A stretch of rope and some strawberry jam could be the first line of defense against diseases that might jump from monkeys to humans.

Zoonotic diseases, those that can be transmitted from animals to humans, represent major threats, as the Ebola outbreak reminds us. Of these, 70% come from wild animals, rather than pets or agricultural species. Diseases jump more easily from our nearer relatives, so fellow primates are a particular risk. To spot the dangers, the University of California Davis has been running the PREDICT Project, which looks out for dangerous disease reservoirs.

A major challenge for the project, however, has been that primates are strangely resistant to having us collect blood samples, or even oral swabs. If you have to anesthetize every monkey you need to sample, progress will be slow, besides the risks posed to the animals involved. Worse still, “Primates are also highly intelligent and quickly learn to evade capture or darting making it difficult to sample multiple individuals in a group or to sample a particular individual at more than one time point,” graduate student Tierra Smiley Evans points out in the journal PloS Neglected Tropical Diseases.

In the paper, Smiley Evans reveals a method for collecting saliva that suits both monkeys and researchers far better: Scientists dip a 15-centimeter (6-inch) piece of nylon or cotton rope into something tasty like strawberry jam and leave it lying around for the target animal to find. "It's important to try and throw the rope without the primate seeing where it came from," said Smiley Evans. "We have to be sneaky. Some species, like macaques, are very bold in urban settings and it's easy to get mobbed by monkeys."

In the course of chewing on the rope, the monkeys leave a saliva sample, which can be tested for viral diseases. Attaching a string, with the researcher holding onto the other end, makes it easier to ensure the monkey doesn't abscond with the jam, rope and all.

The paper outlines the success of the technique when applied to rhesus macaques, olive baboons, red-tailed guenons and L'hoest's monkeys. Simian foamy viruses were detected in some cases, along with herpesviruses, proving it is not just humans who have a problem getting rid of the glitter of the disease world. Nylon ropes retained viruses well, but results for cotton were mixed.

These species were chosen because, although they are wild, they have enough interactions with humans to make disease transmission easy. The macaques roam the grounds of Nepalese temples and often get fed by tourists, while the guenons sometimes approach people for food in Uganda.

Not all pathogens will be found in saliva, but bites are one of the most common vectors, making saliva-borne diseases particularly likely to be transmitted.

"It's important that we're able to sample wildlife in communities where zoonotic diseases are likely to emerge," said Smiley Evans. "This technique is aimed at helping to make that possible."