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Abstract :

The Bluetongue virus serotype 8 (BTV-8) emerged in northern Europe in 2006 causing economic losses in cattle herds. Vaccination has been implemented in France without ex ante evaluation of the risk-benefit ratio. No estimation of losses due to the disease and possible vaccination adverse effects has been performed. The objectives of this thesis were (1) to quantify the average effects of exposure to BTV-8 in dairy herds on milk production and reproductive performance of dairy cows, (2) to quantify the effect of vaccination on fertility and (3) to evaluate whether variation in fertility could contribute to the description of the epizootic spread. The effects of exposure and vaccination were quantified using multivariable statistical models which allowed to take into account known factors that influence performance. Exposure to BTV-8 in dairy herds was associated with an important decrease in fertility and milk production, and with an important increase in abortion risk. Losses increased with the proportion of infected neighbouring herds and decreased when the disease detection was late during the epizootic. The vaccination against BTV-8 using inactivated vaccines was associated with a slight decrease in fertility which had a very limited impact compared to the impact of exposure. A decrease in fertility in non case herds located in the exposed area indicated that some of these herds were infected during the 2007 epizootic. These results could contribute to the evaluation of BTV control measures and surveillance.

Key words :

Bluetongue, dairy cows, performance, epidemiology, statistical models, vaccination