Thermal biology of mosquito-borne disease

Incorporating adult age into mosquito population models: implications for predicting abundances in changing climates

Mosquito-borne diseases (MBDs) pose increasing threats under future climate change scenarios and an understanding of mosquito population dynamics is pivotal to predicting future risk of MBDs. Most models that describe mosquito population dynamics often assume that adult life-history is independent of adult age and yet mosquito senescence is known to affect mosquito mortality, fecundity and other key biological traits. Despite this, little is known about the effects of adult age at the level of the mosquito population, especially under varying temperature scenarios. We develop a stage-structured delayed differential equations (DDEs) model incorporating the effects of the abiotic environment and adult age to shed light on the complex interactions between age, temperature, and mosquito population dynamics. Taking Culex pipiens, a major vector of West Nile Virus, as our study species our results show that failing to consider mosquito senescence can lead to underestimates of future mosquito abundances predicted under climate change scenarios. We also find that the age-dependent mechanisms combined with the effects of density-dependent mortality on the immature stages can result in mosquito abundances decreasing at extreme temperatures. With our work, we underscore the need for more studies to consider the effects of mosquito age. Not accounting for senescence can compromise the accuracy of abundance estimates and has implications for predicting the risk of future MBD outbreaks.

High-resolution spatiotemporal analysis of chikungunya epidemics between 2019 and 2020 in Salvador, Brazil: a municipality-level transmission dynamics study

Background

Chikungunya virus (CHIKV) continues to cause explosive epidemics in Brazil. We investigated its transmission dynamics in Salvador, Brazil, to understand the factors driving its reemergence and spread.

Methods

In this epidemiological study, we analyzed by census tracts the chikungunya cases reported in Salvador during the 2019-2020 epidemics. We used SaTScan software to identify spatiotemporal clusters and assessed how census tract characteristics (socioeconomic, environmental, and prior chikungunya occurrence) influenced chikungunya incidence through a Bayesian spatial model using Integrated Laplace Approximation (INLA).

Findings

Citywide, 19,129 cases (mean age: 40.2, range: 0-112; male: 41.8%, female: 58.0%, non-binary: 0.2%) were reported between 2016 and 2020, with a significant increase in 2019 and 2020 (4549 and 13,071 cases, respectively). We found nine spatiotemporal clusters in 2019 and seven in 2020, with 17.2% (387 of 2252) overlap of census tracts between the two years. The chikungunya incidence by census tract was negatively correlated with income and vegetation but positively correlated with land surface temperature. The census tract level incidence in 2020 exhibited a non-linear correlation with the 2019 incidence; up to a certain level, the 2020 risk increased as the 2019 incidence increased, but when the 2019 incidence was extreme, the 2020 risk was reduced.

Interpretation

These findings suggest that CHIKV transmission is localized, even during what appeared to be a citywide epidemic, creating high-risk pockets within the city. Socioeconomic factors, environmental conditions, and prior chikungunya incidence, probably reflecting herd immunity, all influence case incidence.

Funding

Secretary of Health of Salvador, Federal University of Bahia, Oswaldo Cruz Foundation, National Council for Scientific and Technological Development, Foundation for Research Support of the Bahia State, Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES), Clinical and Applied Research Network in Chikungunya, Global Virus Network, Burroughs Wellcome Fund, Wellcome Trust, and the United States National Institutes of Health.

The Influence of Climate Change on Vector-Borne Diseases in a Wilderness Medicine Context

The imminent climate crisis has been labeled as the biggest health threat humanity must deal with. Vector-borne disease distribution and transmission as well as the population at risk are influenced to a great degree by environmental and climactic factors affecting both the vectors themselves and the causative pathogens. Paired with an increase in worldwide travel, urbanization, and globalization, along with population displacements and migration, elucidating the effects of anthropogenic climate change on these illnesses is therefore of the essence to stave off potential negative sequelae. Outcomes on different vector-borne diseases will be diverse, but for many of them, these developments will result in a distribution shift or expansion with the possibility of (re-)introduction of vector and pathogen species in previously nonendemic areas. The consequence will be a growing likelihood for novel human, vector, and pathogen interactions with an increased risk for infection, morbidity, and mortality. Wilderness medicine professionals commonly work in close relationship to the natural environment and therefore will experience these alterations most strongly in their practice. Hence, this article attempts to bring awareness to the subject at hand in a wilderness medicine context, with a focus on malaria, the most burdensome of arthropod-borne diseases. For prevention of the potentially dire consequences on human health induced by climate change, concerted and intensified efforts to reduce the burning of fossil fuels and thus greenhouse gas emissions will be imperative on a global scale.

Plasticity in mosquito size and thermal tolerance across a latitudinal climate gradient

Variation in heat tolerance among populations can determine whether a species is able to cope with ongoing climate change. Such variation may be especially important for ectotherms whose body temperatures, and consequently, physiological processes, are regulated by external conditions. Additionally, differences in body size are often associated with latitudinal clines, thought to be driven by climate gradients. While studies have begun to explore variation in body size and heat tolerance within species, our understanding of these patterns across large spatial scales, particularly regarding the roles of plasticity and genetic differences, remains incomplete. Here, we examine body size, as measured by wing length, and thermal tolerance, as measured by the time to immobilisation at high temperatures ("thermal knockdown"), in populations of the mosquito Aedes sierrensis collected from across a large latitudinal climate gradient spanning 1300 km (34-44° N). We find that mosquitoes collected from lower latitudes and warmer climates were more tolerant of high temperatures than those collected from higher latitudes and colder climates. Moreover, body size increased with latitude and decreased with temperature, a pattern consistent with James' rule, which appears to be a result of plasticity rather than genetic variation. Our results suggest that warmer environments produce smaller and more thermally tolerant populations.

Multiple blood feeding bouts in mosquitoes allow for prolonged survival and are predicted to increase viral transmission during dry periods

Dry conditions increase blood feeding in mosquitoes, but it is unknown if dehydration-induced bloodmeals are increased beyond what is necessary for reproduction. In this study, we investigated the role of dehydration in secondary blood feeding behaviors of mosquitoes. Following an initial bloodmeal, prolonged exposure to dry conditions increased secondary blood feeding in mosquitoes by nearly two-fold, and chronic blood feeding allowed mosquitoes to survive up to 20 days without access to water. Exposure to desiccating conditions following a bloodmeal resulted in increased activity, decreased sleep levels, and prompted a return of CO2 sensing before egg deposition. Increased blood feeding and higher survival during dry periods are predicted to increase pathogen transmission, allowing for a rapid rebound in mosquito populations when favorable conditions return. Overall, these results solidify our understanding of how dry periods impact mosquito blood feeding and the role that mosquito dehydration contributes to pathogen transmission dynamics.

