(Sat, 27 Mar 2010 12:20:00 +0000)
# 4465
You haven’t seen them all.
At least, not according to a letter that appears in the latest edition of the CDC’s Journal of Emerging Infectious Diseases.
Novel H1N1, as everyone knows by now, is a descendent of a triple reassorted H1N1 swine flu virus that first appeared in American swine herds in 1998. It apparently bounced around in swine herds for a decade before finding the right genetic mutations to adapt to humans.
But H1N1 isn’t the only swine flu virus out there. Known Swine influenza A viruses include H1N1, H1N2, H3N1, H3N2, and H2N3.
Surveillance and reporting of infected herds is suboptimal in this country and around the world, and many farmers find financial disincentives to testing their herds (see Swine Flu: Don’t Test, Don’t Tell).
Today, we’ve news of another triple-reassortant swine flu virus – this time H3N2 – that has been spreading in pigs for more than a decade, that has now shown up in waterfowl in South Dakota.
Volume 16, Number 4–April 2010
Letter
Triple Reassortant Swine Influenza A (H3N2) Virus in Waterfowl
Muthannan A. Ramakrishnan, Ping Wang, Martha Abin, My Yang, Sagar M. Goyal, Marie R. Gramer, Patrick Redig, Monte W. Fuhrman, and Srinand Sreevatsan
To the Editor: In 1998, a new lineage of triple reassortant influenza A (H3N2) virus (TR-H3N2) with genes from humans (hemmaglutinin [HA], neuraminidase [NA], and polymerase basic 1 [PB1]), swine (matrix [M], nonstructural [NS], and nucleoprotein [NP]), and birds (polymerase acidic [PA] and PB2) emerged in the U.S. swine population.
Subsequently, similar viruses were isolated from turkeys (1,2), minks, and humans in the United States and Canada (3,4). In 2007, our national influenza surveillance resulted in isolation of 4 swine-like TR-H3N2 viruses from migratory waterfowl (3 from mallards [Anas platyrrhynchos] and 1 from a northern pintail [Anas acuta] of 266 birds sampled) in north-central South Dakota. We report on the characterization of these TR-H3N2 viruses and hypothesize about their potential for interspecies transmission.
For now, this is mostly a scientific curiosity, not a tangible public health threat. But of course, one could have said the same thing about the triple reassortant H1N1 in pigs 12 months ago.
Which is why many scientists are calling for far more rigorous testing and surveillance of our farm animals.
While one could argue that these viruses have circulated in pigs and other animals for thousands of years without our knowledge, and only rarely have emerged as human health threats, that ignores the recently introduced dynamic of factory farming.
We now put thousands of pigs, and sometimes hundreds of thousands of chickens, in unnaturally close quarters to raise them. This is believed conducive to promoting the spread, and mutation, of certain bacterial and viral pathogens.
Diseases that might never have caught fire fifty years ago, when Old McDonald had a half dozen sows on his farm, have a better opportunity to spread and mutate when introduced into a CAFO (Concentrated Animal Feeding Operation) with thousands of pigs or hundreds of thousands of chickens.
For more perspective on this, you might wish to read Dr. Michael Greger’s Bird Flu: A Virus Of Our Own Hatching (available free, online) and watch his Human Society video on Flu Factories (online here).
The significance of this finding, of a swine H3N2 virus in waterfowl in South Dakota, is less than clear. It may have no public health implications at all, or it could be a harbinger of some future health threat.
Without good, ongoing animal surveillance, it is impossible to establish a baseline and impossible to determine if something new or unusual is happening.
And if the next virus to jump to man is more virulent than novel H1N1, the price of that ignorance could be very high.
Staff Writer
