By Sarah Ruth Bates, MBE
Should scientists tinker with wild mouse genes to make the rodents unsuitable hosts for ticks that carry disease? The ticks that transmit Lyme and other illnesses are thriving, for reasons that likely include climate change, and scientists seeking to protect human health are weighing the pros and cons of previously untested responses.
The Possible Role of Climate Change
The transmission of tick-borne illnesses is spiking, according to CDC data — and Massachusetts is among the states most badly affected, with the fourth highest number of reported tick-borne disease cases. Across the nation, the number of tick-borne disease cases nearly doubled in a single year, from 2015 to 2016, and all evidence points to a continued rise in incidence.
Climate scientists have long predicted increases in tick-borne diseases, such as Lyme, as a consequence of global warming, since warm weather accelerates ticks’ breeding cycles and allows them to live in locales that have historically been too cold for them. Some scientists have drawn a link between climate change and Lyme disease. The Environmental Protection Agency tracks the incidence of Lyme disease as a climate change indicator.
GlobalChange.gov, the US Global Change Research Program, warns that climate change may extend the “Lyme disease season” in the Eastern US.
The science is not settled, however. Experts at the CDC have thus far not linked their data to climate change. Catherine M. Brown, DVM, MSc, MPH, deputy state epidemiologist at the Massachusetts Department of Public Health, points to an alternative (or co-occurring) explanation of the rising Lyme incidence, citing “anthropogenic environmental changes” — patchy reforestation and human encroachment on those environments — which favor the deer and rodent populations that harbor disease-spreading ticks.
Editing Mouse Genes May Thwart Ticks
Whatever the cause, the need for solutions is not disputed: “There is substantial need for the development of innovative methods that effectively reduce the incidence of tick-borne diseases,” says Dr. Brown. “There are many different possible approaches, but nothing has been developed thus far that safely and effectively reduces occurrence of disease.”
Gene-editing technology, which has the potential to disrupt Lyme’s disease vector, may be an answer. At the Massachusetts Institute of Technology, Kevin Esvelt, PhD, assistant professor of media arts and sciences and director of the Sculpting Evolution group, is working on editing the genes of white-footed mice, which carry ticks, to immunize the mice to Lyme.
100 Percent Mouse
Dr. Esvelt and his team are collaborating with local stakeholders on a project called Mice Against Ticks, exploring the possibility of releasing Lyme-resistant mice on Martha’s Vineyard and/or Nantucket. By community request, any mice released on the islands will be “100 percent mouse,” with no foreign DNA. If the island experiment goes ahead and is successful, mainland communities might subsequently use a “daisy drive,” a self-limiting gene drive that is no longer inherited after a certain number of generations, to provide some protection against unanticipated ecological outcomes, says Dr. Esvelt. Such a drive would use CRISPR technology and would introduce the DNA of bacteria into wild mice.
Ethical Dilemmas of Messing with Mice
Editing the genes of a wild population of organisms using CRISPR could potentially yield huge public health benefits. But the transmissibility that makes the technology so effective also carries risks, and it is the burden of scientists to anticipate what could go wrong. “I feel quite a bit of moral responsibility,” Dr. Esvelt says.
In community meetings, he says, people who have contracted a tick-borne illness, or know someone who has, express “a palpable urgency” to taking action. But Dr. Esvelt has purposely slowed the research process, in part by ensuring that each stakeholder committee includes at least one vocal skeptic. “My concern is that someone out there might have some concern that might turn out to be valid,” he says.
Human interventions with the natural environment got us into this situation; Dr. Esvelt wants to take all possible care when intervening again to get us out of it.