Advancing adoptability and sustainability of digital prediction tools for climate-sensitive infectious disease prevention and control

Few forecasting models have been translated into digital prediction tools for prevention and control of climate-sensitive infectious diseases. We propose a 3-U (useful, usable, and used) research framework for advancing the adoptability and sustainability of these tools. We make recommendations for 1) developing a tool with a high level of accuracy and sufficient lead time to permit effective proactive interventions (useful); 2) conducting a needs assessment to ensure that a tool meets the needs of end-users (usable); and 3) demonstrating the efficacy and cost-effectiveness of a tool to secure its adoption into routine surveillance and response systems (used).

Elevating larval source management as a key strategy for controlling malaria and other vector-borne diseases in Africa

Larval source management (LSM) has a long history of advocacy and successes but is rarely adopted where funds are limited. The World Health Organization (WHO) guidelines on malaria prevention recommend the use of LSM as a supplementary intervention to the core vector control methods (insecticide-treated nets and indoor residual spraying), arguing that its feasibility in many settings can be limited by larval habitats being numerous, transient, and difficult to find or treat. Another key argument is that there is insufficient high-quality evidence for its effectiveness to support wide-scale implementation. However, the stagnation of progress towards malaria elimination demands that we consider additional options to the current emphasis on insecticidal commodities targeting adult mosquitoes inside homes. This letter is the result of a global, crossdisciplinary collaboration comprising: (a) detailed online expert discussions, (b) a narrative review of countries that have eliminated local malaria transmission, and (c) a mathematical modeling exercise using two different approaches. Together, these efforts culminated in seven key recommendations for elevating larval source management as a strategy for controlling malaria and other mosquito-borne diseases in Africa (Box 1). LSM encompasses the use of larvicide (a commodity) as well as various environmental sanitation measures. Together, these efforts lead to the long-term reduction of mosquito populations, which benefits the entire community by controlling both disease vector and nuisance mosquitoes. In this paper, we argue that the heavy reliance on large-scale cluster-randomized controlled trials (CRTs) to generate evidence on epidemiological endpoints restricts the recommendation of approaches to only those interventions that can be measured by functional units and deliver relatively uniform impact and, therefore, are more likely to receive financial support for conducting these trials. The explicit impacts of LSM may be better captured by using alternative evaluation approaches, especially high-quality operational data and a recognition of locally distinct outcomes and tailored strategies. LSM contributions are also evidenced by the widespread use of LSM strategies in nearly all countries that have successfully achieved malaria elimination. Two modelling approaches demonstrate that a multifaceted strategy, which incorporates LSM as a central intervention alongside other vector control methods, can effectively mitigate key biological threats such as insecticide resistance and outdoor biting, leading to substantial reductions in malaria cases in representative African settings. This argument is extended to show that the available evidence is sufficient to establish the link between LSM approaches and reduced disease transmission of mosquito-borne illnesses. What is needed now is a significant boost in the financial resources and public health administration structures necessary to train, employ and deploy local-level workforces tasked with suppressing mosquito populations in scientifically driven and ecologically sensitive ways. In conclusion, having WHO guidelines that recognize LSM as a key intervention to be delivered in multiple contextualized forms would open the door to increased flexibility for funding and aid countries in implementing the strategies that they deem appropriate. Financially supporting the scale-up of LSM with high-quality operations monitoring for vector control in combination with other core tools can facilitate better health. The global health community should reconsider how evidence and funding are used to support LSM initiatives.

Climate warming is expanding dengue burden in the Americas and Asia

Climate change is expected to pose significant threats to public health, particularly including vector-borne diseases. Despite dramatic recent increases in the burden of dengue that many anecdotally connect with climate change, the effect of past and future anthropogenic climate change on dengue remains poorly quantified. To assess the link between climate warming and dengue we assembled a dataset covering 21 countries in Asia and the Americas, and found a nonlinear relationship between temperature and dengue incidence with the largest impact of warming at lower temperatures (below about 20°C), peak incidence at 27.8°C, and subsequent declines at higher temperatures. Using this inferred temperature response, we estimate that historical climate change has increased dengue incidence by 18% (11 - 27%) on average across our study countries, and that future warming could further increase it by 49% (16 - 136%) to 76% (27 - 239%) by mid-century for low or high emissions scenarios, respectively, with some cooler regions projected to see dengue doubling due to warming and other currently hot regions seeing no impact or even small declines. Under the highest emissions scenario, we estimate that 262 million people are currently living in places in these 21 countries where dengue incidence is expected to more than double due to climate change by mid-century. These insights highlight the major impacts of anthropogenic warming on dengue burden across most of its endemic range, providing a foundation for public health planning and the development of strategies to mitigate future risks due to climate change.

Understanding the Effect of a Changing Climate on the Re-Emergence of Mosquito-Borne Diseases in Vulnerable Small Island Nations: A Systematic Review

INTRODUCTION

Drastic changes in meteorological variables due to climate change will likely have an implication on the proliferation of vectors such as mosquitoes. Extreme weather events may therefore promote the emergence/re-emergence of mosquito-borne diseases (MBDs) and potentiate the risk of endemicity, particularly, in small island nations.

METHOD

A systematic review was chosen to methodically ascertain the knowledge gaps that exist in determining the influence of the changing climate on MBDs in small islands with vulnerable public health systems. This review was conducted using the PRISMA guidelines.

RESULTS

Following extraction of 600 articles from the databases, 16 studies were determined to meet the selection criteria. The majority of these research papers were from Sri Lanka (n = 9) while the remaining articles were distributed between islands in the Pacific and Atlantic Ocean. Several of these studies used regression modelling techniques to discuss the effect of multiple meteorological variables on the incidence of MBDs. A positive relationship was observed between temperature and the relative risk of MBDs in 72% of the papers. Rainfall enhanced dengue transmission in 84% of the studies included. All the articles discussing the effect of humidity illustrated a similar trend while wind speed was the only climatic variable demonstrating a negative relationship with MBDs.

DISCUSSION

Considering the intricate nature of the non-linear exposure-response link is crucial when estimating the lagged effect of the changing climate on MBDs transmission. Other challenges associated with bias and confounders in the selected studies as well as meteorological data accessibility, were highlighted. Therefore, it was not possible to conclusively establish that the changing climatic variables do influence the spread of MBDs which accentuated the need for conducting further studies to illustrate the effect of changing weather variables on the incidence of MBDs, with an emphasis on vulnerable small island nations.

Prolonged exposure to heat enhances mosquito tolerance to viral infection

How and to what extent mosquito-virus interaction is influenced by climate change is a complex question of ecological and epidemiological relevance. We worked at the intersection between thermal biology and vector immunology and studied shifts in tolerance and resistance to the cell fusing agent virus (CFAV), a prominent component of the mosquito virome known to contribute to shaping mosquito vector competence, in warm-acclimated and warm-evolved Aedes albopictus mosquitoes. We show that the length of the thermal challenge influences the outcome of the infection with warm-evolved mosquitoes being more tolerant to CFAV infection, while warm-acclimated mosquitoes being more resistant and suffering from extensive fitness costs. These results highlight the importance of considering fluctuations in vector immunity in relation to the length of a thermal challenge to understand natural variation in vector response to viruses and frame realistic transmission models.

