You’ve probably been there at some point: Feeling feverish or tired, certain you’re coming down with something — but then when that text message arrives, suddenly going out on the town sounds like a great idea. Just like that, you shake off the sickness.
A new review finds that humans aren’t alone in this ability. In certain social situations, such as the presence of a potential mate, animals from mice to birds to monkeys will reduce their symptoms of disease. And, in this age of animal-borne diseases, understanding when animals are hiding their illness is particularly important for controlling the spread of disease.
The finding is based on the idea, proposed a few decades ago, that some symptoms of sickness — lethargy, loss of appetite, etc. — aren’t an unavoidable product of the disease itself. Rather, they’re the sick individual’s attempt to conserve bodily energy so that the immune system can do its work.
But that opens up the possibility of a trade-off. If symptoms of sickness are optional, scientists have wondered, when and how do animals shut them down?
One such instance is in the presence of a potential mate. Researchers have found that male zebra finches battling infection are able to suppress symptoms in the presence of females and have equal courting success as their healthy brethren.
Sickness suppression tends to work differently for females, who risk spontaneous abortion if they become pregnant while ill. Instead, for females of many species, it’s for reasons of maternal care that they would hide their illness. “For example, a female that has young pups might still need to devote some energy to caring for her pups, even when sick, to ensure their survival,” says Patricia Lopes, author of the paper, which appeared Tuesday in Proceedings of the Royal Society B.
But while hiding illness might allow animals to preserve mating opportunities, keep their social status or increase the survival of their offspring, it also brings risks. It hinders the body’s ability to fight infection, potentially prolonging the disease. It also creates opportunities for the illness to spread, putting increasingly connected animal — and human — populations at greater risk of disease pandemics.
Further research is needed to determine how these behaviors are controlled at a physiological level, as well as the long-term costs to the individual’s health. That will result not only in improved welfare for sick animals, but also more precise strategies to detect and halt the spread of potentially dangerous infectious diseases.
In the end, these sickness “side effects” may play a major part in making the world a healthier place.
Image by WilleeCole Photography / Shutterstock