Swine flu: humans, a dangerous species

It's now fairly certain that humans have returned the favor and given H1N1/2009 to pigs, another example of a cozy flu swapping relationship now almost a century old. At the time of the 1918 pandemic, pigs were also suffering a serious influenza-like illness which was quickly dubbed "hog flu." The pigs got sick suddenly with fever and respiratory symptoms but recovered quickly and mortality was fairly low. The same thing occurred elsewhere (Europe, China) during and after the pandemic, so it wasn't hard to make a connection between the "Spanish flu" and "hog flu." But in 1918 it wasn't known that influenza was a disease caused by a virus. It wasn't until the 1930s that swine influenza was linked to human influenza virus, both the ones circulating in the 1930s and the 1918 virus. For a long time it was thought (and I learned in medical school) that the 1918 pandemic was caused when the virus jumped from pigs to humans. It is only recently, with advanced methods for analyzing the family tree of viruses, that there is good evidence we got the direction wrong: the virus came originally from birds to humans and we then gave it to pigs (Taubenberger et al.; Vana and Westover).

And now it looks like we've done it again:

A farmhand who travelled to Mexico and fell ill upon his return apparently infected the pigs with the H1N1 influenza virus, said David Butler-Jones, Canada's chief public health officer.

“So far, basically what we're seeing in the pig is the same strain as we see in the humans,” Mr. Butler-Jones said.

“The concern is that if it's circulating in a pig herd, that any other humans that come onto the farm might be exposed and be at risk.”

The farm worker returned to Canada from Mexico on April 12 and had contact with the pigs two days later. About 220 pigs in the herd of 2,200 began showing signs of the flu on April 24, said the country's top veterinary officer, Brian Evans of the Canadian Food Inspection Agency.

All of the pigs are recovering or have recovered and the farm worker has also recovered.

One other farm worker subsequently fell ill. It's not yet known if that person caught the swine flu. (Steve Rennie, Helen Branswell, Bob Weber, Canadian Press via The Globe and Mail)

At the outset we didn't know how easy it would be for this to happen, but it shouldn't come as a total surprise. The H1N1/2009 (aka swine flu) has internal genetic segments that are all swine origin, although two of them bear marks of human and avian ancestry. Most Americans also have ancestry from elsewhere at some points in their family trees and even Native Americans belonged to different natural groups ("tribes," now called "nations"). That doesn't prevent any of us from being "American" in almost all respects. We are are adapted to the US cultural and economic environment, whatever our ancestry. Maybe a better analogy, though, would be the game of basketball. This is a worldwide sport that operates by essentially the same rules everywhere. But the styles can be quite different in US colleges, the professional leagues (men's and women's), secondary schools, Western and Eastern Europe, China, etc. Is a US highschool basketball star interchangeable with a Chinese basketball player? Each is adapted to the style, skill level and specific conditions of his team of origin. Each plays well with his or her original team mates but there's no guarantee they will play with another team from a far away place, even if the rules are the same.

Now a swine team is playing in a human environment. They played well together in pigs and, with some relatively small adjustments, seem to have made the transition to humans, too. Where and when they learned to play in the human environment we don't know. But they seem to have retained their ability to play in pigs, too, so maybe it was quite recent.

In the meantime the hog industry has a big problem, mainly economic. The presence of the virus in a country's pigs could affect exports as other countries ban imports from infected areas; productivity, since the pigs get sick; and public relations, since the animal will be stigmatized. It is less of a public health problem because the virus is already circulating among humans. We get it from each other, not pigs. Even if pigs are infected, cooking the pork kills the virus. While contact with raw pork during preparation is a theoretically possible mode of transmission it is unlikely and is a marginal issue in the big picture.

A tangled web and once again, it is humans who are a danger to pigs, not the other way around. We retain our title as one of the most dangerous species in the biosphere.

More like this

It's a tough time of year to make sure there are no infected or contagious humans going to Canadian farms. It's the time of year when Latin American and Caribbean farm workers arrive for seasonal work. And clearly, a time when year round Canadian farm workers take advantage of off season cheap trips to Mexico.

