The news that genetic modification of mosquitoes is being tested as a way to kill off the pests and stem the spread of diseases – an idea that is getting more attention because of the horrifying Zika virus – raises a question for us in New England: Why not use it to wipe out the ticks that spread Lyme disease?
That’s an interesting thought, said Alan Eaton, an entomology professor at the University of New Hampshire and the state’s go-to guy when reporters have questions about insects. (Ticks are arachnids rather than insects – eight legs, fewer body segments, etc. – but let’s not get too pedantic.)
“I attended a (scientific) meeting last month where people were looking at the genetics of the black-legged tick, in order to learn about variability and populations . . . but I haven’t heard of anybody studying it with the question of doing the kind of thing we’re talking about,” Eaton said.
As you may have heard, there are ongoing programs both in laboratories and in at least one field trial in which genetically engineered mosquitoes are released into the wild to kill off their brethren. The bioengineering involves creating a “kill switch” in males that causes most or all of their offspring to die before reaching maturity. There are also efforts to create other genetic changes, such as ensuring that all offspring are males, which don’t bite, or changing the mosquito’s genetics so it can’t pass on a virus that it’s carrying.
There’s no obvious reason why scientists couldn’t do something similar with ticks, either interfering with populations or installing a genetic trait that would interfere with disease transmission.
For an example of the latter idea, consider that it takes a couple of “magic steps” – Eaton’s term – for black-legged ticks to spread the Lyme bacteria to us: First the bacteria must move from tick’s gut into their blood stream, and then from their blood into the salivary gland, both steps are unusual.
That’s why dog ticks don’t spread Lyme disease, Eaton noted: “They don’t have the right physiology.”
If scientists could tweak black-legged ticks’ genetic makeup to prevent just one of those magic steps from happening, they couldn’t spread the Lyme bacteria any more. Problem solved!
Well, not necessarily. For one thing, black-legged ticks pass on other dangerous bacteria, causing ehrlichiosis and babesiosis, that wouldn’t necessarily be affected by tweaks to contain the Lyme bacteria.
Then there’s the time lag.
Even if there is a good genetic way to interfere with bacteria transmission, which is far from certain, “It would be the slow boat to China compared to mosquitoes,” Eaton said.
The complication is life span.
“For mosquitoes, the life cycle is maybe three weeks, so you can cram a bunch of those generations in one year, and have the population explode in a small amount of time,” he said. “For ticks, the life cycle is two years long.”
That means it would take years and years for a genetic trait to spread through an existing population of ticks, like those around your house.
Eaton, it must be said, is cautious about the whole idea of bioengineering pests, even if it involves mutagenesis – making small changes to an existing gene – rather than genetic modification, which can involve inserting genes from a different species.
He agrees that the idea has huge promise for controlling dangerous pests without dousing everything with synthetic pesticides, or using slow and complicated biological controls, but says the peril of unintended consequences is always lurking. For example, maybe modified ticks would suddenly start transmitting a more dangerous virus that doesn’t get passed along when they bite us at the moment; it’s very hard to say in advance.
“All these issues are being thrown at us at once, because of this new opportunity. Now there are questions: Will it work outdoors? Is it safe outdoors?” Eaton said.
“There are really important questions about safety. If you’re doing it by genetically modifying such and such, what’s the possibility that there’s some other outcome we never ever thought of, and now we’ve released it into the environment and we can never bring it back?
“It’s interesting to think about the incredible possibilities, but we also need to think about the real risks.”
In other words, don’t expect to stop tucking your socks into your pants when walking through tick territory any time soon.
(David Brooks can be reached at 369-3313, firstname.lastname@example.org, or on Twitter @GraniteGeek.)