Bovis ISSN 2398-2993

Bovine leukaemia virus

Synonym(s): deltaretrovirus, enzootic bovine leukosis, EBL

Contributor(s): Veronica Fowler , Tammy Hassel

Introduction

Classification

Taxonomy

  • Family: retroviridae.
  • Subfamily: orthoretrovirinae.
  • Genus: deltaretrovirus.
  • Species: bovine leukemia virus.
  • Etymology:
    • Latin: ‘retro’- backwards.  This makes reference to the presence of a reverse transcriptase enzyme in the virus particle which translates viral RNA into double-stranded DNA.

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Clinical Effects

Epidemiology

Transmission

  • The majority of BLV infections are through the transfer of blood containing infected B-lymphocytes. 
  • Transmission associated with medical examination or treatment is responsible for the largest proportion of new infections through procedures such as de-horning, rectal palpation, surgery, injections, and blood collection.
  • Vertical transmission may occur across the placenta from an infected dam to the fetus, by contact with infected blood during birth, or after birth from the dam to the calf through ingestion of infected colostrum.

Pathological effects

  • The majority of BLV infected animals (around 60% to 70%) remain as asymptomatic carriers of the virus.
  • After a period of latency lasting several months to several years approximately one-third of BLV infected cattle develop Persistent Lymphocytosis (PL) which is characterized by a increase in the number of circulating B lymphocytes. PL animals do not develop any other apparent clinical signs but may develop an immunosuppression which predisposes them to secondary bacterial and viral infections.
  • Between 5 and 10% of infected animals will go on to develop bovine lymphosarcoma, usually between the ages of 3 to 8:
    • Tumors in the abomasum, heart, uterus, lungs, intestines, liver, kidney and spinal cord.
    • Problems digesting food and loss of appetite and weight.
    • Weakness, fever and abnormal breathing.
    • Fall in milk production.
    • Bulging eyes.
    • Diarrhea or constipation.
    • Partial paralysis of the hind legs.
    • Ultimately results in death.
    • At necropsy, lymph nodes and a wide range of tissues are found to be affected by tumors.
In the UK Enzootic bovine leukosis is a notifiable disease. That means if you suspect it you must tell the Animal and Plant Health Agency (APHA) immediately. Failure to do so is an offence.

Control

Control via animal

  • Control mechanisms should seek to prevent the transfer of blood containing infected B-lymphocytes.
    • Use a new single-use disposable hypodermic needle for each vaccination or blood sampling.
    • Clean and disinfect blood contaminated equipment for dehorning and other surgical procedures between animals.
    • Use a new or cleaned/disinfected reproductive examination sleeve for each cow.
  • Ensure excellent colostrum hygiene.
  • It is unlikely that BLV can be completely eliminated from herds but it should be possible to decrease the incidence. Latest advice is to look for the super-shedders and remove these from the herd.
    • To identify super-shedders it is possible to perform milk screen ELISAs and also to perform lymphocyte counts.

Control via chemotherapies

  • There is no treatment for BLV infection itself, however if secondary bacterial infection develops antibiotics can be administered.

Vaccination

  • None available.

Diagnosis

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Further Reading

Publications

Refereed Papers

  • Recent references from PubMed and VetMedResource.
  • Meas S, Usui T, Ohashi K, Sugimoto C & Onuma M (2002) Vertical transmission of bovine leukemia virus and bovine immunodeficiency virus in dairy cattle herds. Vet Microbiol 84 (3), 275-82 PubMed.
  • Hopkins S G & DiGiacomo R F (1997) Natural transmission of bovine leukemia virus in dairy and beef cattle. Vet Clin North Am Food Anim Pract 13 (1), 107-28 PubMed.
  • Pelzer K D (1997) Economics of bovine leukemia virus infection. Vet Clin North Am Food Anim Pract 13 (1), 129-41 PubMed.
  • Rodr√≠guez S M, Florins A, Gillet N et al (2011) Preventive and Therapeutic Strategies for Bovine Leukaemia Virus: Lessons for HTLV. Viruses 3 (7), 1210-1248 PubMed.
  • MC Frie, KR Sporer, OJ Benitez, JC Wallace, CJ Droscha, PC Bartlett, PM Coussens (2017) Dairy cows naturally infected with bovine leukemia virus (BLV) exhibit abnormal B and T cell phenotypes after primary and secondary exposure to keyhole limpet hemocyanin, Frontiers in Veterinary Science 4,112.
  • MC Frie, KR Sporer, JC Wallace, RK Maes, LM Sordillo, PC Bartlett, PM Coussens (2016), Reduced humoral immunity and atypical cell-mediated immunity in response to vaccination in cows naturally infected with bovine leukemia virus Veterinary Immunology and Immunopathology 182, 125–135.
 

Other sources of information

Organisation(s)

  • APHA.
  • OIE.

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