Primates use their sense of smell to avoid contamination by intestinal parasites through contact with infected members of their group, a new study has found.

Frequent grooming among mandrills, a primate of the Old World monkey family, is undoubtedly a means of eliminating ectoparasites.

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However, it also plays a major role in social cohesion – helping to soothe tensions after conflict, for example, researchers said.

Researchers from The French National Centre for Scientific Research (CNRS) conducted an experiment using antiparasitics.

They captured infected mandrills, administered the antiparasitic drug, and returned the treated mandrills to their group. Now free of parasites, these primates once again enjoyed frequent grooming.

The team next sought to determine whether olfactory communication could explain avoidance of infected conspecifics or members of the group.

First, chemical analyses showed that fecal odours differed between infected and healthy mandrills. Next the team conducted behavioural experiments under controlled conditions on about 16 captive mandrills.

Researchers collected fecal matter from mandrills at different times – while parasitised and when free of parasites – and rubbed it onto bamboo shoots. These shoots were then presented to captive mandrills.

Scientists noticed that the captive primates sniffed the bamboo set before them but actively avoided those shoots rubbed with infected feces.

Researchers found that mandrills harbouring parasitic protozoans in their digestive tracts were less frequently groomed by their conspecifics than were healthy mandrills.

Groomers especially avoided the perianal zone, which poses a high risk of contagion or disease spread by close contact.

Such selective shunning elegantly demonstrates how olfactory communication may play a role in the behavioural and social avoidance of parasitic infection, researchers said.

Parasites, similarly to kinship ties and social rank, influence mandrill behaviour by shaping social dynamics in their group, said Clemence Poirotte of CNRS.

This study of the evolution of antiparasitic behaviour is currently focused on the influence of parasites spread merely by contact.

The study was published in the journal Science Advances.