Equine Influenza A(H3N8) Virus Isolated from Bactrian Camel, Mongolia

Table

Technical Appendix

Myagmarsukh Yondon, Batsukh Zayat, Martha I. Nelson, Gary L. Heil, Benjamin D. Anderson, Xudong Lin, Rebecca A. Halpin, Pamela P. McKenzie, Sarah K. White, David E. Wentworth, and Gregory C. Gray

Author affiliations: Institute of Veterinary Medicine, Ulaanbaatar, Mongolia (M. Yondon, B. Zayat); National Institutes of Health, Bethesda, Maryland, USA (M.I. Nelson); University of Florida, Gainesville, Florida, USA (G.L. Heil, B.D. Anderson, S.K. White, G.C. Gray); J. Craig Venter Institute, Rockville, Maryland, USA (X. Lin, R.A. Halpin, D.E. Wentworth); and St. Jude Children’s Research Hospital, Memphis, Tennessee, USA (P.P. McKenzie)

Abstract

Because little is known about the ecology of influenza viruses in camels, 460 nasal swab specimens were collected from healthy (no overt illness) Bactrian camels in Mongolia during 2012. One specimen was positive for influenza A virus (A/camel/Mongolia/335/2012[H3N8]), which is phylogenetically related to equine influenza A(H3N8) viruses and probably represents natural horse-to-camel transmission.

Since the first isolation in 1963 of an avian-origin influenza A(H3N8) virus from horses (1), subtype H3N8 influenza viruses have continued to circulate panzootically among horses, causing severe outbreaks of equine influenza respiratory disease. In the United States, these viruses jumped from horses to dogs and continue to circulate among dogs (2,3). In Mongolia, the site of some of the world’s largest epizootics of equine influenza A(H3N8) virus (EIV) infection, transmission of this virus is sustained among 2.1 million free-ranging horses, causing significant economic losses among rural herders. Major epizootics of EIV infection occurred in Mongolia during 2007–2008 (459,000 cases, 24,600 deaths) and again in 2011 (74,608 cases, 40 deaths) (4).

Over previous decades in Mongolia, outbreaks of respiratory disease, thought to be influenza, among camels have been reported. In the 1980s, the virus was characterized, and researchers speculated that it was related to a reassortant influenza A(H1N1) virus vaccine strain, A/PR-8/34 + A/USSR/77, generated in a Soviet laboratory and administered to humans in Mongolia and possibly transmitted from vaccinated humans to camels in a reactivated form (5,6). However, only 1 genetic sequence from this outbreak among camels is available in GenBank: A/camel/Mongolia/1982/H1N1. Despite reports of serologic activity against influenza A virus among camels in several African countries (7,8), the lack of isolated virus from these populations highlights how little is known about the ecology of influenza viruses in camels. Questions about the potential role of camels in human cases of Middle East respiratory syndrome (9) further highlight our lack of knowledge of infectious diseases in camels and the merits of increased surveillance at this unique human–animal interface.

Since January 2011, surveillance of equine influenza viruses has been enhanced in 3 Mongolian aimags (provinces). Surveillance among camels was also initiated in response to anecdotal reports of signs of respiratory illness in Bactrian camels (Camelus bactrianus). We describe the isolation, full-genome sequencing, and phylogenetic characterization of an influenza A(H3N8) virus of equine lineage isolated from a Bactrian camel, thereby identifying a novel route of influenza virus interspecies transmission and raising further questions about influenza A virus ecology in under-studied regions such as Mongolia.

The Study

Thumbnail of The 3 aimags from which nasal swab specimens were collected from healthy Bactrian camels, for influenza A virus testing, Mongolia, 2012. 1, Töv;, 2, Khentii; 3, Dundgovi.

Figure 1. The 3 aimags from which nasal swab specimens were collected from healthy Bactrian camels, for influenza A virus testing, Mongolia, 20121, Töv;, 2, Khentii; 3, Dundgovi.

During January 2012–January 2013, a total of 460 nasal swab specimens were collected through active surveillance of horses and camels in 3 Mongolian aimags (Figure 1) known for high densities of free-ranging horses and camels (Table). Specimens were collected monthly, as weather permitted, from 50 free-ranging horses and 20 free-ranging Bactrian camels that were safely and carefully restrained with halters, ropes, and by hand, according to a protocol approved by the Department of Veterinary and Animal Breeding, Government of Mongolia. During sampling, camels were in a crouched or take-down position. Horse and camel specimens were carefully stored and shipped in separate containers; to prevent cross-contamination with EIV, specimens were separated during laboratory analyses.