Abstract
Bovine leukemia virus (BLV) infects cattle and causes serious problems for the cattle industry, worldwide. Vertical transmission of BLV occurs via in utero infection and ingestion of infected milk and colostrum. The aim of this study was to clarify whether milk is a risk factor in BLV transmission by quantifying proviral loads in milk and visualizing the infectivity of milk. We collected blood and milk from 48 dams (46 BLV seropositive dams and 2 seronegative dams) from seven farms in Japan and detected the BLV provirus in 43 blood samples (89.6%) but only 22 milk samples (45.8%) using BLV-CoCoMo-qPCR-2. Although the proviral loads in the milk tended to be lower, a positive correlation was firstly found between the proviral loads with blood and milk. Furthermore, the infectivity of milk cells with BLV was visualized ex vivo using a luminescence syncytium induction assay (LuSIA) based on CC81-GREMG cells, which form syncytia expressing enhanced green fluorescent protein (EGFP) in response to BLV Tax and Env expressions when co-cultured with BLV-infected cells. Interestingly, in addition to one BLV-infected dam with lymphoma, syncytia with EGFP fluorescence were observed in milk cells from six BLV-infected, but healthy, dams by an improved LuSIA, which was optimized for milk cells. This is the first report demonstrating the infectious capacity of cells in milk from BLV-infected dams by visualization of BLV infection ex vivo. Thus, our results suggest that milk is a potential risk factor for BLV vertical spread through cell to cell transmission.
Highlights
Bovine leukemia virus (BLV) is the etiological agent for enzootic bovine leukemia (EBL), the most common neoplastic disease of cattle
To test whether the quality of the extracted DNA was suitable for Polymerase chain reaction (PCR) amplification, and to examine the efficiency of amplification based on the threshold cycle (Ct) value, all the DNA samples were subjected to real-time PCR analysis of the bovine BoLA-DRA gene, using the BLVCoCoMo-qPCR-2 assay
BoLA-DRA was amplified from blood and milk samples from all the cattle tested with average Ct values of 22.12 and 22.37, respectively, indicating that the quality of both the sample types was suitable for PCR amplification (Figure 1C)
Summary
Bovine leukemia virus (BLV) is the etiological agent for enzootic bovine leukemia (EBL), the most common neoplastic disease of cattle. It belongs to the Deltaretrovirus genus of the Retroviridae family, which includes the human T cell leukemia virus types 1 and 2 [1, 2]. EBL is listed by the World Organization for Animal Health as a problem disease [6, 7] Under these circumstances, it is necessary to decipher the specific routes of BLV-transmission to prevent the spread of infection and to reduce economic loss [1]
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