A. gambiae has been called the world’s most dangerous animal, although strictly speaking that applies only to the female of the species, which does the bloodsucking and harms only indirectly. Its bite is a minor nuisance, unless it happens to convey the malaria parasite, Plasmodium falciparum, for which it is a primary human vector. Although a huge international effort has cut malaria mortality by about half since 2000, the World Health Organization still estimates there were more than 400,000 fatal cases in 2015, primarily in Africa. Children are particularly susceptible. The Bill and Melinda Gates Foundation prioritized malaria in its more than $500 million commitment to fight infectious disease in developing countries. ... Humans have been at war with members of the family Culicidae for over a century, since the pioneering epidemiologist Sir Ronald Ross proved the role of Anopheles in malaria and U.S. Army Maj. Walter Reed made a similar discovery about Aedes aegypti and yellow fever. The war has been waged with shovels and insecticides, with mosquito repellent, mosquito traps and mosquito-larvae-eating fish, with bed nets and window screens and rolled-up newspapers. But all of these approaches are self-limiting. Puddles fill up again with rain; insects evolve resistance to pesticides; predators can eat only so much. ... If Crisanti’s approach works, you could, in theory, wipe out an entire species of mosquito. You could wipe out every species of mosquito, although you’d need to do them one at a time, and there are around 3,500 of them, of which only about 100 spread human disease. You might want to stop at fewer than a dozen species in three genera—Anopheles (translation: “useless,” the malaria mosquito), Aedes (translation: “unpleasant,” the principal vector for yellow fever, dengue and Zika) and Culex (translation: “gnat,” responsible for spreading West Nile, St. Louis encephalitis and other viruses).
Of the 1,301 mosquito-borne cases recorded in the U.S., 97 percent of them are in Puerto Rico, neither a state nor a sovereign nation, but whose people are, nonetheless, U.S. citizens. As of early June, the start of Puerto Rico's long, hot and rainy summer, there are 1,259 recorded cases on the island, though some health officials believe the true number may be more than 80,000. ... unlike Ebola, which causes gruesome symptoms often followed by death, Zika is somewhat of a stealth virus. Most people infected will have no symptoms. Some may come down with conjunctivitis or break out in a skin rash, or experience muscle or joint pain or run a fever. Within a week or so, all of the symptoms, if they even emerged, are gone. In a certain number of cases, however, this may only be the beginning. ... the CDC estimates that it could cost $10 million to care for one microcephalic child. Zika, which seems to be particularly drawn to neurological tissue, may also cause swelling of the brain or spinal cord in adults, and has been linked to Guillain-Barré syndrome, an autoimmune neurological condition that can cause severe, if usually temporary, paralysis. ... But the scariest aspect of Zika is how little scientists actually know about it. ... Zika was first discovered in 1947 in the Zika Forest of Uganda, where researchers were studying the impact of mosquito-borne viruses on rhesus monkeys. Over the next 60 years, there were only 14 documented cases of Zika in humans, mainly in Africa and parts of southern Asia. ... given the prevalence of a host of factors, ranging from effective sanitation to the ubiquity of window screens and air conditioning, this kind of outbreak anywhere in the continental U.S., and much of Europe, for that matter, is unlikely.
Oxitec is trying to leverage this mating instinct to help wipe out one particular species of mosquito: Aedes aegypti, carrier and spreader of some of the worst insect-borne diseases known to medicine—dengue, malaria, and Zika. The A. aegypti mosquito has evolved to survive even the most effective pesticides. It can lay 500 eggs in just a bottle cap’s worth of water, and it prefers to bite humans over animals, so it lives in places where no one thinks to spray, like under the couch. ... The idea behind Oxitec’s experiment is that if enough genetically modified male A. aegypti mosquitoes are released into the wild, they’ll track down large numbers of females in those hard-to-find places and mate with them. The eggs that result from any union with an Oxitec mosquito will carry a fatal genetic trait engineered into the father—a “kill switch,” geneticists call it. The next generation of A. aegypti mosquitoes will never survive past the larval stage, never fly, never bite, and never spread disease. No mosquitoes, no Zika. ... Oxitec is far from the first company or research team that’s tried to sterilize an entire insect population. Scientists have been going after A. aegypti in this way since the 1970s, usually by irradiating them. The problem with radiation is that it makes the mosquitoes too weak to get out and breed. The great innovation of the Oxitec method is that it cleverly achieves the same result as sterilization, while leaving mosquitoes able to do what mosquitoes do. ... Oxitec charges about $7.50 per person per year in each area it treats.