H9N2: The Other Bird Flu Threat

 

 

# 4366

 

 

Influenza viruses are identified by the combination of two proteins found on their surface; hemagglutinin and neuraminidase.

 

There are 16 known types of hemagglutinin (H) and 9 known types of neuraminidase (N).  Theoretically, they can produce 144 different strains of influenza, although not all of these strains of influenza circulate in the wild or can infect humans.

 

In the relatively short history of our observation of the influenza virus, only the H1, H2, and H3 strains have adapted well to people.  

 

On rare occasions humans have been infected by other influenza strains, such as H5N1, H7N7, and H9N2.  These strains are primarily seen in birds, but since they are constantly evolving and mutating, the concern is one might eventually adapt to human hosts.

 

The OIE requires that all detected H5 and H7 infections in birds be reported, and that steps be made to control and eradicate outbreaks.

LPAI (Low Pathogenic Avian Influenza) – which normally does little harm to flocks or humans – has the potential to evolve to HPAI (Highly Pathogenic Avian Influenza) if not controlled, particularly when introduced into a crowded farming environment.

 

H9 viruses are not currently required to be reported, so we don’t have a very good handle on how prevalent it may be around the world.

 

 

The World Health Organization has just issued their semiannual update on avian flu activity where they discuss both the H5N1 and H9N2 viruses.

 

Recent infections detected in two Hong Kong residents (see Another H9 Report From Hong Kong)  who had visited mainland China showed that the H9N2 virus has mutated away from the existing vaccine candidate virus, which is based on a 1999 isolate.   

 

If all of this sounds a bit ominous, it may help to know that all of the H9 human infections detected to date have been relatively mild, that human-to-human transmission has not been detected, and that the H9 virus has managed to circulate in birds for many years without sparking a pandemic.

 

Still, past performance is no guarantee of future results. The WHO recommends the creation of a new vaccine candidate based on this A/Hong Kong/33982/2009-like virus.

 

 

Antigenic and genetic characteristics of influenza A(H5N1) and influenza A(H9N2) viruses and candidate vaccine viruses developed for potential use in human vaccines

February 2010

This summary provides a review on the influenza A(H5N1) and A(H9N2) virus activity and virus characterization, and describes the current status of the development of new A(H5N1) and A(H9N2) candidate vaccine viruses. It is meant to provide guidance for national authorities and vaccine companies on the selection of candidate viruses for use in vaccine development.

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Another H9 Report From Hong Kong

 

# 4190

 

 

For the second time in two months, authorities in Hong Kong have detected a human infection with the H9 avian flu virus.   This is only the 7th known case of H9 jumping to humans, and all of those cases have been reported in either Hong Kong or China.

 

While considered rare, H9 infection in humans may be more common than we know.   According to CIDRAP’s excellent overview Avian Influenza (Bird Flu): Implications for Human Disease:

 

H9 is only known to include LPAI strains. H9N2 viruses had been isolated in multiple avian species throughout Asia, the Middle East, Europe, and Africa.

 

Most of these places are areas where, quite frankly, testing and surveillance for H9 human flu infections are unlikely to occur.

 

Hong Kong appears to be a hotbed for H9 reports simply because they actively test for avian viruses.  A legacy of having narrowly dodged the H5N1 bullet in 1997. 

Last year, in a PLoS ONE  journal article:

 

Wan H, Sorrell EM, Song H, Hossain MJ, Ramirez-Nieto G, et al. 2008 Replication and Transmission of H9N2 Influenza Viruses in Ferrets: Evaluation of Pandemic Potential. PLoS ONE 3(8): e2923. doi:10.1371/journal.pone.0002923

 

Researchers discussed the pandemic potential of the H9 viruses, and they conclude that `results suggest that the establishment and prevalence of H9N2 viruses in poultry pose a significant threat for humans.’ 

 

They go on to say:

 

However, considering the widespread prevalence of H9N2 viruses in poultry, the human virus-like receptor specificity of some avian and swine H9N2 isolates, co-circulation of H9N2 with H3N2 viruses in Asian swine, and the repeated direct transmission to humans, the public health threat of H9N2 viruses cannot be overemphasized.

