Highly Pathogenic Avian Influenza A(H5N8) Virus Spread by Short- and Long-Range Transmission, France, 2016-17

Abstract

We detected 3 genotypes of highly pathogenic avian influenza A(H5N8) virus in France during winter 2016-17. Genotype A viruses caused dramatic economic losses in the domestic duck farm industry in southwestern France. Our phylogenetic analysis suggests that genotype A viruses formed 5 distinct geographic clusters in southwestern France. In some clusters, local secondary transmission might have been started by a single introduction. The intensity of the viral spread seems to correspond to the density of duck holdings in each production area. To avoid the introduction of disease into an unaffected area, it is crucial that authorities limit the movements of potentially infected birds.

Keywords: France; H5N8; avian influenza; epizootic; evolution; genotypes; geoclusters; highly pathogenic; highly pathogenic avian influenza; influenza; transmission; viral zoonoses; viruses; zoonoses.

Figure 1

Distribution of highly pathogenic avian influenza H5N8 cases, France, 2016–17 (database of the French National Reference Laboratory for Avian Influenza). Blue indicates cases in wild birds; red indicates cases in domestic or captive birds. Dashed circles indicate zones of high duck farm density (34).

Figure 2

Distribution of the 3 detected genotypes of highly pathogenic avian influenza H5N8 viruses, France, 2016–17. A) Geographic distribution of genotypes. B) Representation of viral genome. Horizontal bars correspond to the 8 gene segments of each characterized genotype. Segments colored according to phylogenetic cluster.

Figure 3

Minimum spanning tree and map of clusters of highly pathogenic avian influenza H5N8 genotype A viruses, France, 2016–17. A) Geographic clusters. Number of dashes indicates the number of observed mutations between 2 nodes. Circle size corresponds to the number of identical sequences. B) Geographic repartition of genotype in southwestern France. Inset shows identification numbers of affected departments: 12, Aveyron; 31, Haute-Garonne; 32, Gers; 47, Lot et Garonne; 40, Landes; 64, Pyrénées-Atlantiques; 65, Hautes-Pyrénées. Trees created using PopART (32).

Figure 4

Maximum credibility tree of the 8 concatenated gene segments in highly pathogenic avian influenza H5N8 genotype A viruses, France, 2016–17. Tree generated using SDR06 model according to Bayesian method (38). Branch and leaf color indicates geoclusters. The estimated dates of common ancestors and their 95% CIs are indicated for geocluster 1 and geocluster 5

Figure 5

Evolution of highly pathogenic avian influenza H5N8 genotype A viruses, France, 2016–17. A) Bayesian Skygrid plot of viral population size over time. B) Timeline of cases of H5N8 genotype A. Pink indicates geocluster 1; green indicates geocluster 2; red indicates geocluster 3; orange indicates geocluster 4; blue indicates geocluster 5.