Rhesus macaque monkey family in a tree in Himachal Pradesh, India. Credit: Timothy Gonsalves
In February 2021, researchers at Tulane University, Harvard University, MIT and Massachusetts General Hospital identified three factors—obesity, age and date of infection—that make a person a COVID-19 “superspreader.”
Now, scientists at Anglia Ruskin University (UK) have done the same for monkeys, mapping how infectious diseases spread among wildlife populations in hotspot areas where humans and wildlife live in close proximity.
For the study, published in Scientific Reports, the research team monitored the behavior of 10 separate groups of rhesus macaques, long-tailed macaques and bonnet macaques in northern India, Malaysia, and southern India, respectively. The team, including behavioral and infectious disease ecologist Krishna Balasubramaniam, chose these Indian locations specifically because wild macaques frequently share space with humans here—with most interspecies’ interaction related to food.
Balasubramaniam and team gathered detailed behavioral data on interactions between humans and individual monkeys, as well as interactions between monkeys within the same group. They fed that data into mathematical Susceptible-Infected-Recovered epidemiological models 100,000 times to simulate the impact of outbreaks of human diseases of varying transmissibility, from the flu to COVID-19 and the measles.
The study results demonstrate the critical role the centrality of the first-infected macaque plays in the spread—or halting—of viruses. For example, within the macaque group, the size of the virus outbreak was positively predicated by the centrality of the host. In other words, if the monkey was better connected within its social network, it would lead to a larger outbreak—making that first-infected monkey a “superspreader.”
Somewhat surprisingly, this effect significantly increased when researchers examined possible spillover events. Here, based on both its interactions with other monkeys around humans as well as with just humans, the centrality of the superspreader macaque plays an even greater role in predicting the scale of outbreak—more so than how central the macaque is within its own group.
The researchers say this is because macaques may congregate around human-provisioned food alongside other macaques with whom they would normally not interact with. These situations, according got the study results, seem to create additional pathways for disease transmission and therefore lead to larger outbreaks.
“Sources of human-provided food can act as a ‘honeypot’ and lead to macaques coming into very close contact with individuals with whom they may otherwise have less contact, for instance, monkeys from other families or sub-groups,” explained Balasubramaniam. “As well as being ‘superspreaders’ within their species, these individuals with the most human contact also pose the highest risk for interspecies disease transmission events, either from humans into wildlife or vice-versa.”
The infectious disease ecologist says this work could be vital for identifying potential macaque superspreaders—the monkeys that are the most sociable both with other macaques as well as humans.
Targeting these monkeys with vaccinations or other forms of medical treatment, like antimicrobials, could potentially protect both macaque populations and humans in areas where they live in close proximity.
“Through fieldwork and modeling, our research identified which individuals are most likely to act as superspreaders of disease, leading to larger outbreaks. These [individuals] would be the most effective targets for disease control strategies,” concluded Balasubramaniam.