 

If all of this sounds a bit ominous, it may help to know that all of the H9 human infections detected to date have been relatively mild, that human-to-human transmission has not been detected, and that the H9 virus has managed to circulate in birds for many years without sparking a pandemic.

 

Of course, past performance is no guarantee of future results.

 

The H9N2 virus has reassorted into many different clades, some having the ability to bind to α2-6 receptor cells found in the upper airway of humans.   The authors write:

 

A significant proportion of H9N2 field isolates have acquired human virus-like receptor specificity, preferentially binding α2-6 linked sialic acid (SAα2-6) receptors, in contrast to the classic avian virus-like receptor specificity that preferentially binds α2-3 linked sialic acid (SAα2-3) receptors.

 

Interestingly, a few of the H9N2 viruses that recognize SAα2-6 receptors have transmitted directly to humans, causing mild flu-like illness and the consequent fear that they may become pandemic.

 

 

In ferret testing, H9 replicated well but aerosol transmission to contact ferrets did not occur, strongly suggesting the virus must undergo further changes before it could spread efficiently among humans.

Which brings us to today’s story.    

 

Toddler's bird flu infection under study

The Centre for Health Protection is investigating a mild form of avian influenza A H9N2 found in a 35-month-old girl.

 

The toddler lives in Sha Tin. Since late November, she had developed a cough, fever and runny nose and was admitted to Prince of Wales Hospital. She has since recovered, and was discharged on December 11.

 

Lab tests found the bird flu virus in samples from her respiratory system. The World Health Organisation will be alerted. Such H9N2 infections in people are rare, and are usually mild.

 

This is the seventh time that H9 viruses were found in people in Hong Kong since 1999.

 

As a precautionary measure, people are reminded to avoid contact with live poultry to minimise the chance of being infected. For more information about bird flu, visit the centre's website.

 

 

As it exists now, H9 poses a low threat to humans.  

 

Sporadic reports of human infections – particularly when there is no evidence of ongoing transmission – are interesting, but not alarming.

 

But H9, like a number of other avian viruses (H5’s, H7’s) have some pandemic potential, particularly if they can co-circulate with – and pick up genetic material from – other viruses.   This `reassortment’ can conceivably create a new, hybrid strain of influenza.

 

How likely is this to happen?

 

Well, that’s the big question.  No one really knows.

 

We just know that it is possible. 

 

It obviously doesn’t happen often, otherwise we’d be hip deep in new, hybrid viruses all of the time.  But this is essentially the route that the 2009 H1N1 virus took to become a pandemic, and is likely the way the 1957 and 1968 pandemics came about.

 

And so we watch these cases with great interest.  A dangerous reassortment may never occur with the H9 virus, or it could happen tomorrow.

 

Influenza viruses, as they say, are unpredictable.

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Guangdong Woman Ill With H9 Avian Flu

 

# 3938

 

While we normally think of H5N1 when we hear of `avian flu’, the truth is, there are a number of avian influenza viruses out there, and humans have been (on rare occasions) infected with strains of H5, H7,  H9, and H10 influenza.

 

These strains are thought to have some pandemic potential, although none have adapted well enough to humans to spread easily.  The H5, by far, has produced the most concern.

 

Today we’ve word of a rare H9 infection in Hong Kong. This from news.gov.hk

 

 

November 3, 2009

Surveillance

Guangdong woman ill with avian flu

 

The Centre for Health Protection is investigating an imported case of H9 influenza A infection involving a 47-year-old Guangdong woman.

 

She came down with breathlessness and a cough October 26. She came to Hong Kong for medical treatment and was admitted to Queen Mary Hospital October 28. She is stable and staying in isolation.

 

She had an underlying medical condition requiring regular medication. Her family members have been put under medical surveillance.

 

As she was in Guangdong during the incubation period, the centre has informed health authorities there and the World Health Organisation, the Ministry of Health and Macau's health authorities of the development.

 

H9 Influenza A is a mild form of avian flu. Infection in humans is rare.

 

This is the sixth time H9 viruses have been found in humans in Hong Kong. Four girls and a boy were confirmed to have suffered from H9 infection in 1999, 2003, 2007 and 2008.

 

People should avoid contact with live poultry to minimise the chance of being infected with avian flu.

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