Do you know which animal kills the most humans every year? It’s not snakes, scorpions, or any of those obvious choices. It’s not something semi-unexpected like hippos – and no, it’s not our fellow humans either, so stop looking so smug.
Not directly: they aren’t flying around with little syringes full of poison that they inject into their unassuming victims or anything – wait, no, that’s actually pretty much exactly what they do. Mosquitoes’ unbeatable kill count comes down to their habit of transmitting bacteria, viruses, and even parasites into our body when they come for a sip at the ol’ blood banquet.
That’s why, since time immemorial, people have been chasing a fool-proof way to outwit the little pests. Now, after a year-long experiment in the Florida Keys, researchers say they have some positive results from one of the most cutting-edge techniques out there: genetic modification.
“We had quite a few quite a number of key performance outcomes that we were hoping to hit,” said Nathan Rose, head of regulatory affairs at Oxitec, the UK-based biotechnology firm behind the experiment, during a webinar on the results.
“We were able to hit all of those in this trial,” he added.
This isn’t the first experiment aimed at reducing the world’s mosquito problem on the genetic level – it’s not even the first experiment from Oxitec to attempt it. Each method is slightly different, though, and this latest approach saw researchers engineer male Aedes aegypti mosquitoes to carry a gene that is lethal to female offspring. These Oxitec-grown males are then released into the Florida Keys to go find a wild female to mate with (which is, to be fair, a well-established tradition in Florida during Spring.)
“[A] really important part of this project was looking at effective mating by male mosquitoes that we released, and also what happened to the female offspring of these matings,” Rose explained. “And here we confirmed that the larvicidal efficacy of our mosquitoes was 100 percent throughout the project.”
Throughout the experiment, Oxitec researchers carefully harvested more than 22,000 mosquito eggs from traps and brought them back to the lab. There, they screened the resulting larvae for fluorescence – the genetic modification had a secondary effect that made affected mozzies glow. Any that lit up, the scientists tracked through to adulthood.
“We saw that every single fluorescent female larva died before it reached adulthood,” Rose said. “This is what we expected, and it's what we've seen in the field in Brazil and in the lab as well.”
While these results are certainly promising, we’re still very far from proclaiming a new miracle weapon against the world’s mosquitoes. For one thing, the genetic change isn’t permanent – the experiment revealed that mosquito populations no longer carry the lethal gene after two or three months (around three generations of mosquito offspring.)
What’s more, the experiments can’t tell us how well this technique can suppress mosquito populations or suppress the spread of the deadly diseases they transmit. It’s not a limitation of the study – the researchers never intended for the experiment to answer those questions.
“They’re not going to be able to do a trial to show that it actually has a public-health impact,” Thomas Scott, an entomologist at the University of California, Davis, told Nature. “There’s not enough Aedes-transmitted viral infection in the Florida Keys.”
Nevertheless, the Florida Keys Mosquito Control District (FKMCD), a local anti-mosquito group, has high hopes for the new technology.
“Aedes aegypti […] makes up about four percent of our total mosquito collections, but is actually responsible for a hundred percent of the diseases we’ve seen here recently [in the Florida Keys],” FKMCD executive director Andrea Leal explained during the webinar.
“It's very difficult […] to control this mosquito,” she continued. “There is no silver bullet […] you know, we're just really hopeful that we [find] something we can integrate with the rest of our control methods.”