Yale Scientists Find Evidence Healthy Animals Detect and Avoid Sick Animals

A new study by Yale scientists has found that animals can recognize and stay away from other animals that may infect them with a disease.

Professor David Skelly said that research completed in his laboratory in collaboration with Professor Joseph Kiesecker, who is now at Penn State University, shows that healthy animals can distinguish the odors given off by infected animals and will keep their distance from diseased individuals.

“Biologists had long speculated that animals might gain an advantage from being able to avoid diseased animals, but there was no experimental evidence,” said Skelly, a professor of ecology and evolutionary biology at the School of Forestry & Environmental Studies. “If these behaviors are widespread, they could be important in making accurate predictions of the spread of disease.”

Skelly, whose study was published in Proceedings of the National Academy of Sciences, said the authors found that bullfrog tadpoles were able to tell when others of their species were infected with a fungus that attacks the digestive tract. Healthy tadpoles can become sick by spending time near infected animals.

When presented with an infected bullfrog tadpole, the tadpoles moved up to a foot away, he said.

“Healthy tadpoles appear to be able to smell chemicals in the water associated with the tadpole’s illness and stayed away from them,” Skelly said.

The nature of the chemical cue is entirely unknown. “Identifying the cue is a logical next step,” he said.

Skelly and Kiesecker have found that tadpoles are highly sensitive to their environment.

“Our understanding of predators and their prey has changed drastically since it was discovered that many kinds of prey animals can change their behavior and even their body shape when they smell nearby predators,” Skelly said. “Responding to disease risk may be quite similar from an animal’s perspective. In both cases animals appear to be able to use behavior to reduce the chance that they will be harmed or die.”

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