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While H5N1 gets the lion’s share of the media’s attention, there are other influenza viruses in the wild believed capable of sparking the next flu pandemic. Over the past dozen years we’ve seen a number of avian flu strains that have made limited jumps to human hosts.
- In 2003, an outbreak of H7N7 at a poultry farm in the Netherlands went on to infect at least 89 people (mostly mildly, but 1 death), and many more may have been infected subclinically.
- In Egypt - in 2004 - 2 infants were shown to be infected by the H10N7 avian flu virus.
- In 2006 1 person in the UK was confirmed to have contracted H7N3, and the following year, 4 people tested positive for H7N2 – both following local outbreaks in poultry.
But in terms of greatest concern, the closest runner up to H5N1 is probably H9N2 – which is known to have infected a handful of humans, mostly in Asia.
To date, most of these cases have produced relatively mild illness.
Nevertheless, the World Health Organization has announced that work has begun on the creation of an H9N2 candidate vaccine (see WHO Report : Antigenic & Genetic Characteristics of H5N1 & H9N2 Viruses).
Last year, in PNAS: Reassortment Potential Of Avian H9N2 , researchers looked at the reassortment potential of the avian H9N2 virus and H1N1, generating four reassortant viruses, three of which showed efficient respiratory droplet transmission in the ferret model.
These authors had previously successfully created laboratory reassortments between seasonal H3N2 and H9N2.
Experiments that are, in many ways, similar to the H5N1 experiments of Fouchier and Kawaoka that have caused such a stir these past few months, albeit on a (thus far) much-less-pathogenic flu virus.
These successes (and others, see PNAS: Reassortment Of H1N1 And H9N2 Avian viruses), along with the wide geographic distribution of the H9 avian virus in poultry across Asia and the Middle East, have led many researchers to call for better research and surveillance on this avian strain.
Which brings us to a new study, published late last week in the journal Plos One, that looks at the prevalence of antibodies to the H9N2 strain among poultry workers – and the general population – in Pune, India.
Avian Influenza H9N2 Seroprevalence among Poultry Workers in Pune, India, 2010
Shailesh D. Pawar, Babasaheb V. Tandale, Chandrashekhar G. Raut, Saurabh S. Parkhi, Tanaji D. Barde, Yogesh K. Gurav, Sadhana S. Kode, Akhilesh C. Mishra
PLoS ONE 7(5): e36374. doi:10.1371/journal.pone.0036374
Abstract
Avian influenza (AI) H9N2 has been reported from poultry in India. A seroepidemiological study was undertaken among poultry workers to understand the prevalence of antibodies against AI H9N2 in Pune, Maharashtra, India.
A total of 338 poultry workers were sampled. Serum samples were tested for presence of antibodies against AI H9N2 virus by hemagglutination inhibition (HI) and microneutralization (MN) assays.
A total of 249 baseline sera from general population from Pune were tested for antibodies against AI H9N2 and were negative by HI assay using ≥40 cut-off antibody titre.
Overall 21 subjects (21/338 = 6.2%) were positive for antibodies against AI H9N2 by either HI or MN assays using ≥40 cut-off antibody titre. A total of 4.7% and 3.8% poultry workers were positive for antibodies against AI H9N2 by HI and MN assay respectively using 40 as cut-off antibody titre.
This is the first report of seroprevalence of antibodies against AI H9N2 among poultry workers in India.
Although a bit of a gray area, an antibody titer level of ≥40 is generally assumed to be suggestive of a previous (possibly sub-clinical) infection by a specific virus.
Interestingly, none of the 249 sera samples from the general population showed elevated antibody titers to the H9N2 virus (using the ≥40 cut-off standard), but among poultry workers, 21 of the 338 sera samples (6.2%) tested positive for H9N2 antibodies.
A fairly low number given the amount of exposure, but indicative that some transmission of the virus to humans appears to be taking place.
The authors warn that:
The evidence of AI (H9N2) in poultry market may provide the opportunity for human infections and the possibility of reassortment with the existing poultry AI viruses including HPAI H5N1 virus.
Warnings over the pandemic potential of the H9N2 virus are not new. A few notable stories from the past include:
- In December 2008 I ran a blog featuring an interview in which world famous Hong Kong virologist Malik Peiris cautioned that the H9N2 virus may be circulating far more commonly than we believe. Revisiting A Malik Peiris Interview On H9N2.
- In January of 2010, in H9N2: The Other Bird Flu Threat, I wrote about the World Health Organization recommending the creation of a candidate vaccine virus for H9N2.
- And in November 2010, in Study: The Continuing Evolution Of Avian H9N2, we looked at computer modeling that suggested that the H9N2 virus moving towards becoming more `human-adapted’.
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.
Admittedly, the next influenza virus to successfully jump species could come out of left field, as we saw in 2009 with the H1N1 swine flu.
Which is why the global monitoring of influenza viruses - in humans, on the farm, and in the wild - remains crucial if we hope to detect, and prepare for, the next pandemic at the earliest possible moment.
