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Over the past decade, several insect-borne viral diseases have emerged in European ruminants. This is the case of Bluetongue Virus (BTV) serotype 8 bluetongue (BTV), which, after having already appeared in 2007, spread again in France in 2015. An initial study conducted at the BioEpAR joint research unit identified that increasing the proportion of dairy cows with a short gestation period (below the first quartile of the distribution considered normal, i.e. less than 279 days in the Holstein breed - where the average gestation period ranged from 282 days in the Holstein breed to 287 days in the Montbeliarde breed) could be of interest in detecting a bluetongue epidemic. The objective of this second study was to quantify the increase in the frequency of short gestation periods in herds exposed to the virus, distinguishing between farms for which at least one clinical case had been reported and those for which no report had been made.

Exposure to the virus was found to be associated with an increase in the frequency of short gestation in both categories of holdings. However, they were particularly more frequent in flocks with formally reported clinical signs. Finally, the increase in the frequency of short gestation was higher when the cows were exposed to the virus at an advanced stage of gestation. The increase was greatest in herds with reported clinical signs of disease and when virus exposure occurred at an advanced stage of gestation. The frequency of short gestation periods was 19.4% in the absence of virus exposure and 33.6% in cows exposed between 270 and 278 days of gestation (+14.2%).

To our knowledge, this study is the first to quantify the effect associated with virus exposure in cattle. However, the underlying pathophysiological mechanisms remain to be demonstrated. However, our study confirms, for diseases giving rise only to inconsistent and discrete and/or non-specific or non-specific clinical signs, the interest of monitoring the frequency of short gestation periods as an indicator of suspected emergence or reintroduction in a territory.

Partners: this work was carried out in the BioEpAR joint research unit.

Related publication : Nusinovici, S., Madouasse, A., Fourichon, C., 2016. Quantification of the increase in the frequency of early calving associated with late exposure to bluetongue virus serotype 8 in dairy cows: implications for syndromic surveillance. Vet. Res. 47, 18. doi:10.1186/s13567-015-0296-7

Contacts

Scientific contact :

•  Aurélien Madouasse UMR BIOEPAR

Associated Department : Santé animale

Associated Centre: Angers-Nantes Pays de la Loire