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Detecting Spread of Avian Influenza A(H7N9) Virus Beyond China - Volume 21, Number 5—May 2015 - Emerging Infectious Disease journal - CDC

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Detecting Spread of Avian Influenza A(H7N9) Virus Beyond China - Volume 21, Number 5—May 2015 - Emerging Infectious Disease journal - CDC





Volume 21, Number 5—May 2015

Perspective

Detecting Spread of Avian Influenza A(H7N9) Virus Beyond China

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Alexander J. MillmanComments to Author , Fiona Havers, A. Danielle Iuliano, C. Todd Davis, Borann Sar, Ly Sovann, Savuth Chin, Andrew L. Corwin, Phengta Vongphrachanh, Bounlom Douangngeun, Kim A. Lindblade, Malinee Chittaganpitch, Viriya Kaewthong, James C. Kile, Hien T. Nguyen, Dong V. Pham, Ruben O. Donis, and Marc-Alain Widdowson
Author affiliations: Author affiliations: Centers for Disease Control and Prevention (CDC), Atlanta, Georgia, USA (A.J. Millman, F. Havers, A.D. Iuliano, C.T. Davis, R.C. Donis, M.-A. Widdowson); CDC, Phnom Penh, Cambodia (B. Sar); Ministry of Health, Phnom Penh (L. Sovan); National Institute of Public Health, Phnom Penh (S. Chin); CDC, Vientiane, Laos (A.L. Corwin); National Center for Laboratory Epidemiology, Vientiane (P. Vongphrachanh);Ministry of Agriculture and Forestry, Vientiane (B. Douangngeun); Thailand Ministry of Public Health–CDC Collaboration, Nonthaburi, Thailand (K.A. Lindblade); National Institute of Health, Nonthaburi (M. Chittaganpitch); Ministry of Agriculture and Cooperatives, Bangkok, Thailand (V. Kaewthong); CDC, Hanoi, Vietnam (J.C. Kile); Ministry of Health, Hanoi (H.T. Nguyen); Ministry of Agriculture and Rural Development, Hanoi (D.V. Pham)

Abstract

During February 2013–March 2015, a total of 602 human cases of low pathogenic avian influenza A(H7N9) were reported; no autochthonous cases were reported outside mainland China. In contrast, since highly pathogenic avian influenza A(H5N1) reemerged during 2003 in China, 784 human cases in 16 countries and poultry outbreaks in 53 countries have been reported. Whether the absence of reported A(H7N9) outside mainland China represents lack of spread or lack of detection remains unclear. We compared epidemiologic and virologic features of A(H5N1) and A(H7N9) and used human and animal influenza surveillance data collected during April 2013–May 2014 from 4 Southeast Asia countries to assess the likelihood that A(H7N9) would have gone undetected during 2014. Surveillance in Vietnam and Cambodia detected human A(H5N1) cases; no A(H7N9) cases were detected in humans or poultry in Southeast Asia. Although we cannot rule out the possible spread of A(H7N9), substantial spread causing severe disease in humans is unlikely.
Novel low pathogenic avian influenza (LPAI) A(H7N9) virus emerged in February 2013 and, as of March 3, 2015, a total of 602 laboratory-confirmed human infections, including 227 deaths, had been reported (1–3). Most human cases have had live poultry or live-bird market (LBM) environmental exposure; person-to-person spread appears infrequent (4). However, as circulation of A(H7N9) virus becomes more widespread, the probability increases for mutations enabling efficient person-to-person transmission.
Similar fears accompanied the reemergence in 2003 of highly pathogenic avian influenza (HPAI) A(H5N1) virus, which caused ≈45 human cases in Vietnam and Thailand within 12 months. As of March 3, 2015, A(H5N1) virus had resulted in 784 human cases, including 429 deaths, in 16 countries and poultry outbreaks in 53 countries (3,5–7). In response to these outbreaks, avian influenza surveillance systems were created to monitor A(H5N1) activity and to detect other novel influenza viruses.
In contrast to the rapid international spread of A(H5N1) virus in poultry and humans within 12 months after its reemergence, no autochthonous A(H7N9) cases in animals or humans have been reported outside mainland China (3), despite a higher incidence of reported A(H7N9) than A(H5N1) cases in humans; A(H7N9) detection in poultry and humans; and the presence of the virus in border provinces in southern, western, and northeastern China (2,8,9). Surveillance systems in Southeast Asia have detected new A(H5N1) cases in humans and poultry since the A(H7N9) virus was first identified (3). Whether the absence of reported A(H7N9) among humans or poultry outside mainland China represents a lack of spread or whether regional surveillance systems are insufficiently sensitive to detect A(H7N9) remains unclear. Because A(H5N1) virology and epidemiology differ from those of A(H7N9), assessing how A(H7N9) might spread and whether surveillance would detect it remains critical for countries to prepare control measures and to monitor virologic and epidemiologic changes.
We highlight differences and similarities between A(H5N1) and A(H7N9) viruses and hypothesize scenarios related to possible A(H7N9) virus spread. Then we describe human and animal influenza surveillance data from 4 Southeast Asian countries where A(H5N1) has been detected—Vietnam, Cambodia, Laos, and Thailand—to assess the likelihood that surveillance systems designed for A(H5N1) would have detected human or animal A(H7N9) infections during the predominant months of A(H7N9) virus circulation during 2014.
Thumbnail of Avian influenza A(H7N9) in humans, China, 2013–2014. Data were obtained from the World Health Organization as reported from the National Health and Family Planning Commission (http://www.who.int/influenza/human_animal_interface/influenza_h7n9/en/).

