Abstract
Bovine leukemia virus (BLV) is a retrovirus closely related to the human T-lymphotropic virus type 1 (HTLV-1). BLV is a major animal health problem worldwide causing important economic losses. A series of attempts were developed to reduce prevalence, chiefly by eradication of infected cattle, segregation of BLV-free animals and vaccination. Although having been instrumental in regions such as the EU, these strategies were unsuccessful elsewhere mainly due to economic costs, management restrictions and lack of an efficient vaccine. This review, which summarizes the different attempts previously developed to decrease seroprevalence of BLV, may be informative for management of HTLV-1 infection. We also propose a new approach based on competitive infection with virus deletants aiming at reducing proviral loads.
Highlights
As early as in the 19th century, a series of reports already described the occurrence of clinical signs associated with enzootic bovine leukosis (EBL)
Alone had no effect in simian T lymphotropic virus type 1 (STLV-1) infected monkeys but significantly reduced the proviral load (PVL) when combined with AZT [167]
When the PVLs are high, human T-lymphotropic virus type 1 (HTLV-1) transmission could be impaired with anti-retroviral drugs such as AZT
Summary
As early as in the 19th century, a series of reports already described the occurrence of clinical signs associated with enzootic bovine leukosis (EBL). Diffusion and wide spread of the disease occurred by the introduction of European cattle breeds in countries free of the disease Despite all these pieces of evidence, the infectious nature of EBL etiological agent was discovered many decades later based on epidemiological evidence [7]. The great majority of BLV-infected animals (around 70%) are asymptomatic carriers of the virus In these animals, neither clinical symptoms nor alteration of the total lymphocyte count are evidenced. One-third of BLV-infected bovines develop a benign polyclonal proliferation of B cells called persistent lymphocytosis (PL). This clinical condition is characterized by an increase in the absolute number of peripheral blood circulating B lymphocytes associated with an inversion of the B/T lymphocyte ratio [9,14,17,18]. Besides an impact on survival, BLV infection impairs the immune system leading to opportunistic infections [25,26,27]
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