Bovine leukemia virus discovered in human blood

Abstract

Background: Bovine leukemia virus (BLV) infection is widespread in cattle globally and is present in marketed beef and dairy products. Human infection with BLV has been reported in breast and lung cancer tissues and was significantly associated with breast cancer in 3 case-control studies. The purpose of this current research was to determine if BLV is present in human blood cells and if antibodies to BLV are related to blood cell infection.

Methods: Standard liquid PCR and Sanger DNA sequencing were used to test for BLV in buffy coat cells (leukocytes and platelets) of blood specimens from 95 self-selected female subjects. Enzyme-linked immunosorbent assay (ELISA) for IgG, IgM, and IgA was used to detect antibodies to BLV in the plasma of the corresponding blood samples.

Results: BLV DNA was detected in the buffy coat cells of blood in 33/95 (38%) of the subjects by PCR and DNA sequencing. IgG antibodies were detected in 30/95(32%), IgM in 55/95(58%), and IgA in 30/95(32%) of the subjects. There was no significant correlation between presence of the antibodies and presence of BLV DNA.

Conclusions: This first report of BLV in human blood raises the question of whether infection of leukocytes could conceivably lead to leukemia as it does in infected cattle. Also, system wide circulation of infected blood cells could facilitate BLV transit to various internal tissues/organs with potential for their infection and subsequent development of cancer. The most likely route of BLV transmission to humans would be zoonotic, as a foodborne infection. Although eradicated from cattle in some countries, BLV still has a high rate of infection in the Americas, the Middle East, and parts of Europe and Asia. This report of BLV in the blood layer containing human leukocytes/platelets adds important information which could be useful to elucidate possible routes of transmission of BLV to humans and to prevent further human infection.

Keywords: Bovine leukemia virus; Human blood; Zoonotic infection.

Fig. 1

Partial sequences of the long terminal repeat (LTR) promoter region of BLV based on DNA from blood cells of the 23 KPM study subjects positive for the LTR (long terminal repeat) promoter region of BLV. These sequences are compared to 9 GenBank reference sequences [20] (top left column) from 6 of the 10 BLV genotypes established through comparisons of the env sequences of BLV isolated from cattle [1]. No reference sequences of the LTR region were available in GenBank from 3 of the genotype groups (7, 10,11). The reference sequence accession code, specimen country of origin, and genotype group are as follows (genotypes in parentheses are probable, based on country of origin, but not proven by phylogenetics): EF600696.1 and DQ288175.1 - USA, (genotype 1 or 3); HE967301.1 – Uruguay, (genotype 1); K02120.1 – Japan, (genotype 1 or 3); FJ914764.1 – Argentina, genotype 2; AH001143.2 and AH002557.2 – Belgium, (genotype 4); M38278.1 – Russia, (genotype 4,7, or 8); DQ288218 – Costa Rica, genotype 5; The first base of each 10 bases is directly under the first digit of the base pair (bp) number. Dots indicate nucleotide bases identical to the consensus. Letters indicate bases differing from the consensus of the reference sequences. Figure formatting was done with GeneDoc (https://genedoc.software.informer.com)