Evaluation of natural transmission of bovine leukaemia virus within dairy herds of Argentina

Abstract

SUMMARYThe purpose of this study was to describe patterns of seroconversion to bovine leukaemia virus and to estimate the main parameters needed for future model building. A longitudinal study was carried out between February 1999 and November 2001 in seven commercial dairy farms in Argentina using 1535 lactating cows. Time-interval parameters were analysed using a parametric survival model with shared frailty, time until infection was analysed using a Bayesian intervalcensoring survival model and the infection transmission parameter (b) was estimated by a generalized linear model. The reproduction ratio (R 0 ) was calculated. In total, 1000 cows tested positive and 494 tested negative. The predicted median age at infection was 4 . 6 years for seroconverted cows. For infected herds, the proportion of positive calves was as high as for infected cows and showed a large proportion of infected breeding heifers. Peaks in the overall average incidence per season-year were observed during autumn and spring. Results reveal that the period around parturition is a high-risk period. Moreover, heavily infected herds seem to have an increased proportion of young stock infected. The overall b was estimated as 2 . 9/year (95 % CI 1 . 9-3 . 7) and combined with a relatively long infectious period it resulted in a high reproductive ratio (R 0 =8 . 9). Therefore, a high effectiveness of control measures needs to be achieved to eradicate the disease.

Tumorigenesis related to retroviral infections

“…Several leukemia-related retroviruses are transmitted via infected cells [56]. For example, bovine leukemia virus (BLV) that causes enzootic bovine leucosis, characterized by lymphosarcoma in cattle [57], can be transmitted by different routes including oral inoculation of BLV infected cells [32], vertical transmission, or insect bites [58].…”

“…There is an increasing incidence of AIDS-related diseases in countries where antiretroviral medications are not yet widely available [39,60]. Moreover, BLV-associated lymphomas in cattle create another issue that has a great economic impact on the livestock sector for many countries, especially in low-income regions [58]. Although the prevalence of non-Hodgkin lymphoma is higher in developed countries, the ratios of mortality-to-incidence rates are higher in the lowand middle-income countries [61].…”

Transmission of bovine leukaemia virus within dairy herds by simulation modelling

“…Parameter values for disease transmission were derived from previously published data [8] (Table 2) and were assumed to be constant over time and equal for the three age groups. Mortality related to BLV infection was only considered for the adult age group because the time needed to develop tumours is longer than the rearing period from calf to adult [12].…”

“…Due to the stochastic nature of the infection process there will be some probability that minor outbreaks will take place and infection will go extinct by chance. In our previous study [8], using data obtained from an observational study we estimated the value of R 0 as 8 . 8.…”

Enzyme-Linked Immunosorbent Assays Using the Recombinant gp51 and p24 of Bovine Leukemia Virus for Immunodetection of the Disease

“…The economic impact of this disease lies not only in direct losses for confiscation at the slaughterhouse, but also the associated carrier status of the animal, with an important decrease in animal productivity [4]; that also include the costs of veterinary services, diagnosis and treatment of the disease, as well as the costs of early animal replacement [5].…”