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Brazil Fights Dengue With Modified Mosquitoes

Nov 05, 2014 05:41 PM EST
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With Jack o' Lanterns rotting on our doorsteps and a crisp chill in the air, the last thing you may be worried about is a mosquito bite. However, these pests are still a very real concern some parts of the world.

Experts in Brazil have been releasing modified mosquitoes in the thousands for the last few months in a unique effort to fight the spread of a painful disease known as Dengue fever.

The fever is rarely fatal, with only about one percent of all infections resulting in severe hemorrhagic conditions that kill. However, any fatalities at all makes the virus a more pressing concern than chikungunya, another mosquito-borne illness that has also recently made its way across the Southern Hemisphere.

Brazil has recently experienced an alarming number of cases of this harmful disease, prompting officials to look to the modification of mosquitoes for relief.

So how would that work? Unlike their pesky female counterparts, male mosquitoes don't feed on blood. Instead, they exist only to mature into an adult, mate with a female, and then die. This makes them ideal candidates for modification, because they can influence the reproduction process without posing a threat to humans.

Nature World News has previously reported on mosquito control through male modification. Studies have shown that DNA manipulation can essentially tip the gender scales in insects, with the female offspring of modified males never surviving past infancy. As the short-lived mosquitoes continue to reproduce, modified males become more and more common, leading to fewer biting and potentially Dengue-carrying females with each generation.

However, ecologists have voiced concerns that such an approach could quickly eradicate mosquito populations for good, leaving some specialized species without their prey. That's where British biotech firm Oxitec has stepped in, offering a softer approach.

Simply Sterile

Instead of releasing a self-sustaining means of population destruction, the firm simply releases thousands of sterile males into a population at planned intervals. As females often only mate with one male before dying, introducing sterile males can influence the number of overall larvae in a generation while still ensuring that some females survive. (Scroll to read on...)

According to The Times of India, the firm's faculties made the Brazilian city of Campinas, outside Sao Paulo, the first city in the world to specifically tackle Dengue outbreaks in this way.

"Brazil has one of the highest incidences of dengue in the world," Jair Virginio, who oversaw test of the Oxitec approach in the field, said in a statement. "We urgently need new tools to control the dengue mosquito, which is growing exponentially despite all the efforts made ​​in recent decades to control it with conventional methods."

According to Oxitec, approved commercial trials of this approach have already resulted in success, with target populations declining between 92 and 99 percent in parts of Bazil and the Cayman Islands in the Caribbean.

Now the biotech firm is collaborating with Gangabishan Bhikulal Investment and Trading Limited (GBIT) to develop and produce the modified mosquitoes in India.

Better Bacteria

However, this isn't the only approach desperate Brazilian officials are willing to try.

Near the start of last month, Brazilian researchers at the Fiocruz institute released thousands of mosquitoes infected with a bacteria that suppresses Dengue fever, making it much more difficult for the virus to jump to a human host.

This was part of an ongoing international research program called Eliminate Dengue (ED) that already has plans to involve communities from Australia, Brazil, China, Columbia, Indonesia, and Vietnam.

According to the program, they use an intracellular bacteria, called Wolbachia, to target the Dengue virus in mosquito hosts. Common among 60 percent of all insect species, the bacteria serves as a kind of supplementary immune system for bugs, and cannot transfer to humans. However, until now, it was never part of the Dengue-carrying mosquito (Aedes aegypti) biome.

By releasing Wolbachia infected mosquitoes into wild populations, the researchers hope that the bacteria will spread to offspring, becoming increasingly common. When the bacteria comes across the Dengue virus, it will allegedly attack the virus, preventing it from multiplying in a mosquito host. In this way mosquito populations are left whole as Dengue numbers drop.

"We believe that Wolbachia based strategies represent a practical environmentally sensitive approach to dengue suppression with the potential for area-wide implementation at low cost," the ED team reports. "The method is also compatible with existing control approaches like insecticide application and should also augment the effectiveness of a future vaccine once developed."

Interestingly, unlike Oxitec's sterilization approach, the ED program has only seen small-scale deployment in Brazil. The first city-wide experiment was actually launched in the ironically named city of Townsville, Australia just last week.

Unforeseen Consequences

Differences in funding aside, one of the reasons ED might be taking things slower is that the Wolbachia approach is not as extensively studied as insect sterilization. Sterilization has been used as a population control mechanism in pests for decades, even if it is just now becoming commercially viable to control mosquitoes.

Using specialized bacteria, on the other hand, is a new and sometimes unpredictable can of worms.

Back in July, it was revealed that while Wolbachia may be effective at stopping the moderately dangerous Dengue fever, it could actually make the infamous West Nile virus even more of a nightmare.

"Our results point to a previously unforeseen complication," researcher Jason Rasgon told Entomology Today. "These mosquitoes had significantly higher West Nile virus infection rates seven days after we fed them [Wolbachia] infected blood."

In other words, the mosquitoes infected with the supposedly "good" bacteria wound up becoming even more vulnerable to an infection of West Nile virus.

Interestingly, this contradicts studies overseen by the US Environmental Protection Agency back in 2013, standing only to prove that much more needs to be understood about the bacterial approach before it can be applied on a large scale.

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