Temporal associations between microclimate, adult Aedes mosquito indices, and dengue cases at the residence level in Malaysia: Implications for targeted interventions

INTRODUCTION

Dengue continues to be a major public health concern in Malaysia, as evidenced by the significant surge in cumulative dengue case numbers and deaths in 2023 compared to the previous year. While previous studies have explored the interplay of abiotic and biotic factors of mosquito density and dengue cases on a local scale in Malaysia, there is a notable gap in the research focusing on adult Aedes mosquito populations.

AIMS

This study aims to contribute to the existing knowledge by investigating the association and time lags (TLs) between daily microclimate (DM), mosquito indices (MIs), and dengue cases at the residence level.

METHODS

In this longitudinal study, field data were collected over 26 weeks using data loggers, gravid oviposit sticky (GOS) traps, and non-structural 1 (NS1) test kits in both non-dengue hotspot (NDH) and dengue hotspots (DH). The collected data encompassed DM variables, vegetation cover (VC), MIs, and number of dengue cases. An autocorrelation analysis was conducted to determine the TLs between MIs and their preceding values, while a cross-correlation analysis revealed the TLs between MIs and DM variables.

RESULTS

The study indicated there are positive correlations between the adult index (AI) of Ae. albopictus, their preceding values and rainfall at an NDH. Conversely, the AIs of total Aedes at the DH exhibited positive correlations with their preceding values, temperature, rainfall, and maximum relative humidity (RH), but negative correlations with the mean and maximum RH. The dengue-positive trap index (DPTI) of total Aedes at DHs demonstrated positive associations with their preceding values, mean temperature, minimum temperature, maximum RH, and rainfall, with negative correlations observed for the maximum temperature, mean RH, and minimum RH. Similar trends were identified for the Ae. aegypti and Ae. albopictus at DHs. The association between dengue cases, DM, and MIs was inconclusive due to underreported cases.

CONCLUSIONS

This study highlighted the DM and TLs of dengue virus-infected and non-infected adult female Aedes mosquitoes using onsite data collection. Furthermore, this study presents a replicable methodology that can be adopted by researchers worldwide for investigating the dynamics of dengue transmission in similar settings. The findings offer valuable insights for decision-makers, providing them with evidence-based information to implement targeted interventions and strategies aimed at controlling Aedes mosquito populations and mitigating the spread of dengue virus infections.

Malaria survey data and geospatial suitability mapping for understanding spatial and temporal variations of risk across Kenya

Malaria remains a public health concern in Kenya where children and pregnant women are vulnerable groups. The common interventions in place to fight malaria include using insecticide-treated bed nets (ITNs), knowledge and awareness about malaria, and intake of malaria anti-malaria drugs. Despite the availability of these interventions, Kenya still records more than 10,000 clinical cases annually. In this study, we examined how malaria and interventions varied across Kenya for 2015 and 2020. We analyzed the Kenya Malaria Indicator Survey (N = 10,072) for 2015 and, (N = 11,549) for 2020, and climate data with Fuzzy overlay method to examine how malaria and its interventions relate to environmental conditions required for malaria. The study found that 79 % of malaria cases were distributed in lake endemic, 11 % in coastal endemic, 7 % in highland epidemic, and 3 % in seasonal zone. Use of Insecticide-treated bed nets (ITNs) was 77 % in lake endemic, 13 % in coastal endemic, 9 % in highland epidemic, and 1 % in seasonal zone. Knowledge about malaria was 82 % in lake endemic, 9 % in highland epidemic, 6 % in coastal endemic, and 3 % in seasonal zone. Additionally, based on climate data, lake endemic zone was 94 % suitable for malaria transmission compared to other zones. Despite the use of ITNs and awareness about malaria, malaria transmission continues to be a threat especially in counties in the lake endemic zone. Furthermore, place of residence, climate factors, ownership of ITNs may be associated with malaria in the region.

Ecological risk factors for the establishment of West Nile virus in Britain

West Nile virus (WNV) is a zoonotic mosquito-borne virus which is emerging across Europe, largely due to climate and other environmental changes. Detection of WNV at increasingly northern latitudes raises concern that WNV may be introduced to Britain, where ecological conditions could eventually support sustained transmission. Establishment of WNV depends on spatial and temporal overlap between infectious migratory birds and native vectors. However, understanding of the distributions and phenology of key vector species in Britain is incomplete and must be updated to prioritise activities for WNV surveillance and response. Here, we review recent findings related to WNV ecology in continental Europe and the ecology of British mosquito species in order to evaluate the risk of WNV establishment in Britain.

Systematic shifts in the variation among host individuals must be considered in climate-disease theory

To make more informed predictions of host-pathogen interactions under climate change, studies have incorporated the thermal performance of host, vector and pathogen traits into disease models to quantify effects on average transmission rates. However, this body of work has omitted the fact that variation in susceptibility among individual hosts affects disease spread and long-term patterns of host population dynamics. Furthermore, and especially for ectothermic host species, variation in susceptibility is likely to be plastic, influenced by variables such as environmental temperature. For example, as host individuals respond idiosyncratically to temperature, this could affect the population-level variation in susceptibility, such that there may be predictable functional relationships between variation in susceptibility and temperature. Quantifying the relationship between temperature and among-host trait variation will therefore be critical for predicting how climate change and disease will interact to influence host-pathogen population dynamics. Here, we use a model to demonstrate how short-term effects of temperature on the distribution of host susceptibility can drive epidemic characteristics, fluctuations in host population sizes and probabilities of host extinction. Our results emphasize that more research is needed in disease ecology and climate biology to understand the mechanisms that shape individual trait variation, not just trait averages.

Thermal variation influences the transcriptome of the major malaria vector Anopheles stephensi

The distribution and abundance of ectothermic mosquitoes are strongly affected by temperature, but mechanisms remain unexplored. We describe the effect of temperature on the transcriptome of Anopheles stephensi, an invasive vector of human malaria. Adult females were maintained across a range of mean temperatures (20 °C, 24 °C and 28 °C), with daily fluctuations of +5 °C and -4 °C at each mean temperature. Transcriptomes were described up to 19 days post-blood meal. Of the >3100 differentially expressed genes, we observed shared temporal expression profiles across all temperatures, suggesting their indispensability to mosquito life history. Tolerance to 20 and 28 ( + 5°C/-4°C) was associated with larger and more diverse transcriptomes compared to 24 ( + 5 °C/-4 °C). Finally, we identified two distinct trends in gene expression in response to blood meal ingestion, oxidative stress, and reproduction. Our work has implications for mosquitoes' response to thermal variation, mosquito immune-physiology, mosquito-malaria interactions and the development of vector control tools.

