Bluetongue Serotype 8 Epizootic Wave, France | CDC EID

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Volume 16, Number 12–December 2010
Research
Anatomy of Bluetongue Virus Serotype 8 Epizootic Wave, France, 2007–2008

Benoit Durand, Comments to Author Gina Zanella, Fabienne Biteau-Coroller, Caroline Locatelli, Florence Baurier, Cécile Simon, Eric Le Dréan, José Delaval, Eric Prengère, Véronique Beauté, and Hélène Guis
Author affiliations: Agence Française de Sécurité Sanitaire des Aliment, Maisons-Alfort, France (B. Durand, G. Zanella); Centre International de Recherche Agronimique pour le Développement, Montpellier, France (F. Biteau-Coroller, H. Guis); Laboratoire Départemental d'Analyses 08, Hagnicourt, France (C. Locatelli); Laboratoire Départemental d'Analyses 18, Bourges, France (F. Baurier, C. Simon); Laboratoire Départemental d'Analyses 35, Rennes, France (E. Le Dréan); Laboratoire Départemental d'Analyses 36, Chateauroux, France (J. Delaval); Laboratoire Départemental d'Analyses 37, Tours, France (J. Delaval, E. Prengère); and Laboratoire Départemental d'Analyses 49, Angers, France (V. Beauté)

Suggested citation for this article

Abstract
The introduction of bluetongue virus serotype 8 into northern Europe at the end of summer 2006 initiated one of the most widespread epizootics of bluetongue infection ever to occur. In winter 2007–2008, a cross-sectional serologic study was conducted in France along a transect perpendicular to the epizootic wave. Cattle herd-level seroprevalence varied from 4% to 100%, and animal-level seroprevalence from <1% to 40%. Only a low proportion of seropositive herds reported clinical cases in 2007. Sheep flocks were less frequently affected than cattle herds. The local occurrence of clinical cases and environmental indicators linked to forests were seropositivity risk factors, whereas the local density of cows had a protective effect. Overall results suggest that amplification of virus circulation in affected herds played a limited role in the epizootic wave diffusion and that bluetongue virus serotype 8 circulation in natural ecosystems could have played a substantial role in this progression. Bluetongue is a vector-borne viral disease of wild and domestic ruminants caused by Bluetongue virus (BTV; family Reoviridae, genus Reovirus). Twenty-four serotypes of this virus are described, principally transmitted by several species of biting midges belonging to the genus Culicoides (Diptera: Ceratopogonidae). Until 1998, Europe was considered BTV free except for occasional incursions into the Iberian Peninsula, Cyprus, and Greek islands. In 1998, an unprecedented series of successful introductions of BTV serotypes occurred in countries in southern, western, and central Europe (1). Unexpectedly, in 2006, BTV serotype 8 (BTV-8) was introduced in Belgium, close to the borders with Germany and the Netherlands (2,3), and quickly spread in these 3 countries. By the end of 2009, BTV-8 had spread to most countries in western and central Europe, including the United Kingdom, Denmark, Norway, Sweden, Czech Republic, Hungary, Austria, Italy, Luxembourg, Spain, and France. In France, the first clinical case was reported in late August 2006 near the border with Belgium. In July 2007, bluetongue reappeared there (4) and quickly progressed westward and southward, with the virus causing clinical cases in 10,500 herds in 2007 and in 26,500 herds in 2008. By the end of 2007, BTV-1 was introduced in southern France, resulting in a second epizootic wave that progressed northward during 2008; by late 2008, most of the French territory had been affected by BTV-1, BTV-8, or both serotypes (Appendix Video). A vaccination campaign launched in 2008 stopped the epizootic in 2009. During the winter of 2007–2008, the end of BTV transmission (during the vector inactivity period) offered the opportunity to study the epizootic wave. The objectives of this study were to describe the first of these 2 epizootic waves and to analyze the respective parts played by within- and between-herd dynamics in BTV-8 progression, the relationship between the progression of infection and that of clinical cases, and the environmental features that influenced the progression of BTV-8. Materials and Methods

Seroprevalence rates were estimated at the herd and animal levels in cattle and sheep along an east–west transect perpendicular to the epizootic wave. By comparing serologic results with clinical outbreaks, we estimated the proportion of silently infected herds or flocks (i.e., herds in which BTV-8 had circulated without any reported clinical cases) and variations in the outbreak along the transect. Main herd-level seropositivity risk factors were investigated (species, occurrence of clinical cases), as well as local seropositivity risk factors (animal density, land cover and landscape indices, occurrence of clinical cases).

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Suggested Citation for this Article

Durand B, Zanella G, Biteau-Coroller F, Locatelli C, Baurier F, Simon C, et al. Anatomy of Bluetongue virus serotype 8 epizootic wave, France, 2007–2008. Emerg Infect Dis [serial on the Internet]. 2010 Dec [date cited].
http://www.cdc.gov/EID/content/16/12/1861.htm

DOI: 10.3201/eid1612.100412

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Benoit Durand, Anses, Laboratoire de Santé Animale, 23 avenue du Général de Gaulle, 94706 Maisons-Alfort CEDEX, France; email: benoit.durand@anses.fr