The dog has been called man鈥檚 best friend, but rats certainly have never been referred to in that endearing fashion.聽Yet, they can save lives as well as dogs; maybe even better.聽How?聽By using their remarkable sense of smell.聽Dogs of course have a great sense of smell.聽A woman's dog had been known to save her life聽by constantly sniffing at a mole on her leg, which turned out to be a malignant melanoma.聽It seems that unusual protein synthesis as happens in such tumors is accompanied by unique odours.聽Indeed, the fact that diseases have certain smells has long been known.聽The ancient Chinese supposedly diagnosed some diseases by sniffing a patient鈥檚 saliva as it was dropped into a flame.聽But the human nose isn鈥檛 nearly as reliable as that of a rat.
Bart Weetjens, a Belgian researcher working in Tanzania came up with an interesting idea triggered by the Dutch word for tuberculosis, 鈥渢ering.鈥澛營t translates as 鈥渢he smell of tar,鈥� apparently because tuberculosis patients exude a tar-like scent.聽Weetjens wondered whether it might be possible to diagnose the disease in its incipient stage, when the human nose would pick up nothing, but a more sensitive one might.聽This would be of tremendous potential benefit because some two and a half million people a year die from TB, mostly in the developing countries.聽With early detection the disease is curable, but early detection is very difficult. In fact, it takes experts looking through a microscope at sputum smears taken over several days to confirm the presence of disease.聽Weetjens was familiar with some work using rats to sniff out landmines.聽The rodents were trained by rewarding them with food at the appropriate time to sniff out explosives.聽In Mozambique a dozen rats successfully sniffed out twenty land mines.聽And no, the rats didn鈥檛 blow up.
So if they could sniff out explosives, why not TB?聽Saliva from tuberculosis patients was put in little dishes and when the rats approached the samples they were rewarded with peanuts and bananas, which are rat delicacies.聽They learned well.聽When tested with 10,000 saliva samples, the trained rodents sniffed out the ones infected with the tuberculosis bacterium 77% of the time.聽 They did even better when confronted by bacteria grown in culture dishes.聽They got these right over 90% of the time.
Now is your doctor going to reach into his drawer to take out a couple of rats on your next office visit? Probably not.聽Tuberculosis is not a widespread problem here in North America.聽But in sub-Saharan Africa or in Southeast Asia, rats just may be the way to go.聽And who knows? Eventually they may even be trained to sniff out other diseases.聽Cat scans have proven themselves, so why should we be surprised by a rat scan?
