A tiger mosquito is seen in this photo provided by the National Institute of Infectious Diseases.

       The Mainichi Shimbun answers some common questions readers may have about mosquito bites, which don't hurt but do itch, and what it could mean for the future of medicine.

       Question: Mosquito season is upon us. But we often notice their bites only after they start to itch --- why is it that they don't really hurt?

       Answer: Mosquitos' mouthpart, their proboscis, are needle-shaped for blood-sucking purposes. It is thought that their bites barely hurt because the part of their mouth that pierces the skin is thinner than a single hair -- which is about a tenth of a millimeter -- thereby hardly stimulating the sensory neurons. But now in addition to that, recent research has revealed that mosquito saliva has a pain-relieving effect.

       Q: What does that mean?

       A: Mosquitos suck blood while pumping their host with saliva, which includes compounds to prevent blood clotting. Compounds in the saliva are also known to cause an itchy allergic reaction. But a research team led by Makoto Tominaga, professor at the National Institute for Physiological Sciences in the central Japan city of Okazaki, Aichi Prefecture, conducted experiments in which mice were administered a compound from chili peppers and wasabi horseradish, which cause pain, and a compound from chili peppers and wasabi mixed with mosquitos' saliva. The mice's reactions were compared, and the results reportedly showed that the mosquito-saliva compound suppressed the mice's pain response.

       Q: It's like an anesthetic injection then?

       A: Pain occurs when the signal from a stimulated sensory neuron reaches the brain. But mosquito saliva can reportedly suppress sensory functions and make the host feel less pain; a mechanism that has never been employed in conventional painkillers.

       Q: Does this mean mosquito saliva is special?

       A: Similar effects to their saliva have been confirmed in experiments using a protein called "sialorphin" present in many animal species' saliva. It is likely animals lick their wounds because their saliva offers pain relief. It is expected that advanced research on saliva's components could lead to the development of new painkillers.

       (Japanese original by Tomoko Mimata, Science and Environment News Department)

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