HOW TO WIN THE WAR ON RATS
Rats are responsible for more human deaths than any other mammal. For centuries we have tried to find ways to exterminate them – but now a Buddhist biologist claims to have found a gentler solution. Jordan Kisner reports
First, the myths. There are no “super rats”. Apart from a specific subtropical breed, they do not get much bigger than 20 inches long, including the tail. They are not blind, nor are they afraid of cats. They do not carry rabies. They do not, as was reported in 1969 regarding an island in Indonesia, fall from the sky. Their communities are not led by elusive, giant “king rats”. Rat skeletons cannot liquefy and reconstitute at will. (For some otherwise rational people, this is a genuine concern.) Consider this the good news.
In most other respects, “the rat problem”, as it has come to be known, is a perfect nightmare. Wherever humans go, rats follow, forming shadow cities under our metropolises, and hollows beneath our farmlands. They thrive in our squalor, making homes of our sewers, abandoned alleys and neglected parks. They poison food, bite babies, undermine buildings, spread disease, decimate crop yields, and very occasionally, eat people alive. A male and female left to their own devices for one year – the average life span of a city rat – can beget 15,000 descendants.
There may be no “king rat”, but there are “rat kings”, groups of up to 30 rats whose tails have knotted together to form one giant, swirling mass. Rats may be unable to liquefy their bones to slide under doors, but they don’t need to: their skeletons are so flexible that they can squeeze their way through any hole or crack wider than half an inch. They are cannibals, and they sometimes laugh (sort of) – especially when tickled. They do not carry rabies, but a 2014 study from Columbia University found that the average New York City subway rat carried 18 viruses previously unknown to science, along with dozens of familiar, dangerous pathogens, such as C. difficile and hepatitis C. Collectively, rats are responsible for more human deaths than any other mammal on Earth.
Humans have a peculiar talent for exterminating other species. In the case of rats, we have been pursuing their total demise for centuries. We have invented elaborate, gruesome traps. We have trained dogs, ferrets and cats to kill them. We have invented ultrasonic machines to drive them away with high-pitched noise. (Those machines, still popular, do not work.) We have poisoned them in their millions. In 1930, faced with a rat infestation on Rikers Island, New York City officials flushed the area with mustard gas. In the late 1940s, scientists developed anticoagulants to treat thrombosis in humans – and some years later, super-toxic versions of the drugs were developed to kill rats by making them bleed to death from the inside after a single dose. Cityscapes and farmlands were drenched with thousands of tons of these chemicals. During the 1970s, we used DDT. These days, rat poison is not just sown in the earth by the truckload, it is rained from helicopters that track rats by radar – in 2011, 80 metric
tonnes of poison-laced bait were dumped onto Henderson Island, home to one of the last untouched coral reefs in the South Pacific. In 2010, Chicago officials went “natural”: reasoning that a natural predator might track and kill rats, they released 60 coyotes wearing radio collars onto the city streets.
Still, here the rats are. Why? “Frankly, rodents are the most successful species,” Loretta Mayer told me recently. “After the next holocaust, rats and Twinkies will be the only things left.” Mayer is a biologist. In 2007, she co-founded Senestech, a biotech start-up that offers the promise of an armistice in a conflict that has lasted thousands of years. The concept is simple: rat birth control.
The rat’s primary survival skill, as a species, is its unnerving rate of reproduction. Female rats ovulate every four days, copulate dozens of times a day and remain fertile until they die. (Like humans, they have sex for pleasure as well as for procreation.) This is how you go from two to 15,000 in a single year. When poison or traps thin out a population, they mate faster, until their numbers regenerate. Conversely, if you can keep them from mating, colonies collapse in weeks and do not rebound. Senestech, based in Flagstaff, Arizona, claims to have created a liquid that will do exactly that. In tests conducted in Indonesian rice fields, South Carolina pig farms, the suburbs of Boston, and the New York City subway, the product, called Contrapest, caused a drop in rat populations of roughly 40% in 12 weeks. This autumn, for the first time, the company is making Contrapest available to commercial markets in the US and Europe. The team at Senestech believes it could be the first meaningful advance in the fight against rats in a hundred years, and the first viable alternative to poison. Mayer was blunt about the implications: “This will change the world.”
Mayer is a tall, vigorous woman in her mid-60s with bright eyes, spiky grey hair and a toothy grin. Her ideologies of choice are Buddhism and the Girl Scouts. “It’s kind of my core,” she said, “to do for others.” In conversation, her manner is so upbeat that she seems to be on the verge of bursting into song. When asked how she is doing, she frequently responds in a near-rapture: “If I was any better, I’d be a twin!” Mayer came to science later than usual, in her mid-40s, after a stint as the international vice president of Soroptimist, a global volunteer organisation dedicated to improving the lives of women. The career change was unexpected, even to her. After a close friend died suddenly of a heart attack, Mayer called up a biologist she knew and asked how something like this could have happened. The biologist had no satisfying answer; she explained that while heart disease in men had been thoroughly studied, little attention had been devoted to postmenopausal heart disease in women. “Well, you’ve got to change it,” Mayer replied, outraged. The biologist was otherwise occupied, so Mayer decided to do it herself. At 46, she entered a PHD programme in biology at Northern Arizona University.
“Rat skeletons are so flexible that they can slip through any crack wider than half an inch. Very occasionally, they eat people alive”
After graduate school, her initial research as a professor of biology focused on artificially inducing menopause in lab mice, so that she could study changes in the postmenopausal heart. Three years into her efforts, Mayer was contacted by Patricia Hoyer, a colleague in Phoenix, who said she had stumbled across a chemical that seemed to make mice infertile without having any other effects. Together, Mayer and Hoyer synthesised a new compound, which they called Mouseopause.
