Epidemic bovine leukemia was first described by Knuth and Volkmann in the late 19th century. In 1969, Miller of the United States isolated leukemia virus from bovine blood lymphocytes. In 1974, the disease was also found in China and spread in China, causing serious losses to the cattle industry. The main symptoms of this disease are enlargement of the anterior shoulder, abdomen and parotid lymph nodes of cattle, and protrusion of the eyeball in some cases. In a word, the symptoms are different from the organs of tumorigenesis. There are not many reports about cow leukemia. Here we briefly introduce the related content of cow leukemia.
1. Pathogeny
Bovine leukemia virus cells are mostly irregular cells, most of which are round and some are oval. Among them, the ratio of the nucleus to plasma is abnormal. The diameter of the virus cells is 80-120 nm. The cells are surrounded by bilayer membranes, and there are 11 nm long bulges on the membranes. The virus proliferates by germination, i.e. germination on the cell surface and releases to form another new cell.
Bovine lymphoblastic leukemia (BLL) is a type C virus, which can exist in lymphocyte all the time and has infective activity. After the virus infects the cells, the virus hides in the inner of the cell membrane. Therefore, the surface of the cell membrane does not show the antigen of the virus, so the host can not immunize it.
2. Epidemiology
Viral transmission is mainly through contact, usually through blood and secretions for horizontal and vertical transmission. Bovine lymphoblastic leukemia can be transmitted vertically, and bull cattle are the main source of infection. Blood-sucking insects, operations, blood transfusions and so on can cause infections. Because leukemia is a cancerous change, the immune system function of cattle infected with the disease will slowly decline, but there are also cattle with leukemia symptoms are not obvious, if not detected in time, it is easy to cause other cattle to be infected.
3. Clinical symptoms
There are two clinical manifestations of bovine leukemia, one is sub-clinical type, which is characterized by no tumor, slow cell proliferation, and no obvious symptoms. The disease can last for many years or even for life, with less harm. The other is clinical type, manifested clearly, mainly in the following aspects.
1) Enlargement of lymph nodes. The location of lymph node enlargement is mainly body surface, rectum, parotid, head, and neck, anterior femur, etc.
2) Body temperature. The bovine body temperature of the diseased cattle is normal in the early stage, and it will rise to 39.5-40.3 in the middle and later stages.
3) Mental state. The dairy cows with leukemia had a normal mental state at the beginning, but their appetite was unstable, sometimes good or bad.
4) Deterioration of beef. When cattle become sick, besides blood disease, the meat of diseased cattle also changes, which shows that the amino acid of beef, liver and myocardium decreases and the proportion of fat and protein decreases, but the proportion of water increases. Meat is difficult to ripen in making food.
5) Nutrition status. There was no effect in the early stage of the disease, but with the deterioration of the disease, the tumors increased, and gradually became thin, cows would have a decline in milk production. Besides, according to the location of the tumors, the abnormal expansion of the tumors will oppress the nerve organs, leading to organ dysfunction in cattle, and may appear symptoms such as black stool, dyspnea, even asphyxia, lying down, diarrhea and vomiting, and so on.
4. Pathological and histological changes
Leukemia cattle have different pathological manifestations depending on the location of the disease. The main manifestations are enlargement of lymph nodes at the site of the disease, and some of the lymph nodes feel mobile. Most will also have bodyweight loss, anemia, and other symptoms. Cells infiltrate in some areas, such as the heart, stomach, and spinal cord. But there is no brain damage.
Histological changes showed that primitive and immature lymphocytes were common in the affected parts of cattle, and hemorrhage and necrosis occurred in the enlarged lymph nodes. Tumor cells infiltrate, destroy and even replace normal cells in organs.
5. Diagnosis
The diagnosis of leukemia in cattle is often based on the symptoms of lymphadenopathy in cattle. If bovine lymphadenopathy is obvious and hard, and inguinal lymphadenopathy can be detected by rectal examination, then leukemia is diagnosed. Besides, we can also check whether there is a significant increase in lymphocyte as a diagnostic basis. Because in the early stage of cattle leukemia, when no obvious lymph node enlargement can be seen, the white blood cells will increase significantly. Diagnostic personnel can check the changes of blood picture of cattle as a basis for diagnosis. If the lymphocyte of diseased cattle increases by more than 70%, the tumor cells will appear. Serum tests and DNA tests can also be used to diagnose the disease. The latest real-time fluorescence quantitative detection is also a very good detection method.
6. Prevention and control
Dairy cows with leukemia will have multiple lymph node enlargement, body-weight loss, low milk production rate. If the tumors occur on the ovaries, they will also lead to infertility, affecting reproductive capacity, and the pasture has to eliminate them, causing great economic losses to the dairy farm. The prevention and treatment of cow leukemia mainly include the following points.
1) Clean and disinfect the cattle farm, drive out blood-sucking insects (such as flies, mosquitoes, etc.), and regularly disinfect the cowshed;
2) The prevention of infections should be carried out during the management of inserting nose rings and whistling in cattle breeding.
3) Special attention should be paid to the treatment of bovine diseases. It should be clearly stipulated that needles should be used only once to prevent cross-infection caused by blood transfusion, operation, and injection.
4) Serological tests and treatments can be carried out in cattle farms once every three years.
5) Eliminate positive dairy cows to prevent horizontal infection and vertical transmission of genetic factors.
6)Feed sterilized milk to healthy cattle.
7. Conclusion
Leukosis in Dairy Cows is a kind of infectious disease, which is harmful to dairy cows. To do a good job in defense and inspection is an effective way to reduce losses. At present, besides serum examination, quarantine, isolation, slaughter of positive dairy cows and optimization of dairy cow population are the best prevention and control methods.