Bovine leukemia virus (BLV) is a bovine virus closely related to HTLV-I, a human tumour virus. BLV is a retrovirus which integrates a DNA intermediate as a provirus into the DNA of B-lymphocytes of blood and milk. It contains an oncogene coding for a protein called Tax. Nevertheless in its natural host the cattle leukemia is rare. Because the oncogenic properties of the virus were discovered early, a search for evidence of pathogenicity humans started soon after discovery. Mostly farm workers drinking raw milk were tested for disease, especially for leukemia. But neither leukemia nor other signs of infection could be detected. So many in many states it was not tried to get rid of this infection. Testing strategies have recently changed since the virus was first detected in Cows.
Many potential routes of BLV transmission exist. Transmission through procedures that transmit blood between animals such as gouge dehorning, vaccination and ear tagging with instruments or needles that are not changed or disinfected between animals is a significant means of BLV spread. Rectal palpation with common sleeves poses a risk that is increased by inexperience and increased frequency of palpation. Transmission via colostrum, milk, and in utero exposure is generally considered to account for a relatively small proportion of infections. Embryo transfer and artificial insemination also account for a small number of new infections as long as common equipment and/or palpation sleeves are not used. While transmission has been documented via blood feeding insects, the significance of this risk is unclear. The bottom line appears to be that transmission relies primarily on the transfer of infected lymphocytes from one animal to the next and that BLV positive animals with lymphocytosis are more likely to provide a source for infection.
In general BLV causes only a benign mononucleosis-like disease in cattle. Only some animals later develop a B-cell leukemia called enzootic bovine leukosis. Under natural conditions the disease is transmitted mainly by milk to the calf. Infected lymphocytes transmit the disease too. So for artificial infection infected cells are used or the more stable and even heat resistant DNA. Virus particles are difficult to detect and not used for transmission of infection. It is possible that a natural virus reservoir exists in the water buffalo (Wiki: Bovine leukemia virus).
Molecule Role Annotation :
The bovine leukemia virus (BLV) envelope gene encoding extracellular glycoprotein gp51 (encoded by env gene) and transmembrane glycoprotein gp30 was cloned into a vehicle expression vector under the human cytomegalovirus (CMV) intermediate early promoter. The intramuscular injection of this plasmid vector generated a cellular immune response. Seven out of ten cows vaccinated with the DNA construct resisted a drastic challenge (Brillowska et al., 1999).
Description:
The bovine leukemia virus (BLV) envelope gene encoding extracellular glycoprotein gp51 (encoded by env gene) and transmembrane glycoprotein gp30 was cloned into a vehicle expression vector under the human cytomegalovirus (CMV) intermediate early promoter (Brillowska et al., 1999).
Efficacy:
The intramuscular injection of this plasmid vector generated a cellular immune response. Seven out of ten cows vaccinated with the DNA construct resisted a drastic challenge (Brillowska et al., 1999).
2. Bovine Leukemia Virus Vaccine pBLV6073DX
a. Type:
Recombinant vector vaccine
b. Status:
Licensed
c. Host Species for Licensed Use:
Cattle
d. Antigen
Vaccine strain (pBLV6073DX) with a point mutation in the transmembrane protein gene (T>G at nucleotide 6073) and a partial deletion of the R3-G4 sequences (between positions 6614 and 6997). (Suárez et al., 2022)
The proviral construct inserted in the pSP64 vector (Promega) was amplified in Escherichia coli C3040 (New England Biolabs). The standard protocol for production of the inoculum was based on transfection of a monolayer of CHOK1 cells in 25 cm2 cell culture flasks with 2.6 µg of pBLV6073DX and 5.2 µg of linear polyethylenimine (Polysciences) in the presence of 3 ml EMEM (Sigma-Aldrich). Four hours post-transfection, 3 ml of EMEM supplemented with 10% FBS (Internegocios SA) and 3% trehalose were added. Seventy-two hours post-transfection, lysate aliquots (6 ml/dose) were preserved at -80°C in the presence of 15% trehalose. (Suárez et al., 2022)
g. Immunization Route
subcutaneous injection
IV. References
1. Brillowska et al., 1999: Brillowska A, Dabrowski S, Rułka J, Kubiś P, Buzała E, Kur J. Protection of cattle against bovine leukemia virus (BLV) infection could be attained by DNA vaccination. Acta biochimica Polonica. 1999; 46(4); 971-976. [PubMed: 10824867].
2. Kabeya et al., 1996: Kabeya H, Ohashi K, Ohishi K, Sugimoto C, Amanuma H, Onuma M. An effective peptide vaccine to eliminate bovine leukaemia virus (BLV) infected cells in carrier sheep. Vaccine. 1996; 14(12); 1118-1122. [PubMed: 8911007].
3. Larsen et al., 2013: Larsen A, Gonzalez ET, Serena MS, Echeverría MG, Mortola E. Expression of p24 gag protein of bovine leukemia virus in insect cells and its use in immunodetection of the disease. Molecular biotechnology. 2013; 54(2); 475-483. [PubMed: 22829115].
4. Usui et al., 2003: Usui T, Konnai S, Tajima S, Watarai S, Aida Y, Ohashi K, Onuma M. Protective effects of vaccination with bovine leukemia virus (BLV) Tax DNA against BLV infection in sheep. The Journal of veterinary medical science / the Japanese Society of Veterinary Science. 2003; 65(11); 1201-1205. [PubMed: 14665749].
