The itchiness of a mosquito bite isn't just an annoyance: the inflammation that makes you want to scratch dramatically boosts the infection rate for viruses - like Zika, dengue or yellow fever - that the insect is carrying, a new study has revealed.
Writing in Immunity, Leeds University scientist Clive McKimmie and his colleagues have shown that components of a mosquito's saliva, introduced into the skin when the mosquito feeds, act like a magnet for the immune system, triggering an inflammatory response that attracts a range of cell types to the bite site.
This natural reaction, characterised by an itchy bump on the skin, is intended to neutralise bacterial and other parasites attempting to gain a toe-hold. But, as the Leeds team found, some of the incoming immune cells are particularly susceptible to viral infection and the swelling of the tissue also increases the retention time of the virus at the location.
This means that, through the action of its bite, the mosquito creates a virus-friendly niche capable of dramatically increasing infection rates.
In experiments, the team showed that the same dose of virus (they tested a Semliki Forest virus (SFV) and a bunyavirus, both of which are naturally mosquito-borne) introduced into the skin of mice with an accompanying mosquito bite led subsequently to ten-fold higher levels of circulating virus in the bloodstreams of the animals.
Injecting virus alongside immune-stimulating molecules mimicking a mosquito bite also boosted infection rates, while blocking the inflammatory response at the bite site had the opposite effect.
McKimmie is optimistic that the findings might lead to a new way to control mosquito-spread infection. "We tested two very different types of virus, which work in very different ways, and got the same result," says McKimmie.
"So we think that this might point to a new way to block mosquito-borne illness..."