Forest edge landscape context affects mosquito community composition and risk of pathogen emergence

Forest edges, where humans, mosquitoes, and wildlife interact, may serve as a nexus for zoonotic arbovirus exchange. Although often treated as uniform interfaces, the landscape context of edge habitats can greatly impact ecological interactions. Here, we investigated how the landscape context of forest edges shapes mosquito community structure in an Amazon rainforest reserve near the city of Manaus, Brazil, using hand-nets to sample mosquitoes at three distinct forest edge types. Sampling sites were situated at edges bordering urban land cover, rural land cover, and natural treefall gaps, while sites in continuous forest served as controls. Community composition differed substantially among edge types, with rural edges supporting the highest species diversity. Rural edges also provided suitable habitat for forest specialists, including key sylvatic vectors, of which Haemagogus janthinomys was the most abundant species sampled overall. Our findings emphasize the importance of landscape context in assessing pathogen emergence risk at forest edges.

Seroprevalence, incidence estimates, and environmental risk factors for dengue, chikungunya, and Zika infection amongst children living in informal urban settlements in Indonesia and Fiji

BACKGROUND

The burden of Aedes aegypti-transmitted viruses such as dengue, chikungunya, and Zika are increasing globally, fueled by urbanization and climate change, with some of the highest current rates of transmission in Asia. Local factors in the built environment have the potential to exacerbate or mitigate transmission.

METHODS

In 24 informal urban settlements in Makassar, Indonesia and Suva, Fiji, we tested children under 5 years old for evidence of prior infection with dengue, chikungunya, and Zika viruses by IgG serology. We used a catalytic model using seroprevalence and mean age to estimate annual incidence of dengue in each country. We also conducted detailed questionnaires to evaluate environmental risk factors for a positive serology result. Dengue risk factors were evaluated for children by univariate and multivariable logistic regression accounting for settlement as a fixed effect. Trash and flooding were additionally evaluated as dengue risk factors at the settlement level by univariate linear regression.

RESULTS

In Fiji and Indonesia respectively, 46% and 33% of children under 5 years old were seropositive for dengue, 3% and 3% for chikungunya, and 9% and 2% for Zika. In Indonesia, children living in a household where trash is routinely collected and removed were significantly less likely to be dengue seropositive in both unadjusted and adjusted models [adjusted model: OR 0.3 (95% CI: 0.1-0.8)]. In Indonesia, settlements with a higher proportion of households reporting flooding also had lower dengue rates (slope = 0.44; p-value: <0.05).

CONCLUSIONS

Household trash collection and community flood management are important targets for interventions to mitigate the increasing risk of Aedes aegypti-transmitted viruses.

Nonlinear effects of temperature on mosquito parasite infection across a large geographic climate gradient

Temperature drives ectothermic host - parasite interactions, making them particularly sensitive to climatic variation and change. To isolate the role of temperature, lab-based studies are increasingly used to assess and forecast disease risk under current and future climate conditions. However, in the field, the effects of temperature on parasitism may be mediated by other sources of variation, including local adaptation. To address the key knowledge gaps of how temperature influences host - parasite interactions and whether thermal responses measured in controlled experiments capture infection across temperature gradients in nature, we paired an extensive field survey of parasitism-by the ciliate Lambornella clarki on its tree hole mosquito host, Aedes sierrensis -with laboratory experiments describing parasitism thermal performance curves (TPCs) for six host populations from varying climates. We also investigated the mechanisms underlying the thermal biology of the host - parasite interaction by separately measuring TPCs for infection, host immunity, and parasite growth rates. Along the west coast of North America, across an 1100 km climate gradient spanning 12°C mean rainy season temperature variation, we found that parasitism peaked at intermediately cold temperatures, and was consistent both between field seasons and with the lab experiment results. The experiments produced no evidence of host intraspecific variation in temperature sensitivity to parasitism. Importantly, parasitism peaked at temperatures below the thermal optimum for free-living L. clarki due to the balance of temperature effects on parasite growth and reproduction against the strength of the host melanization immune response. The results suggest that nonlinear responses to temperature drive parasitism in nature, and that simple lab and field studies can accurately capture the thermal biology of multilayered host - parasite interactions. Data and code for this submission are provided on Dryad: http://datadryad.org/stash/share/CfZkk4LsJzljetJJnFZMDMrjuciTXMxrkrc95I2J3tA .

Climate Change and Malaria: A Call for Robust Analytics

Mosquito ecology and behavior and malaria parasite development display marked sensitivity to weather, in particular to temperature and precipitation. Therefore, climate change is expected to profoundly affect malaria epidemiology in its transmission, spatiotemporal distribution and consequent disease burden. However, malaria transmission is also complicated by other factors (e.g. urbanization, socioeconomic development, genetics, drug resistance) which together constitute a highly complex, dynamical system, where the influence of any single factor can be masked by others. In this study, we therefore aim to re-evaluate the evidence underlying the widespread belief that climate change will increase worldwide malaria transmission. We review two broad types of study that have contributed to this evidence-base: i) studies that project changes in transmission due to inferred relationships between environmental and mosquito entomology, and ii) regression-based studies that look for associations between environmental variables and malaria prevalence. We then employ a simple statistical model to show that environmental variables alone do not account for the observed spatiotemporal variation in malaria prevalence. Our review raises several concerns about the robustness of the analyses used for advocacy around climate change and malaria. We find that, while climate change's effect on malaria is highly plausible, empirical evidence is much less certain. Future research on climate change and malaria must become integrated into malaria control programs, and understood in context as one factor among many. Our work outlines gaps in modelling that we believe are priorities for future research.

Local tree cover predicts mosquito species richness and disease vector presence in a tropical countryside landscape

CONTEXT

Land use change and deforestation drive both biodiversity loss and zoonotic disease transmission in tropical countrysides. For mosquito communities that can include disease vectors, forest loss has been linked to reduced biodiversity and increased vector presence. The spatial scales at which land use and tree cover shape mosquito communities present a knowledge gap relevant to both biodiversity and public health.

OBJECTIVES

We investigated the responses of mosquito species richness and Aedes albopictus disease vector presence to land use and to tree cover surrounding survey sites at different spatial scales. We also investigated species compositional turnover across land uses and along environmental gradients.

METHODS

We paired a field survey of mosquito communities in agricultural, residential, and forested lands in rural southern Costa Rica with remotely sensed tree cover data. We compared mosquito richness and vector presence responses to tree cover measured across scales from 30m to 1000m, and across land uses. We analyzed compositional turnover between land uses and along environmental gradients of tree cover, temperature, elevation, and geographic distance.

RESULTS

Tree cover was both positively correlated with mosquito species richness and negatively correlated with the presence of the common invasive dengue vector Ae. albopictus at small spatial scales of 90 - 250m. Land use predicted community composition and Ae. albopictus presence.

