and disinfect it regularly in accordance with the plan. Disinfection can be applied to 3% formalin or 70% alcohol for environmental spraying. When disinfecting, it is necessary to leave no dead corners. The enclosures are disinfected after a thorough cleaning. Disinfection should pay attention to changing the disinfectant liquid regularly to avoid pathogen resistance and lead to unsatisfactory disinfection effects.
6.2 Therapeutic measures This disease should be treated on the principle of group culling. For individual sick cattle with mild lesions, the lesion site can be washed with 0.1% potassium permanganate and then coated with glycerol or glacial boronic acid. It can delay the development of the disease, and can also play a certain therapeutic effect, and at the same time need to cooperate with symptomatic treatment. Broad-spectrum antibiotics are also used to prevent secondary infection in sick cattle.
Source: Veterinary Guide Author: Ding Zheng; Copyright belongs to the original author, hereby thank you to the reprint platform and the author, the article is mainly for everyone to learn, exchange for the purpose. If this article infringes on your rights and interests, please leave a message or contact us by phone to delete it immediately!
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