Peril of play

As any parent or teacher knows, kids that play together get sick together. The same is true for chimpanzees, a new study shows. But the animals’ ills can have much more serious consequences than a head full of lice, and researchers are urging precautionary measures to protect chimps from humanborne diseases.

The new analysis examined long-term demographic and behavioral data from two chimpanzee communities in TaïNational Park in the Ivory Coast. Repeated outbreaks of two human respiratory viruses in recent years had killed many of the chimps, and the researchers began scrutinizing the patterns of deaths to see if environmental conditions such as cycles of drought or rain might have helped transmit the pathogens.

To the researchers’ surprise, the cycles mirrored the classic cycles of disease transmission seen in human children, the team reports in the June 18 PLoS One .

“It was quite unexpected. We didn’t find a strong environmental signal, but found the same cycle as kids who go to school and come home with all sorts of possible diseases,” says Christophe Boesch, of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, who led the work with colleague Peter Walsh.

Three ages stood out as precarious in the life of a chimp. High mortality rates occurred at birth, at age 2 1/2 and when the chimps were about 6 years old. Chimps are weaned from their mother’s milk when they are about 6, which can mean harder times. But at about 2 to 2 1/2, they are usually healthy and extremely playful, spending twice as much time playing and interacting with twice as many partners than older chimps.

“They wrestle, play chasing games, jump on one another and bite and pull hair, laughing all the time,” says Boesch. “It’s a time of very close contact, for sure.”

The analysis also revealed how a deadly outbreak, combined with the reproductive cycle of the moms, can propagate the problem. Female chimps get pregnant soon after a child’s death, so an outbreak with many deaths prompts a new cycle of pregnancies. Three years later there is another group of similarly aged, playful, gregarious chimps, spreading germs along with their joy.

The work highlights the susceptibility of apes, many of which are endangered, to threats from infectious disease in addition to habitat destruction and poaching, comments Tony Goldberg, a pathobiologist at the University of Illinois at Urbana-Champaign College of Veterinary Medicine.

“We need to step up research on pathogens and what interactions with people are bringing them in,” he says. In some areas, a chimp’s primary human contact will be with research scientists or ecotourists. But Goldberg notes that in areas where humans have encroached on forest, chimps will leave the woods to raid crops. Other animals may be exposed to human pathogens by hunters.

“We need to upgrade our preventative measures,” Goldberg says.

Boesch agrees. Simple steps, like requiring researchers and tourists to wear surgical masks or wash their boots in a bleach bath, could limit disease transmission. There also may be times, such as these years of peak play, when tourism should be curbed, he says.

The particular viruses killing these animals are innocuous in humans, Goldberg notes, so most people probably don’t know that they are carrying them. “One shudders to think of what would happen to these populations if a highly pathogenic virus such as influenza was introduced.”