A new study from Purdue University has revealed that vervet monkeys tend to keep their distance from others when they are dealing with a parasitic infection.
Study lead author and biological anthropologist Dr. Brandi Wren spent a year studying wild vervet monkeys in South Africa. She documented the parasite loads of individual monkeys, as well as social grooming behavior within groups.
Dr. Wren found that monkeys carrying certain gastrointestinal parasites did not groom others as much as those without the parasite.
Vervet monkeys share more than 90 percent of their DNA with humans, and have also been known to exhibit anxiety and hypertension. These are conditions the are not often found in non-human animals.
By studying the physiology, genetics, and behavior of vervet monkeys, biologists can better understand certain aspects of human biology.
“We have so many behavioral similarities; the roots and nuances of social behavior tend to be similar across all of the primates, especially from monkeys to humans,” said Dr. Wren.
“This study shows some of those similarities down to, when we feel sick, we don’t want to talk to anybody. ‘You can rub my back, whatever, but I really want to be left alone.’ We see a lot of similarities in how humans and monkeys interact within their own groups.”
The gastrointestinal parasites that Dr. Wren investigated are not typically spread through social contact, but through contaminated soil or substances in the environment. However, the research shows that the parasites may be spread through social contact, and can significantly affect an individual’s social behavior.
After studying social interactions combined with data on infection from fecal samples, the researchers found that monkeys infected with whipworm spent less time grooming other monkeys.
“Infected individuals show a little bit of lethargy, but the interesting thing is that they still let other individuals groom them; they just don’t groom others. They also don’t cuddle with the other monkeys as much. It appears they just don’t feel well.”
Dr. Wren noted that the difference in social behavior is not so stark that it is noticeable just by observing the monkeys.
“There’s no way we would have been able to tell which monkeys were infected just from observation. There are no other signs of the infection, other than the social behavior. And the change is often so hard to detect. It takes following one individual for a substantial time and collecting the data to see it. The effect is hidden in this complex web of interactions,” explained Dr. Wren.
“There are some individuals you watch and you think, ‘Gosh, this guy is such a jerk! He always lets everybody groom him, but he doesn’t groom anybody else! What we’re attributing to personality or attitude could just be because he has a gut full of parasites.”
According to the experts, the monkeys’ behavior parallels human behavior during the pandemic. Like vervet monkeys, humans crave social contact, can spread diseases through social contact, and tend to withdraw a bit during an illness.
“All these social behaviors affect health on a practical level,” said Dr. Wren. “We know COVID-19 is spread through close social contact. A fascinating thing about studying other species, and one reason to observe and understand them, is that we are always learning new things. There is always more to learn. Even when we’re looking at previous research, even when we thought we understood the results, we still may not know the whole picture.”
The study is published in the journal PLOS ONE.