University of Massachusetts Amherst researchers have made a promising discovery that could lead to the development of a natural and effective tick repellent. They have shown that a naturally occurring compound secreted by the skin of donkeys effectively repels adult Ixodes scapularis ticks—the most frequent human-biting tick in the U.S. Commonly known as the deer tick, this species of arthropods is responsible for spreading Lyme disease, anaplasmosis and babesiosis—bacterial infections that can sometimes cause serious and long-lasting illness.

Currently, the most effective tick repellents contain ingredients like DEET and permethrin, which are safe when used as directed but are not benign or ideal, and some people simply don’t like to use them.

“There is a strong public desire for ‘natural’ means of killing and repelling ticks,” says microbiologist Stephen Rich, executive director of the New England Center of Excellence in Vector-borne Diseases (NEWVEC) at UMass Amherst.

Different tick species feed off different vertebrates, explains Eric Siegel, lead author of the research published in the journal PLOS ONE and a doctoral student at NEWVEC. “Some animals are good hosts, and some are bad,” he says.

The sebaceous glands of horses and donkeys create secretions that keep their skin moist and include allomones, or chemical substances that affect the behavior of other plant and animal species. Previous research has shown that ticks that feed off horses but not donkeys will be repelled from horses when the horses’ smell is masked using one of the compounds, known as (E)-2-octenal, secreted by donkey skin.

“It’s one of the different smells that you find on a donkey that you don’t find on a horse,” Siegel says. “So, to ticks, the horse doesn’t smell like the host they’re used to. The ticks don’t like it, and so they won’t feed on it. Our assessment that we can repel ticks with this compound means that, in theory, we could either put it on ourselves or put it on dogs, and the ticks will not want to go near it.”

In the lab, Siegel and team showed that they could prevent deer ticks from moving from point A to point B when octenal is placed between the points. “It was as effective, or more so, than DEET, and it was even more effective with male ticks than females,” Siegel says.

The experiments were carried out in 2023, when a group of high school students were participating in a 10-week summer program in Rich’s Laboratory of Medical Zoology. “A cool part of this paper is that four of the authors were high school students,” says Rich, senior author. The co-authors are Sophia Goodnow, Elizabeth MacLeod, Sarah Nicolson and Lucy Thompson. “They set up and did the preliminary experiments on their own,” Siegel says.

The researchers are collaborating with Gearjump Technologies, which addresses complex global problems in health care, vector control and plant protection, to work on the development of a deer tick repellent with octenal as the active ingredient. In addition to repelling ticks from people, octenal might be turned into something that could control deer tick populations in the outdoors.

“One avenue is, can we substitute the use of pesticides and use this in the environment to repel ticks?” Siegel says.