Current Developments in the Epidemiology and Control of Enzootic Bovine Leukosis as Caused by Bovine Leukemia Virus

Abstract

Enzootic Bovine Leukosis (EBL) caused by the bovine leukemia virus (BLV) has been eradicated in over 20 countries. In contrast, the U.S. and many other nations are experiencing increasing prevalence in the absence of efforts to control transmission. Recent studies have shown that BLV infection in dairy cattle has a greater impact beyond the long-recognized lymphoma development that occurs in <5% of infected cattle. Like other retroviruses, BLV appears to cause multiple immune system disruptions, affecting both cellular and humoral immunity, which are likely responsible for increasingly documented associations with decreased dairy production and decreased productive lifespan. Realization of these economic losses has increased interest in controlling BLV using technology that was unavailable decades ago, when many nations eradicated BLV via traditional antibody testing and slaughter methods. This traditional control is not economically feasible for many nations where the average herd antibody prevalence is rapidly approaching 50%. The ELISA screening of cattle with follow-up testing via qPCR for proviral load helps prioritize the most infectious cattle for segregation or culling. The efficacy of this approach has been demonstrated in at least four herds. Breeding cattle for resistance to BLV disease progression also appears to hold promise, and several laboratories are working on BLV vaccines. There are many research priorities for a wide variety of disciplines, especially including the need to investigate the reports linking BLV and human breast cancer.

Bovine Leukaemia Virus: Current Epidemiological Circumstance and Future Prospective

“…Traditional management practices are recommended for the control of BLV transmission, including: the single use of hypodermic needles and reproductive examination sleeves; use of AI instead of natural breeding; control of biting arthropods; feeding calves only heat-treated colostrum or colostrum replacements; and the cleaning and disinfection of blood-contaminated equipment that is reused during surgical operations, such as application of ear tags, tattooing, and dehorning through use of chloroform, ether, and UV. Application of all these practices might eventually reduce the prevalence of BLV-infected cattle to a sufficiently low level to introduce a test and cull policy [39,219]. Moreover, vertical disease spread can be avoided by the freezing and thawing of the colostrum and milk (at −25 • C for one night followed by thawing) before feeding calves.…”

Evidence of bovine leukemia virus circulating in sheep and buffaloes in Colombia: insights into multispecies infection

“…The presence of BLV in multiple species, its high prevalence rate (62%) in cattle in Colombia [40], and the potential for co-circulation of the virus in cattle and humans [33] should raise concerns for regulatory agencies and livestock producers, as BLV infections are unfavorable for the animal production sector [16,17], and the zoonotic potential of the virus has implications for human health [31,74]. Accumulating evidence in the literature suggesting that BLV can infect multiple species should raise concerns about elevated dissemination rates on mixed-species farms, in wildlife reservoirs, and in accidental hosts, which could hamper prevention and control strategies to stop the spread of the virus.…”

“…The other 30% develop persistent lymphocytosis, and between 5 and 10% develop leukemia/lymphoma, which is the most advanced stage of the disease [15]. BLV infection leads to economic losses in the livestock industry, as it increases the risk of secondary infections in the host, decreases milk production, favors weight loss, and increases the risk of abortions and other unfavorable clinical outcomes [16,17].…”

Improving of the Nested PCR for Detection of Bovine Leukemia Virus

“…The virus causes a persistent, life-long infection in a subset of B-cells. Malignant tumors (lymphomas) ultimately develop in 2-5 % of infected animals predominantly in adult cattle older than 3-5 years [1][2][3][4]. Nowadays EBL is seen general biological importance because BLV is structurally and functionally related to other primate and human retroviruses (primate T-lymphotropic virus 1, 2 and 3 (PTLV-1, -2, -3).…”

“…In the last years topicality of the BLV is increasing in view of new information related to human breast cancer [21]. It leads to new research in this area and the development of new methods of BLV identification in cattle to eradicate infected animals [17,18,[22][23][24][25][26].…”