A study of monkey poop suggests that viruses that cause human diarrhea are common in macaques and other nonhuman primates in Southeast Asia. The animals, which live in close contact with humans across the region, carry a wide variety of astroviruses, pathogens that commonly cause diarrhea in people and can also infect the kidney, liver, and brain, researchers report this week in PLOS Pathogens.
Astroviruses are not usually deadly, but the new data suggest that they are less discriminating with regard to what they infect than researchers had thought, raising the possibility that different strains could trade genetic material in monkey hosts and give rise to new forms that might cause more serious disease in people.
Many viruses commonly pass from one host species to another. Middle East respiratory syndrome is thought to pass from camels to humans and may be hosted by a bat species as well. Ebola can pass from apes and antelopes—and perhaps bats—to humans. But earlier studies of astroviruses—so called because they look like stars under an electron microscope—had suggested that they were choosier about their hosts. Few of them that infect humans had been found in animals, and most astrovirus types had been found in just a single host species. Lisa Jones-Engel, a primatologist and infectious disease expert at the University of Washington, Seattle, and virologist Stacey Schultz-Cherry at St. Jude Children’s Research Hospital in Memphis, Tennessee, and their colleagues wondered whether the wild monkeys that are ubiquitous in Southeast Asian cities and villages also harbor astroviruses, and if so, what types.
The researchers collected fecal samples from wild and captive macaques, langurs, gibbons, baboons, and mandrills from Bangladesh and Cambodia. In both countries, wild monkeys live in cities and villages, foraging for food among humans—and in their trash. (Gibbons are found mostly in the forest or in captivity, and baboons and mandrills—native to Africa—were sampled in zoos.) Despite the large numbers of the animals, “finding monkey feces is not as easy as you would think,” Jones-Engel says. “It takes a little work.” Promising places to look include on top of fences and walls and any site of “a good monkey fight,” she says, because “there are going to be feces that were flying.” In all, the team collected more than 800 samples from Bangladesh and 68 from Cambodia.
The researchers found astroviruses in 7.7% of their samples. To their surprise, most of the astroviruses closely resembled viruses known to infect humans. They also found primates that were infected with astroviruses closely related to those found in birds, pigs, cattle, and dogs. That suggests that the viruses have a chance to recombine and form new variants if multiple versions infect the same monkey at the same time. Jones-Engel says monkeys might be especially good at picking up a wide variety of viruses, because they spend time both in the treetops—exposed to avian viruses—and on the ground, where they encounter human and other mammalian viruses.
Bats, which are thought to be particularly good virus hosts, had been fingered as a primary reservoir of astroviruses. But the researchers found that the monkeys harbor a much wider variety of astroviruses than bats do. That may not be the whole story, cautions Jonathan Epstein, an infectious disease expert at EcoHealth Alliance in New York City. “So far, most of the astroviruses described in bats have been from China, so there's still more to learn about bat astrovirus diversity,” he says.
The findings seem to defy the common wisdom that astroviruses are picky about their hosts, but to Epstein, the results make sense. “Macaques and many other nonhuman primates live so closely among people—they drink the same water and they often rummage through garbage looking for food which can contain human waste,” so they have plenty of chances to pick up human viruses. “Our genetic relatedness and close ecological connection to nonhuman primates seems to predispose us to sharing viruses—and that can happen in both directions,” he says. Jones-Engel agrees. She notes that biomedical researchers use macaques in part because they can offer good models of human disease. And her previous studies of enteroviruses in Southeast Asia showed that viruses that infect humans were more common in wild monkeys than monkey-specific viral species.
It isn’t clear whether the “human” astroviruses make the monkeys sick. The researchers couldn't study that question because they could not tell which monkey any specific poop sample came from, Jones-Engel says. But in general, they didn’t notice any symptoms resembling human astrovirus infection among the animals living around their study sites. Diarrhea is rare in monkeys, she says. “I’ve seen a lot of monkey shit in 30 years, and [diarrhea] is really unusual.” Macaques, especially, seem to have adapted to close contact with human pathogens, she says. “For the most part macaques are pretty bomb-proof. They seem to be able to handle infectious disease pretty well.”
That’s all the more reason to keep tabs on the viruses they harbor, she says. The monkeys “showed us that these astroviruses have a lot more flexibility in them than we thought, and because of that we need to keep a closer eye on them.” Epstein agrees. The study “highlights the importance of looking at viral diversity in wildlife that live in close association with people.”?