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Killer germs under melting ice
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Years ago I sent you a question about the possibility of global warming uncovering nasty things under the ice caps. Are we at risk of reawakening some kind of killer virus or bacteria that's just been waiting for an opportunity like this to feast?

Cecile Johnston, Vermont

Sorry to be late getting back to you, Cecile, but you should be grateful. Here's why:

1. There are indisputably killer germs trapped in the tundra. All we don't know is who, or what, is doomed.

2. There's nothing you can do about it anyway. Your original question came in 13 years ago (we looked it up). So, thanks to my procrastination, you've enjoyed 13 years of ignorance-fueled bliss.

3. But now you've gone and asked again, and guess what: your carefree days are over. French scientists recently reported finding a giant viable virus in 30,000-year-old Siberian permafrostviable being understood to mean infectious. The bug only kills amoebas, which those taking the narrow view of things may figure means they're off the hook. But the more imaginative can reflect: First the viruses came for the amoebas. Then they came for me.

4. You know what, though? I'm not going to worry about it. It's not that I discount the possibility of bad things coming out of the permafrost. It's just that we're likely to have bad things coming at us from all over. Why sweat a few thawed germs?

About those germs. The microbe threat you hear most about nowadays is viruses. These strange pathogens are basically just pieces of genetic code in a container, with no metabolism until they're attached to a host. Strictly speaking they're not alivewhich means, and I admit this sounds ominous, they can't be killed.

Viruses' innate hardiness allows them to remain intact in extreme conditions. All viruses contain either RNA or DNA; it's estimated mutations can occur in up to 50 percent of the genetic code before the virus's viability is threatened. Cold doesn't faze thempolio, influenza, and many other types of virus are known to survive freezing.

True, because viruses work by insinuating themselves into their host's genetic code, they tend to be confined to certain species. But that's no sure thing. Viruses frequently jump across species lines; one virus typically found in sea lions, for example, can also infect pigs, fish, rabbits, cattle, and humans.

Viruses aren't indestructible, of course. Oxidation, freeze-thaw cycles, and natural chemical reactions can all break down the DNA and RNA in ancient microbes. Theoretical considerations suggest no genetic material can survive intact beyond 2 or 3 million years. But that leaves lots of time during which countless viruses could have evolved and been trapped in ice.

The researchers who discovered the 30,000-year-old bug above claim it's the oldest known virus that's still infectious. The RNA of a common tomato-plant virus was recovered from Greenlandic glacial ice formed between 500 and 140,000 years agoviability unknown. But just wait.

The scenario that has some scientists worried is called "genome recycling." It goes like this: (1) virus-bearing ice in polar regions thaws and the meltwater enters local lakes; (2) migratory waterfowl who summer at said lakes drink the water; (3) the ingested viruses recombine in the birds' guts with similar modern viruses, producing nightmarish new strains; (4) the birds poop out the invigorated germs on their return to temperate regions; (5) oh, shit.

Here's the thing, though. Scary as the above may sound, the danger of the next global pandemic originating in polar meltwater so far is entirely speculative. I don't claim it'll never happen. On the contrary, circumstantial evidence suggests we've already had a few small-scale viral infections due to germs liberated by thawing.

But the major epidemics of our times have mostly originated in hot regions. HIV is thought to have emerged from nonhuman primates in central Africa. Ebola virus was first seen in what was then Zaire (now Democratic Republic of Congo). West Nile virus came from (duh) the West Nile region of Uganda. New influenza strains commonly come out of the cities of East and Southeast Asia. Dengue fever and malaria, two scourges of long standing, are largely confined to the tropics.

There are lots of reasons for this, but one of the more obvious is that cold is a barrier. While viruses themselves can survive freezing temperatures, the insects and other critters that carry viruses generally don't. In fact, one of the less-publicized dangers of global warming is that mosquito-borne diseases such as dengue fever, malaria, and West Nile virus will be spread into higher elevations and latitudes, as rising temperatures make it possible for mosquitoes to reach areas they once found too chilly.

OK, we've all seen one version or another of The Thing (or, as in your columnist's case, read the originating John W. Campbell novella, Who Goes There?), about frozen horrors in the Antarctic ice that revive when thawed. So it's not surprising a lot of people are gazing apprehensively at developments in polar regions. All I'm saying is: watch your back.