Abstract
Bovine leukaemia virus (BLV) is a deltaretrovirus that is closely related to human T-cell leukaemia virus types 1 and 2 (HTLV-1 and -2). It causes enzootic bovine leukosis (EBL), which is the most important neoplastic disease in cattle. Most BLV-infected cattle are asymptomatic, which potentiates extremely high shedding rates of the virus in many cattle populations. Approximately 30% of them show persistent lymphocytosis that has various clinical outcomes; only a small proportion of animals (less than 5%) exhibit signs of EBL. BLV causes major economic losses in the cattle industry, especially in dairy farms. Direct costs are due to a decrease in animal productivity and in cow longevity; indirect costs are caused by restrictions that are placed on the import of animals and animal products from infected areas. Most European regions have implemented an efficient eradication programme, yet BLV prevalence remains high worldwide. Control of the disease is not feasible because there is no effective vaccine against it. Therefore, detection and early diagnosis of the disease are essential in order to diminish its spreading and the economic losses it causes. This review comprises an overview of bovine leukosis, which highlights the epidemiology of the disease, diagnostic tests that are used and effective control strategies.
Highlights
Bovine leukaemia virus (BLV) is a deltaretrovirus that belongs to the Retroviridae family.It is closely related to human T-cell leukaemia virus types 1 and 2 (HTLV-1 and -2) [1,2] and to simian T-cell leukaemia viruses (STLVs)
The age of cattle plays a pivotal role in the seroprevalence of BLV, which increases with age until cattle older than two years show seroprevalence rates that are almost twice those found in younger animals [123]
This study showed that passage was via a blood-borne pathogen, such as HTLV-1 or HTLV-2 [1]
Summary
Bovine leukaemia virus (BLV) is a deltaretrovirus that belongs to the Retroviridae family. The disease causes huge economic losses worldwide through both direct and indirect costs: directly because milk production is reduced, the disease has an extreme impact on reproduction, and some cows must be culled prematurely; and indirectly because imports are restricted of animals from BLV-infected areas [11,12,13,14,15]. For these reasons, the World Organisation for Animal Health (OIE) has listed EBL as a disease that can cause drastic impacts on international trade [16]. The aim of this review is to highlight the current epidemiological situation regarding BLV infection and to provide information about some strategies that can be used to fight the disease worldwide, with special reference to some future prospective studies
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