Effect Measure

Human swine flu in pigs

When swine flu appeared, the pork producers were keen to say there was no connection or relationship between pigs and swine flu (even though the virus’s genetic segments were all of swine origin). They didn’t want anyone to call it swine flu, giving rise to the celebrated naming controversy. But then we started seeing pigs infected with human pandemic swine flu, both in the lab and in pig herds. It’s likely the pigs got it from us, although which direction things went in isn’t completely clear. But originally the virus made the jump from pigs to humans, probably sometime in late 2008 or early 2009, and now it’s likely moving back and forth. Finding the human virus in pig herds in Canada, the US, Norway, Argentina and Northern Ireland, the current official line from the ag industry is, “No surprise. Nothing to see. Move right along.”

Health experts said the three pigs with the H1N1 virus did not show any symptoms of illness. It?s unknown what happened to those pigs. Health experts say even if they were sent to be slaughtered, it should not cause any concern for humans. People cannot contract H1N1 from eating pork.

The pork industry is being advised to monitor their herds for signs of illness. Ag experts said swine that contract H1N1 usually recover. State health leaders say there is no public health threat as a result of the latest findings. (Judy Ambroz, Fox Philly)

I’m not sure if Minnesota state public health leaders were being coy when they said there was no public health risk “as a result of the latest findings,” but there is most certainly a public health issue from pigs becoming a reservoir for this human virus. The US Secretary of Agriculture, Tom Vilsack, and the National Pork Producers Council take pains to stress you can’t get swine flu from eating pork — assuming no one eats raw or rare pork. But that doesn’t mean there still aren’t public health concerns.

The first is that industrial pork production packs large numbers of animals together in unsanitary and highly stressful conditions, the perfect incubator for a more virulent virus. In this setting there is a selective advantage to produce more numerous and perhaps more severe symptoms because sick animals can transmit the virus easily, even if they sicken and die. So the establishment of this new ecological niche for the virus in animals in contact with humans and consumers is a concern.

At the moment the virus isn’t even making the pigs sick, so it is most likely H1N1 pigs are moving into the food chain. If you cook the pork you will kill (more accurately, inactivate) the virus. But the pork on the dinner plate isn’t the only consumer or health concern. Infected and uncooked pork and even infected live pigs routinely come in contact with people in the process of husbandry, slaughter, butchering, packaging and food preparation. While it is most likely true you can’t get swine flu from eating pork, there are many other possible modes of transmitting infection from infected swine.

I understand why the pork producers are nervous. One report suggests a farmer or big agribusiness company has lost $15 to $30 on every pig sold since the outbreak started, and if herds become widely infected that could get worse. If the virus becomes more virulent in pigs, even if it is just in pigs, producers could lose the whole cost of the animal, since animals that are obviously sick are not supposed to be slaughtered (although we know they sometimes are).

I agree with the pork producers and the Secretary of Agriculture and almost everyone else who knows about this that the discovery of more pig herds infected with this virus is “no surprise.” I don’t agree that makes it no big deal from the public health point of view. Whether it is or isn’t we’ll have to see. Yet while the pork industry is officially on record favoring increased testing and surveillance of the swine population, it is not really to their advantage. They’d rather not know.

Widespread and endemic infection of the pig herds everywhere with this virus would also be “no surprise.” Given the biology and the circumstances, the big surprise would be if it didn’t happen.

Comments

  1. #1 phytosleuth
    October 20, 2009

    Along with testing sentinel pigs, it might be a wise decision to test those working with the pigs on a regular basis. Just plain good surveillance

  2. #2 ConnectRN
    October 20, 2009

    We are putting aside extra N95 masks to distribute to the pig farmers to use to protect their herds.

  3. #3 Paula
    October 20, 2009

    Revere, you write, parenthetically, “(even though the virus’s genetic segments were all of swine origin)”; I’m not a microbiologist, so maybe am just confused here, but . . . *all* of them? And agreed re the factory farming. Especially if the pigs or the people are anywhere near the chickens (or local crows, for that matter).

  4. #4 revere
    October 20, 2009

    Paula: Yes, all of them. They are the result of a quadruple reassortment between a triple reassorted North American swine flu from the 90s and a Eurasian swine flu more recently. The 1990s triple reassortant had human and bird segments in it, but it has been in swine most recently and for a while.

    Here’s an earlier post with more info in it:

    http://scienceblogs.com/effectmeasure/2009/04/swine_flu_more_on_the_genetics.php

  5. #5 anna sophia
    October 20, 2009

    From Ontario Ministry of Ag & Rural Affairs: H1N1 in turkey flock in Ontario – let’s see, humans, swine, birds. More reservoirs. More concern.

  6. #6 Don S
    October 20, 2009

    Obviously it is no surprise that this would go back into pigs; it would be a bigger surprise if it didn’t indeed. There is no news here.

    The big worry is not that it is in pigs here. The big worry is that this is a bug that will go into 30-40% of humans across the globe all around the same time and into pigs across the globe and into birds across the globe to some nonzero number. Including in China, Egypt, Thailand, and Indonesia, where H5N1 (Asian Avian)is endemic. Every individual organism, of any species, that gets co-infected with H1N1 and H5N1 is a reassortment opportunity. How many “at bats” will it take to create a human to human transmissible bug that shares some of the greater virulence of H5N1? I don’t know and I know no one else does either. Maybe it is not possible; maybe it will only take a few swings … but in any case it will have a lot of swings given its willingness to swing all ways.

