The causative agent and symptoms of leukemia in cattle, how is the danger to humans transmitted
Infectious diseases are common in dairy farming. Infectious agents can infect various organs, even the blood. Viral leukemia is a serious illness that can affect all breeds. Consider the causes of the appearance, stages and symptoms of cattle leukemia, diagnostic and therapeutic measures, whether there is a danger of the disease for humans.
What is the cause and how is the virus transmitted?
The causative agent of leukemia in cattle is bovine leukemia virus (BLEV), of the Retroviridae family, which is morphologically similar to the virus that causes leukemia in other animal species. The virus is able to remain in the cell for a long time in a bound state with the genome, showing no activity. It is activated when metabolic processes and immunological protection of the body deteriorate.
Leukemia (hemoblastosis, leukemia) is a tumor disease of the blood that can be asymptomatic. It is manifested by the proliferation of cells of the hematopoietic and lymph-forming organs, which then infiltrate into other organs, where tumors appear. They can form in the lymph nodes, spleen, heart, kidneys, abomasum, kidneys.
The virus is transmitted to cattle, buffaloes, zebu and sheep. The causative agent lives in the external environment for a short time, loses its infectious properties in 3-6 hours, and dies when exposed to common disinfectants. In fresh milk, the virus persists for 18 days; when pasteurized, it dies in a few seconds.
Healthy animals become infected through blood and saliva when mated. Calves - through colostrum and milk, 10-20% are born already infected. The virus is believed to be carried by blood-sucking insects. Infection is facilitated by crowded housing, grazing of the herd on a common grazing, feeding calves with milk from sick cows, using sick bulls for mating. Bovine leukemia is now considered a disease that poses a threat to the gene pool of breeds and reduces the number of productive livestock.
Stages and symptoms
The course of the disease is divided into several stages, which are characterized by certain disorders and symptoms. Pathogenesis is determined by the interaction of the virus and the cell. The predominantly latent form is characteristic of leukemia.
The disease begins with the activation of the pathogen; various unfavorable external or internal factors can become activators.
Incubation
It may take 2 or more weeks from infection to the appearance of the first signs. The early stage of the disease is asymptomatic, the productivity and reproductive function of cows remain at the same level.At this time, the sick animal is already spreading the virus. The cow, despite the presence of the pathogen in the body, may never get sick with leukemia, the pathogens will remain in the body in a passive state, but will be transmitted to other animals with the patient's secretions.
Hematological
At this stage, pathological changes begin to manifest themselves in the blood of infected animals, which flows through the vessels, and not only in the hematopoietic organs. In leukemic individuals, the condition worsens, they quickly get tired, poorly absorb food, reduce milk yield, and lose weight.
Digestive disorders, weakening of the heart, yellowness or cyanosis of the mucous membranes are common.
Breathing becomes heavy, dewlap, abdomen, udder swell in animals, urine flow is impaired. Superficial lymph nodes on the jaw, udder, near the ears, above the knees increase. They are dense or slightly elastic, mobile and do not hurt.
Tumor
This stage is manifested by the emaciation of cows, their lymph nodes enlarge, their eyes bulge. Such individuals of cattle often get sick, often remain barren, there may be abortions, and the number of calves born decreases. Cow productivity is dropping.
Young cows show tumors in the lower neck, thymus and skin. Due to a decrease in leukocytes and the appearance of pathological forms of cells in the peripheral blood, the immune system is quickly depleted, and the calves die. Calves are acutely ill and may die within a few weeks of the onset of symptoms.
Diagnostic measures
In the early stages of the disease, leukemia in cattle is detected by enzyme immunoassay and using the polymer chain reaction. The diagnosis is made according to the data of epizootological, virological, histological, hematological studies, as well as taking into account clinical signs. In a hematological study, the number of leukocytes, young cells and the number of lymphocytes is determined in percentage. Auxiliary diagnostic methods - biopsy of lymph nodes, liver and spleen.
What if a cow has leukemia?
The disease is chronic and severe, which causes significant damage to the animal's body, therefore it is not treated. The virus can be inserted into the genes of the cell, and so far no drugs have been developed with which to remove it from there. There is no official therapy for the treatment of leukemia in cows, and there are no alternative methods.
When sick individuals are identified, they are separated from the herd and reared separately or immediately slaughtered. If there are more than 10% of such individuals, they are slaughtered, the rest are examined every 3 months. If there are many cases, animals are handed over for slaughter and replaced with new ones.
Possible complications and consequences for the animal
Cows with leukemia will die because no treatment has been developed. When this happens depends on the health of the animal and how long it can resist the disease. Carriers, if they are not sick, can live for many years; the unactivated virus will not affect health and performance. It is not recommended to breed carriers of the leukemia virus.
Prevention
When buying new animals for a herd, you need to conduct a study of their blood, try to choose individuals from farms that are free from disease. If the analysis determines that they are healthy, they can be introduced into the herd, the infected ones can be sent to fattening. Such cows should be kept separate from the rest, fed with immunostimulating supplements.
Calves born to leukemic cows should also be tested for the virus.Equipment and milking machines, if possible, should be used individually or at least disinfected before milking healthy animals. If there is no healthy bull in the herd, artificial insemination can be used. The room where the cows stood must be cleaned and disinfected with 2-3% sodium hydroxide solution.
Is there a danger to humans?
The virus from cows is not transmitted to humans, and the disease does not develop. Therefore, you can work with animals without fear of infection. But there are sanitary requirements for milk and meat.
You can drink milk, but only after 5 minutes of boiling or pasteurization. When a certain temperature is reached, 2 tens of seconds are enough for viruses in milk to die. Milk can also be disinfected under ultraviolet radiation. However, the quality of milk remains low. You cannot cook yogurt, cheese, or dry from it. It contains more protein than usual and less dry matter. The toxins produced by the virus remain in it.
Meat is not suitable for consumption if internal organs and muscles are affected. If the muscles are not affected by tumors, it is boiled before use or sent for processing for meat products.
Cattle leukemia is an incurable disease; animals in any farm can get sick. The main way to prevent the spread of disease in the herd is through preventive measures. If a cow becomes infected and the disease begins to develop, it is doomed. After a while, the animal will die. All that can be done is to intensively feed him or slaughter him right away.
The economic damage from cattle leukemia is determined by the loss of funds during the forced slaughter of livestock, the death of animals, and a decrease in milk and meat productivity. The volume of sold young stock is also decreasing. Today, leukemia is considered a disease that threatens the breeding gene pool of cattle breeds.