In 2005, Mayer received a telephone call from a veterinarian in Gallup, New Mexico, who had read about her research. The Navajo reservation where he worked was overrun by wild dogs. There were too many to spay and neuter, so he was euthanising almost 500 a month. “If you could do for a dog what you can do for a mouse, I could stop killing dogs out here,” he told her. When Mayer arrived in Gallup and saw the piled corpses, she agreed to test Mouseopause on an initial group of 18 dogs. “I held up that first puppy, who I called Patient Zero,” she told me, “and I said, ‘I don’t know what this is gonna do to you, but you will live on a satin pillow the rest of your days’.” The injection made the dogs infertile, but left them otherwise happy and healthy. (Mayer brought home all 18 dogs and built a kennel in her yard to house them until she could find homes for them. Patient Zero, renamed Cheetah, lived with her until she died of old age – though the pillow was fleece.)
The next call came from Australia in 2006. Biologists there wanted an adaptation of Mouseopause for rats. Rats, they told her, were eating 30% of the rice crop in Australia and Indonesia. If she could reduce the rat population by even half, they claimed, the crops that would be saved could feed millions of people. Mayer was moved by the idea of finding a solution to rat overpopulation that was neither lethal nor toxic. Since its invention, rat poison has been our primary method of curbing rat populations, but it is dangerous. Ingested in high doses, it’s fatal to humans, and it poses a particular risk to children, since it’s sweet and brightly coloured. In the US alone, more than 12,000 children per year, most of whom live below the poverty line, are accidentally poisoned by pesticide meant for rats. The collateral damage inflicted by rat poison also extends to the environment, leaching into the soil and poisoning house pets, farm animals, and wildlife that feed on rats. Worst of all, rat poison is not very effective at eliminating large infestations. As long as there is still a food source, colonies bounce back.
Persuaded by the research, and by her wife, fellow biologist Cheryl Dyer, Mayer decided to devote her career to developing a new, smarter way to control the rat population. In 2007, they founded Senestech. “People say never to invest with a husband and wife team,” Mayer joked to me. “I say, ‘Oh, absolutely not! Then you have dominance.’ But wife and wife? Works great!” For Dyer and Mayer, the immediate problem was obvious: while the lab mice and feral dogs had received injections in controlled studies, wild rats would have to eat the formula of their own volition. Rats are neophobic – they avoid what they don’t know. What’s more, city rats are already well fed. It was Dyer’s job to make Mouse opause not just edible but delicious – a tricky proposition since its active ingredient, 4-vinylcyclohexene diepoxide (VCD), is bitter and caustic. Rats have the same taste preferences as humans – they love fat and sugar.
Dyer was also tasked with the greater challenge of adapting Mouseo pause to work on rats, which are much hardier than mice. While VCD caused the eggs in mouse ovaries to degenerate rapidly, female rats were far less susceptible. Dyer added a second active ingredient: triptolide, which stunted any growing eggs. The results were better, but still not good enough. “They just had smaller litters, goddammit,” she said. Eventually, out of curiosity and desperation, Dyer fed it to both males and females. The result was dramatic. It turns out that the triptolide destroyed sperm – the males became sterile almost immediately after ingesting the formula. This was a total surprise: no one had ever tested triptolide on male rats before. Test after test: no pups.
After three years of research and development, they had a product that worked and did not harm other animals. (The active ingredients are metabolised by the rat’s body in ten minutes, which means any predator that then eats the rat is not affected; and the compound quickly breaks down into inactive ingredients when it hits soil or water.) Contrapest, the finished product, is viscous and sweet. Pink and opaque, it tastes like nine packets of saccharine blended into two tablespoons of kitchen oil. “Rats love it,” Dyer said. “Love it!”
On a Tuesday night in August, Mayer and Dyer held a celebration for staff and investors on the back patio of their rural wood cabin near San Francisco. The company had just received US Environmental Protection Agency registration, a process that usually takes years. It was not a typical investors dinner, but then, Senestech’s nearly 700 stakeholders are mostly firemen. While most biotech start-ups are funded by investment bankers and venture capitalists, Mayer chose to pursue small private investors, all of whom she knows by name. It was a pure accident of networking that so many of them turned out to be firemen, but she is thrilled with the situation. “Firefighters really believe in doing good,” Mayer explained to me. “And they’re like teenage girls. Once one of them
invested, they all wanted in.”
There were perhaps 25 people gathered on the patio, eating tacos and drinking from Mayer and Dyer’s impressive liquor collection, but they made noise for 50. About half seemed to be wearing Hawaiian patterned shirts. When the time came for Mayer to give a speech, she demurred for a moment before standing. Her toast turned briefly into an anecdote about flattening mouse skeletons in lasagne tins. “But seriously,” she continued, “We knew [this day] would come. It’s great to be riding this wave with you. It’s just so sweet.” Glasses heaved into the air. It sounds crazy: a band of animal lovers and firemen in the mountains of Arizona, led by a Buddhist girl scout, making a pink milkshake for rats that may eventually improve the lives of millions of people. But Mayer is unruffled by scepticism. “I mean, why squabble over something and say, ‘I can’t do that.’ Make it so. Find a way. There’s always a way.”
A longer version of this article first appeared in The Guardian © Jordan Kisner 2016. Last week we incorrectly attributed the adaptation of Unleashing Demons by Craig Oliver to the Daily Mail. This should have been credited to The Mail on Sunday.
“In the US alone, more than 12,000 children every year are accidentally poisoned by pesticides meant for rats”