Reassortment is the mechanism where two different flu viruses infect the same cell simultaneously, and swap genetic material, producing a new, hybrid virus. - Credit AFD
At the same time that mainland China is experiencing their third winter wave of H7N9 infections, Hong Kong and the rest of southern China are embroiled in a particularly nasty H3N2 seasonal flu epidemic.
Regarding severe cases, from noon yesterday (February 7) to noon today, four additional cases of influenza-associated admission to intensive care units or death (including two deaths) among adults aged 18 or above have been recorded under the enhanced surveillance in collaboration with public and private hospitals reactivated since January 2.
This brings the total number to 218 ( 142 deaths) so far. Among them, 207 were A(H3N2), five were B and six were A pending subtype. In the last winter season in early 2014, 266 (133 deaths) were filed.
Meanwhile, no additional cases of severe paediatric influenza-associated complication or death among children aged under 18 have been reported since yesterday via the ongoing reporting system. The total this year hence remains at 11 (no deaths) and all were A(H3N2). In 2014, 27 (four deaths) were filed.
Things are so bad - that while located in the Northern Hemisphere - Hong Kong is making arrangements to purchase a quantity of the recently revised Southern Hemisphere vaccine, as announced yesterday in New flu vaccine ready by April.
A couple of weeks ago, in Hong Kong CHP Update On Imported H7N9 Case, we looked at published reports saying that HK CHP director Dr. Ko Wing-man had publically expressed concerns over the possibility that this year’s seasonal flu, and the H7N9 virus, could cross paths and create a new, reassorted virus.
Today, based on reports in the South China Morning Post and Sputniknews, Dr. Ko Wing-man has apparently once again voiced those concerns.
Hong Kong's health minister stated that rampant seasonal flu in Hong Kong and the recent strain of bird flu detected in poultry could together give rise to a deadly new virus.
MOSCOW, (Sputnik) – The rampant seasonal flu in Hong Kong and the recent strain of bird flu detected in poultry could together give rise to a deadly new virus, Hong Kong's health minister said Sunday.
“If a person contracts two viruses, a gene recombination is likely to happen,” Ko Wing-man was quoted as saying by the South China Morning Post, adding that the mutation could lead to a more contagious virus.
A novel/seasonal flu reassortment is not a new concern, nor is this scenario limited to H7N9, or the H3N2 virus. Anytime two different flu viruses inhabit the same host (human, avian, porcine, etc.) at the same time, the potential for seeing a reassortant virus exists.
Most of the time, however, the resultant hybrid virus fails to thrive and spread, and it is never even noticed.
But when you have an abundance of seasonal flu co-circulating with a novel flu virus like H7N9, the odds of seeing a someone infected with both subtypes – admittedly a rare event – go up. And the more opportunities these viruses have to get together, the better the chances are they will produce an offspring.
Last month, in EID Journal: Timing of Influenza A(H5N1) in Poultry and Humans Worldwide, 2004–2013, we looked exactly these concerns, albeit focusing on H5N1 and seasonal flu interactions. The author’s wrote:
Co-circulation of influenza A(H5N1) and seasonal influenza viruses among humans and animals could lead to co-infections, reassortment, and emergence of novel viruses with pandemic potential.
Previously, in the Lancet: Coinfection With H7N9 & H3N2, we saw the first evidence of co-infection with the newly emerged H7N9 virus and a seasonal flu virus in a human. While last October, in EID Journal: Human Co-Infection with Avian and Seasonal Influenza Viruses, China, we looked at co-infections in 2 patients in Hangzhou, in January 2014.
In all of three of these cases, no reassortant virus was detected.
But In 2011, an influenza co-infection in Canada led to the creation of a unique hybrid reassorted virus (see Webinar: pH1N1 – H3N2 A Novel Influenza Reassortment), although it was not passed on to anyone else.
And in 2010, in EID Journal: Co-Infection By Influenza Strains, I wrote about a study in New Zealand during the opening months of the 2009 pandemic that discovered at least 11 co-infections (out of 1,044 samples tested) with the older seasonal H1N1 virus and the newly emergent pandemic H1N1 virus.
While rarely detected, influenza A coinfections are probably more common than we realize. Luckily, most do not result in the production of a hybrid strain, else we’d be hip deep in novel viruses all the time.
Over the past few years we’ve seen a growing list of novel (avian, swine, canine) flu viruses emerge (H5N3, H5N2, H5N5, H5N6, H5N8, H7N9, H10N8, H3N8, H6N1, H1N1v, H1N2v, H3N2v, etc. . .), and each carries some risk of reassortment.
With other novels viruses, or with human viruses. Or conceivably both.
How big that risk really is, in terms of producing a pandemic virus, is unknown. Most of these reassortant hybrids will fail and fade away unnoticed, either being biologically `flawed’ in some way, or simply not as competitive as existing strains.
The odds of any one viral assignation producing a viable, humanized virus is probably fairly remote.
The concern is, if these viruses get enough rolls of the genetic dice, they will eventually roll a natural. Which is why we watch Hong Kong, mainland China, and Egypt so carefully this time of year.