Mosquito-borne viruses are a growing global threat. Initial viral inoculation occurs in the skin via the mosquito ‘bite’, eliciting immune responses that shape the establishment of infection and pathogenesis. Here we assess the cutaneous innate and adaptive immune responses to controlled Aedes aegypti feedings in humans living in Aedes-endemic areas. In this single-arm, cross-sectional interventional study (trial registration #NCT04350905), we enroll 30 healthy adult participants aged 18 to 45 years of age from Cambodia between October 2020 and January 2021. We perform 3-mm skin biopsies at baseline as well as 30 min, 4 h, and 48 h after a controlled feeding by uninfected Aedes aegypti mosquitos. The primary endpoints are measurement of changes in early and late innate responses in bitten vs unbitten skin by gene expression profiling, immunophenotyping, and cytokine profiling. The results reveal induction of neutrophil degranulation and recruitment of skin-resident dendritic cells and M2 macrophages. As the immune reaction progresses T cell priming and regulatory pathways are upregulated along with a shift to Th2-driven responses and CD8+ T cell activation. Stimulation of participants’ bitten skin cells with Aedes aegypti salivary gland extract results in reduced pro-inflammatory cytokine production. These results identify key immune genes, cell types, and pathways in the human response to mosquito bites and can be leveraged to inform and develop novel therapeutics and vector-targeted vaccine candidates to interfere with vector-mediated disease.

Metagenomic next-generation sequencing (mNGS) is the process of sequencing all genetic material in a biological sample. The technique is growing in popularity with myriad applications including outbreak investigation, biosurveillance, and pathogen detection in clinical samples. However, mNGS programs are costly to build and maintain, and additional obstacles faced by low- and middle-income countries (LMICs) may further widen global inequities in mNGS capacity. Over the past two decades, several important infectious disease outbreaks have highlighted the importance of establishing widespread sequencing capacity to support rapid disease detection and containment at the source. Using lessons learned from the COVID-19 pandemic, LMICs can leverage current momentum to design and build sustainable mNGS programs, which would form part of a global surveillance network crucial to the elimination of infectious diseases.

The year 2019 witnessed the highest number of dengue cases ever reported globally. We analyzed epidemiological, serological, and phylogenomic data to investigate the drivers of the 2019 epidemic in Cambodia. Using epidemiological models fit to a 19-year national dataset, we identified an overall trend of declining annual force of infection (FOI) for dengue virus (DENV) in Cambodia, interspersed with FOI spikes corresponding to epidemic year caseloads that exceeded demographic predictions. We constructed time-resolved phylogenetic trees with 105 DENV genomes sequenced from the 2019 Cambodian epidemic, paired with historical Southeast Asian data, to document the first-recorded introduction of DENV-2 Cosmopolitan genotype into Cambodia. This introduction yielded highly localized transmission and decreased genomic diversity when compared to endemic DENV-1, supporting the hypothesis of epidemic invasion. Introduction of this genetically distinct lineage into a population with limited prior immunity-paired with a spike in FOI-was a key driver of the 2019 Cambodian epidemic.

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Mosquito-borne viruses are a growing global threat. Initial viral inoculation occurs in the skin via the mosquito ‘bite’, eliciting immune responses that shape the establishment of infection and pathogenesis. To understand these phenomena, we assessed the cutaneous innate and adaptive immune responses via controlled Aedes aegypti feedings in humans living in an Aedes-endemic country. Gene expression profiling and immunophenotyping revealed induction of neutrophil degranulation and recruitment of skin-resident dendritic cells and M2-macrophages. As the immune reaction progressed over time, T cell priming and regulatory pathways were upregulated along with a shift to a Th2-driven response and CD8+ T cell activation. In accordance, participants’ bitten skin cells produced less pro-inflammatory cytokines when stimulated by Ae. aegypti salivary gland extract. These results identify key immune genes, cell types, and pathways in the human response to mosquito bites that can be leveraged to develop novel therapeutics and vector-targeted vaccine candidates to arboviral diseases.Graphical Abstract