Dengue fever is so excruciating that it is often called the “bone breaker,” causing severe pain in the joints and abdomen, vomiting, and circulatory system failure. It's nearly impossible to treat, so the only way to cut down on incidences of the disease is to decrease the number of mosquitoes that carry it. One startling effective way to do that: genetically modifying mosquitos so their offspring won't survive. A year-long trial with genetically modified mosquitoes in northeast Brazil has been the most successful yet, reducing the population of the disease-carrying insects by 95 percent, according to a study published last week in PLOS Neglected Tropical Diseases.
The British biotech company Oxitec has been developing a unique form of pest control for over a decade. Since dengue is primarily spread through the mosquito species Aedes aegypti, Oxitec has engineered a male mosquito that, to female mosquitoes in the wild, looks just like the usual males. However, when the mosquitoes mate, their young carry a mutation that kills them before they're able to reproduce or transmit the disease.
Juazeiro, a city in northeast Brazil, was a great place to try them out. After it was wiped out for 20 years, dengue has been on the rise in Brazil, with an estimated 16 million new cases every year. Many of the mosquitoes that carry the disease are also resistant to pesticides, which meant that Brazilians were left with few options to decrease dengue's prevalence. The neighborhood in which the researchers tested the modified mosquitoes was a low-income area with high rates of dengue infection, according to local public health officials. Over a one-year period, the researchers released the modified males into the local environment and monitored the resulting eggs, looking for a characteristic fluorescent marker engineered into the males' genome. In the course of that year, the number of disease-carrying mosquitoes decreased by 95 percent as compared to a control group in a neighborhood next door.
This isn't Oxitec's first attempt to decrease the prevalence of disease-carrying mosquitoes—the company did another trial in the Cayman Islands in 2010—but this test was the most successful. The researchers hope to scale up their efforts to eradicate dengue and the insects that carry it in a larger area.