Vector surveillance during a major CHIKV outbreak in southeastern Brazil
Description
Brazil is considered an epicenter for the emergence and re-emergence of arboviruses, which pose significant challenges to public health. The mid-sized city of São José do Rio Preto (SJdRP), located in northwestern São Paulo State, is hyperendemic for arboviral diseases, with an increasing number of reported cases each year. Notably, despite this epidemiological context, only 62 chikungunya fever (CHIKF) cases were officially reported in SJdRP between January 2015 and October 2023, suggesting cryptic circulation of chikungunya virus (CHIKV). In contrast, CHIKF notifications increased markedly across São Paulo State in 2024. Given the clinical overlap among arboviral febrile illnesses, particularly in dengue-endemic areas, the rise in CHIKV cases complicates differential diagnosis and highlights the need for robust surveillance systems. In this context, entomological surveillance is a valuable tool for the early and accurate detection of arboviruses. It enables the identification of emerging or increasing viral activity, supports the prediction of potential outbreaks, and guides targeted control efforts to mitigate public health impact. Therefore, in this study, we conducted monthly collections of adult mosquitoes across multiple neighborhoods in SJdRP and applied molecular assays to detect CHIKV RNA. Positive specimens were further analyzed through virus isolation, whole-genome sequencing, and phylogenetic reconstruction. Our results demonstrate that entomological surveillance allowed for early detection and tracking of CHIKV dissemination across the city, revealing an overall CHIKV RNA detection rate of 5.5% in mosquito samples. Detection rates began rising in December 2023, peaking in May 2024, in parallel with an increase in confirmed human CHIKF cases in the same period. Phylogenetic analysis indicated that the re-emergence of CHIKV in the region was driven by multiple introduction events, primarily originating from southeastern Brazil. These introductions likely facilitated viral establishment within a dense and susceptible vector population, contributing to extensive transmission and culminating in a large-scale CHIKF outbreak. Together, our findings reinforce the critical role of entomological surveillance in areas with co-circulating arboviruses. When integrated with ongoing clinical and laboratory surveillance of human cases, vector monitoring constitutes a powerful approach for guiding timely public health interventions, disrupting transmission chains, and reducing the likelihood of future epidemic waves.
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Institutions
- Faculdade de Medicina de Sao Jose do Rio Preto