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Medellin: Where people learn to love mosquitoes

  • Published at 11:17 pm October 22nd, 2019
Aedes aegypti mosquitoes are seen inside Oxitec laboratory in Campinas, Brazil, on February 2, 2016 Bigstock

Instead of trying to kill mosquitoes, they are instead breeding and releasing thousands of those

A new study in the journal Nature Microbiology has found that nearly half the world’s population could be at risk of catching mosquito-borne diseases like zika, dengue, chikungunya, and yellow fever by 2050.

But scientists have been working for years to eliminate such diseases with a counter-intuitive notion: instead of trying to kill mosquitoes, they are instead breeding and releasing thousands of those.

The latest battleground is the city of Medellin in Colombia.

When Nelly Patino, a teenage schoolgirl, first heard of plans in 2017 to breed and release thousands of mosquitoes in her local neighbourhood in Medellin, she thought the authorities had gone mad. Like many of the impoverished communities sprawling around the city’s green mountains, Santa Cruz had just been hit once again by another deadly outbreak of the tropical mosquito-borne disease dengue fever.

“Why, if there are so many mosquitoes, are they going to release more?” Patino recalls herself panicking, having seen a number of neighbours fall sick and even die from the illness. “More mosquitoes mean more epidemic.”

But World Mosquito Program (WMP) had approached her and other community peoples with the hope of making Santa Cruz the latest guinea pig for their novel program which could rid the neighbourhood – and one day potentially the world – of some of the deadliest mosquito-borne diseases.

After two years, Patino realizes not only have there been no further outbreaks of dengue, there are fewer mosquitoes than ever. 

The Aedes aegypti mosquito, popularly known as Aedes, is a carrier of dengue – which infects 390 million people annually and kills tens of thousands. The insect also carries chikungunya, yellow fever and the zika virus, which has been linked to birth defects across the world.

O'Neill, head of the WMP, dusted off an old concept and turned it into a viable way to fight disease.

Karen Robles, an entomologist at the WMP’s base in Medellin, explained that O’Neill’s research focused on Wolbachia, a species of bacteria naturally present in up to 60% of insect species, including some mosquitoes. They aren’t usually found in Aedes, but when they are, they suppress viruses by boosting the insects’ immune system and competing for key molecules such as cholesterol. These two factors drastically lower the probability of viruses growing successfully and being transmitted to humans.

The other useful quality of Wolbachia is that it spreads through the mosquito population in a self-sustaining way. If a male with Wolbachia mates with a female without it, her eggs won’t hatch, but if a female with Wolbachia mates with a male without it, she will still pass on the bacteria.

Combined, these quirks of biology mean that over time the overall number of mosquitoes and the rates of virus transmission of these viruses will both decrease.

Unlike a chemical or genetic intervention, research shows that it is difficult for viruses such as dengue to quickly develop resistance to the Wolbachia intervention.