In defense of "Swine Flu"

Granjas Carroll de Mexico.

That's the industrial pig farm, partly owned by Smithfield Foods, in the Mexican town of La Gloria that was home to the first human case of the current swine flu. Smithfield is the world's largest manufacturer of pork products. Granjas Carroll is an almost inconceivably large pig farm; it raises one million pigs per year, and keeps them in tight, unsanitary quarters that are ideal for the development and the spread of deadly diseases.

There's a serious rebranding effort under way, led by the pork industry, to call swine flu by its technical name, H1N1. (Actually, its technical name is more accurately AH1N1, but this rebranding effort is aimed not so much at accuracy as at avoiding using the word "swine," so the "A" is typically dropped.) The pork lobby apparently has friends in high places, from CNN to the CDC to President Obama, and the rebranding is starting to stick. But I don't want to play along.

H1N1??

Influenza comes in 3 main strains, A, B, and C, of which A is the most common. These viruses are characterized according to the form of two proteins, hemagglutinin (H) and neuraminidase (N). Both of these proteins can come in multiple, related but slightly different forms, which are given different numbers. The influenza commonly called "avian flu" or "bird flu" is an AH5N1 form. Many (but not most) cases of seasonal flu, which kills ~30,00-40,000 Americans every year and ~half a million people around the world, are caused by an AH3N2 form.

But when was the last time you told your boss you couldn't make it into work because you had a touch of H3N2?

Moreover, not only is the rebranding effort kind of weird, but, under the guise of being more specific and more accurate, it is in fact less specific and less accurate. "Swine flu 2009" did not have a meaning until the outbreak of the current AH1N1 form that showed up in La Gloria and has been spreading around the world since. It now has a very specific meaning; it refers to a particular virus, and when someone talks about swine flu 2009 it specifies the particular virus in the same way as talking about water specifies H2O. AH1N1, however, refers to any influenza virus characterized by the hemagglutanin 1, neuraminidase 1 proteins. Swine flu 2009 is one such virus. Spanish Flu of 1918 was another. And many cases of ordinary seasonal flu are caused by virus that is of the AH1N1 subtype (serotype). In other words, although "H1N1" sounds more sciency and specific than "swine flu," the difference between the terms is actually more akin to the difference between "polar molecule-based liquid" and "water". The former sounds more scientific, but the latter is more specific.

Did the current outbreak swine flu originate at Granjas Carroll? It is not clear. Initial tests indicate that the strain responsible for human infections is not present at that farm, but it will take some pretty good evidence to convince me that a pig-based influenza strain did not have something to do with the million pig farm in the town in which the virus first affected people.

Whatever turns out to be the case, though, this question obscures a larger point. Industrial farms place us all at risk for deadly viral and bacterial infections.

All else being equal, a microbe is more harmful or deadly to the extent that it rapidly makes many copies of itself. There is, of course, a huge amount of scatter associated with this statement. Some microbes produce harmful toxins even without rapidly multiplying, while others (such as E-coli in our gut) can peaceably maintain a symbiosis with us even in very large quantities. But as a general rule of thumb, larger microbe populations tend to be associated with worse host outcomes.

A microbe that maintains a large population in its host increases its probability of spreading to other hosts. There is, therefore, a general selective pressure on microbes to be deadly.

This pressure is generally offset, however, by the fact that sick and dying hosts tend not to be very mobile, and therefore tend to be rather ineffective at spreading the microbe to new hosts. In the wild, forms of viruses/bacteria that completely incapacitate their hosts tend not to be passed on, which means that the prevailing forms tend to be ones that are less deadly, and less incapacitating.

The difference between Ebola and the common cold is instructive. Ebola causes a rapid and rather gruesome death. As a result, people tend to avoid those who are sick with Ebola virus. Ebola, thankfully, has not spread rapidly in human populations, and this might be part of the reason why. Common cold, on the other hand, annoys its victims, but leaves them able to go about their daily activities, where they encounter many new potential hosts for the virus. Everyone gets colds, and the cold virus is so successful in large part because it leaves its victims relatively healthy.

On crowded, cramped, unsanitary industrial farms, the ordinary selective pressure against overly incapacitating a host is removed from the process of microbe evolution. The remaining selective pressure is the standard one: replicate as fast as possible, without regard to the health of the host.

Incidentally, this is why many public health procedures have a dual benefit: (1) the obvious one — reduce rate of transmission; and (2) the nice corollary — make diseases evolve to less deadly forms. As an example of (2), mosquito netting has caused malaria to evolve to less deadly forms. In regions affected by malaria, when there is no mosquito netting, even immobile, dying people can be bitten by mosquitos who carry the disease to new victims. But when houses have mosquito netting, forms of the disease that force victims to stay inside do not get passed on and the only forms that do get passed on are ones that are mild enough to allow victims to walk outside while sick. Similarly with HIV and condoms: in a region where people often use condoms, HIV must keep its host alive for long enough for a rare event (a moment of poor judgment, or a broken condom) to happen that allows it to be passed on. In regions, such as Sub Saharan Africa and Souteast Asia, where promiscuity without use of condoms is common, HIV faces no such selective pressure, and forms of the virus are favored that tend to be deadly much faster.

Did this swine flu come from this particular swine farm? It seems likely to me that it did, but the answer might turn out to be no. But is swine flu related to people and animals associating in close quarters, and to the kind of dense packing of animals that happens at factory farms? While I cannot prove this, it seems incredibly likely. What's more, regardless of the origin of swine flu 2009, future pandemics are likelier in a world that has lots of human-animal interaction at large factory farms than in a world that doesn't.

The pork industry is concerned that the name "swine flu" will lead people to stop eating pork out of worry that it will sicken them. Although it is bad for public health if people think that the only way to get sick from swine flu is by eating pork products (and I do know of at least one person who is under this misimpression), it will be good for public health over the long term if factory farms cease to exist. If people stop eating pork out of a misguided attempt to avoid swine flu, I will still be happy, because the decline of the meat industry will tend to make us all safer over the long run.

The upshot is that meat is too cheap, because when we buy meat we do not pay the full longterm cost. We don't pay for the environmental costs (both the damage to rivers, streams, and the water supply caused by the feces of millions of pigs, cows, chickens per farm; and the contribution to global warming, etc.), and we don't pay for the probability of spawning dangerous diseases. I'm not saying we should eliminate meat. I'm just saying that it should be priced appropriately, taking into full account the negative externalities associated with it.

Changing how we interact with our food constitutes items 117-128 on my to-do list for if I ever become czar of the world. Given that a czarship does not appear to be in my imminent future, I'll just do my small part by proudly continuing to call it "Swine Flu."