Bovine leukemia virus infection - diagnostics, eradication, and anthropozoonotic potential (background) (review)

Of tumor diseases in the global animal husbandry industry, the greatest danger is bovine leukemia. Since the last century, this neoplastic disease has remained relevant for veterinary medicine and, in addition, more and more questions arise concerning the potential threat of the Bovine leukemia virus (BLV) for humans. The problem is being discussed (G.Yu. Kosovskiy et al., 2016) which additionally stimulates both fundamental research of the pathogen and the pathology, as well as the methods for detection to improve dairy cattle breeding and veterinary safety. A number of publications are devoted to BLV prevalence, peculiarities, the prospects for improving animal health and welfare based on selection and vaccines developed in the world (S.G. Hopkins et al., 1997; M.A. Juliarena et al., 2017). In our report, we retrospectively compare the experience of BLV eradication in the USSR, Russia and abroad, additionally focusing on the possible role of this pathogen in the occurrence of cancer in humans. In veterinary practice, serological tests, i.e., immunodiffusion (ID) assay in agar gel and enzyme-linked immunosorbent assay (ELISA) are mostly used to detect the BLV infection. G.C. Buehring et al. (2019) reported the detection of BLV proviral DNA in blood leukocytes in 38 % of patients examined by PCR and DNA sequencing. IgG antibodies to BLV were detected in 32 %, IgM - in 58 %, and IgA - in 32 % of the samples tested. Accumulated data indicate metabolic changes in the BLV-positive animals, e.g., disorder in the metabolism of tryptophan, a critical essential acid, leading to the accumulation of dangerous endogenous metabolites in the body. Particularly, free tryptophan, indole and anthranilic acid increased in level 4-8-fold are deposited in the organs of the immune and hematopoietic system (lymph nodes, spleen, liver), in the mammary gland, lungs, and kidneys. It has been established that the milk of leukemic animals differs from the milk of healthy cows in terms of physicochemical, bacteriological (lysozyme), technological parameters and mineral composition. In C57 mice fed with pasteurized milk and heat-treated meat from ID-positive cows, the blood cell profile changed. Available data drive to the unambiguous conclusion that the products derived from BLV-infected cattle pose an increased risk to humans. Despite the lack of convincing evidence of the BLV pathogenicity for humans, concerns about the etiological role of this virus in the occurance of cancer in humans additionally necessitates continuing research on the control and eradication of this common oncogenic retro-virus in livestock farms.