Until the mid-1990s, avian influenza viruses were thought to pose only a very limited threat to human health, and the few novel human infections that had been detected, had generally been mild.
That notion abruptly changed in 1997 when 18 people contracted H5N1 in Hong Kong, and six of them died.A massive campaign of poultry eradication bought a 5 year respite, but in 2003 two members of a family turned up in Hong Kong with the virus after visiting Fujian Province, China (see WHO H5N1 timeline). A third family member had died on the Mainland, but no tests were taken.
From this sputtering and uncertain beginning (see chart above), H5N1 began to spread - at first across Southeast Asia (Vietnam, Laos, Cambodia, Thailand) - and within a couple of years, into Europe, Africa, and the Middle East.
For several years Indonesia and Vietnam were the world's hot spots for human infection, but eventually that focus would shift to Egypt.Along the way, the virus was also changing, diversifying into new clades and subclades. The H5N1 virus circulating in Indonesia was genetically distinct from the H5N1 found in China, or that spreading in Egypt.
For the first decade, H5N1 stood pretty much alone at the top of our avian flu worry list, albeit with some second tier viruses (H7N7, H5N2, H9N2, etc.) in the wings. In 2013, H7N9 - a worthy contender to H5N1 - emerged in China, and has (at least for now) replaced H5N1 as our biggest concern.
But it wasn't alone.Several other HPAI viruses, able to infect humans - all originating from China - would emerge in 2013 and 2014; H10N8 and H5N6. Earlier this year, we saw the first known human infection with H7N4 (see UK PHE Guidance & Risk Assessment On Human H7N4 In China).
While novel flu viruses can emerge from anywhere on the globe, Eastern China has an impressive record of spawning new subtypes (see Viral Reassortants: Rocking The Cradle Of Influenza).
This week the World Health Organization has published a review of human infections with avian flu viruses in the Western Pacific over the past 15 years.It's a long and informative read, and discusses in frank terms some of the challenges in getting accurate data, and the likelihood of seeing additional novel viruses emerge from this region in the future.
I've only excerpted the abstract and some comments from the Conclusions. Follow the link to read it in its entirety.
From H5N1 to HxNy: An epidemiologic overview of human infections with avian influenza in the Western Pacific Region, 2003–2017
Sarah Hamid,a Yuzo Arima,b Erica Dueger,a,f Frank Konings,a Leila Bell,a Chin-Kei Lee,c Dapeng Luo,d Satoko Otsu,e Babatunde Olowokure,a Ailan Lia and WPRO Health Emergencies Programme Teama
a WHO Regional Office for the Western Pacific.
b National Institute of Infectious Diseases, Japan.
c WHO Country Office China.
d WHO Country Office Lao People's Democratic Republic.
e WHO Country Office Viet Nam.
f Influenza Division, Centers for Disease Control and Prevention, Atlanta, GA, USA.
AbstractSince the first confirmed human infection with avian influenza A(H5N1) virus was reported in Hong Kong SAR (China) in 1997, sporadic zoonotic avian influenza viruses causing human illness have been identified globally with the World Health Organization (WHO) Western Pacific Region as a hotspot. A resurgence of A(H5N1) occurred in humans and animals in November 2003.
Between November 2003 and September 2017, WHO received reports of 1838 human infections with avian influenza viruses A(H5N1), A(H5N6), A(H6N1), A(H7N9), A(H9N2) and A(H10N8) in the Western Pacific Region. Most of the infections were with A(H7N9) (n = 1562, 85%) and A(H5N1) (n = 238, 13%) viruses, and most (n = 1583, 86%) were reported from December through April. In poultry and wild birds, A(H5N1) and A(H5N6) subtypes were the most widely distributed, with outbreaks reported from 10 and eight countries and areas, respectively.
Regional analyses of human infections with avian influenza subtypes revealed distinct epidemiologic patterns that varied across countries, age and time. Such epidemiologic patterns may not be apparent from aggregated global summaries or country reports; regional assessment can offer additional insight that can inform risk assessment and response efforts. As infected animals and contaminated environments are the primary source of human infections, regional analyses that bring together human and animal surveillance data are an important basis for exposure and transmission risk assessment and public health action. Combining sustained event-based surveillance with enhanced collaboration between public health, veterinary (domestic and wildlife) and environmental sectors will provide a basis to inform joint risk assessment and coordinated response activities.
ConclusionsDespite these limitations, disseminating regional analyses can improve Member States' situational awareness, knowledge of the epidemiology in neighbouring countries as well as of the broader regional perspective, and risk assessment and response efforts.
This analysis specifically demonstrates the usefulness of combining multiple sources of surveillance data for better informed risk assessments, including those based on the WHO Tool for Influenza Pandemic Risk Assessment.57 Moreover, using multiple sources of information helps to assess potential surveillance biases, thereby improving decision-making.(Continue . . . )
Further sporadic human infections with avian influenza viruses are likely to occur. Although A(H5N1) incidence may have declined, A(H7N9) virus has emerged, and other avian influenza viruses have been detected in recent years.
In China, country of the origin of recently identified avian influenza virus strains, the poultry industry has expanded greatly in the past two decades.58 In many areas, the close proximity of humans and animals increases the risk of human exposure to zoonotic influenza viruses.3 As infected animals or contaminated environments are the primary sources for human infection, risk assessments should incorporate a One Health approach and gather information from all relevant sectors. Continued surveillance at the human–animal interface is imperative for all avian influenza viruses.
Every sporadic human infection provides a virus with an opportunity to change its genetic makeup, increasing the possibility of an influenza virus with pandemic potential to arise.
Strengthened communication and collaboration between animal and human health sectors at subnational, national, regional and global levels are necessary to monitor the dynamics of influenza virus activity. An APSED approach that aligns with One Health initiatives combining sustained event-based surveillance with enhanced collaboration between the human, animal (domestic and wildlife) and environmental sectors will provide a basis to inform joint risk assessment and coordinate response capacities.
Hamid S, Arima Y, Dueger E, Konings F, Bell L, Lee CK, et al. From H5N1 to HxNy: An epidemiologic overview of human infections with avian influenza in the Western Pacific Region, 2003–2017. Western Pac Surveill Response J. 2018 Jul;9(2). doi:10.5365/wpsar.2018.9.2.001