Biology subjects

Sambado, S.

Publications and source records attributed to Sambado, S..

4 recordsLinked to original sources

bioRxiv2026

Water availability has stronger effects on West Nile virus dynamics in water-limited regions

West Nile virus dynamics are shaped by hydrological conditions that influence mosquito habitat and pathogen transmission, but identifying causal relationships is difficult in managed landscapes where irrigation decouples local water conditions from precipitation, complicating climate-disease inference. We address this challenge using a 21-year panel of more than 19 million Culex tarsalis mosquitoes from Californias Central Valley, applying fixed-effects panel models to estimate how surface water availability affects mosquito abundance and infection rates while accounting for spatial differences and shared temporal variation. We find that wetter conditions lead to higher mosquito abundance but slightly lower infection rates, suggesting divergent responses of vector population growth and pathogen amplification. These patterns are consistent across multiple hydrological measures, including drought indices, soil moisture, surface water, and evapotranspiration. Effects are strongest in water-limited regions, where hydrological variability is greatest and buffering by snowmelt-fed river systems is weakest. Overall, hydrological conditions exert contrasting effects on key components of West Nile virus dynamics, and these relationships are strongly conditioned by human water management. Our results highlight how irrigation decouples local hydrological conditions from broader climatic variability, underscoring the need for fine-scale hydrological data and panel-based approaches to identify drivers of disease dynamics in human managed landscapes.

ecology↗

bioRxiv2025

Climate warming and urbanization may expand dengue transmission risk in California

BackgroundWhile primarily a disease of tropical and subtropical regions, dengue outbreaks are increasing in non-endemic regions due to environmental change and increasing travel and trade. For these non-endemic regions, estimating the risk of dengue is challenging as transmission is driven by both local environmental conditions and the introduction of viremic travelers. In this study, we aimed to estimate current and future dengue risk in California, USA--a region that has recently experienced its first cases of locally-acquired dengue. MethodsWe modeled dengue risk as the product of three key components needed for local transmission--vector presence, temperature-suitability for pathogen transmission, and viral introductions via travel-associated cases--estimated using vector and case surveillance, sociodemographic, and environmental data. We estimated risk for locations and months where local transmission was reported in 2023-2024 to define a threshold level of risk. We then projected monthly, census tract-level risk under both current conditions and future scenarios of climate warming and urban expansion. FindingsApproximately 18.2 million (95% CI: 17.9-18.3) California residents--primarily in the Central Valley and the Los Angeles and San Diego metropolitan areas--currently live in areas where peak monthly dengue risk exceeds levels estimated during observed local transmission. Under moderate scenarios of climate warming and urban expansion, an additional 4.1 million (95% CI: 3.7-4.6) California residents may be at risk by mid-century, with the largest increase in risk estimated for September and for the Sacramento Valley and coastal southern California regions. Outside the summer months and beyond the Central Valley and southern California, current and future risk remains low due to one or more major bottlenecks to transmission. InterpretationOur study identifies the specific regions and months conducive to dengue transmission in the non-endemic setting of California. At present, this covers a substantial portion of the state and is projected to expand under on-going climate warming and urbanization. Our results underscore the need for sustained vector control, and timely detection and management of travel-associated cases. Research in ContextO_ST_ABSEvidence before this studyC_ST_ABSDengue is considered endemic in over 125 countries and rapidly expanding its range, aided by climate warming, urbanization, and global travel and trade. Estimating transmission risk in newly emerging regions is critical for public health preparedness and depends on both local environmental conditions and the introduction of viremic travelers. We searched PubMed from database inception to May 8, 2025, for articles published in English using search terms "dengue", "model", "non-endemic", and their common textual variants. We identified 75 relevant studies modeling dengue transmission risk in non-endemic settings. However, nearly all were focused on one or two major determinants of transmission (eg, climate, vector population dynamics, or case importations) and/or did not include future projections. We found no studies that developed and validated a model of dengue transmission risk in non-endemic settings that incorporated vector, pathogen, and human suitability factors, and applied this model to project future risk. Added value of this studyThis study provides a novel approach to model dengue transmission risk in emerging regions that integrates the major factors driving transmission--vector presence, temperature suitability, and travel-associated cases. We apply this model to California--an emerging center of transmission risk in the continental USA--to identify the times and regions where risk exceeds levels observed during recent local transmission. We found that approximately 18.2 million California residents may be at risk based on this threshold, with an additional 4.1 million potentially at risk by mid-century under a moderate scenario of warming and urban expansion. Implications of all the available evidenceOur study identifies the hotspots of dengue transmission risk at a fine spatial and temporal resolution (census tract, month) in a highly populous and globally-connected region of emerging dengue risk. These risk estimates, and the regionally-specific bottlenecks to transmission that we identify can inform targeted disease surveillance and prevention strategies. Further, our findings have implications for other emerging regions including the southern USA and southern Europe, suggesting that the risk of local dengue transmission may increase under ongoing climate warming, urbanization, and global travel.

