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Mosquitoes take on rabbit fever and win

August 16, 2016   /   by Michele McDonald

Studying mosquito peptides could lead to new sources of antibiotics. ThinkStock photo.

Even though mosquitoes are better known for causing itchy bites and spreading disease, their immune systems may contain clues for how to stop bacterial infections, according to new George Mason University research.

Researchers at George Mason who are investigating potential new sources of antibiotics are looking at unlikely sources including alligator blood and mosquitoes, said Monique van Hoek, a professor in Mason’s School of Systems Biology and at the National Center for Biodefense and Infectious Diseases.

Mosquitoes, in particular the Aedes albopictus species, are well-known conveyers of disease from yellow fever to Zika. Still, the pesky insect doesn’t fall to the illness that it passes to its victims.

Mason researchers are studying how mosquitoes and their victims are affected by the Francisella bacteria, which causes tularemia, better known as rabbit fever. The infection caused by this bacteria attacks the lungs, liver and spleen. Naturally occurring and on the rise, this bacteria hits small mammals but also can infect humans.

Like anthrax, Francisella was weaponized in the ’60s by the United States and the Soviets, as it is especially dangerous when inhaled into the lungs.

In this case, the question was whether mosquitoes spread the disease or whether the mosquitoes make compounds that kill the bacteria, and stop bacterial infection from spreading, van Hoek said.

Monique Van Hoek

“We infected mosquito cells in the lab with Francisella bacteria, to see how the mosquito cells responded,” she explained.

When infected, the insects’ cells unleash antimicrobial peptides––tiny proteins that are part of a body’s innate immune system. These peptides fight against bacterial invaders by targeting the membrane of the bacteria.  

The result? The mosquito peptide killed the bacteria, van Hoek said. “Now, our next question is whether the mosquito actually transmits the bacteria or if the bacteria are killed while inside the mosquito.”

More study into these insect peptides could lead to new sources of antibiotics, said Akanksha Kaushal, van Hoek’s research assistant who worked on the project and recently earned a master’s degree in biology from Mason. She’s also studied bedbugs and their antimicrobial peptides in a 4-VA-funded project.

“The main takeaway from this mosquito research is that insects are amazing and contain these antimicrobial peptides,” Kaushal said.

Unfortunately, mosquito peptides don’t tackle most viruses like they do bacteria, van Hoek said, so viruses such as Zika transmit easily from mosquito to bitten victim. It’s also possible for mosquitoes to transmit rabbit fever if they’ve bitten an infected animal and have blood on their mandibles when they bite another animal, she said.

Mosquito population control still is the best defense against mosquito-transmitted disease, van Hoek said. That means clearing standing water and eliminating other breeding areas. The insects already are moving farther north, thanks to an increasingly warmer climate that’s increased their range, she said.

“The simple things are really important—controlling mosquitoes in the environment should help control Zika and West Nile virus,” she said.   

A Mason Provost Summer Research Award and a DTRA grant helped fund the research. Van Hoek worked on the project with a team including Kaushal, postdoctoral fellow Kajal Gupta, and high-school student Ruhee Shah, who teamed up with van Hoek in summer 2014 as part of the Aspiring Summer Scientists Internship Program.