We're going to be eating a lot of cheap barbecued pork in the U.S. and Canada this summer. They'll be giving it away.

Second weird thought of the day:

Given the possibility that H1N1 could mutate and become much more virulent in the months and years ahead; is it to your advantage to catch the weaker version of the virus now and to then be resistant to future, perhaps more dangerous forms of H1N1?

Pat here's your question (I think, worded a little differently) from a blog by Vincent Racaniello Ph.D., Professor of Microbiology at Columbia University Medical Center. (He's doing the answering)


A: Do not attempt to become infected now; the outcome of influenza infection may not be benign.

FWIW, not having pork in your diet,is probably not the worst lifestyle change one could make.... I have donned my flamesuit for all you pig-huggers out there..

I would like to re-post a question that I posted too far back to possibly receive an answer (Posted at yesterday's: "Swine flu: case definitions and tough decisions." But it is relevant (I believe) to your current post, as well. It remains unanswered and I beg everyone's indulgence if it makes no sense:

Phillip: To clarify my 11:41 question, which you claim "no one" can understand (I assume you're representing this entire blog audience), I quote Snowys Owl's post above. She doesn't I.D. who "Mr. Evans" is, but she quotes him as follows: "âAt this point in time, the issue of this being a human virus, having been introduced to the pigs, and the characterization of this virus, shows it is still that virus,â he said. âThere's been no adaptation identified through the transfer from humans to pigs at this time.â
âThe chance that these pigs could transfer virus to a person is remote,â Mr. Evans said.

Outside of Evans' quote, Snowy then adds: "The H1N1 virus, which is made up of swine flu genes, is believed to have jumped to humans some time back and has been passing person to person"

That was the basis for my 11:41 question: re-phrased, the same virus has demonstrated that, at some time in the past, pigs *did* transmit it to humans. Currently it is readily tranmissible H2H, and even now seems to be transmissible human to pig. My question: why and when did it become a *remote* possibility that pigs could transfer virus back to humans (thus completing the transmission cycle), if it is assumed that at one time that was exactly what happened, and it is known to be the same virus.

Relevance of the question: If that is a misstatement, and it is *still* readily transmissible from pigs to humans, this indeed does represent a "hot spot" for a mutation situation, upon which, Phillip, you and I (I believe)seem to agree.

sorry, but I can't find anything suggesting that the 1918
virus went from humans to swine and not vice versa
in the public parts (abstracts) of those papers:
(Taubenberger et al.; Vana and Westover).

the papers themselves are not public , so I must
assume that they don't want us to know.

anon: Look again at the Taubenberger abstract ("avian source"). Just because you can't get a copy doesn't mean it isn't public. It is available to anyone with access to a library that carries the journal or has a subscription. You have jumped to an unwarranted conclusion.

panfluwatch, Egypt's decision may not be foolish. If and when swine flu hits Egypt, there could well be a strong religious backlash against swine growers that might be worse for them than loosing their herds now. Remember how religious fanatics in this country blamed Katrina on a planned gay parade and on gambling - even when no plausible connection exists connections are made. The connection with the swine would feel more convincing to the fanatic religious folks in Egypt.

Crofsblog post an interesting article from Peter Palese and I tought it would be pertinent to cross-posted here.

Why swine flu isnât so scary
2 May 2009

Peter Palese has written an excellent opinion piece for the Wall Street Journal on why swine flu is not that scary.

First, Palese reviews the concerns about the new H1N1 viruses.

Next, he argues why we should be optimistic:

1. In 1976 there was a an outbreak of an H1N1 swine virus in Fort Dix, New Jersey, which showed human to human transmission but did not go on to become a highly virulent pandemic strain.

2. The presently circulating swine virus is most likely not more virulent than the other seasonal strains we have experienced over the last several years.

3. The current swine virus lacks an important molecular signature (the protein PB1-F2) which was present in the 1918 virus and in the highly lethal H5N1 chicken viruses. If this virulence marker is necessary for an influenza virus to become highly pathogenic in humans or in chickens, then the current swine virus doesnât have what it takes to become a major killer.