ecology↗

bioRxiv2025

The paradoxical impact of drought on West Nile virus risk: insights from long-term ecological data

Mosquito-borne diseases are deeply embedded within ecological communities, with environmental changes - particularly climate change - shaping their dynamics. Increasingly intesense droughts across the globe have profound implications for the transmission of these diseases, as drought conditions can alter mosquito breeding habitats, host-seeking behaviors, and mosquito-host contact rates. To quantify the effect of drought on disease transmission, we use West Nile virus (WNV) as a model system and leverage a robust mosquito and virus dataset consisting of over 500,000 trap nights collected from 2010-2023, spanning a historic drought period followed by atmospheric rivers. We pair this surveillance dataset with a novel modeling approach that incorporates monthly changes in bird host community competence, along with drought conditions, to estimate the effect of drought severity on WNV risk using panel regression models. Our results show that while drought decreases mosquito abundances, it paradoxically increases WNV infection rates. This counterintuitive pattern likely stems from reduced water availability, which concentrates mosquitos and pathogen-amplifying bird hosts around limited water sources, thereby increasing disease transmission risk. However, the magnitude of the effect depends critically on mosquito species, suggesting species-specific behavioral traits are key to understanding the effect of drought on mosquito-borne disease risk across real landscapes.

ecology↗

bioRxiv2024

Ecological and socioeconomic factors associated with globally reported tick-borne viruses

BackgroundPublic health resources are often allocated based on reported disease cases. However, for lesser-known infectious diseases, such as tick-borne viruses, disease risk reporting should account for more than just the biology of the disease and include mediating factors such as socioeconomics which can determine if an infection gets reported. ObjectivesWe aim to identify country-level ecological and socioeconomic factors important to reporting tick-borne viruses and examine whether countries with more economic resources have a higher likelihood of reporting resource intensive incidences. Our study goals are to determine potential country-level interventions that could enhance recognition of and reduce the health burden associated with tick-borne viruses. MethodsWe apply machine learning to the most comprehensive tick-borne virus database, ZOVER, with a curated global trait matrix of 23 environmental and socioeconomic predictors. ResultsWe identified socioeconomic factors driving reported tick-borne viruses captured in the database at a country level. Countries that were more likely to report tick-borne viruses had a lower Gini Index (i.e., countries with less inequalities such as Nordic countries), increased dollars spent on pesticide imports, and had institutions (i.e., IVSA chapter) or individuals with agricultural, forestry, or veterinary knowledge (i.e., % of tertiary grads) present. Additional characteristics included countries with a lower percent of population exposed to conflict also had a higher probability of reporting a tick-borne virus. As expected, broad environmental factors such as the Koeppen-Geiger climate classification zone was important and identified Mediterranean climate or humid subtropical climate as environmentally suitable zones for reported tick-borne viruses. DiscussionFor environmentally persistent pathogens, the role of ancillary factors mediating reporting must be considered for allocating resources to interventions. In addition, while direct interruption of transmission is important, socioeconomic interventions may be the greatest tool to reduce local disease burden.

ecology↗