The causative agent and symptoms of leukemia in cattle, how is the danger to humans transmitted

The causative agent and symptoms of leukemia in cattle, how is the danger to humans transmitted

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Infectious diseases are common in dairy farming. The causative agents of infection can affect 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 are the causes and how is the virus transmitted?

The causative agent of leukemia in cattle is bovine leukemia virus (BLEV), of the Retroviridae family, 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 with a deterioration in metabolic processes and immunological protection of the body.

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, buffalo, zebu and sheep. The causative agent lives for a short time in the external environment, loses its infectious properties in 3-6 hours, 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 mating. Calves - through colostrum and milk, 10-20% are born already infected. It is believed that the virus is 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 as 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.


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. A cow, despite the presence of a 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.


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 not uncommon.

Breathing becomes heavy, the 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.


This stage is manifested by the emaciation of cows, their lymph nodes are enlarged, their eyes bulge. Such individuals of cattle often get sick, more often remain barren, there may be abortions, and the number of calves born is decreasing. The productivity of cows 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. In calves, the disease is acute 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 hematological examination, the number of leukocytes, young cells and the number of lymphocytes in percentage terms is determined. Auxiliary diagnostic methods - biopsy of lymph nodes, liver and spleen.

Expert opinion

Zarechny Maxim Valerievich

Agronomist with 12 years of experience. Our best summer cottage expert.

Leukemia is differentiated from tuberculosis, actinomycosis, traumatic pericarditis, hepatitis, mastitis, reticulitis, brucellosis and paratuberculosis.

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 that can be used 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, as no treatment has been developed. When this happens depends on the health of the animal, 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.


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. You need to keep such cows separately from the rest, feed them 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 will be enough for the viruses in the milk to die. Milk can also be disinfected under ultraviolet radiation. However, the quality of milk remains low. You cannot cook yoghurt, cheese from it, or dry it. It contains more protein than usual and less dry matter. The toxins produced by the virus remain in it.

Meat is unsuitable 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.

Watch the video: Introduction to Hematological cancers u0026 Acute Myeloid leukemia (August 2022).