Mosquito saliva contains a viral RNA compound that actively suppresses human immune responses to help orthoflaviviruses establish infection from the moment of a bite, according to a study published in Nature Communications. Researchers from the IRD, CNRS, the University of Montpellier, and Mahidol University discovered that this salivary component, known as sfRNA, inhibits the body’s initial immune activation, allowing viruses such as Zika and West Nile to gain time at the bite site.
Orthoflaviviruses transmitted by mosquitoes account for approximately 500 million infections annually across tropical and subtropical regions. Despite this high disease burden, the mechanisms allowing these pathogens to establish themselves in the skin after inoculation remained largely unclear. To investigate these dynamics, the research team utilized an in vivo transmission model developed at Vectopôle, a laboratory in Montpellier dedicated to vector research.
The experiments demonstrated that greater quantities of sfRNA in mosquito saliva lead to stronger promotion of infection and enhanced viral spread. When a mosquito bites, the human body typically triggers an innate immune response to detect the virus and limit replication. However, the study showed that the injected sfRNA blocks the activation of this defense system. This discovery was observed across two distinct orthoflavivirus-vector pairs: West Nile virus transmitted by Culex mosquitoes and Zika virus transmitted by Aedes tiger mosquitoes.
Flavivaccine Project Targets Salivary RNA Mechanisms
Identifying sfRNA in the saliva of multiple vector species suggests that subverting early immune responses through saliva is a shared mechanism among orthoflaviviruses. This finding points toward universal prevention strategies that target the shared facilitation mechanism rather than individual viral strains. Building on these results, IRD researchers have initiated a vaccination strategy directed against this salivary compound. The approach is currently under optimization for clinical-scale application through the Horizon Europe Flavivaccine project, which aims to develop prevention tools against endemic diseases in the Global South.
Frequently Asked Questions About Mosquito Saliva and Viral Transmission
How does sfRNA in mosquito saliva affect the human immune system?
Injected sfRNA inhibits the activation of the body’s innate immune response—specifically blocking MDA5-mediated early interferon responses—which prevents the host from effectively limiting viral replication at the bite site during the initial stages of infection.
Which mosquito species and viruses were evaluated in this research?
Researchers examined West Nile virus transmitted by common Culex mosquitoes and Zika virus transmitted by Aedes tiger mosquitoes, identifying sfRNA in the saliva of both species.
What is the goal of the Horizon Europe Flavivaccine project?
The project focuses on developing and optimizing a clinical-scale vaccination strategy targeting the newly identified salivary compound to prevent multiple orthoflavivirus infections in endemic regions.
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