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1. Micro-climate to macro-risk: mapping fine scale differences in mosquito-borne disease risk using remote sensing

   https://doi.org/10.1088/1748-9326/ac3589  

   Boser, Anna; Sousa, Daniel; Larsen, Ashley; MacDonald, Andrew (November 2021, Environmental Research Letters)

   Abstract Mosquito-borne diseases (MBD) threaten over 80% of the world’s population, and are increasing in intensity and shifting in geographical range with land use and climate change. Mitigation hinges on understanding disease-specific risk profiles, but current risk maps are severely limited in spatial resolution. One important determinant of MBD risk is temperature, and though the relationships between temperature and risk have been extensively studied, maps are often created using sparse data that fail to capture microclimatic conditions. Here, we leverage high resolution land surface temperature (LST) measurements, in conjunction with established relationships between air temperature and MBD risk factors like mosquito biting rate and transmission probability, to produce fine resolution (70 m) maps of MBD risk components. We focus our case study on West Nile virus (WNV) in the San Joaquin Valley of California, where temperatures vary widely across the day and the diverse agricultural/urban landscape. We first use field measurements to establish a relationship between LST and air temperature, and apply it to Ecosystem Spaceborne Thermal Radiometer Experiment data (2018–2020) in peak WNV transmission months (June–September). We then use the previously derived equations to estimate spatially explicit mosquito biting and WNV transmission rates. We use these maps to uncover significant differences in risk across land cover types, and identify the times of day which contribute to high risk for different land covers. Additionally, we evaluate the value of high resolution spatial and temporal data in avoiding biased risk estimates due to Jensen’s inequality, and find that using aggregate data leads to significant biases of up to 40.5% in the possible range of risk values. Through this analysis, we show that the synergy between novel remote sensing technology and fundamental principles of disease ecology can unlock new insights into the spatio-temporal dynamics of MBDs. 

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2. Management Implications of Shifting Culex quinquefasciatus West Nile Virus Transmission Suitability in Florida

   https://doi.org/10.1177/15303667261426902  

   Ryan, Sadie J; Lippi, Catherine A (August 2026, Vector-Borne and Zoonotic Diseases)

   Background:West Nile virus (WNV), a mosquito-borne flavivirus, has circulated in the United States since 1999. In 2025, Florida was home to 24 million people, with projected increases in population and urbanization in a changing climate. The southern house mosquito,Culex quinquefasciatus, is found in every county, and is a major vector for WNV. Describing shifting WNV transmission risk is important to inform public health and vector control planning. Materials and Methods:Using published estimates of thermal suitability of WNV transmission byCx. quinquefasciatus, with climate models and population data, we calculated and mapped baseline and projected county-level transmission suitability and people at risk for 2000, 2030, and 2050. Five general circulation models and two mitigation scenarios (SSP2-4.5, SSP5-8.5) were used to explore future trajectories. Results:At baseline, all 67 counties in Florida experienced 5–9 months of transmission suitability. Using the year 2000 census estimates, 2.33 million people in 2 counties experienced 9 months, and in 2030, across climate models, 8.93-12.26 million people (10–20 counties; SSP2-4.5), and 8.95–18.10 million people (11–26 counties; SSP5-8.5) are projected to experience 9 or more months of transmission suitability. In 2050, for both SSP2-4.5 and SSP5-8.5, 17.08–20.42 million people (23–26 counties), ranging to approximately 70% of the projected population of Florida will experience 9 or more months. The 10 most populated counties in 2000 are projected to experience 1–3 months of additional climate-driven transmission suitability in the future. Conclusion:The southern house mosquito was previously managed as a seasonal nuisance in Florida, but now represents an increasing public health exposure risk. Projections across climate trajectories underscore an increasing suitability and exposure risk for WNV in Florida, ranging as high as around 70% of the population exposed to suitable climate conditions for transmission for 9 or more months of the year in the 2050s. This means the types of operations and number of employees needed in vector control and public health will also increase. 

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3. Transmission of West Nile and five other temperate mosquito-borne viruses peaks at temperatures between 23°C and 26°C

   https://doi.org/10.7554/eLife.58511  

   Shocket, Marta S; Verwillow, Anna B; Numazu, Mailo G; Slamani, Hani; Cohen, Jeremy M; El Moustaid, Fadoua; Rohr, Jason; Johnson, Leah R; Mordecai, Erin A (September 2020, eLife)

   null (Ed.)

   The temperature-dependence of many important mosquito-borne diseases has never been quantified. These relationships are critical for understanding current distributions and predicting future shifts from climate change. We used trait-based models to characterize temperature-dependent transmission of 10 vector–pathogen pairs of mosquitoes ( Culex pipiens , Cx. quinquefascsiatus , Cx. tarsalis , and others) and viruses (West Nile, Eastern and Western Equine Encephalitis, St. Louis Encephalitis, Sindbis, and Rift Valley Fever viruses), most with substantial transmission in temperate regions. Transmission is optimized at intermediate temperatures (23–26°C) and often has wider thermal breadths (due to cooler lower thermal limits) compared to pathogens with predominately tropical distributions (in previous studies). The incidence of human West Nile virus cases across US counties responded unimodally to average summer temperature and peaked at 24°C, matching model-predicted optima (24–25°C). Climate warming will likely shift transmission of these diseases, increasing it in cooler locations while decreasing it in warmer locations. 

