Reassortant highly pathogenic influenza A(H5N6) virus in Laos

Abstract

In March 2014, avian influenza in poultry in Laos was caused by an emergent influenza A(H5N6) virus. Genetic analysis indicated that the virus had originated from reassortment of influenza A(H5N1) clade 2.3.2.1b, variant clade 2.3.4, and influenza A(H6N6) viruses that circulate broadly in duck populations in southern and eastern China.

Figure 1

Locations of cases of highly pathogenic avian influenza in poultry caused by influenza A(H5N6) virus in Laos, March 2014. Dark gray shading indicates the 2 districts (Muang Nan and Muang Xayabouly) situated at the boundaries of Luang Prabang and Xayabouly Provinces, where villages with infected poultry were located. Affected birds were associated with regular consignments of mixed poultry transported from Jinghong and elsewhere in Yunnan Province, China.

Figure 2

Phylogenetic analyses of influenza A(H5N6) viruses detected in Laos, March 2014, on the basis of the hemagglutinin (HA) and N6 neuraminidase (NA) genes. A) HA subtree showing relationships of emergent influenza A(H5N6) viruses with clade 2.3.4 H5 avian influenza viruses and B) NA subtree showing relationships with Asian lineage N6 avian influenza viruses. Vertical lines denote H5 subtype virus clades on the HA tree and the WD/ST/192/04 (A/wild duck/Shantou/192/2004)-like N6 gene pool on the NA tree. Proposed clade 2.3.4.6 has not been formally recognized by the World Health Organization/World Organisation for Animal Health/Food and Agricultural Organization of the United Nations H5N1 Evolution Working Group. Black diamonds indicate viruses identified in this study, white diamonds indicate Asian influenza A(H5N6) viruses identified in other studies, and black circles indicate viruses previously identified in Laos. All viruses are subtype H5N1 unless otherwise indicated. Bootstrap values ≥70% from 1,000 replicates are indicated at relevant nodes, and scale bars indicate nucleotide substitutions per site. The full HA and NA trees are provided in the online Technical Appendix Figure, panels A and B (http://wwwnc.cdc.gov/EID/article/21/3/14-1488-Techapp1.pdf).