Bovine Leukosis: Prevention and Control Measures

Bovine Leukosis

Bovine Leukosis (Leucosis bovis) is a chronic infectious disease of a tumor nature.
It is manifested by lymphocytosis and tumor growth of hematopoietic and other organs and tissues.
The pathogen is an RNA-containing virus of the family Retroviridae, genus Deltaretrovirus.
Diagnosis is based on serological, hematological, or pathomorphological studies.

Study measures of general and specific prevention of Bovine Leukosis.
Understand veterinary and sanitary measures carried out in a disadvantaged farm.
Learn methods of health-improving farms from Bovine Leukosis depending on its spread.

Sick and infected cattle are the source of the pathogen.
Infection occurs vertically (mother to fetus) and horizontally (enterally and parenterally).
The development of the disease is caused by immune insufficiency and genetic predisposition.
Clinical signs vary:
- Non-specific: exhaustion, cardiovascular system issues, edema.
- Characteristic: increase and consolidation of lymph nodes (submandibular, pre-scapular, supra-nameless), exophthalmos, enlargement of the liver and spleen.
- Pronounced signs in the terminal (tumor) stage.

Based on determining quantitative and qualitative changes in blood composition (total white blood cells, leucogramme, pathological cell forms).
Results are compared with the "leukosis key" for diagnosis in animals of different ages.
Leuco- and lymphocytosis progressing within 6 months is a reliable indicator.
Consider aleukemic cases where the blood picture remains normal.

True Leukosis (hemoblastosis):
- Enlarged spleen, capsule may rupture.
- Enlarged, mobile lymph nodes with smooth capsules, shiny cut, smoothed pattern.
Reticuloses:
- Spleen is not enlarged.
- Enlarged lymph nodes with rough capsules, fused with surrounding tissues.
All forms:
- Focal or diffuse growths of gray-white or gray-pink color in the liver, kidneys, thicker heart muscle, and other organs.

Serological tests:
- Agar gel immunodiffusion (AGID): detects antibodies to specific antigens of the bovine leukemia virus in blood serum.
PCR.

Blood with anticoagulant.
Blood serum.
Pieces of affected organs (spleen, lymph nodes, liver, kidneys, heart, rennet walls, uterus, skeletal muscles) in fresh form with ice or in 10% formalin solution.

Measures are carried out according to the Rules (2021).
Infected animals: clinically healthy animals with antibodies to BLV (detected by serologic test).
Sick animals: animals with antibodies to BLV and characteristic quantitative and qualitative changes in blood composition.
Farms are considered prosperous if scheduled tests and slaughter do not detect leukemia.

Complete the farm livestock from prosperous farms, confirmed by a veterinary certificate.
Preventive quarantine of all incoming animals for 30 days, with clinical and serological tests.
Prevent contact between healthy and disadvantaged livestock on pasture and watering.
Monitor post-slaughter expertise in meat processing plants, on-farm animal slaughter, autopsy of animal corpses.
Comply with asepsis and antiseptics during veterinary manipulations, use sterile tools.
Implement veterinary, sanitary, and hygienic norms of feeding, maintenance, and usage.

Indicators of post-slaughter expertise in meat processing plants.
Expert data for on-farm animal slaughter, autopsy of animal corpses.
Results of planned serological and hematological tests for Leukosis.
Results of control slaughter of animals with increased lymphocytes in 1 mkl of blood and pathomorphological studies.

Farms with Bovine Leukosis are declared disadvantaged and quarantined based on the chief state veterinary inspector's recommendation and local administration's decision.
A comprehensive plan for improving the disadvantaged farm is approved.
The plan includes restrictive, veterinary, sanitary, organizational, economic, and special measures with timelines and responsible persons.

Under quarantine:
- Export of animals from the herd for breeding and use purposes is prohibited without permission.
- Regrouping of cattle inside the farm is prohibited without permission.
- Use of breeding bulls for free mating of cows and heifers is prohibited.
- Use of non-sterile tools and devices for veterinary and zootechnical treatment is prohibited.

Determine the option of fighting Leukosis based on serological research results:
- OPTION 1: Up to 5% of infected and sick animals detected.
- OPTION 2: More than 5% of cows and heifers are sick or infected.
Health-improving measures:
- Isolation and immediate slaughter of sick animals.

Farms with up to 5% infected/sick animals are isolated and slaughtered within 15 days of diagnosis.
Subsequent serological studies and PCR are performed every 90 days with mandatory removal of infected animals.
Two consecutive negative results with a 90-day interval are required.

If more than 5% of animals are infected, they are isolated in a reservation.
Examined every 6 months via hematological methods.
Animals with identified blood changes are recognized as sick and sent for slaughter within 15 days.

Milk and colostrum from sick cows are destroyed.
Milk from infected cows is heat-treated (pasteurization at 85 °C for 10 minutes or boiling for 5 minutes) or sent to a dairy processing plant.
Milk from healthy animals is exported or processed independently.
Livestock premises and equipment are disinfected (2% hot formaldehyde solution, 2% hot caustic soda solution), focusing on blood-contaminated areas.
Manure and wastewater are disposed of according to established procedures (disinfected biothermal).

The farm is considered healthy after:
- Withdrawal of all sick and infected animals.
- Two consecutive negative serological examinations (90-day interval) of all livestock older than 6 months.
- Negative PCR results of calves from 15 days to 6 months.
- Implementation of veterinary and sanitary measures.