Cow viral diarrhea, also known as mucositis, belongs to the flaviviridae plague virus is a single-strand RNA virus. It can cause pneumonia in cows, severe diarrhea, wasting, decreased milk production, inflammatory erosion of the mucosa of the digestive tract, necrosis of lymphoid tissue of the intestinal wall, etc. Infected cows are mainly divided into two types, one acute type, one is chronic type, the clinical symptoms of the two types are different, most cows are not easy to be found in the early stage of infection with chronic viral diarrhea, and after infection with acute type, a variety of clinical symptoms will soon appear, which should be diagnosed and treated according to the pathogenesis characteristics, which can reduce the impact on the cow body and control the spread of the disease.
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The disease is widespread around the world, and in recent years, the infection rate in some countries and regions has continued to be very high, often with hidden infections, causing huge economic losses to the dairy farming industry. In 1980, China introduced seeds from abroad to bring this disease into China, and with the transfer of domestic dairy cows from all over the country, the epidemic continued to spread, making some farms have different degrees of infection. Sick and poisoned cows are the main source of infection, and the secretions and excrement of sick cows contain viruses that can be infected horizontally in the digestive tract or respiratory tract, or vertically through the placenta. The probability of acute cases occurring in new endemic areas is relatively high, and the incidence and mortality rate are lower in old-endemic areas, but the hidden infection rate is more than 50%. There is no seasonal characteristic of viral diarrhea in dairy cows, which can occur all year round, while the incidence of spring and winter is relatively high, and cows of any breed and age can be infected. Cows aged 6-18 months are mostly infected, accounting for about 5% of the morbidity and 90%-100% of the mortality rate. The disease is often in an explosive epidemic state, with buffalo, cattle, sheep, goats, pigs, etc. all susceptible to infection and can be transmitted with poison.
2. Clinical symptoms
Acute type: the onset of the diseased cattle suddenly, the body temperature rises to 40-42 ° C in the first 2-3 days, and then falls to a normal state. Sick cattle experience mental malaise, decreased appetite, rapid heartbeat, salivation, faster breathing rate, and foul breathing. In the later stages of aggravation, the oral mucosa has symptoms such as damage and erosion, and the cows have severe salivation symptoms and watery diarrhea, and the feces in the late stage of the disease have mucus and blood. Some sick cattle also have skin damage and erosion in the hooves, which affects the normal walking of dairy cows.
Chronic type: the symptoms of the onset of such diseased cattle are not obvious, the body temperature will not rise significantly, but it is also slightly higher than the normal body temperature, and the symptoms of diarrhea are relatively small, and there are usually nasoscopic lesions, increased eye secretions, oral inflammation and erosion between the hooves and toes. Some sick cattle will have intermittent diarrhea symptoms, sick cattle dehydration is more serious, rapid emaciation, if not timely treatment can easily lead to the death of sick cattle.
Cows infected with viral diarrhoeal diseases generally develop immunosuppression within 1-2 weeks and are susceptible to secondary infections due to the influence of other harmful bacteria.
3. Sources of infection and routes of transmission
Sick cattle and cattle carrying viruses in the body are the source of infection of this disease, the blood of sick cattle, the internal tissues of the body, the body secretions, feces, milk are present in the virus, the above substances and healthy cattle after contact with the respiratory tract, oral transmission, but also through production, mating and other ways of virus transmission.
4. Diagnosis
1. Diagnosis of clinical symptoms
Dairy cows infected with viral diarrhoeal diseases have fewer clinical symptoms, and only a few sick cows in the herd experience mild symptoms. Sometimes there is a sudden onset of illness in the entire herd. The diagnosis of the disease is usually based on the diarrhea symptoms of the sick cow and the body temperature of the sick cow is observed. Acute illness can be diagnosed if the body temperature is up to 40 to 42 °C, the stool is watery, smelly, and mucus and bubbles are present. Chronic cattle with increasingly emaciated, slow growth and lameness can be diagnosed.
2. Serological diagnosis
To ensure the accuracy and validity of the diagnosis results, serological diagnosis is usually also used. Neutralizing antibody testing is a more commonly used one, and the accuracy of the results can be guaranteed, but some sick cattle are seroposid in the immune tolerance stage, which is prone to missed tests. The agar diffusion test is relatively simple to operate and can quickly obtain results, but the sensitivity ratio is relatively low. In the actual diagnosis, the appropriate detection method can be selected according to the specific needs.
5. Prevention and control measures
Viral diarrhea is a more serious disease during dairy farming, and the clinical manifestations and symptoms of sick cattle are more diverse. In order to effectively prevent and control the occurrence of this disease, it is necessary to be able to accurately identify and eliminate sick cattle to prevent continuous infection of sick cattle, and to effectively control the situation of vertical infection. Quarantine work needs to be done during breeding, and cattle with persistent infections need to be culled. However, because the clinical symptoms of infected cattle are not obvious, there will be continuous detoxification, resulting in a large-scale spread of the disease. Breeders must pay attention to the identification and elimination of sick cattle, which is an important way to control the epidemic and reduce losses.
At the same time, for the introduction of foreign species must do a good job of quarantine work, after entering the farm need to be isolated for observation, you can also use laboratory testing to detect the introduction, determine all negative before you can mix with the original dairy cows in the farm to prevent the introduction of virus. Cows are generally immunized to enhance their immunity, usually inactivated vaccines or live attenuated vaccines, and the cows are vaccinated at a specific stage. Cows during pregnancy cannot be immunized, but can be immunized for the first time after the colostrum immunity has disappeared after the calf is born, boosted immunization 21 days after the first exemption, and then immunized every 4-6 months.
For infected cattle, it is also necessary to take targeted methods for treatment, and to replenish water to sick cattle in time to prevent dehydration and achieve effective protection of the gastrointestinal mucosa. Choosing the right antidiarrheal cardiotonic fluid can improve the immunity of sick cattle and shorten the recovery cycle. Antibiotics and sulfonamides can also be used to improve the effectiveness of treatment
Sixth, farmers must do a good job in epidemic quarantine in the daily management and breeding process, and pay attention to the quarantine and prevention and control of foreign introductions, so as to prevent the introduction of viruses from affecting the cows in the farm. If an abnormal situation is found in the cow, it should be reported to the relevant departments in time to achieve early detection, early diagnosis and early treatment to ensure the prevention and control effect of the disease.
Author: Sheng Liu Senior Veterinarian