Abstract
Although natural suckling from dams with bovine leukemia virus (BLV) has not been recommended in Japan, the frequency of BLV transmission through natural suckling under natural conditions is still unclear. The purpose of this study was to elucidate the risk of BLV transmission through natural suckling. Dams with BLV were classified into three groups (high, middle, low) based on the proviral loads (PVLs). PCR positivity of their colostrum and the correlations between the ratios of calves with BLV and types of feeding milk were analyzed. In dams with low PVLs, no colostrum or calves were confirmed to have BLV. In dams with middle and high PVLs, 17 out of 25 (68.0%) colostrum were PCR positive, and 10 out of 23 (43.4%) and 13 out of 29 (44.8%) calves with natural suckling and artificial rearing were infected with BLV, respectively. No difference was confirmed between the infection rates of natural-suckled and artificially reared calves. Thus, we concluded that the avoidance of natural suckling from dams with BLV and the introduction of artificial rearing were low priority countermeasures against BLV transmission.
Highlights
Bovine leukemia virus (BLV), a member of the Retroviridae family and the Deltaretrovirus genus, is an etiological agent of fatal B-cell leukemia and malignant lymphoma in cattle, which are, together, known as enzootic bovine leukosis (EBL)
In the case of natural suckling, 60.0% (6/10) and 30.7% (4/13) of the calves born from dams with high and middle proviral loads (PVLs) were infected with BLV, respectively
In the case of artificial rearing, 46.6% (7/15) and 50.0% (8/16) of the calves born from dams with high and middle PVLs were infected with BLV, respectively
Summary
Bovine leukemia virus (BLV), a member of the Retroviridae family and the Deltaretrovirus genus, is an etiological agent of fatal B-cell leukemia and malignant lymphoma in cattle, which are, together, known as enzootic bovine leukosis (EBL). More than 95% of BLV-infected cattle remain EBL-free for life, one to five percent of such cattle develop EBL several years after infection [1,2]. New Zealand and many Western European countries have successfully eliminated BLV. BLV continues to spread across the world, and high seroprevalence has been confirmed in many countries including Japan and the USA [3,4]. BLV establishes lifelong infections, and no vaccines or therapeutic agents are available for preventing BLV infection or EBL development. Preventing infection in cattle is the only measure for reducing EBL
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