Bluetongue virus serotype 8 infection and performance in dairy cattle herds

National and/or international context/ issues/ problematic

Following the emergence of BTV-8 in Northern Europe in 2006, vaccination was introduced in France to limit the spread of the virus. No ex ante evaluation of the benefit/risk ratio of vaccination has been performed. This type of assessment requires knowledge, in particular about losses caused by the disease and potential side effects of vaccination on cattle performance.

Exposure to BTV-8 on performance leads to a degradation of the zootechnical performance of the animals: decreases in reproductive performance and milk production. However, the associated losses have not been precisely quantified.

Results

BTV-8 infection in a previously naïve cattle population is associated with reduced milk production performance and fertility and an increased risk of abortion. These effects are important in terms of magnitude and duration (3% decrease in milk production over a 6-month period and 12% decrease in fertility on average in infected herds where clinical signs have been observed and reported).

Decreases in fertility have also been detected in herds not reported infected by the surveillance system and located in areas of the epizootic. This effect corresponds to 60% of the effect quantified in the notified infected herds. This effect could be estimated using an innovative spatial statistical method, kriging, which made it possible to predict a probable date of infection for these herds. Considering the effects at the scale of a region, the cumulative losses of infection are therefore significant. Decreases in animal performance also provide additional information from disease surveillance on the likely date of virus introduction into the herds. Indeed, declines in performance are detectable on average a few weeks before signs are detected. They are also very early in herds where the disease was detected late. This indicates that virus circulation in the herds is generally earlier (up to 10 weeks) than the detection of infection by the farmers.

Finally, vaccination against BTV-8 with an inactivated vaccine is associated with a very slight decrease in fertility (4%). The major performance losses associated with exposure, compared to the very limited side effects of vaccination, seem to justify the strategies that have been implemented in the field.

Perspectives/eventual impact

Quantification of the performance effects of BTV-8 and vaccination against BTV-8 are useful (i) for the economic evaluation of the consequences of this epizootic and (ii) for the evaluation of control strategies against BTV-8 (e.g. evaluation of the benefit-risk ratio of vaccination). The evaluation of these strategies a posteriori provides valuable elements of decision support, which can be mobilised in the event of a re-emergence of the virus.

In view of the performance variations revealed in infected herds, it would be interesting to assess whether monitoring performance variations can be integrated as an alert system within the framework of syndromic surveillance of the emergence of epizootic diseases (study in progress within the UMR). This requires prior study of the capacity of such a system to rapidly detect deviations from expected performance, without having a priori information on the occurrence and timing of herd exposure in a region.

Partners

Union Bretonne des Groupements de Défense Sanitaire, Direction Générale de l'Alimentation (Brittany Union of Health Defence Groups)

Valorisation

Communication of the results in working groups with stakeholders in health management and contribution to the drafting of documents for livestock advisors and breeders :

• Special file Catarrhal Ovine Fever. Sanitary echo. The newsletter of the Breton GDS. Dec. 2010
• Vaccination against CFO: what impact on the fertility of cattle herds? The Institute of Animal Husbandry. Collection l'essentiel. June 2012

Publications

• Nusinovici S, Seegers H, Joly A, Beaudeau F, Fourichon C. 2011. A side effect of decreased fertility associated with vaccination against bluetongue virus serotype 8 in Holstein dairy cows. Prev. Vet. Med. 101:42-50
• Nusinovici, S., H. Seegers, A. Joly, F. Beaudeau, and C. Fourichon. 2012a. Quantification and at-risk period of decreased fertility associated with exposure to Bluetongue virus serotype 8 in naïve dairy herds. Journal of dairy science 95:3008-20
• Nusinovici, S., H. Seegers, A. Joly, F. Beaudeau, and C. Fourichon. 2012b. Increase in the occurrence of abortions associated with exposure to Bluetongue virus serotype 8 in naïve dairy herds. In press. Theriogenology 78:1140-51
• Nusinovici S, Souty C, Seegers H, Beaudeau F, Fourichon C. Decrease in milk yield associated with exposure to Bluetongue virus serotype 8 in cattle herds. En révision (Journal of dairy science)
• Nusinovici S, Seegers H, Souty C, Monestiez P, Joly A, Beaudeau F, Fourichon C. Infection par le virus Bluetongue sérotype 8 et performances dans les troupeaux bovins laitiers. Bulletin épidémiologique, santé animale et alimentation n°51 p 13
• Nusinovici S. Infection par le virus Bluetongue sérotype 8 et performances dans les troupeaux bovins laitiers. Thèse d’université soutenue le 16 décembre 2011, Oniris, Nantes