The bovine leukemia virus (BLV) causes leukemia or lymphoma in cattle. Although most BLV-infected animals do not develop the disease, they maintain the transmission chain of BLV at the herd level. As a feasible approach to control the virus, selection of cattle carrying the BoLA-DRB3*0902 allele has been proposed, as this allele is strongly associated with a BLV infection profile or the low proviral load (LPL) phenotype. To test whether these cattle affect the BLV transmission chain under natural conditions, selected BLV-infected LPL-BoLA-DRB3*0902 heterozygous cows were incorporated into a BLV-negative dairy herd. An average ratio of 5.4 (range 4.17-6.37) BLV-negative cows per BLV-infected cow was maintained during the 20mo of the experiment, and no BLV-negative cattle became infected. The BLV incidence rate in this herd was thus zero, whereas BLV incidence rates in different local herds varied from 0.06 to 0.17 cases per 100 cattle-days. This finding strongly suggests that LPL-BoLA-DRB3*0902 cattle disrupted the BLV-transmission chain in the study period.
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.
La leucosis bovina enzoótica, causada por el virus de la leucosis bovina (BLV), es la enfermedad tumoral más frecuente del bovino. Las razas bovinas de leche y de carne son susceptibles a la infección por BLV y al linfosarcoma; sin embargo la enfermedad es más prevalente en rodeos lecheros, principalmente debido a las prácticas de manejo. La patogenicidad del BLV en el bovino está asociada a la genética del animal. La mayoría de los bovinos infectados por el BLV son asintomáticos, por lo que la infección puede pasar desapercibida cuando los índices de infección son relativamente bajos. En ausencia de medidas de control, el virus se disemina lentamente entre los animales del rodeo. El BLV causa importantes pérdidas productivas, no sólo debido a la mortandad de animales con linfosarcoma, sino también por las restricciones al comercio de animales infectados y sus subproductos. Existen distintas alternativas para el control del BLV, adecuadas para distintas situaciones epidemiológicas. Hasta el momento no existe ningún tratamiento o vacuna eficaz para el control de este virus. Cuando la prevalencia de infección es baja, inferior al 10-15% de animales infectados, se recomienda identificar y eliminar la totalidad de los animales infectados. Esta alternativa no se adecúa a rodeos con altas prevalencias de infección, como ocurre con la mayoría de los rodeos lecheros en Argentina. La selección genética de animales resistentes a la diseminación del BLV surge como una estrategia natural para limitar la diseminación de este virus y, por ende, para el control del linfosarcoma asociado.
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