Battling Bites

Blocking Mosquito-Borne Diseases

As the days grow longer and warmer, summer fun beckons. Swimming, sports, and picnics go hand in hand with warmer weather. But so do bug bites. Mosquitoes in particular can ruin a day outside. And their bites aren’t just itchy and irritating. They can also spread disease.

The list of illnesses carried by mosquitoes keeps growing. Some, like malaria, are rarely seen in the United States. Others, like dengue fever, are spreading in the Southern states as temperatures get warmer. And others, like West Nile virus, now pop up seasonally in most parts of the country.

NIH-funded researchers are working to help stop the spread of mosquito-borne diseases. They’re testing ways to stop mosquitoes from biting people and keep those who are bitten from getting sick.

Blocking Disease

For decades, researchers have been trying to develop vaccines to protect people against mosquito-borne diseases. But most haven’t been as effective as hoped, explains Dr. Matthew Memoli, an infectious diseases researcher at NIH.

“And there’s a lot of mosquito-borne diseases,” he says. “If you make a vaccine for every single one, that’s a lot of vaccines to have to develop.”

But what if you could vaccinate people against mosquitoes? That may sound far-fetched, but Memoli’s lab has been trying to do just this. When a mosquito bites you, their saliva gets under your skin. This saliva contains compounds that make it easier for a mosquito to suck blood. It also has compounds that help any disease the mosquito is carrying to get into your body.

“When you get bitten by a mosquito, you have an allergic response to the saliva,” explains Memoli. That response causes an itchy bump to appear after a bite. This is normal, but it can interfere with your body’s ability to fight germs. “When that allergic response gets turned on, the anti-infection response gets turned down,” Memoli says.

So Memoli’s team is testing a vaccine that helps the body’s defense system recognize mosquito saliva. They hope it can help the body prevent infections from sneaking in. In a small study, the team found that the vaccine was safe and boosted people’s defense responses. They now hope to test the vaccine in areas of the world where the risk of deadly mosquito-borne diseases is high.

Deterring Mosquitoes

One of the best ways to avoid mosquito-borne diseases is to prevent bites in the first place. People can take certain steps to protect themselves.

“We have personal repellents, like DEET, which you can put on,” says Dr. Carolyn McBride, who studies mosquito biology at Princeton University. Tools like mosquito nets can also prevent bites. But to keep diseases from spreading, they need to be used by everyone in an area.

Researchers want to develop better ways to prevent mosquito bites. But first they have to figure out how mosquitoes sense people. How do they find us to bite us?

McBride and her team recently uncovered a set of chemicals that the Aedes aegypti mosquito detects to let it home in on people. These chemicals include certain fats and other substances in and on human skin. They found that a specific mixture of these substances could attract mosquitoes from several feet away. They hope this knowledge can be used to design new ways to repel or trap mosquitoes, over large areas.

“This would allow us to push mosquitoes away from all the houses in high-risk neighborhoods. Or to place a trap where we can pull them in and kill them,” McBride explains. This would allow for better control of mosquitoes than requiring everyone to protect themselves.

Her team is now looking at a different kind of sensing: how mosquito eggs sense when it’s time to hatch. “If we can understand that, we could screen for compounds that block hatching,” McBride says. “Maybe chemicals that are otherwise safe, but if you sprinkle them on all the places mosquitoes lay their eggs, the eggs never hatch.”

Reducing the Spread

If there were fewer biting mosquitoes around, there would be less disease.

“But trying to keep mosquitoes down to a low level is really hard,” says Dr. Zach Adelman, a mosquito geneticist at Texas A&M University. “They’re really resilient. Spraying insecticides can get them temporarily. But they always come back.”

To disrupt this cycle, researchers have been working on an idea called reduce and replace. First, insecticides would be used to lower the mosquito population in an area. Then, before they could bounce back, new mosquitoes that are less likely to infect people would be introduced in their place.

Many ideas are being tested to make mosquitoes that can’t spread disease. One is infecting them with bacteria called Wolbachia. This doesn’t kill the mosquitoes. But mosquitoes that carry it have a harder time passing viruses on to people.

Adelman’s lab is looking at ways to modify the Stretches of DNA that define characteristics like size and disease resistance. genes mosquitoes carry to make them less able to spread disease. For example, mosquitoes aren’t normally affected when they pick up the virus that causes dengue fever. Adelman and his team are trying to make a mosquito that would die when exposed to the virus. This would lower the chances that infected mosquitoes bite people and spread the disease.

They’re also making sure that such gene changes would be temporary. “People want to know: What happens if these technologies don’t work out? Can you stop them? If they’re temporary, people are much more likely to want to try them,” Adelman says.

While researchers continue to work on ways to battle mosquitoes, there are simple steps you can take to reduce bites right now. See the Wise Choices box for tips.