Menopausal Mice May Hold Key to Control Breakthrough

Dr. Loretta Mayer, a researcher studying heart disease in menopausal women in the 1990s, needed a non-reproductive animal model for experimentation. When she began publishing papers about the menopausal mouse she and her team had created, a global group of scientists focused on solving Southeast Asia’s food shortage took note. They reached out to Mayer with a challenge.

“They said, ‘If you can make a mouse non-reproductive for the purpose of research, surely you can make a rat non-reproductive for the purpose of food security,’” recounts Mayer. “Rats had been consuming or damaging 20 to 40 percent of the crops that were desperately needed for human consumption. A study in Indonesia revealing that a 50-percent drop in the female rat population would cut rat-induced crop damage by 80 percent convinced us to take our technology in this new direction.”

Mayer and her partner, Dr. Cheryl Dyer, formed a company, Flagstaff, Ariz.-based SenesTech, which would be devoted to the development of ContraPest, their rat contraceptive product. They attended conferences to share their progress and discuss the science behind their ongoing studies with colleagues worldwide. That’s when Tom Lamb, chief of Innovation and Technology at the New York City Metropolitan Transit Authority (NYC MTA), suggested they share the new technology in the United States as well as abroad. While his primary concern was the rat infestation in the New York subway system, his suggestion led to SenesTech’s earning a grant from the National Institutes of Health (NIH) that funded the NYC MTA study.

In August, the U.S. Environmental Protection Agency (EPA) granted SenesTech registration of ContraPest. Limited distribution of the product began in late October. Mayer says it will be made available first to the municipalities involved in pilot programs; later it will be available to the private PMP market.

HOW CONTRAPEST WORKS. ContraPest is a liquid contraceptive bait whose active ingredient, 4-vinylcyclohexene diepoxide (VCD), targets the reproductive organs of rats, accelerating the depletion of eggs in females and, in conjunction with another chemical, triptolide, causes testicular disruption in males. The rat’s fertility is compromised as soon as the first intake of the bait.

“It took us six years to get the formula just right,” Mayer says. “We were also challenged to get the taste, the sweetness, right. VCD burns like the hottest jalapeño, and triptolide is very bitter. We worked on the palatability for years. We couldn’t be satisfied when our lab rats chose to eat it; we had to make sure it would win a taste test compared with the competition: New York trash.”

Another challenge was determining the form the bait would take. In test after test, rats preferred liquid over solid or semisolid — not surprising given rats need to consume 10 percent of their body weight in liquid every day, says Mayer.

The liquid bait is housed in a controlled delivery system designed to prevent non-target animals from feeding. It features inserts that are easy to monitor and switch out when bait levels get low. Once in place, the filled inserts slowly drain into an attached tray, creating a pool of product that emulates a natural puddle, making it attractive to rats.

“ContraPest is not a risk to handlers, nor to non-target species, and resistance over time is not an issue,” says Mayer. “The label allows management of Norway and roof rat populations in indoor applications plus outdoor applications within a foot of man-made structures. We are working with EPA to expand the label for broader outdoor application over the next year.”

SenesTech is also working on technology adjustments for managing mice, and recently completed work with Texas A&M that showed promising results for feral hogs. Mayer, Dyer and their team also continue to work with scientists in Southeast Asia, aiding in food-security efforts there.

“Now that we’ve proven rodent population management is not only possible but also humane, sustainable and effective, we can look toward applying our models to other species and situations,” says Mayer. “We are always looking for balance. We’ve tried to create a tool that will help restore balance by reducing out-of-control pest infestations to a more manageable level.”

The author is a frequent contributor to PCT magazine.