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Quantifying bluetongue vertical transmission in French cattle from surveillance data

Courtejoie, Noémie, Bournez, Laure, Zanella, Gina, Durand, Benoît
Veterinary research 2019 v.50 no.1 pp. 34
Bluetongue virus, bluetongue, heifers, livestock and meat industry, models, monitoring, pregnancy, probability, reverse transcriptase polymerase chain reaction, serotypes, transplacental transmission, vector-borne diseases, virus transmission, France
Bluetongue is a vector-borne disease of ruminants with economic consequences for the livestock industry. Bluetongue virus serotype 8 (BTV-8) caused a massive outbreak in Europe in 2006/2009 and re-emerged in France in 2015. Given the unprecedented epidemiological features of this serotype in cattle, the importance of secondary routes of transmission was reconsidered and transplacental transmission of BTV-8 was demonstrated in naturally and experimentally infected cattle. Here we used surveillance data from the on-going outbreak to quantify BTV-8 vertical transmission in French cattle. We used RT-PCR pre-export tests collected from June to December 2016 on the French territory and developed a catalytic model to disentangle vertical and vector-borne transmission. A series of in silico experiments validated the ability of our framework to quantify vertical transmission provided sufficient prevalence levels. By applying our model to an area selected accordingly, we estimated a probability of vertical transmission of 56% (55.8%, 95% credible interval 41.7–70.6) in unvaccinated heifers infected late in gestation. The influence of this high probability of vertical transmission on BTV-8 spread and persistence should be further investigated.