CONCLUSIONS

The results suggest that local tree cover preservation and expansion can support mosquito species richness and reduce disease vector presence. The identified spatial range at which tree cover shapes mosquito communities can inform the development of land management practices to protect both ecosystem and public health.

Impacts of Weather Anomalies and Climate on Plant Disease

Predicting the effects of climate change on plant disease is critical for protecting ecosystems and food production. Here, we show how disease pressure responds to short-term weather, historical climate and weather anomalies by compiling a global database (4339 plant-disease populations) of disease prevalence in both agricultural and wild plant systems. We hypothesised that weather and climate would play a larger role in disease in wild versus agricultural plant populations, which the results supported. In wild systems, disease prevalence peaked when the temperature was 2.7°C warmer than the historical average for the same time of year. We also found evidence of a negative interactive effect between weather anomalies and climate in wild systems, consistent with the idea that climate maladaptation can be an important driver of disease outbreaks. Temperature and precipitation had relatively little explanatory power in agricultural systems, though we observed a significant positive effect of current temperature. These results indicate that disease pressure in wild plants is sensitive to nonlinear effects of weather, weather anomalies and their interaction with historical climate. In contrast, warmer temperatures drove risks for agricultural plant disease outbreaks within the temperature range examined regardless of historical climate, suggesting vulnerability to ongoing climate change.

Mosquitoes Reared in Nearby Insectaries at the Same Institution Have Significantly Divergent Microbiomes

The microbiome influences critical aspects of mosquito biology and variations in microbial composition can impact the outcomes of laboratory studies. To investigate how biotic and abiotic conditions in an insectary affect the composition of the mosquito microbiome, a single cohort of Aedes aegypti eggs was divided into three batches and transferred to three different climate-controlled insectaries within the Liverpool School of Tropical Medicine. The bacterial microbiome composition was compared as mosquitoes developed, the microbiome of the mosquitoes' food sources was characterised, environmental conditions over time in each insectary were measured, and mosquito development and survival were recorded. While developmental success was similar across all three insectaries, differences in microbiome composition were observed between mosquitoes from each insectary. Environmental conditions and bacterial input via food sources varied between insectaries, potentially contributing to the observed differences in microbiome composition. At both adult and larval stages, specific members of the mosquito microbiome were associated with particular insectaries; the insectary with less stable and cooler conditions resulted in a slower pupation rate and higher diversity of the larval microbiome. These findings underscore that even minor inconsistencies in rearing conditions can affect the composition of the mosquito microbiome, which may influence experimental outcomes.

Risk of Aedes-borne diseases in and around the Tanzanian seaport of Tanga despite community members being more concerned about malaria

BACKGROUND

Increased global trade, while beneficial economically, can also increase the spread of vector-borne diseases, particularly those transmitted by Aedes mosquitoes spreading via trade routes. Given the heightened trade-induced activity at ports of entry, it is particularly crucial to assess the risk of mosquito-borne diseases in these settings. This study compared the risks of Aedes-borne disease in and around the eastern Tanzanian seaport of Tanga.

METHODS

A 200 m × 200 m grid-based system was used to sample mosquitoes within the port area, and in surrounding areas at 2 km, 2.5 km, and 5 km away, between June and December 2023. We characterized mosquito breeding habitats, collected mosquito larvae using standard dippers and tested susceptibility of raised adult Aedes aegypti populations to different insecticides. Adult mosquitoes were collected using BG sentinel traps (daytime) and Centers for Disease Control (CDC) light traps (night-time). Additionally, more than 200 port users and neighboring residents were surveyed to assess their experiences with and perceptions of mosquito biting and disease risks.

RESULTS

There were 2931 breeding sites, with (60.8%, n = 1782) positive for Aedes larvae. The percentage of water-holding containers infested with Aedes immatures, i.e., the container index (CI), was highest in the port area (66.2%), and lowest 5 km away (44.6%). The port area also had a greater proportion of temporary breeding sites (64.9%) than did the surrounding areas. The adult mosquito surveys revealed 20,449 mosquito species including: Culex quinquefasciatus (56.2%), Mansonia uniformis (38.6%), Ae. aegypti (5.1%), Anopheles gambiae (0.1%), and Anopheles funestus. Ae. aegypti were more abundant in the port area than in the surrounding areas (P < 0.001), whereas Culex sp., and Mansonia sp., were significantly outside (P < 0.001). Adult Anopheles sp., were found only in the port area, but Anopheles larvae were found both within and outside the port areas. Tests on Ae. aegypti sp., revealed susceptibility to bendiocarb and DDT, and resistance to permethrin. Awareness of mosquito-borne diseases among respondents was high for malaria (64.8%), but low for dengue (26.3%) and Chikungunya (1.7%). Most respondents reported being bothered by mosquitoes mostly at night (53.4%) or in the evening (40.7%). In addition to insecticidal bednets, which are used primarily against malaria, preventive measures for Aedes-borne diseases are limited.

CONCLUSIONS

This study identified significant potential risk of Aedes species, specifically Ae. aegypti sp., and associated diseases, but low perception of risk and inadequate personal protection measures in the study area. This low perception of risk highlights the need to improve public knowledge of the transmission and control of Aedes-borne diseases.

Association between climate change and patient health outcomes: a mixed-methods systematic review

INTRODUCTION

Climate change poses significant threats to the environment, biodiversity, and socioeconomic stability worldwide. Its impact on human health, particularly within healthcare systems, is growing in concern. Nurses, as front-line healthcare workers, play a crucial role in addressing climate-related health risks. However, there is a gap in understanding nursing perspectives on climate change and its implications for patient health outcomes.

AIM

To synthesize empirical evidence on the association between climate change and patient health outcomes from a nursing perspective.

METHODS

A mixed-methods systematic review was conducted following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). The search was carried out in January 2024 in six scientific databases including CINAHL, PubMed, Scopus, ProQuest, Web of Science, and OVID Nursing. Studies focusing on climate change and patient health outcomes from a nursing perspective were included. Data extraction, quality appraisal, and synthesis were performed systematically.

RESULTS

The systematic review included 18 studies of a mainly quantitative nature. Three main themes emerged as follows: Climate Healthcare Interplay; Future Nurses as Agents of Change; and Navigating Sustainability Challenges in Nursing. These themes highlighted nurses' awareness of the interrelation between climate and health, the need for environmental education in nursing, and the challenges that hinder sustainable nursing practices.

CONCLUSION

This review underscores the importance of integrating climate change topics into nursing education and fostering organizational support for sustainable nursing practices. Addressing these challenges is essential for nurses to mitigate the health risks posed by climate change effectively.