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4. Urban Warming Challenges Verification of Frost Advisories and Freeze Warnings in Madison, Wisconsin

   https://doi.org/10.1175/WAF-D-22-0164.1  

   Williamson, Meirah; Kucharik, Christopher J. (June 2023, Weather and Forecasting)

   Abstract Urban heat islands (UHIs) may increase the likelihood that frost sensitive plants will escape freezing nighttime temperatures in late spring and early fall. Using data from 151 temperature sensors in the Madison, Wisconsin, region during March 2012–October 2016, we found that during time periods when the National Weather Service (NWS) issued freeze warnings (threshold of 0.0°C) or frost advisories (threshold of 2.22°C) were valid, temperatures in Madison’s most densely populated, built-up areas often did not fall below the respective temperature thresholds. Urban locations had a mean minimum temperature of 0.72° and 1.39°C for spring and fall freeze warnings, respectively, compared to −0.52° and −0.53°C for rural locations. On average, 31% of the region’s land area experienced minimum temperatures above the respective temperature thresholds during freeze warnings and frost advisories, and the likelihood of temperatures falling below critical temperature thresholds increased as the distance away from core urban centers increased. The urban–rural temperature differences were greatest in fall compared to spring, and when sensor temperatures did drop below thresholds, the maximum time spent at or below thresholds was highest for rural locations during fall freeze warnings (6.2 h) compared to urban locations (4.8 h). These findings potentially have widely varying implications for the general public and industry. UHIs create localized, positive perturbations to nighttime temperatures that are difficult to account for in forecasts; therefore, freeze warnings and frost advisories may have varying degrees of verification in medium-sized cities like Madison, Wisconsin, that are surrounded by cropland and natural vegetation. Significance StatementThe purpose of this study was to understand whether the urban heat island effect in Madison, Wisconsin, creates localized temperature patterns where county-scale frost advisories and freeze warnings may not verify. Approximately one-third of Madison’s urban core area and most densely populated region experienced temperatures that were consistently above critical low temperature thresholds. This is important because gardening and crop management decisions are responsive to the perceived risk of cold temperatures in spring and fall that can damage or kill plants. These results suggest that urban warming presents forecast challenges to the issuance of frost advisories and freeze warnings, supporting the need for improved numerical weather prediction at higher spatial resolution to account for complex urban meteorology. 

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5. Temperature and time of host-seeking activity impact the efficacy of chemical control interventions targeting the West Nile virus vector, Culex tarsalis

   https://doi.org/10.1371/journal.pntd.0012460  

   Kalmouni, Joshua; Will, James B; Townsend, John; Paaijmans, Krijn P (August 2024, PLOS Neglected Tropical Diseases)

   Mireji, Paul O (Ed.)

   West Nile virus (WNV) is the leading mosquito-borne disease causing-pathogen in the United States. Concerningly, there are no prophylactics or drug treatments for WNV and public health programs rely heavily on vector control efforts to lessen disease incidence. Insecticides can be effective in reducing vector numbers if implemented strategically, but can diminish in efficacy and promote insecticide resistance otherwise. Vector control programs which employ mass-fogging applications of insecticides, often conduct these methods during the late-night hours, when diel temperatures are coldest, and without a-priori knowledge on daily mosquito activity patterns. This study’s aims were to 1) quantify the effect of temperature on the toxicity of two conventional insecticides used in fogging applications (malathion and deltamethrin) toCulex tarsalis, an important WNV vector, and 2) quantify the time of host-seeking ofCx.tarsalisand other local mosquito species in Maricopa County, Arizona. The temperature-toxicity relationship of insecticides was assessed using the WHO tube bioassay, and adultCx.tarsalis, collected as larvae, were exposed to three different insecticide doses at three temperature regimes (15, 25, and 35°C; 80% RH). Time of host-seeking was assessed using collection bottle rotators with encephalitis vector survey traps baited with dry ice, first at 3h intervals during a full day, followed by 1h intervals during the night-time. Malathion became less toxic at cooler temperatures at all doses, while deltamethrin was less toxic at cooler temperatures at the low dose. Regarding time of host-seeking,Cx.tarsalis,Aedes vexans, andCulex quinquefasciatuswere the most abundant vectors captured. During the 3-hour interval surveillance over a full day,Cx.tarsaliswere most-active during post-midnight biting (00:00–6:00), accounting for 69.0% of allCx.tarsalis, while pre-midnight biting (18:00–24:00) accounted for 30.0% ofCx.tarsalis. During the 1-hour interval surveillance overnight,Cx.tarsaliswere most-active during pre-midnight hours (18:00–24:00), accounting for 50.2% ofCx.tarsaliscaptures, while post-midnight biting (00:00–6:00) accounted for 49.8% ofCx.tarsalis. Our results suggest that programs employing large-scale applications of insecticidal fogging should consider temperature-toxicity relationships coupled with time of host-seeking data to maximize the efficacy of vector control interventions in reducing mosquito-borne disease burden. 

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