Science Finds an Answer for Parasites

Arthur Caplan

Countless diseases are transmitted to animals and humans by helminths (worms) and ectoparasites, most of which don’t seem to play any great positive role in nature: they simply prey on the rest of it. The list of these parasitic felons includes mosquitoes, ticks, fleas, kissing bugs, hookworms, tapeworms, guinea worms, and roundworms. These nuisances give us—and our animals—every­thing from malaria, trichinosis, Chagas disease, Lyme disease, heartworm disease, typhus, and West Nile to encephalitis. A new and exceptionally nasty threat has recently appeared in the United States, having traveled via mosquitoes from Africa to Asia to Europe to the Caribbean.

It is called Chikungunya, an African word for “bent over in pain.” No specific treatment, vaccine, or preventative drug exists for this virus. If it does not kill you, the severe pain it causes takes a week or more to go away. The only prevention is avoiding mosquito bites—good luck with that! So another horrid vector- or parasite-borne disease is roaming around the world due to improved transportation, people living closer to wild areas, the reduced use of pesticides, and climate change. That’s the bad news. What is good news, however, is that at the same time chikungunya showed up, a long-term solution to many mosquito-, tick-, worm-, and flea-carried diseases came on the scene.

This solution is a new technique called “gene drive.” Through its use, scientists could cause particular genes, including artificial ones, to spread quickly through a species as its members reproduce. If gene drive is used to introduce a set of lethal genes into a mosquito genome, then in time there will be no more mosquitoes—or, at least a lot fewer. Voilà, no more chikungunya!

Gene drive was first proposed as a theoretical possibility more than a decade ago. Thanks to a recent advance in gene editing—a method called “CRISPR,” in which many genes are snipped out of or pasted into a living creature’s reproductive material all at once—that theory has become reality. Genetically altered creatures can spread lethal genes—or merely neutralizing genes—to others of their species through sexual reproduction. The more rapidly a species reproduces, the faster the desired changes can spread. Humans are kind of slow when it comes to generational change. Mosquitoes, fleas, and ticks are much faster.

It is even possible to speed up the spread of genes through sex. The chance of a gene being passed on to a given offspring is 50 percent, but an organism’s chromosomes can be engineered to alter those odds. Researchers have already designed mosquitos that produce only sterile males. These can be released in the wild to cause a population crash, thereby rapidly reducing malaria, West Nile, and chikungunya.

So just as yet another nasty disease appears, science has found a powerful new genetic weapon to take it on. But the news is not all good. What can be engineered to get rid of pests can also be engineered to make nastier ones than naturally exist. A method that can spread genes to get rid of disease-carrying vectors and parasites may alter the environment in ways that we did not anticipate, with very negative results. A technique that spreads altered genes rapidly may not be easy to reverse. And altered species may go places where they are not wanted, outcompeting natural ones and wreaking ecological havoc.

There are likely to be quasi-religious objections to using gene drives, too. “We should not alter nature,” “We should not play God,” and “It is not humanity’s place to design a safer world” come to mind. Those arguments I am not buying.

We alter nature for better and worse every day through agriculture, medicine, technology, migration, engineering, horticulture, landscaping, and a thousand other human practices. When we make a mess of things—say, heating up the world or polluting our oceans and lakes—then complaints are in order. But to say we ought not change a thing or try to design a safer world is to say, “Hello and welcome, chikungunya.”

For too long, all we have been able to do in order to avoid many pest- and parasite-borne diseases is to try to avoid contact with the organisms, vaccinate against their diseases, or seek to control them with nasty chemicals. Genetic engineering by means of gene drives holds out the prospect of getting rid of disease-bearing creatures that do nothing in nature but attack us or valuable plants and animals. Wiping out or reducing useless pests means saving untold numbers of lives and fortunes in health-care and disability costs, improving the economy, lowering the burden of current pest-control on the environment, and perhaps finding a way to adjust to changes in climate.

But yes, gene drives also hold the potential for abuse, accidents, terrorism, and inadvertent destruction of our ecosystem. It is one hell of a trade-off—one that requires the world to engage in discussing the pros and cons now. Chik­ungunya and its many other gruesome friends don’t mind our holding off on utilizing gene drives for a very long time.


Arthur L. Caplan is the Drs. William F. And Virginia Connolly Mitty Professor of Bioethics at New York University and director of the Division of Medical Ethics at New York University Langone Medical Center.

Arthur Caplan

Arthur Caplan is director of the University of Pennsylvania’s Center for Bioethics and a nationally prominent voice in the debates over cloning and other bioethical concerns.


There are risks, but the prospect of reducing parasitic diseases through gene-drive genetic engineering seems too good to pass up.

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