Investigating the Effects of Microclimate on Arboviral Kinetics in Aedes aegypti

Aedes aegypti are indoor-dwelling vectors of many arboviruses, including Zika (ZIKV) and chikungunya (CHIKV). The dynamics of these viruses within the mosquito are known to be temperature-dependent, and models that address risk and predictions of the transmission efficiency and patterns typically use meteorological temperature data. These data do not differentiate the temperatures experienced by mosquitoes in different microclimates, such as indoor vs. outdoor. Using temperature data collected from Neiva Colombia, we investigated the impact of two microclimate temperature profiles on ZIKV and CHIKV infection dynamics in Ae. aegypti. We found that the vector mortality was not significantly impacted by the difference in temperature profiles. Further, we found that the infection and dissemination rates were largely unaffected, with only ZIKV experiencing a significant increase in infection at outdoor temperatures at 21 days post-infection (dpi). Further, there was a significant increase in viral titers in the abdomens of ZIKV-infected mosquitoes at 21 dpi. With CHIKV, there was a significant titer difference in the abdomens of mosquitoes at both 7 and 14 dpi. While there were differences in vector infection kinetics that were not statistically significant, we developed a simple stochastic SEIR-SEI model to determine if the observed differences might translate to notable differences in simulated outbreaks. With ZIKV, while the probability of secondary transmission was high (>90%) under both microenvironmental scenarios, there was often only one secondary case. However, CHIKV differences between microenvironments were more prominent. With over 90% probability of secondary transmission, at indoor conditions, the peak of transmission was higher (over 850 cases) compared to the outdoor conditions (<350 cases). Further, the time-to-peak for indoor was 130 days compared to 217 days for outdoor scenarios. Further investigations into microenvironmental conditions, including temperature, may be key to increasing our understanding of the nuances of CHIKV and ZIKV vectorial capacity, epidemiology, and risk assessment, especially as it affects other aspects of transmission, such as biting rate. Overall, it is critical to understand the variability of how extrinsic factors affect transmission systems, and these data add to the growing catalog of knowledge of how temperature affects arboviral systems.

Human outbreaks of a novel reassortant Oropouche virus in the Brazilian Amazon region

The Brazilian western Amazon is experiencing its largest laboratory-confirmed Oropouche virus (OROV) outbreak, with more than 6,300 reported cases between 2022 and 2024. In this study, we sequenced and analyzed 382 OROV genomes from human samples collected in Amazonas, Acre, Rondônia and Roraima states, between August 2022 and February 2024, to uncover the origin and genetic evolution of OROV in the current outbreak. Genomic analyses revealed that the upsurge of OROV cases in the Brazilian Amazon coincides with spread of a novel reassortant lineage containing the M segment of viruses detected in the eastern Amazon region (2009-2018) and the L and S segments of viruses detected in Peru, Colombia and Ecuador (2008-2021). The novel reassortant likely emerged in the Amazonas state between 2010 and 2014 and spread through long-range dispersion events during the second half of the 2010s. Phylodynamics reconstructions showed that the current OROV spread was driven mainly by short-range (< 2 km) movements consistent with the flight range of vectors. Nevertheless, a substantial proportion (22%) of long-range (>10 km) OROV migrations were also detected, consistent with viral dispersion by humans. Our data provide a view of the unprecedented spread and evolution of OROV in the Brazilian western Amazon region.

How Much Warming Can Mosquito Vectors Tolerate?

Climate warming is expected to substantially impact the global landscape of mosquito-borne disease, but these impacts will vary across disease systems and regions. Understanding which diseases, and where within their distributions, these impacts are most likely to occur is critical for preparing public health interventions. While research has centered on potential warming-driven expansions in vector transmission, less is known about the potential for vectors to experience warming-driven stress or even local extirpations. In conservation biology, species risk from climate warming is often quantified through vulnerability indices such as thermal safety margins-the difference between an organism's upper thermal limit and its habitat temperature. Here, we estimated thermal safety margins for 8 mosquito species that are the vectors of malaria, dengue, chikungunya, Zika, West Nile and other major arboviruses, across their known ranges to investigate which mosquitoes and regions are most and least vulnerable to climate warming. We find that several of the most medically important mosquito vector species, including Ae. aegypti and An. gambiae, have positive thermal safety margins across the majority of their ranges when realistic assumptions of mosquito behavioral thermoregulation are incorporated. On average, the lowest climate vulnerability, in terms of both the magnitude and duration of thermal safety, was just south of the equator and at northern temperate range edges, and the highest climate vulnerability was in the subtropics. Mosquitoes living in regions including the Middle East, the western Sahara, and southeastern Australia, which are largely comprised of desert and xeric shrubland biomes, have the highest climate vulnerability across vector species.

New York State Climate Impacts Assessment Chapter 07: Human Health and Safety

New Yorkers face a multitude of health and safety risks that are exacerbated by a changing climate. These risks include direct impacts from extreme weather events and other climate hazards, as well as indirect impacts occurring through a chain of interactions. Physical safety, physical health, and mental health are all part of the equation-as are the many nonclimate factors that interact with climate change to influence health outcomes. This chapter provides an updated assessment of all these topics at the intersection of climate change, public health and safety, and equity in the state of New York. Key findings are presented below.

Managing vector-borne diseases in a geoAI-enabled society. Malaria as an example

More than 17 % of all infectious diseases are caused by vector-borne diseases resulting in more than 1 billion cases and over 1 million deaths each year. Of these malaria continues to be a global burden in over eighty countries. As societies become more digitalised, the availability of geospatially enabled health and disease information will become more abundant. With this, the ability to assess health and disease risks in real-time will become a reality. The purpose of this study was to examine how geographic information, geospatial technologies and spatial data science are being used to reduce the burden of vector-borne diseases such as malaria and explore the opportunities that lie ahead with GeoAI and other geospatial technology advancements. Malaria is a dynamic and complex system and as such a range of data and approaches are needed to tackle different parts of the malaria cycle at different local and global scales. Geospatial technologies provide an integrated framework vital for monitoring, analysing and managing vector-borne diseases. GeoAI and technological advancements are useful for enhancing real-time assessments, accelerating the decision making process and spatial targeting of interventions. Training is needed to enhance the use of geospatial information for the management of vector-borne diseases.

Climate change, its impact on emerging infectious diseases and new technologies to combat the challenge

ABSTRACTImproved sanitation, increased access to health care, and advances in preventive and clinical medicine have reduced the mortality and morbidity rates of several infectious diseases. However, recent outbreaks of several emerging infectious diseases (EIDs) have caused substantial mortality and morbidity, and the frequency of these outbreaks is likely to increase due to pathogen, environmental, and population effects driven by climate change. Extreme or persistent changes in temperature, precipitation, humidity, and air pollution associated with climate change can, for example, expand the size of EID reservoirs, increase host-pathogen and cross-species host contacts to promote transmission or spillover events, and degrade the overall health of susceptible host populations leading to new EID outbreaks. It is therefore vital to establish global strategies to track and model potential responses of candidate EIDs to project their future behaviour and guide research efforts on early detection and diagnosis technologies and vaccine development efforts for these targets. Multi-disciplinary collaborations are demanding to develop effective inter-continental surveillance and modelling platforms that employ artificial intelligence to mitigate climate change effects on EID outbreaks. In this review, we discuss how climate change has increased the risk of EIDs and describe novel approaches to improve surveillance of emerging pathogens that pose the risk for EID outbreaks, new and existing measures that could be used to contain or reduce the risk of future EID outbreaks, and new methods to improve EID tracking during further outbreaks to limit disease transmission.