Figure 1. Avian influenza A(H7N9) in humans, China, 2013–2014. Data were obtained from the World Health Organization as reported from the National Health and Family Planning Commission (http://www.who.int/influenza/human_animal_interface/influenza_h7n9/en/).
Since A(H7N9) emerged, 2 complete waves of infections have occurred; the second wave is defined as cases occurring during October 1, 2013–September 30, 2014 and affecting mostly the southeastern provinces of China (Figure 1). A third (ongoing) wave is defined as cases since October 1, 2014. A(H7N9) virus does not transmit easily between humans, and person-to-person spread has been limited to 2 or possibly 3 generations of transmission (2,4). Assuming transmission remains unchanged, geographic spread probably will occur through travel of infected humans or infected poultry. Several persons exposed to A(H7N9) virus in China traveled to Hong Kong, Taiwan, Malaysia, and Canada; became ill; and were deemed to have imported infections (2). Additional sporadic A(H7N9) infections might occur in travelers, but appropriate isolation measures should prevent further spread (2).
Thumbnail of Initial 2-year spread of human cases and poultry outbreaks of influenza A(H5N1) in China and Southeast Asia, December 2003–2005. Data on A(H5N1) in humans were obtained from the World Health Organization (http://www.who.int/influenza/human_animal_interface/en/). Data on outbreaks of A(H5N1) in poultry were obtained from the World Organisation for Animal Health (outbreaks before 2005 from http://www.oie.int/en/animal-health-in-the-world/the-world-animal-health-information-system/data

Figure 2. Initial 2-year spread of human cases and poultry outbreaks of influenza A(H5N1) in China and Southeast Asia, December 2003–2005. Data on A(H5N1) in humans were obtained from the World Health Organization...
LBMs create environments that can amplify avian influenzas viruses and increase risk of human infection (5,19,26). Large informal poultry movements between China and Southeast Asian countries also pose a risk for spread (8,27). The first confirmed human A(H5N1) case outside China occurred in December 2003 in Vietnam and foreshadowed the virus’ rapid regional spread in humans and poultry (Figure 2). Phylogeographic studies suggest that A(H5N1) virus was introduced to Vietnam from China through these poultry trade routes; A(H7N9) virus is similarly likely to be introduced in domestic poultry in Vietnam (27,28). However, because A(H7N9) preferentially infects different poultry species than A(H5N1), different poultry value chains might be implicated in this potential spread.
Wild migratory birds have contributed to spread of A(H5N1) virus along regional flyways (29,30). A(H7N9) virus was detected in a nonmigratory wild sparrow in China during spring 2013 but has not been identified in other wild bird species (13). This finding suggests that A(H7N9) infection is not widespread in wild birds, and the possible risk for regional spread by wild birds is currently low.


Surveillance for Avian Influenza in Southeast Asia

Thumbnail of Severe acute respiratory infection (SARI) and Influenza-like Illness (ILI) sentinel sites in Vietnam, Thailand, Cambodia, and Laos. A given location might have >1 SARI or ILI sentinel site. SARI sites in Laos include planned SARI sites and 8 nonsentinel SARI sites. (The Lang Son and Quang Ninh province sites continue to operate. The Hanoi site operated until June 2014.)

Figure 3. Severe acute respiratory infection (SARI) and influenza-like Illness (ILI) sentinel sites in Vietnam, Thailand, Laos, and Cambodia. A given location might have >1 SARI or ILI sentinel site. SARI sites in...
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Dr. Millman is a medical doctor and an Epidemic Intelligence Service Officer assigned to the Influenza Division at the Centers for Disease Control and Prevention. His research interests include influenza, emerging infections, surveillance, and advanced molecular diagnostics

Acknowledgments



We thank Prabda Prapasiri, Pui Chor, Sonja Olsen, Do Thuy Trang, Sam Dowell, Susan Trock, and geospatial analysts from the Agency for Toxic Substances and Disease Registry, Geospatial Research Analysis and Services Program.
This work was funded by the Centers for Disease Control and Prevention. Data collection was funded by national governments and international organizations.

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Figures

Tables

Technical Appendix

Suggested citation for this article: Millman AJ, Havers F, Iuliano AD, Davis CT, Sar B, Sovann L, et al. Detecting spread of influenza A(H7N9) virus beyond China. Emerg Infect Dis [Internet]. 2015 May [date cited]. http://dx.doi.org/10.3201/eid2105.141756
DOI: 10.3201/eid2105.141756
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