South Chungcheong Province – Credit Wikipedia
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Although considered to pose a far lower risk to humans and poultry than do the H5 and H7 strains of avian flu, H9N2 has been known to infect humans - and while generally producing mild symptoms – is considered to have at least some degree of pandemic potential.
Since H9N2 circulates in many regions of the world where influenza testing is rarely done, we don’t really know how often this virus infects humans.
Over the past dozen years a small handful of cases have been identified – mostly in Hong Kong (see CIDRAP Avian Influenza (Bird Flu): Implications for Human Disease).
Last year Bangladesh detected a human infection and sent a virus sample to the CDC for development into a `seed strain’ for possible use in a vaccine (see CIDRAP NEWS Bangladesh shares H9N2 virus).
Which brings us to a report from Xinhua News this morning on an outbreak of avian flu in Korea – first feared to be H5 – but now shown to be H9N2.
S. Korea confirms outbreak of low pathogenic avian influenza
English.news.cn 2012-03-13 18:32:00
SEOUL, March 13 (Xinhua) -- South Korea on Tuesday confirmed an outbreak of a low pathogenic avian influenza virus in chickens previously tested positive for avian flu, the government said Tuesday.
The Ministry for Food, Agriculture, Forestry and Fisheries said the birds at a poultry farm in South Chungcheong Province were found to have been infected with the low pathogenic H9N2 strain of the avian influenza virus that is less damaging to both birds and humans.
Quarantine authorities conducted thorough examinations after six of 10 chickens at the farm tested positive for avian flu. Some 100 chickens at the farm had shown symptoms of avian flu.
The ministry ordered the affected farm to remain under watch until restrictions on travel to and from the site will be removed.
After the widespread outbreaks of H5N1 last year in South Korea that led to the culling of millions of birds, it is no doubt a relief to officials that this turned out to be an LPAI H9 virus.
Unlike the H7 and H5 avian flu strains, poultry (and swine) infections by the H9N2 virus are not required to be reported to the OIE. So we have far less data on how widespread H9N2 might be.
Despite causing rare human infection, H9N2 would likely need to acquire a number of genetic changes before it could pose a serious public health threat.
Which is why we concern ourselves with influenza’s ability to reassort with other co-circulating flu strains. Reassortment happens when two different influenza viruses co-infect the same host and swap genetic material.
In February of 2011, in PNAS: Reassortment Of H1N1 And H9N2 Avian viruses, we saw research from Chinese scientists that created – using reverse genetics – 128 reassorted viruses from the avian H9N2 virus and the (formerly pandemic) H1N1 virus.
In mouse testing, they found half of the hybrid viruses were biologically `fit’ as far as replication goes, and 8 hybrids were significantly more pathogenic than either of their parental viruses.
Research such as this shows the potential for the H9N2 virus to move towards a more `humanized’ pathogen. And with H1N1 and H9N2 both known to be circulating in pigs in Asia, there are ample opportunities for them to co-infect the same host.
While admittedly not at the top of our viral hit parade, H9N2 still commands respect. A few notable H9N2 stories from the past include:
- In December 2008 Revisiting A Malik Peiris Interview On H9N2
- In January of 2010, in H9N2: The Other Bird Flu Threat
- And in November of 2010 Study: The Continuing Evolution Of Avian H9N2
It is worth remembering that while everyone was watching the H5N1 virus for development, the 2009 H1N1 pandemic emerged from a completely unexpected region (North America), species (swine), and viral strain (H1).
All of which highlights the importance of establishing better global surveillance of humans, and farm animals, for the next emerging influenza virus.
Regardless of its strain.