The impact of natural climate variability on the global distribution of Aedes aegypti: a mathematical modelling study

BACKGROUND

Aedes aegypti spread pathogens affecting humans, including dengue, Zika, and yellow fever viruses. Anthropogenic climate change is altering the spatial distribution of Ae aegypti and therefore the locations at risk of vector-borne disease. In addition to climate change, natural climate variability, resulting from internal atmospheric processes and interactions between climate system components (eg, atmosphere-land and atmosphere-ocean interactions), determines climate outcomes. However, the role of natural climate variability in modifying the effects of anthropogenic climate change on future environmental suitability for Ae aegypti has not been assessed fully. In this study, we aim to assess uncertainty arising from natural climate variability in projections of Ae aegypti suitability up to the year 2100.

METHODS

In this mathematical modelling study, we developed an ecological model in which Ae aegypti population dynamics depend on climate variables (temperature and rainfall). We used 100 projections of future climate from the Community Earth System Model, a comprehensive climate model that simulates natural climate variability as well as anthropogenic climate change, in combination with our ecological model to generate a range of equally plausible scenarios describing the global distribution of suitable conditions for Ae aegypti up to 2100. Each of these scenarios corresponds to a single climate projection, allowing us to explore the difference in Ae aegypti suitability between the most-suitable and the least-suitable projections.

FINDINGS

Our key finding was that natural climate variability generates substantial variation in future projections of environmental suitability for Ae aegypti. Even for projections generated under the same Shared Socioeconomic Pathway (SSP) scenario (SSP3-7.0), in 2100 climatic conditions in London might be suitable for Ae aegypti for 0-5 months of the year, depending on natural climate variability.

INTERPRETATION

Natural climate variability affects environmental suitability for important disease vectors. Some regions could experience vector-borne disease outbreaks earlier than expected under climate change alone.

FUNDING

Engineering and Physical Sciences Research Council and Wellcome Trust.

Associations between weather and Plasmodium vivax malaria in an elimination setting in Peru: a distributed lag analysis

Background

Plasmodium vivax (Pv) is the predominant malaria species in countries approaching elimination. In the context of climate change, understanding environmental drivers of transmission can guide interventions, yet evidence is limited, particularly in Latin America.

Objectives

We estimated the association between temperature and precipitation and Pv malaria incidence in a malaria elimination setting in Peru.

Methods

We analyzed malaria incidence data from 2021-2023 from 30 communities in Loreto, Peru with hourly weather data from the ERA5 dataset and land cover data from MapBiomas. Predictors included average weekly minimum and maximum temperature, high heat (>90th percentile mean temperature), total weekly precipitation, and heavy rain (>90th percentile total precipitation). We fit non-linear distributed lag models for continuous weather predictors and generalized additive models for binary predictors and the lookback period was 2-16 weeks. Temperature models adjusted for total precipitation; precipitation models adjusted for maximum temperature. We performed subgroup analyses by season, community type, and distance to forest edge.

Results

The median vs. lowest values of weekly average minimum temperature was associated with 2.16 to 3.93-fold higher incidence 3-16 weeks later (5-week lag incidence ratio (IR) =3.93 [95% CI 2.18, 7.09]); for maximum temperature, the association was hump-shaped across lags, with protective associations at 1-2 and 15-16 week lags and 1.07-1.66-fold higher incidence at 6-13 week lags. High heat (>27.5°C) was associated with 1.23 to 1.37-fold higher incidence at 5--9 week lags (9-week lag IR = 1.25 [1.02, 1.53]). Associations between total precipitation and malaria incidence were hump-shaped across lags, with the strongest positive association at 750 mm of precipitation at a 9-week lag (IR=1.56; [1.27, 1.65]). Heavy rain (>186mm) was associated with 1.22-1.60-fold higher incidence at 2-10 week lags (9-week lag IR=1.23 [1.02, 1.49]).

Discussion

Higher temperatures and precipitation were generally associated with higher malaria incidence over 1-4 months.

Seroprevalence, incidence estimates, and environmental risk factors for dengue, chikungunya, and Zika infection amongst children living in informal urban settlements in Indonesia and Fiji

Background

The burden of Aedes aegypti-transmitted viruses such as dengue, chikungunya, and Zika are increasing globally, fueled by urbanization and climate change, with some of the highest current rates of transmission in Asia. Local factors in the built environment have the potential to exacerbate or mitigate transmission.

Methods

In 24 informal urban settlements in Makassar, Indonesia and Suva, Fiji, we tested children under 5 years old for evidence of prior infection with dengue, chikungunya, and Zika viruses by IgG serology. We used a catalytic model using seroprevalence and mean age to estimate annual incidence of dengue in each country. We also conducted detailed questionnaires to evaluate environmental risk factors for a positive serology result. Dengue risk factors were evaluated for individual children by univariate and multivariable logistic regression accounting for settlement as a flxed effect. Trash and flooding were additionally evaluated as dengue risk factors at the settlement level by univariate linear regression.

Results

In Fiji and Indonesia respectively, 46% and 33% of children under 5 years old were seropositive for dengue, 3% and 3% for chikungunya, and 9% and 2% for Zika. In Indonesia, children living in a household where trash is routinely collected and removed were signiflcantly less likely to be dengue seropositive in both unadjusted and adjusted models [adjusted model: OR 0.3 (95% CI: 0.1-0.8)]. In Indonesia, settlements with a higher proportion of households reporting flooding also had lower dengue rates (slope = 0.44; p-value: <0.05).

Conclusions

Household trash collection and community flood management are important targets for interventions to mitigate the increasing risk of Aedes aegypti-transmitted viruses.

Present and future suitability of invasive and urban vectors through an environmentally driven mosquito reproduction number

Temperature and water availability significantly influence mosquito population dynamics. We have developed a method, integrating experimental data with insights from mosquito and thermal biology, to calculate the basic reproduction number ([Formula: see text]) for urban mosquito species Aedes albopictus and Aedes aegypti. [Formula: see text] represents the number of female mosquitoes produced by one female during her lifespan, indicating suitability for growth. Environmental conditions, including temperature, rainfall and human density, influence [Formula: see text] by altering key mosquito life cycle traits. Validation using data from Spain and Europe confirms the approach's reliability. Our analysis suggests that temperature increases may not uniformly benefit Ae. albopictus proliferation but could boost Ae. aegypti expansion. We suggest using vector [Formula: see text] maps, leveraging climate and environmental data, to predict areas susceptible to invasive mosquito population growth. These maps aid resource allocation for intervention strategies, supporting effective vector surveillance and management efforts.

