Swedish researchers claim to have solved the mystery of how some animals can sniff out sickness.
Ivan Rodriguez at the University of Geneva, Switzerland, and colleagues have found a type of smell receptor in mice that appears to respond to disease-related molecules produced by bacteria, viruses, or as the result of inflammation, reports New Scientist.
To reach the conclusion, Rodriguez's team took tissue from the vomeronasal organ - a pheromone-detecting sense organ found in the nasal cavity of mice, and some other mammals - and searched for genes expressing possible smell receptors.
They identified five receptors closely related to a class of receptor already known to help immune cells hone in on pathogens and inflammation.
Further experiments showed that these vomeronasal receptors could be activated by molecules related to disease, which are excreted in urine when animals are sick.
Rodriguez believes the receptors could ultimately be incorporated into an artificial nose that would detect illness.
"The receptors are very versatile, so you won't be able to say 'this is the disease', but you might be able to say 'this [person] is sick'," he said.
The study has been published in Nature.