Dengue spread across southern Brazil as mosquito infestation expanded
Dengue reached more municipalities in Brazil’s southernmost state as mosquito infestation expanded. An observational study combines surveillance and viral genomes to trace the change across 2015–2023. Some lineages appear to have persisted between years, while measured climatic suitability showed no clear upward trend within the period. The findings leave their winter survival mechanism unresolved.
Science··Morning
More municipalities crossed the dengue threshold
Dengue spread more widely during 2015–2023 in the southern Brazilian state of Rio Grande do Sul. In a peer-reviewed observational study, the count of municipalities with annual incidence of 20 or more cases for every 100,000 residents rose from 22 to 254. Case burden rose particularly after 2020. The researchers combined disease notifications with mosquito surveillance, population distribution and environmental measurements rather than testing a control intervention.[1]
Viral genomes indicate persistence across years
An additional 665 viral genomes helped reconstruct dengue’s movement. Genetic relationships were consistent with some lineages persisting locally between successive years. The state’s Northwest and Metropolitan regions emerged as important transmission hubs. How the virus crossed winters remains unresolved: the genetic patterns cannot distinguish passage through mosquito eggs, low-level winter transmission and unnoticed introductions from neighboring areas.[1]
Seasonal climate suitability remained important
Mosquito infestation and population density were associated with dengue burden. Climate suitability retained a seasonal connection with transmission, but neither annual suitability nor the suitable season showed a clear increase within the study period. Longer-term climate effects remain possible. Uneven genomic sampling and reliance on symptomatic patients seeking care also leave gaps in the reconstruction, including potentially unobserved asymptomatic transmission.[1]