    Worst case scenario? It happens this month in Egypt with someone who then goes on the Haj next month. If there is better way to spread a new bug than putting hundreds of thousands of people in tight quarters for a month and then returning them to the far flung corners of the globe then I do not know what it could be.

    I hope that such is less likely than my inadequate PICU capability for the surge fear is, because that makes my PICU inadequacy fears look very mild indeed.

  7. #7 Paula
    October 20, 2009

    Revere, re #4–that is one terrific and informative blog. Thank you.
    Don S.–oh yes, or even without the Haj. Or troop movements (“incursions”), for that matter.

  8. #8 Anne
    October 20, 2009

    What would be the public health effects of it if some pig- and chicken-consuming country decided to be brutal about it and simply slaughter and dispose of all the pigs and chickens in their country? I realize the economic disruption would be pretty severe, possibly even by comparison with a pandemic, but would it make a substantial difference to short- or long-term public health in that country? (Let’s say a wealthy Western nation, so nobody’s starving for lack of pork or chicken.)

  9. #9 Peter Christian Hall
    October 20, 2009

    Not to mention the connections between MRSA and the swine industry. I don’t have the links handy, but the Dutch have tracked enormous problems in areas with pig farms and New York Times columnist Nicholas Kristof wrote a scary piece about an Indiana county full of MRSA…and swine farms.

    Swine flu has reminded us all that the pork factories are as bad as the poultry industry facilities described so well by Dr. Greger in ‘Bird Flu: A Virus of Our Own Hatching.’

    People can laugh all they like about this or that vaccine, or which company is profiting from flu scares, but there will be a lot more of them (and MRSA, and who-knows-what-else?) as long as we base our diet on such dangerously rendered protein sources.

    Stay well, PCH

  10. #10 Don S
    October 20, 2009

    #8, Egypt did kill off their pigs. All it accomplished was creating a garbage crisis. The garbage was being collected by workers who fed it to their pigs; no pigs, no reason to pick up the garbage, mess in the streets. See http://www.voanews.com/english/2009-10-16-voa16.cfm

    “Cairo is crowded, noisy and now smellier. In recent months, trash in both poor and middle class districts has been piling up.

    The pileup is partly related to the swine flu. To combat the H1N1 virus, the Egyptian government slaughtered all the country’s pigs even though the World Health Organization said the move was misguided.

    The organic waste that was once collected by the so called “zabaleen” to feed their stock of pigs is now ending up in the streets. Some residents have resorted to burning it.”

  11. #11 Sungold
    October 21, 2009

    The CDC page I stumbled on today re: “Swine Flu” would be hilarious if it weren’t so misleading. The CDC advances the argument that swine flu infects pigs but poses no danger to humans. And this page is dated … June 2009!

    The reassortment scenarios have me worried, too. I appreciate Don’s comments on them, though they’re not going to help me sleep easy tonight.

  12. #12 bryan
    October 25, 2009

    Sungold, there’s a big blue box on that link that states “This page contains background information about influenza in pigs. This page does NOT contain information about 2009 H1N1 influenza. . .that is spreading from person to person around the world.”

  13. #13 Lois Klein, R.N., P.H.N.
    October 29, 2009

    Today I went to my local PHD with copies of Canada’s recommendation regarding the “sequential” administration of H1N1 and seasonal flu vaccines, based on their 4 studies of 2,000 people. They found that those who received seasonal flu first, were more susceptible to H1N1 flu.

    However the epidemiologist to whom I spoke about the advisability of administering H1N1 vaccine before seasonal flu vaccine (which is how Canada is doing it, and they’re thinking of scrapping the seasonal flu vaccine program in favor of mass innoculations against H1N1 flu) said that the CDC’s viewpoint is that their studies “couldn’t be replicated”. So we’re giving whatever gets here first.

    Now studying H1N1 and seasonal flu vaccines effects here could only have started since the end of August, when seasonal flu vaccine was released, and H1n1 vaccine became available in the USA, in limited quantity only this month. In order to try to replicate Canada’s studies, we’d need funding and time, of which we’ve had little. Canada accepted the Glaxo-Smithe H1N1 vaccine, while the FDA still hasn’t approved it for use here.

    That put up some red flags for me, about the CDC. I’m all for allegiance to one’s country, but fabricating research is going too far. I did get H1N1 flu 2 weeks after receiving the seasonal flu vaccine, so my opinion may be biased, too. Then again, I’m a Canadian educated Public Health Nurse who was born in Canada of an American parent, and have dual citizenship. Coagulation in my petri dish body occurs occasionally (although my mother always raved about how much better a country the USA is).

  14. #14 revere
    October 29, 2009

    Lois: So far I haven’t seen the Skowronski work but I don’t quite understand what you are saying. NIH did study the sequence issue in clinical trials, but only for the extent to which antibodies indicated an interaction. According to NIH, there is no problem on that score, although again, I haven’t seen the data. There have been multiple attempts to check (replicate in your terms) the Canadian data, including attempts in Canada, and as far as has been announced, no one else can get the same result. I think that’s what the epidemiologist meant by saying the result couldn’t be replicated. The basic question will only be answered after the flu season when the proper studies have been done (one hopes that the relevant national agencies are collecting the data that would be required to anser it).