Watch: Genetically-modified mosquitoes released in Florida
Thousands of genetically-modified mosquitoes have been released in Florida as part of a scientific experiment.
In some parts of the world, mosquitoes transmit a range of life-threatening infections, including the viruses dengue and Zika.
When pregnant women are infected, Zika can cause babies to be born with abnormally small heads, prompting the World Health Organization (WHO) to declare a Brazilian outbreak a public health emergency in 2016.
Although usually mild, dengue can cause patients to vomit blood, lose consciousness or even die.
Both viruses have been reported in the US, with incidences expected to become more commonplace as climate change progresses.
Scientists from the UK biotech firm Oxitec have therefore released genetically-modified male mosquitoes in six Florida Keys neighbourhoods.
The males, which do not bite or transmit infections, then mate with wild females. A gene is passed on to their female offspring that causes them to require a dash of the antibiotic tetracycline to survive past the larval stage. Over time, fewer adult females are expected to circulate.
This comes after scientists from the University of Glasgow warned climate change makes it "plausible" another infection transmitted by mosquitoes, the West Nile virus, could reach the UK in the next 20 to 30 years.
At this time of year, newly-hatched mosquitoes swarm flower pots, rubbish bins and ditches on the Florida Keys islands.
The US Environmental Protection Agency has signed off the experiment, with Oxitec officials hoping modified male mosquitoes may one day be approved for release nationwide.
The species Aedes aegypti – which spreads dengue and Zika – makes up just 4% of Florida Keys' total mosquito population, but is said to be responsible for nearly all disease transmission.
A. aegypti is increasingly developing resistance to conventional insecticides.
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In a past experiment, Florida Keys officials infected male mosquitoes with the parasite Wolbachia. When the males mated with uninfected females, the eggs did not hatch.
While the experiment was a success, more than one technique is likely required.
"What they've [mosquitoes] shown us over and over again is if we are not very subtle and if we just try to kill them, they will find a way out," Professor Flaminia Catteruccia, from Harvard, told The Wall Street Journal.
Globally, mosquito-transmitted dengue is said to have increased 30-fold over the past 50 years due to rising temperatures, travel and urban sprawl. At present, more than 20,000 people die from dengue complications every year.
By 2080, A. aegypti mosquitoes are expected to have spread from their native tropical and subtropical regions to 159 countries.
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"Oxitec is basically positioning themselves for the coming decades, when climate change makes the mosquitoes become denser and move farther north, and you're more likely to get sustained transmission of these kinds of diseases," said Dr Kevin Esvelt, from the Massachusetts Institute of Technology.
Oxitec CEO Grey Frandsen has called the experiment "a landmark project", adding "it's a very big step for the field".
The scientists are developing eight genetically-modified insects in all. These include two types of mosquitoes that transmit malaria, as well as worms, moths and flies that ordinarily feed on crops.
Watch: Dengue case in Miami