Sunday, June 12, 2016

Hong Kong's Bird Flu Dilemma


Just over 19 years ago - in May of 1997 - Hong Kong was ground zero for the first H5N1 outbreak in humans.  A 3-year-old boy was admitted to Queen Elizabeth Hospital with a fever, and a week later died from acute respiratory, multi-organ failure, and DIC (Disseminated intravascular coagulation).

The boy tested positive for Influenza A, but attempts to identify the subtype the infection (H1, H2, or H3) failed.  Samples were forwarded to labs in the US (CDC), London, and the Netherlands. 

It would eventually be the lab run by Albert Osterhaus in the Netherlands that would identify the culprit as avian H5N1, skewing forever the idea that only H1, H2, and H3 viruses posed a serious health threat to humans.

Despite this worrisome finding, no other cases were reported that summer. For a time, it seemed like a one off case.

But in November a `second wave' began, which lasted through December, involving 17 additional patients, five of whom died.  With more cases to examine, the epidemiological investigation tied most them to poultry exposure - and when combined with H5N1's avian gene set - pointed directly to live bird markets.

A ban was placed on importing poultry from the mainland, and over several days 1.2 million chickens  along with hundreds of thousands of other poultry, were destroyed.

Since the virus hadn't adapted well enough yet to humans to spread easily, this bold response stopped the outbreak in its tracks, and a feared global pandemic was avoided.

The full and fascinating details of this first outbreak can be read in Interspecies transmission of influenza viruses: H5N1 virus and a Hong Kong SAR perspective  by Shortridge KF1, Gao P, Guan Y, Ito T, Kawaoka Y, Markwell D, Takada A, Webster RG.

While their actions drove H5N1 to ground until 2003, five years later Hong Kong was hammered again by the arrival of the SARS epidemic (see SARS and Remembrance), which saw 1750 local cases and 286 deaths.

The full story of the SARS outbreak is both long, and fascinating, and I heartily recommend both Karl Taro Greenfeld’s  The China Syndrome: The True Story of the 21st Century's First Great Epidemic and David Quammen’s excellent book  Spillover: Animal Infections and the Next Human Pandemic.

Out of these two public health crises came the realization that Hong Kong's 7 million residents were highly vulnerable to infectious disease threats - particularly those originating on the mainland. 

That led to the creation of Hong Kong's CHP (Centre for Health Protection) which is arguably one of the most advanced and proactive public health agencies in the world.

While Hong Kong's defenses have improved remarkably over the past dozen years, the number of infectious disease threats likewise has continued to grow.  

As an international city that receives millions of visitors each year, Hong Kong is vulnerable to a myriad of imported diseases, including MERS-CoV, Zika, and Yellow Fever.

But of particular concern, in the past few years H5N1 has been joined by two other deadly avian viruses on the Mainland; H7N9 and H5N6.

Despite continual vigilance, and a horrendously expensive poultry surveillance and testing system, last week it was discovered (see H7N9 Detected At Tuen Mun Live Market) that a sample collected 20 days earlier had tested positive.

Belatedly, several thousand birds were culled, live poultry sales were halted for 4 days, and an investigation was launched into the source (still inconclusive).

While no other positive samples were discovered, this incident has raised serious questions (again) over the government's ability to keep avian flu out of live bird markets. 

Additionally, avian flu is normally a cool or cold weather concern, so finding a positive sample in mid-May has raised some expert eyebrows.  The warm May weather likely prevented greater spread, but the next time conditions might not be so kind.

Yesterday, in a televised interview, Professor Kwok-Yung YUEN, who heads the Department of Microbiology at Hong Kong University, warned that no amount of testing and surveillance would keep H7N9 out of Hong Kong's live markets forever. 

While advocating a ban on live poultry sales, he also warned that the May detection may signal the virus is becoming better adapted to warmer weather. 


Yuen Kwok-yung said quarantine measures will not prevent the virus to enter the retail market.

Yan Oi market in Tuen Mun earlier found in the local live poultry manure samples H7N9 avian flu virus, Yuen Kwok yung, Department of Microbiology, Faculty of medicine, University of Hong Kong, said the virus was first detected here at home is a big deal when measures to prove that even the tightest and most expensive in the world, were unable to prevent the virus entering the retail market, the Administration should review whether to continue using the existing expensive and quarantine measures.

Yuen Kwok-yung last summer found the bird flu virus is not unusual, it is a serious warning, due to the avian flu virus is more active in less than 20 degrees Celsius circumstances, present findings suggest the virus may be more active in winter, or even human bird flu cases.

He said this is the first time in Hong Kong live poultry H7N9 virus was found in the samples, even with virus genome analysis in poultry species, neither can they compare, so don't waste looking with a virus source, mistakes have a great chance.

Yuan also said that for the foreseeable future still occasionally found avian influenza viruses, and culling, compensation. Measures to prove that even the tightest and most expensive in the world, were unable to prevent the virus entering the retail market and measures itself, there are errors, even if it increases the number of sampling errors will still exist, so the Administration should review whether to continue using the existing expensive quarantine measures.

He cited large numbers of Hong Kong said mainland poultry rapporteur H7N9 in serum up to 15%, with H5N1 virus to 0.8% per cent, proved H7N9 virus transmitted 15 times times greater opportunities than the H5N1, Hong 30%.

Yuen Kwok-yung said, the most effective prevention method is banning sale of live poultry markets, reducing the risk of virus infection, Singapore, and Taiwan, and Japan and other neighboring countries and regions, has been implementing centralized slaughtering, and Taiwan, and Japan have mobile apps for people to order chicken, people just a phone order, delivered directly by the farm fresh chicken slaughter.

The evidence that closing live-bird markets reduces the spread of the H7N9 virus (at least for now) is solid (see The Lancet: Poultry Market Closure Effect On H7N9 Transmission), making it the obvious first step in breaking the chain of transmission.

The problem is, purchasing live market birds is deeply ingrained in Chinese culture, as it reassures the buyer that the bird is both fresh and healthy.  
While previous attempts to move away from live poultry sales have met with fierce public resistance on the mainland, the combined memories of SARS and H5N1 in Hong Kong might be enough to sway public opinion there.

Particularly if `cracks' in their poultry defenses - like the one announced last week - continue to appear.


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