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  • Richard Conniff writes about behavior, in humans and other animals, on two, four, six, and eight legs, plus the occasional slither.

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To Stop Tobacco Smugglers, Send in a Very Large Rat

Posted by Richard Conniff on June 16, 2014

Have banana? Will travel.

Have banana? Will travel.

Every year, large criminal organizations smuggle enough tobacco for 657 billion cigarettes across international borders. That amounts to almost 12 percent of the tobacco trade, and it costs governments $40 billion to $50 billion a year in lost tax revenue. But the more important result is that smuggling makes cigarettes available far more cheaply, thus increasing the number of people who smoke. Smuggling often happens with the reported complicity of big tobacco companies, who profit by it. And yet stopping or slowing the trade would prevent 164,000 premature deaths every year by 2030, mostly in poor countries that are already afflicted with other health threats.

How to get there? It may take a rat to catch a rat, according to a new study in the Journal of Veterinary Behavior. Specifically, it may take batteries of African giant pouched rats lined up at seaports, like a different kind of longshoreman, to locate shipments of illicit t0bacco by sniffing the air from shipping containers.

These rats are in fact giants, relative to most other rats, with some weighing in at more than four pounds. They’re native to much of Africa, and still relatively common in the wild there. The “pouched” in their common name refers to their chipmunk-like cheek pouches. African giant pouched rats can live in captivity for eight years, making them popular as pets in some areas, and even the researchers in the new study dignified their test rats with names. (Ethnically diverse names, at that. They sound like a New York law firm: Harrison, Habreeze, Myron, and Bravo.)

This species, Cricetomys gambianus, has already demonstrated its remarkable olfactory powers as a cheap and efficient way of detecting and removing land mines from war zones.With training, these rats are not only sensitive enough to smell land mines underfoot, but—critically—they are also light enough not to explode them. Handlers follow behind the leashed rat and mark all mines for removal crews. The Belgian nonprofit APOPO (the full name translates to “Anti-Personnel Landmines Detection Product Development”) reports that since it started mine-clearing operations in Mozambique in 2006, the rats have helped find and clear more than 3,000 land mines.

More recently, African giant pouched rats have gone to work in the medical world, helping to detect hidden cases of tuberculosis, a deadly disease that is once again epidemic in many developing countries. The conventional method of detection requires a trained technician to examine a patient’s saliva sample through a microscope, and the average human can handle only about 40 samples a day. A trained rat can check that many specimens in seven minutes, according to APOPO. Deployed in partner hospitals in Tanzania in 2010, the rats increased the tuberculosis detection rate by 43 percent in the first year.

The protocol used for sniffing out tuberculosis is essentially the same as the one now being proposed for detecting illegal tobacco shipments.  It involves a special cage with 10 sample wells in the bottom. The rat sniffs each well briefly and pauses when it detects the target scent. In training, getting the target right brings a food reward, and the rat quickly becomes adept at running down the line and stopping at the smell it has learned to associate with the reward.

For the tobacco study, researchers stored filter paper near packs of cigarettes, and other forms of tobacco, for a period of days to weeks. Sometimes they added in extra scents, like curry or coffee, to confuse the test rats. Then they ran the paper samples through the test cages of Harrison, Habreeze, Myron, and Bravo. Harrison seems to have been the ace of the group, scoring 100 percent for seven cigarette brands. But all four rats managed to spot 80 percent or 90 percent of the cigarette samples, with false positives well under 1 percent.

Couldn’t dogs, those other celebrated sniffers, do just as well? It’s possible, but the rats are easier to house, feed, and maintain, says APOPO researcher Amanda Mahoney. They’re also easy to ship wherever they’re needed, and they don’t have to bond with an individual to do their work.

Mahoney and her coauthors acknowledge that there is still plenty of additional research needed before African giant pouched rats go to work in seaports around the world. It remains to be seen, for instance, just how many hours a day a rat can spend sniffing and still remain effective. Using rats would also require developing a system to draw air from shipping containers through filters, which the rats would then examine.

But if it happens, it will be yet another example in the surprising list of ways rats are now helping humans breathe easier.

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