Bovine leukemia virus: current perspectives

Abstract

Enzootic bovine leukosis, caused by bovine leukemia virus (BLV), is the most common neoplasm of dairy cattle. Although beef and dairy cattle are susceptible to BLV infection and BLV-associated lymphosarcoma, the disease is more commonly detected in dairy herds, mostly because of the management practices in dairy farms. The pathogenicity of BLV in its natural host, the bovine, depends mainly on the resistance/susceptibility genetics of the animal. The majority of infected cattle are asymptomatic, promoting the extremely high dissemination rate of BLV in many bovine populations. The important productive losses caused by the BLV, added to the health risk of maintaining populations with a high prevalence of infection with a retrovirus, generates the need to implement control measures. Different strategies to control the virus have been attempted. The most effective approach is to identify and cull the totality of infected cattle in the herd. However, this approach is not suitable for herds with high prevalence of infection. At present, no treatment or vaccine has proven effective for the control of BLV. Thus far, the genetic selection of resistant animals emerges as a natural strategy for the containment of the BLV dissemination. In natural conditions, most of the infected, resistant cattle can control the infection, and therefore do not pass the virus to other animals, gradually decreasing the prevalence of the herd.

Polymorphism of Haplotypes of Bovine Leukemia Virus

“…Data from the previous study indicate an increase in viral load and white blood cell count when C> G is replaced [38], which clearly refutes the assumption that the BLV masking vector is determined by the LRT region. A comparison of our own studies and published data [2,19,36] more likely confirms the hypothesis about the function of the LRT region a regulator of the viral particles synthesis. Taking into account the principles of genetic control, it is difficult to predict [14] that the regulator itself could be a factor in recognition of the virion by the host's immune system on the basis of the "friend or foe" principle.…”

“…It is noteworthy that only 25% of all selected infected animals did not show clinical signs of leukemia expressed by the leukocyte formula. Earlier studies show that the latent leukemia is characteristic for at least 70% of the carriers [2,35,36]. Moreover, both BLV haplotypes are more aggressive in this study, causing a large proportion of clinical cases of leukemia, even in comparison with the results of typing of animals from other farms in the Novosibirsk Region [31].…”

“…At present, leukemia is the most common epizootic disease of cattle in Russia and an in number of foreign countries [1][2][3]. It is the cause of 40% to 66% of infectious pathologies of cattle [4,5].…”

“…It is known that the so-called mutator genes that catalyze mutagenesis are localized in the LTR region of BLV [2]. Some studies have shown the relationship of mutations in the LTR region of BLV with the characteristics of the course of infection [2,26].…”

“…It is known that the so-called mutator genes that catalyze mutagenesis are localized in the LTR region of BLV [2]. Some studies have shown the relationship of mutations in the LTR region of BLV with the characteristics of the course of infection [2,26]. Long circular repeats of the proviral DNA of the BLV virus contain sequences predisposed to the formation of such noncanonical DNA structures as G4 quadruplexes [11,25,27] and triplexes [28].…”