# 5965
According to the FAO, the world produces somewhere on the order of 100 million tonnes of pork every year, and that number is expected to increase by another 20% by 2020.
By then, roughly half of the world’s pork supply will come from China (cite).
Swine are highly susceptible to the influenza virus, and are capable of serving as `mixing vessels’, allowing them to reassort into new hybrid strains.
Reassortment happens when two different influenza viruses co-infect the same host, swap genetic material, and produce a hybrid virus.
That is essentially what happened in 2009, when the H1N1 swine flu virus emerged after bouncing around swine herds for a decade or more, picking up genetic changes along the way.
And not surprisingly, this recently emergent `humanized’ H1N1 virus has re-entered the swine population and is once again mixing and matching with other circulating swine flu viruses.
In recent months we’ve been following reports of a handful of sporadic human infections across three states (Indiana, Pennsylvania, Maine) by a swine H3N2 virus that has reassorted with – and borrowed the M gene segment from – the pandemic H1N1 virus.
So far, the number of cases is small, and the CDC states there is no evidence that this emerging hybrid virus is spreading in an efficient or sustained manner. But the concern is, that over time it might evolve into a more human-adapted virus.
For some recent coverage of these trH3N2 cases, you may wish to revisit:
CDC Update On trH3N2 Swine Infections
Maine Confirms A 2nd trH3N2 Case
CDC Update On trH3N2 Cases
A 5th trH3N2 SOIV Report
CDC Update On Recent Novel Swine Flu Cases
MMWR: Swine-Origin Influenza A (H3N2) Virus Infection in Two Children
Given the potential for the creation and emergence of novel influenza viruses, surprisingly little testing and surveillance of pigs takes place around the world.
Even in the U.S. some hog farmers are reluctant to allow their herds to be tested (see Swine Flu: Don’t Test, Don’t Tell) out of fears that the discovery of a new swine flu virus would depress pork sales.
As might be expected, Hong Kong - which was the first battleground for the H5N1 bird flu virus in 1996, and which had to deal with SARS in 2003 – has a very aggressive surveillance system.
Today the HKSAR government has released the latest results from their ongoing slaughterhouse surveillance program conducted by the University of Hong Kong.
Between August and mid-October 1,000 pigs were tested, and while no `human H1N1’ viruses were detected, 15 reassorted H3N2 viruses with (unspecified) genetic contributions from the 2009 H1N1 virus were discovered.
First, some excerpts from the press release, then I’ll return with a little more.
FEHD releases results of regular influenza virus surveillance in pigs from August to October
Hong Kong (HKSAR) - The Centre for Food Safety (CFS) of the Food and Environmental Hygiene Department (FEHD) today (November 16) announced results of the regular influenza virus surveillance programme on pigs conducted by the University of Hong Kong (HKU) for August to mid October at the Sheung Shui Slaughterhouse.
Among some 1 000 samples tested, no human swine influenza virus (pandemic H1N1) was detected. However, 15 samples were found to contain a virus that was essentially a swine influenza H3N2 virus but had picked up some genes of human swine influenza virus. The same virus was also found in the last round of surveillance programme for May to July.
The HKU expert in charge of the surveillance programme,professor JSM Peiris, reiterated that this swine influenza H3N2 virus, which carried the genes of the human swine influenza virus, is unlikely cause any major human health risk or problems in food safety.
Under the regular influenza virus surveillance programme for pigs, the CFS has been helping HKU researchers to collect blood and tracheal and nasal swabs from pigs at the Sheung Shui Slaughterhouse twice a month to monitor influenza virus activity in pigs.
"CFS will continue to monitor reports of the HKU surveillance programme and make announcements on a regular basis. Results will be announced immediately if there are significant public health impacts," the spokesman said.
While this report describes these reassorted swine H3N2 viruses as having `picked up some genes of human swine influenza virus’, it provides no further details.
It would be of interest to see just how closely related these reassorted viruses are to the trH3N2 isolates that have recently been detected in the United States over the past few months.
Hopefully we’ll get a more specific description of these H3N2 reassortants over time.
For now, and until such time that these reassortants evolve to become more easily transmissible among humans, they pose a relatively low public health threat.
While it is always possible that the next pandemic will emerge from the wild, the odds say it will come from a farm – where large numbers of animals intermingle, swap viruses, and come in daily contact with humans.
Which is why increasing our surveillance of livestock for zoonotic diseases must become a priority.
Over the past 5 years, we’ve revisited the subject of influenza reassortment dozens of times. For more on this topic, you may wish to visit:
Virology Journal: Receptor Cells In Minor Poultry Species
mBio: A/H1N1 Potential For Mutation
Study: The Continuing Evolution Of Avian H9N2
EID Journal: Co-Infection By Influenza Strains
EID Journal: Swine Flu Reassortants In Pigs
If You’ve Seen One Triple Reassortant Swine Flu Virus . . .
And as always, if you have not already read it, I highly recommend Helen Branswell’s Scientific American article called Flu Factories.
