New clinical pattern of Bluetongue serotype 8 in continental France

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Zientara, Stéphan | Vinomack, Chloé | Bréard, Emmanuel | Viarouge, Cyril | Postic, Lydie | Belbis, Guillaume | Rivière, Julie | Sailleau, Corinne | Vitour, Damien | Zanella, Gina

Edité par CCSD -

International audience. France is infected with two Bluetongue serotypes, BTV-4 and BTV-8. Since mid-December 2018, cases of calves born blind, puny and dying in a few days or weeks have been reported in different departments in continental France. The brains of these calves showed hydranencephaly lesions. Since January 2019, the number of reported cases has increased considerably. According to analyses carried out in departmental laboratories (positive PCR on calf blood samples) and in the Maisons-Alfort animal health laboratory of the NRL-ANSES (BTV National reference laboratory) (positive PCR in the blood and calves' spleen), it is very likely these clinical signs are attributable to bluetongue virus serotype 8 (BTV-8). Indeed, the NRL tested brains of these calves which proved to be negative for the Schmallenberg virus, another possible cause of this type of clinical manifestation. The detection of PCR-positive calves, less than one week old and born during the vector inactivity season, suggests that they were infected in utero. It appears that in infected farms, 2% to 15% of newborn calves were affected by these clinical manifestations. Investigations are under way to study this phenomenon more precisely, in partnership with local services. As of March 2019, the NRL has received and analyzed 418 blood samples from such calves (94% were serotype 8 RT-PCR positive).After a brief description of BTV emergence in France, this paper will describe the new clinical and epidemiological pattern of BTV-8 in France and the molecular characterization of four BTV-8 isolates obtained from “dummy” calves.

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