Effect Measure

Influenza/A viruses naturally infect aquatic wildfowl like ducks and there are a lot of influenza/A subtypes besides the H5N1 that has been in the news. Some people are heavily exposed to wild ducks, namely serious duck hunters and game handlers. Why don’t they get infected with some of the other influenza virus subtypes? It turns out nobody has looked to see if they do until now. In a paper just published in CDC’s journal, Emerging Infectious Diseases scientists from the University of Iowa and St. Jude’s Children’s Hospital report that on occasion it is possible to see evidence of infection with other influenza/A subtypes.

The study looked at blood samples from 39 Iowa duck hunters and 68 Iowa Department of Natural Resources game handlers, many of whom worked banding (marking) wild ducks. Three of these subjects had antibodies against one influenza subtype, H11N9, the first time we have seen evidence of human infection from this virus and the first report of transmission to humans of influenza virus from wild birds. All of the positive subjects had long time and substantial histories of contacts with wild ducks, one as a hunter with a history of one to two months duck hunting in the marshes per year harvesting 100 ducks and handling another 300 per season. This even exceeded the two DNR employees who also had in excess of 30 year histories. None of the three were smokers (a risk factor for other zoonotic diseases, presumably from the hand to mouth contamination entailed by smoking) and none used any personal protective gear while working or hunting. No health histories were obtained so it isn’t known if the subjects experienced any symptoms. For other avian viruses (H5N1 excepted) when illnesses occur they are usually mild or asymptomatic. Infections with both H7 and H9 subtypes have previously been reported, but not H11.

How do we interpret these findings? Previous studies infecting human volunteers with H4N8, H6N1 and H10N7 were successful resulting in some viral shedding and mild symptoms but not detectable antibody response (Beare and Webster, “Replication of avian influenza viruses in humans,” Arch Virol. 1991;119(1-2):37-42). Thus we know that humans can be infected but not show serological signs. The evidence of H11 infection in three subjects may be because the H11 subtype is more immunogenic, produces a heavier infection or because the current assays were more sensitive than those used in the previous 1991 study. The absence of serological evidence of H4 and H6 antibodies despite the fact that these subtypes are quite prevalent in wild ducks ducking the hunting and banding seasons suggests the sensitivity of the assay is not the explanation, however.

Taken together, the authors suggest that infection with avian infuenza/A subtypes may be more common than serological evidence indicates. Whether this also holds true for the H5N1 subtypes we don’t know, but it does raise the question as to whether still scant negative seroprevalence data for H5N1 accurately reflects the rate of infection in human populations in contact with infected poultry, sick patients and possibly other animal reservoirs.

Comments

  1. #1 tan06
    July 27, 2006

    How did the researchers take the sample/population together? Did those hunters come from a list, did they check hunters who had died recently or some years ago?

  2. #2 TwoCrow
    July 27, 2006

    I think they were all living hunters and dnr officers. Nobody died from it. Of course it makes sense– most of us probably have zillions of antibodies to all sorts of things we’ve been exposed to but nobody ever bothered to test for.

  3. #3 revere
    July 27, 2006

    tan06: list of living hunters and employees. You can read the details at the link I provided which is to the actual paper.

    TwoCrow: But it isn’t obvious we’d have antibodies to viruses specific to toher species, and in fact most of those tested didn’t.

  4. #4 Wayne
    July 28, 2006

    In my humble opinion I believe the signifigance of the Duck Hunter paper is that the world is slowly being poisoned by the bird flu virus and this is reflected in the flu antibodies of the duck hunters blood.We don,t live in an environment we are extentions of it.As the bird flu virus sreads through the environment more people from different areas of our environment will show signs of contact with the virus.The duck hunters are just the thin edge of the wedge.

  5. #5 TwoCrow
    July 28, 2006

    Revere: I didn’t say it was “obvious”, I said it made sense to me. I thought I was vague enough saying “zillions of things” but I take from your reply that anti-bodies are only in relation to viruses. My interest in biology and evolution didn’t develop until I was decades out of school and there are sad gaps in my terminology and grasp of concepts. I am a farmer and I have daily contact with multiple species of domestic animals and fleeting contact with vast numbers of wild creatures. All I know is that my children who have had surrepticious slurps from the stock tank when water at the house was too far, waded in the mud with baby pigs, camped out with the pet goat, been in and out of the river all summer, and run barefoot through the cow pasture despite being told to put on their boots are all vastly healthier than their friends in town. (So much so that I recently found out the doctor took us off his records since he thought we’d moved) I assume at least part of it is attributable to being exposed to so much, um, stuff.

  6. #6 revere
    July 28, 2006

    Wayne: Remember that it isn’t one virus (“the virus”) but many different viruses. In this case it isn’t the one we have been worried about, but another one. This kind of cross species infection is of unknown frequency. It may be common, as Two Crow implies, or very uncommon as we assumed.

    TwoCrow: Yes, I understood you didn’t say obvious, I did. I wasn’t criticizing you, just making a point about the paper, which is it found something that wasn’t obvious. It may make sense to you for whatever reason, which is fine. It means it wasn’t a surprise, nor was it a surprise to me. I’m guessing it is a lot more common than we thought, which was my point, too. But we don’t know until we look, which is what was important here.

  7. #7 cougar
    July 28, 2006

    I’d like to echo what TwoCrow said about his kids being so healthy despite their constant contact with so many potentially “germy” environments. I know this isn’t true across the board, and certainly genetics may play a big part, but I’ve always suspected that our culture’s preoccupation with killing germs, etc. is actually weakening our immune systems. I get cut and scraped all the time, never apply medication and hardly ever get infections. And I too work in dirty, germy environments. I grew up this way. Does anyone know of studies that have been done on immune system health and overuse of antibiotics and other meds? I know we’re breeding hardier bugs, but are we also creating weaker immune systems?

  8. #8 Ground Zero Homeboy
    July 28, 2006

    There is a solid study correlating asthma with having no exposure to barnyard animals before 5-7 years old. Too lazy to look it up. Germany I think.
    The key was exposure to various endotoxins created by barnyard bacteria.

  9. #9 Ground Zero Homeboy
    July 29, 2006

    There are a bunch of studies on this now. Bacterial endotoxin and fungal glucans are common research targets. A survey:

    http://reason.com/rb/rb010301.shtml

    Reason Magazine. Forgive me father for I have sinned.

  10. #10 cougar
    July 29, 2006

    GZH: thanks for the link – while specifically targeting asthma, the conclusion that asthma risk is increased later in life given a “cleaner” environment in childhood confirms my own suspicions. Instead of being so germophobic, we should be more concerned with training our immune systems to fight off these nasty little invaders.

  11. #11 revere
    July 29, 2006

    Be aware the dirt hypothesis about asthma is highly controversial and not generally acceepeted. That doesn’t mean it’s wrong, obviously. Remember, too, that vaccinations are an exercise of our immune systems. The world is still a very germy place, no what we do to it. Most of our germicides are ineffective for anything except company profits.