4. Since people have been exposed to H1N1 viruses over many decades, we likely have some cross-reactive immunity against the swine H1N1 virus. While it may not be sufficient to prevent becoming ill, it may very well dampen the impact of the virus on mortality. I would postulate that by virtue of this âherd immunityâ even a 1918-like H1N1 virus could never have the horrific effect it had in the past. The most likely outcome is that the current swine virus will become another (fourth) strain of regular seasonal influenza.


Well, at least the manufacturers are going to be cranking up production of antivirals as agriculture starts to administer them in bulk to pigs.

They won't be useful for long, but they'll be available.

By D. C. Sessions (not verified) on 03 May 2009 #permalink

I don't believe the avian components need to pass directly from birds to human. A multiple infection of swine having having an avian influenza, human influenza and swine influenza could be the source of the influenza which sickened pigs in 1918 and jumped to humans. Kansas has been suspected as being the source of the 1918 virus and had a large swine population.

After the mild phase in 1918 in the US in spring, it jumped to Europe and the rest of the world. This was in the midst of WW I, where the virus found in Europe a large population with high population density of people whose immune systems would have been depressed as a result of the war, stress and poor nutrition. It is in Europe that the virus evolved to become more virulent over the summer, and then returned to the US with those troops returning home.

These conditions do not exist today. It is just as likely the virus will mutate to spread more easily, yet be less lethal, than follow the 1918 evolution. After the 2nd wave in 1918, each successive wave became less virulent.

@ SnowyOwl:

I should start out by saying that Dr. Palese is a world-class virologist, and I am not. Applied public health is more my area of expertise, and I do not in any way pretend to his level of knowledge about the structure and function of the flu virus.

I certainly hope that he is correct, and since I'm not about to subscribe to the WSJ just for the sake of reading his article, I'll have to rely on Crofsblog's extract of his argument for my understanding of what the good doctor is saying.

It's worth noting that among the list of "concerns" identified by Dr. Palese and included in Crofsblog's post, points 2, 3 & 4 would seem to significantly temper the conclusions presented in the "reasons to be optimistic" section.

Additionally, I remember hearing in a CDC news conference -I believe in response to a rather insistent question from a journalist with the New Scientist- that early tests showed no useful cross-reactive immunity was likely between this strain and currently circulating H1N1 seasonal flu viruses.

Lastly, with n=2 for the 1918 H1N1 and the current H5N1, I wonder if we aren't putting to much stock in the importance of one particular virulence marker. That is, might there be some confusion between what is necessary and what is sufficient?

The PB1-F2 might be able to cause high virulence without being the only possible cause of high virulence. That is, it might be a sufficient, but not necessary cause.

I don't mean to imply that there's any reason to panic, because there isn't. But I wouldn't like the public or the response community to grow too sanguine until we know for sure what we're up against.

The 1918 pandemic started off with a kinder, gentler first wave in the spring before becoming far more lethal in the fall. If we let down our guard now, and that pattern repeats itself, we will not soon be forgiven.

"These conditions do not exist today."

Not in the developed world.

By Phillip Huggan (not verified) on 03 May 2009 #permalink

Thanks anyway (for nothing) group, but the first paragraph of Crof's H5N1 last posting answers my question, spot on.

"The discovery of the new swine flu in pigs on an Alberta farm raises a spectre that worries influenza experts: the possibility of the virus moving back and forth between humans and pigs, giving it more chances to mutate along the way."

Guess the question was so stupid or incomprehensible, huh, Phil?

Yep. Get a hobby. You are seeking status from a group of strangers (apart from some doctors who may know eachother). People are ignoring you because you are being obnoxious; either people don't know your question or don't have the answer. I was being polite but now you are singling me out. Fuck off.

By Phillip Huggan (not verified) on 03 May 2009 #permalink

Phil, baby, I don't know you from Adam, and vice versa. You started this little pissing contest by calling me stupid this morning and then announcing for the whole group that my posted question was incomprehensible (is that your idea of being polite). I didn't single you out; you're suffering from a slight case of projection, as it's identified in the field of psychology.

