Proactive Strategies to Block Mosquito-Borne Diseases

With the arrival of longer, warmer days, the allure of summer activities grows. Swimming, sports, and picnics are synonymous with the season's warmth. However, the increase in outdoor activities also brings the nuisance of bug bites. Mosquitoes, especially, can spoil outdoor enjoyment, and their bites are more than just itchy and annoying—they can also be vectors for disease.

The number of diseases transmitted by mosquitoes is increasing. While some diseases, such as malaria, are uncommon in the United States, others, including dengue fever, are expanding in the southern states with rising temperatures. Additionally, diseases like the West Nile virus have become seasonal occurrences in many regions of the country.

Researchers funded by the NIH are developing strategies to halt the spread of diseases transmitted by mosquitoes. They are exploring methods to prevent mosquito bites and protect individuals who have been bitten from falling ill.

Preventing Diseases

For many years, scientists have endeavored to create vaccines that can safeguard individuals from mosquito-transmitted illnesses. However, the effectiveness of these vaccines has often fallen short of expectations, as noted by Dr. Matthew Memoli, a researcher specializing in infectious diseases at the 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.”

What if it were possible to vaccinate people against mosquitoes? While it might seem unlikely, Memoli's laboratory is actively pursuing this goal. When a mosquito bites, its saliva enters your skin, containing substances that facilitate blood feeding. This saliva also includes compounds that assist in the transmission of any diseases the mosquito may be harboring.

“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.

Memoli's team is developing a vaccine aimed at enabling the body's immune system to identify mosquito saliva. Their goal is to block infections at their entry point. Initial trials have shown the vaccine to be safe and effective in enhancing immune responses. The team is now looking to conduct tests in regions where there is a high risk of lethal diseases transmitted by mosquitoes.

Deterring the Mosquitoes

Preventing mosquito bites is a crucial step in avoiding mosquito-borne illnesses. Individuals can adopt specific measures to safeguard themselves effectively.

“We have personal repellents, like DEET, which you can put on,” says Dr. Carolyn McBride, who studies mosquito biology at Princeton University.

Mosquito nets are effective in preventing bites; however, to halt the spread of diseases, their use must be widespread within a community.

Researchers are seeking improved methods to prevent mosquito bites. To achieve this, they must first understand how mosquitoes detect humans. What mechanisms do they use to locate us for biting?

McBride and her team have recently discovered a range of chemicals that allow the Aedes aegypti mosquito to target humans. These chemicals consist of specific fats and substances found on and within human skin. They determined that a particular combination of these substances has the potential to lure mosquitoes from a distance. Their aspiration is that this discovery will lead to the development of innovative methods to repel or capture mosquitoes across extensive 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 exploring a unique type of sensing mechanism: the process by which mosquito eggs determine the optimal 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.”

Lowering the Potential Spread

A reduction in the number of biting mosquitoes would likely lead to a decrease in disease transmission.

“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 break this cycle, researchers are exploring a strategy known as reduce and replace. Initially, insecticides would be deployed to decrease the mosquito population. Subsequently, before the population could recover, mosquitoes engineered to be less likely to transmit diseases would be released to supplant them.

Numerous strategies are under exploration to engineer mosquitoes incapable of transmitting diseases. One such method involves infecting them with a bacterium known as Wolbachia. While this infection does not eliminate the mosquitoes, it does impede their ability to transfer viruses to humans.

Adelman's laboratory is exploring methods to alter the genes of mosquitoes to reduce their capacity to transmit diseases. Typically, mosquitoes are not harmed by contracting the virus responsible for dengue fever. Adelman's team is working on creating a mosquito that would perish upon contracting the virus, thereby decreasing the likelihood of infected mosquitoes biting humans and propagating 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.

Source: NIH