Because of a problem with the body’s immune response that wasn’t previously known.
It’s no secret that mosquito bites are itchy and irritating, but new research has found that the little red bumps may actually drive a more rapid spread of viral infections, increasing the risk of severe diseases like Zika and dengue.
"Mosquito bites are not just annoying — they are key for how these viruses spread around your body and cause disease," senior author Clive McKimmie, a research fellow at the University of Leeds’ School of Medicine, said in a press statement.
In the new research, which appears in the journal Immunity, the scientists used mice to study the bites of the Aedes aegypti mosquito, which is the species that spreads infections like Zika, dengue, and chikungunya.
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When a mosquito bites, its saliva triggers an immune response in our bodies. White blood cells, including neutrophils and other myeloid cells, rush to the site to help fight the foreign substance off.
However, the researchers discovered that the white blood cells don’t always end up helping — they can end up getting infected by the mosquito-borne virus and inadvertently replicate it.
To come to this finding, the team injected a virus — Semliki Forest virus (SFV), a mosquito-borne virus that is a close relative of the chikungunya virus — into the mosquito bites of mice immediately after they were bit by an A. aegypti mosquito. They compared the reactions of these mice to those who were injected with SFV without being bit.
They observed that the viruses failed to replicate well in the mice who didn’t have mosquito bites, but the presence of the bite inflammation resulted in a high virus level in the skin.
Take a look at the graphic below to see the team’s findings broken down in an illustration.
Credit: Pingen et al./Immunity 2016
"This was a big surprise we didn't expect," said McKimmie, whose team also worked with colleagues at the University of Glasgow. "These viruses are not known for infecting immune cells.
"And sure enough, when we stopped these immune cells coming in, the bite did not enhance the infection anymore,” he explained.
McKimmie says that the researchers now want to investigate whether anti-inflammatory creams could stop the viruses from establishing an infection if they were applied soon enough after the bite inflammation appears.
"This research could be the first step in repurposing commonly available anti-inflammatory drugs to treat bite inflammation before any symptoms set in," McKimmie said in the release. "We think creams might act as an effective way to stop these viruses before they can cause disease."
He adds that this preventative technique could help with a number of other viruses out there if it’s proven effective.
"There are estimated to be hundreds of other mosquito-borne viruses out there and it's hard to predict what's going to start the next outbreak,” he said.
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