Do you still speak for the whole group when you label my posts as obnoxious and my motives for seeking information as seeking status from a group of strangers? I was under the impression that this blog welcomed everyone concerned about this I.D. event, folks of all levels of smarts and education.

revere, does this jerk speak for you? If so, just give me the word, and I'm out of here. Othewise, Phil, you FUCK OFF!

no you fuck off

By Phillip Huggan (not verified) on 03 May 2009 #permalink

Discovery of new swine flu in Alberta pigs raises spectre that worries experts
By Allison Jones And Helen Branswell, THE CANADIAN PRESS


The discovery of the new swine flu in pigs on an Alberta farm raises a spectre that worries influenza experts: the possibility of the virus moving back and forth between humans and pigs, giving it more chances to mutate along the way.


While the development did not come as a surprise to the World Health Organization or other experts, they expressed concern.

"We expected that at some point since this virus has swine virus elements that we would find possibly the virus in swine pigs in the region where the virus is circulating," Dr. Peter Ben Embarek, a WHO food safety scientist, said Sunday from Geneva.

Measures should be taken to prevent further human exposure to sick animals because of a risk people around the pigs could become infected, Embarek said.

"It has happened in the past with classical swine influenza," he said.

Dr. Ruben Donis, head of the molecular genetics branch of the influenza division at the US Centers for Disease Control, said the movement of a virus from one species to another creates more opportunities for mutations.

While it isn't a given that any changes in the virus would mean it becomes more virulent - causes more severe disease - that cannot be ruled out, he said.

"It's possible," Donis said in an interview from Atlanta. "We have to consider all options."

Donis was especially concerned about the virus getting seeded in pig populations on small farms that don't have the same level of biosecurity as larger operations.

Another worker on the Alberta farm subsequently fell ill, but it's not yet known if that person caught the swine flu.

The whole article worth reading


"PHOENIX - In a press conference Saturday, Maricopa County health director Bob England said they will stop ordering school closures if a student or staff member is diagnosed with swine flu. ... Based on data collected in the past week, there's nothing that suggests the H1N1 flu is behaving differently than the common seasonal flu, England said."


The experts I've listened to have generally said it is too early to say for sure that H1N1 is no worse than seasonal flu.

England did say that he would close schools if conditions worsened.

Has the virus mutated to F.U.H1N1?

Nice link glock. I never considered temperature as a flu factor. Maybe a (or another) reason why flu likes high altitude cities.
What is the expected time until a pig Swine Flu vaccine is developed? For humans of this strain it is 3-6 months and I'm sure they'll push for before Northern Hemisphere winter. Same timeline for oinker vaccine? If it appears the genetics of Swine Flu infected oinkers at two or more different infected pig farms diverges, does that mean a vaccine for oinkers won't work? I hope the pig farm surveillence is up to snuff (non-existent in Port Coquitlam).

By Phillip Huggan (not verified) on 03 May 2009 #permalink

Phil I think the temperature mutations relate to host organism body temps. We are about 36.8C, chickens 42, pigs 39.

But as the animals look from Napoleon to Pilkington, from man to pig and from pig back to man, they find that they are unable to tell the difference.

By Animal Farm (not verified) on 03 May 2009 #permalink

Phillip, Paul: Enough. Behave or I will ban you both.

Imagine this comedy of errors by the CDC and WHO in the presence of future bioterror...
CDC doesn't read their emails; don't see where I'm supposed to post if banned.

By Phillip Huggan (not verified) on 04 May 2009 #permalink

Phillip, let's consider yesterday a bad day for both of us. We shouldn't be snarking each other when there's a real enemy out there - the virus.

I know you're a bright and committed scientist and, as for myself, I'm engaged on a very steep learning curve. That's probably why I was so sensitive to the "stupid" remark; but we're big guys now, and should be standing shoulder to shoulder against a common enemy.

We both respect revere too much to engage in such a poor show on his highly visible blog.

I offer you my virtual hand in peace and friendship, and in all sincerity.

Peace Brother,

What's the exact structure of swine flu?