NEW YORK—Genetic researchers are exploring a safe way to deal with the millions of buried land mines left behind from conflicts around the world: build a better mouse.
Two scientists changed a gene in the nose of bomb-sniffing mice so that neurons normally set to detect thousands of aromas are tuned solely to the odor of TNT, the most commonly used mine explosive. The researchers at Hunter College of the City University of New York say their genetically modified mouse will be 500 times as sensitive to TNT as normal rodents.d
While still experimental, these mutant mice one day could replace the trained rodents and dogs, magnetometers and machines now used to help clear mine fields that, on average, kill or injure a dozen civilians every day in accidental explosions.
"Mice have some advantages as mine detectors because they are cheaper to manage and house, and easier to breed" than other animals, said molecular neurobiologist Charlotte D'Hulst, who developed the new breed of mice at Hunter College with her laboratory director, neuroscientist Paul Feinstein.
By most estimates, there are 110 million unexploded land mines in former war zones across 70 countries. In Bosnia-Herzegovina alone, mine sweepers have located 18,000 mine fields, each containing an unknown number of explosives. In Iraq, there are an estimated 25 million land mines. In Mozambique, about 20 people step on a mine every month, according to the United Nations.
To clear such hazards safely, military combat crews use armored behemoths like the 60-ton remote-controlled M1 Panther vehicle and the Aardvark Mark IV carrier, which flails suspect terrain with 72 chains to trigger buried explosives.
But when the military isn't around, civilians are left to their own devices. For them, mine sweeping in 2011 was a $662 million private enterprise.
In the search for a more-efficient mine sweeper, researchers have experimented with ultrasound probes, seismic sensors, Doppler radar, vapor-sensitive films and ultraviolet light. They have bred plants that change color in the presence of explosives. At the University of Montana, scientists once tried training swarms of bees to home in on TNT.
Stymied, scientists keep returning to a sensor perfected by evolution—the nose.
Explosives such as TNT have a subtle but distinct aroma related to their chemical composition.
But bomb-sniffing dogs, a staple of security squads, are too expensive—as much as $25,000 per animal—and too unreliable for routine mine-sweeping, according to experts at the Lawrence Livermore National Laboratory. In Tanzania, mine-sweepers are training local rats, which scratch when they sniff out land mines.
"The rats are relatively fast and accurate compared to other techniques," said Christophe Cox, head of a mine-clearing group called Apopo in Morogoro, Tanzania. Working on a leash, one of the group's trained African rats can clear an area in 30 minutes that would normally take someone with a metal detector two days, Mr. Cox said.
Starting in 2008, the group used 40 trained rats to clear more than 1,400 acres of mine fields in Mozambique at a cost of $7.2 million. Next month, it expects to start work with a squad of 15 trained rats in Angola, where as many as six million land mines remain from a civil war.
Each rat, however, takes nine months to train and costs $7,900, Mr. Cox said.
To breed a better mine-sweeper, the Hunter researchers took advantage of the recent discovery of a receptor in the rodent brain for the odor of a chemical known as 2,4-dinitrotoluene (DNT), which is essentially the same as TNT, which stands for trinitrotoluene.
All told, a normal mouse has about 10 million neurons devoted to smells. Each odor-sensing neuron has just one type of aroma receptor. Each type is controlled by just one gene. In all, there are a thousand different genes for odor receptors in the mouse brain.
To make their mice hypersensitive to explosives, the researchers altered the gene responsible for the DNT receptor so that the transgenic mice have as many as one million neurons in which the odor receptor is tuned to the fragrance of a land mine.
"Our presumption is that having more odor detectors will make the mouse a more sensitive detector," said Dr. Feinstein.
Animal-behavior researcher Alan Poling of Western Michigan University, who has studied the mine-sweeping rats, isn't sure how much heightened sensitivity will help. "When we think of the shortcomings of the rats, sensitivity is not viewed as one," he said. "If they were much more sensitive, we might have a problem with false positives."
At Hunter College, the researchers this month are breeding hundreds of the mice for laboratory tests. But it may be five years before they are ready for a field trial, in which researchers could work out how best to use the animals' sensitivity to TNT.
"The real proof," Dr. Feinstein said, "is whether you can send out a mouse into a field and safely clear mine fields."
Write to Robert Lee Hotz at email@example.com
A version of this article appeared March 9, 2013, on page A3 in the U.S. edition of The Wall Street Journal, with the headline: Sniffing Out a More-Efficient Mine Sweeper.