How rope and jam can screen monkeys for disease

Red-tailed guenon in Bwindi Impenetrable Forest region, Uganda. (Credit: T. Smiley Evans via PLOS Neglected Tropical Diseases)

Scientists have figured out a noninvasive way to screen for diseases that can jump from monkeys to humans. The key ingredients? Rope and a dollop of strawberry jam.

Global disease surveillance has been performed for years, but the logistics of screening primates for zoonotic pathogens— diseases that can be passed from animals to humans—have often presented a challenge because invasive sampling techniques, such as collecting blood or using oral swabs, require anesthesia in the field.

“It’s important that we’re able to sample wildlife in communities where zoonotic diseases are likely to emerge,” says Tierra Smiley Evans, a graduate student researcher at University of California, Davis. “This technique is aimed at helping to make that possible.”

monkey with jam on rope
L’hoest’s monkey in Bwindi Impenetrable Forest region, Uganda. (Credit: T. Smiley Evans via PLOS Neglected Tropical Diseases)

Simple and affordable

The new method opens new doors for the study of primates as sources of diseases that could affect humans in remote tropical settings, says Christine Kreuder Johnson, professor and surveillance lead for the PREDICT project and senior author of the study in the journal PLOS Neglected Tropical Diseases.

“This method is already being deployed in multiple countries throughout the world as part of the PREDICT project and is expanding our ability to investigate primate populations that we were previously unable to sample.”

The simple and affordable method involves a six-inch piece of weaved rope made from nylon or cotton that is dipped into an attractant such as strawberry jam. The ropes are tossed near the animals being targeted for sampling, which pick up the ropes, chew on them, and later drop them. Researchers can then collect saliva from the discarded ropes.

“It’s important to try and throw the rope without the primate seeing where it came from,” Smiley Evans says. “We have to be sneaky. Some species, like macaques, are very bold in urban settings and it’s easy to get mobbed by monkeys.”

The sample is taken to a lab, where teams test it for viral diseases that may pose a direct threat to humans.

Going viral

In this study, oral samples were collected from multiple species, including rhesus macaques in Nepal and olive baboons, red-tailed guenons, and L’hoest’s monkeys in Uganda. A variety of viruses, including herpesviruses and simian foamy viruses, were detected in those samples.

Wild primates are prime candidates for passing diseases to humans because they are closely related to us genetically and, in many parts of the world, regularly come into contact with people.


For example, at sacred temples in Kathmandu, Nepal, rhesus macaques roam the temple grounds and exist among the tourists and locals who pass through the temple. Food and other items can often exchange hands. And in the remote town of Buhoma in Uganda, red-tailed guenons come down from the trees to investigate people and look for food.

These kinds of human-animal interactions need monitoring most, the researchers say, because they lend themselves to the spillover of pathogens that can cause a pandemic.

Viruses that originate in wild animals account for more than 70 percent of emerging zoonotic diseases in humans, including viruses that have caused pandemics such as HIV/AIDS, epidemics such as Ebola, and smaller outbreaks like Marburg hemorrhagic fever.

The USAID Emerging Pandemic Threats Program and a William J. Fulbright Fellowship provided to Smiley Evans funded the work.

Source: UC Davis