Invited review: Bovine leukemia virus—Transmission, control, and eradication

Abstract

Bovine leukemia virus (BLV) infection, endemic in North American dairy herds, has production-limiting effects. A literature review of available papers published since 1995 concerning BLV transmission and its control was conducted. Although confirmed transmission routes were reviewed (blood, natural breeding, in utero, colostrum, and milk), there is still a lack of detailed information on other specific risks for transmission (e.g., contact transmission and hoof-trimming knives). Eradication of BLV has been achieved by combined management, segregation, and culling approaches. In contrast, although sole implementation of best management practices aimed at prevention of BLV transmission has decreased within-herd BLV prevalence, it has not eradicated BLV from a herd. Therefore, control and eradication of BLV by best management practices only should be further investigated. Additionally, the role of proviral load in infected cattle was investigated. Cattle with a high proviral load seem to be more likely to infect others, whereas those with a very low proviral load seem to have low risks of transmitting BLV. Information on proviral load could be taken into account when controlling BLV in high-prevalence herds. In conclusion, there is a need for detailed, large-scale studies investigating roles of specific transmission routes, knowing proviral load of infected individuals.

Assessment of Natural Transmission of Bovine Leukemia Virus in Dairies from Southern Chile

“…It does not necessarily indicate a different susceptibility due to age or a relationship between age and viral load, as other studies have attempted to establish and failed to do [38]. One limitation of this study was that we did not include young calves that could also be infected and spread the virus given that vertical transmission is documented [39,40].…”

Diagnosis of Ruminant Viral Diseases with Loop-Mediated Isothermal Amplification

“…Recently, BLV was found to be in circulation in sheep in Colombia [ 45 ]. Infection affects B cells in cattle, impairs the immune system, reduces milk yield, shortens lifespan, and causes tumor formation in approximately 1–5% of animals [ 46 , 47 ]. BLV infection spread to the herd during standard farm practices via infected blood or bodily fluids and vertical transmission is possible to the fetus as well [ 48 ].…”

Dairy Cows Experimentally Infected With Bovine Leukemia Virus Showed an Increased Milk Production in Lactation Numbers 3–4: A 4-Year Longitudinal Study

“…Therefore, the possible effects of BLV infection on dairy cattle, including reduced milk yield, increased somatic cell count (SCC), and early slaughter, have attracted more attention (Erskine et al, 2012 ; Bartlett et al, 2013 ) because the positive rates are higher with the extension of feeding time than those in beef cattle. In the absence of an effective treatment and commercial vaccines, quarantine and early slaughter are the only feasible ways to control the transmission of BLV (Kuczewski et al, 2021 ). BLV was only eradicated from some Western European countries, Australia, and New Zealand and was endemic in other countries, including China, Brazil, and the United States (LaDronka et al, 2018 ; Ma et al, 2021 ; Ramalho et al, 2021 ).…”

“…BLV naturally infects cattle ( Bos taurus and Bos indicus ), buffaloes ( Bubalus bubalis ), and capybaras ( Hydrochoerus hydrochaeris ) and can experimentally challenge and generate an immune response in a wide range of animal species, including sheep, goat, pig, rabbit, rat, and chicken (Mammerickx et al, 1981 ; Olson et al, 1981 ; Altanerova et al, 1990 ; Kucerova et al, 1999 ; Krasnikova et al, 2019 ; Porta et al, 2019 ). Among these animals, sheep was most commonly employed as they develop tumors earlier and more frequently following challenge (Kuczewski et al, 2021 ). Most of the studies carried out the cytodynamics in BLV-infected ewes as a model; nonetheless, there are significant differences between cattle and ewes in the response to BLV infection (Florins et al, 2007 ).…”