By SHOKO TAMAKI/ Staff Writer
November 11, 2025 at 07:00 JST
The Asian tiger mosquito carries dengue and other viruses. (Provided by the National Institute of Infectious Diseases)
Components in mosquito saliva enhance the infectivity of viruses, including dengue, Zika fever and Japanese encephalitis, that the insects transmit to humans, a study has found.
A group of researchers from Juntendo University in Tokyo and other institutions said their findings represent a step toward developing medicines that can counter such viruses.
As a defense reaction of the human body, innate immune cells crowd a mosquito bite area that has been infiltrated by any of the many mosquito-carrying viruses.
However, some of those innate immune cells are permissive to the viruses.
The research team scrutinized the workings of mosquito saliva, which had drawn the attention of researchers but had yet to be known specifically.
The team first confirmed that infections progress faster, or symptoms are more serious, in mice inoculated with a mixture of mosquito saliva extracts and viruses than in mice inoculated with the viruses alone.
The researchers also combined viruses with different chemical compounds and administered the mixtures to mice to determine which of the various receptors in the body are most involved in the process of detecting foreign substances.
The experiment showed that mosquito saliva strongly stimulates a receptor called TLR2 (Toll-like receptor 2).
The scientists also found that stimulation of TLR2 ends up attracting neutrophils, a type of immune cell, to the mosquito bite site. The neutrophils then summon innate immune cells that are virus-permissive.
“The viruses are taking advantage of a signaling pathway, which is originally designed for eliminating pathogens, and are using it to their convenience to spread infections,” said Toru Okamoto, a Juntendo University professor of virology and a leading member of the research team. “It’s such a clever strategy.”
Okamoto said, however, that it remains unknown which molecules in mosquito saliva are the direct stimulants for TLR2.
He plans to address the question in future studies.
No specific medicine is currently available against mosquito-borne viruses, so treatment is centered on easing symptoms.
Dengue cases are particularly prevalent. According to World Health Organization figures, about 400 million individuals are infected with dengue annually, with symptoms showing in about 100 million of them.
Okamoto said he hopes to help develop new drugs based on the findings of the latest study.
The research results were published in Cell Reports, a U.S. science journal (https://doi.org/10.1016/j.celrep.2025.116210).
A peek through the music industry’s curtain at the producers who harnessed social media to help their idols go global.
A series based on diplomatic documents declassified by Japan’s Foreign Ministry
Here is a collection of first-hand accounts by “hibakusha” atomic bomb survivors.
Cooking experts, chefs and others involved in the field of food introduce their special recipes intertwined with their paths in life.
A series about Japanese-Americans and their memories of World War II