Remote sensing of temperature-dependent mosquito and viral traits predicts field surveillance-based disease risk

Mosquito-borne diseases contribute substantially to the global burden of disease, and are strongly influenced by environmental conditions. Ongoing and rapid environmental change necessitates improved understanding of the response of mosquito-borne diseases to environmental factors like temperature, and novel approaches to mapping and monitoring risk. Recent development of trait-based mechanistic models has improved understanding of the temperature dependence of transmission, but model predictions remain challenging to validate in the field. Using West Nile virus (WNV) as a case study, we illustrate the use of a novel remote sensing-based approach to mapping temperature-dependent mosquito and viral traits at high spatial resolution and across the diurnal cycle. We validate the approach using mosquito and WNV surveillance data controlling for other key factors in the ecology of WNV, finding strong agreement between temperature-dependent traits and field-based metrics of risk. Moreover, we find that WNV infection rate in mosquitos exhibits a unimodal relationship with temperature, peaking at ~24.6-25.2°C, in the middle of the 95% credible interval of optimal temperature for transmission of WNV predicted by trait-based mechanistic models. This study represents one of the highest resolution validations of trait-based model predictions, and illustrates the utility of a novel remote sensing approach to predicting mosquito-borne disease risk.

Regional variation in the landscape ecology of West Nile virus sentinel chicken seroconversion in Florida

How landscape composition and configuration impact the distribution of multi-vector and multi-host mosquito vector-borne disease systems, such as West Nile virus (WNV), remains challenging because of complex habitat and resource requirements by hosts and vectors that affect transmission opportunities. We examined correlations between landscape composition and configuration and 2018 WNV sentinel chicken seroconversion in Florida, USA across the state and within five National Oceanic Atmospheric Administration (NOAA) bioclimatic regions to understand strength and variation of landscape effects during an elevated transmission year. Although few landscape studies have examined WNV in Florida, we expected higher percentages of residential or medium-developed landscapes and more fragmented landscapes would be positively correlated with WNV seroconversion owing to the main mosquito vector habitats and avian host distributions. However, we expected to find variation in the importance of forest, wetland, and agriculture landscapes across bioclimatic regions in the state. WNV seroconversion rates were calculated using Florida 2018 Department of Health WNV sentinel chicken seroconversion data from 187 flocks maintained by mosquito control programs. Percent land cover and edge density metrics were calculated for multiple land cover classes and within multiple buffer distances from chicken coops using 2019 National Land Cover Data. We used binomial generalized linear mixed effects models to calculate the importance of landscape metrics to WNV seroconversion. We found no statewide predictors of seroconversion, but as expected, the importance of landscape varied across regions. In the north-central part of the state, we found higher seroconversion in less populated suburban areas while higher seroconversion in south-central Florida was correlated with fragmented forested areas within 0.5 km of coops and intact woody wetland areas within 2 km of coops. This work corroborates previous findings that consistent landscape predictors of WNV are difficult to identify across broader geographic areas and sets the stage for additional work that incorporates climate and landscapes interactions for a greater understanding of WNV ecology in this geographic region.

Extreme precipitation, exacerbated by anthropogenic climate change, drove Peru's record-breaking 2023 dengue outbreak

Anthropogenic forcing is increasing the likelihood and severity of certain extreme weather events, which may catalyze outbreaks of climate-sensitive infectious diseases. Extreme precipitation events can promote the spread of mosquito-borne illnesses by creating vector habitat, destroying infrastructure, and impeding vector control. Here, we focus on Cyclone Yaku, which caused heavy rainfall in northwestern Peru from March 7th - 20th, 2023 and was followed by the worst dengue outbreak in Peru's history. We apply generalized synthetic control methods to account for baseline climate variation and unobserved confounders when estimating the causal effect of Cyclone Yaku on dengue cases across the 56 districts with the greatest precipitation anomalies. We estimate that 67 (95% CI: 30 - 87) % of cases in cyclone-affected districts were attributable to Cyclone Yaku. The cyclone significantly increased cases for over six months, causing 38,209 (95% CI: 17,454 - 49,928) out of 57,246 cases. The largest increases in dengue incidence due to Cyclone Yaku occurred in districts with a large share of low-quality roofs and walls in residences, greater flood risk, and warmer temperatures above 24°C. Analyzing an ensemble of climate model simulations, we found that extremely intense March precipitation in northwestern Peru is 42% more likely in the current era compared to a preindustrial baseline due to climate forcing. In sum, extreme precipitation like that associated with Cyclone Yaku has become more likely with climate change, and Cyclone Yaku caused the majority of dengue cases across the cyclone-affected districts.

Forecasting malaria dynamics based on causal relations between control interventions, climatic factors, and disease incidence in western Kenya

Background

Malaria remains one of the deadliest diseases worldwide, especially among young children in sub-Saharan Africa. Predictive models are necessary for effective planning and resource allocation; however, statistical models suffer from association pitfalls. In this study, we used empirical dynamic modelling (EDM) to investigate causal links between climatic factors and intervention coverage with malaria for short-term forecasting.

Methods

Based on data spanning the period from 2008 to 2022, we used convergent cross-mapping (CCM) to identify suitable lags for climatic drivers and investigate their effects, interaction strength, and suitability ranges on malaria incidence. Monthly malaria cases were collected at St. Elizabeth Lwak Mission Hospital. Intervention coverage and population movement data were obtained from household surveys in Asembo, western Kenya. Daytime land surface temperature (LSTD), rainfall, relative humidity (RH), wind speed, solar radiation, crop cover, and surface water coverage were extracted from remote sensing sources. Short-term forecasting of malaria incidence was performed using state-space reconstruction.

Results

We observed causal links between climatic drivers, bed net use, and malaria incidence. LSTD lagged over the previous month; rainfall and RH lagged over the previous two months; and wind speed in the current month had the highest predictive skills. Increases in LSTD, wind speed, and bed net use negatively affected incidence, while increases in rainfall and humidity had positive effects. Interaction strengths were more pronounced at temperature, rainfall, RH, wind speed, and bed net coverage ranges of 30-35°C, 30-120 mm, 67-80%, 0.5-0.7 m/s, and above 90%, respectively. Temperature and rainfall exceeding 35°C and 180 mm, respectively, had a greater negative effect. We also observed good short-term predictive performance using the multivariable forecasting model (Pearson correlation coefficient = 0.85, root mean square error = 0.15).

Conclusions

Our findings demonstrate the utility of CCM in establishing causal linkages between malaria incidence and both climatic and non-climatic drivers. By identifying these causal links and suitability ranges, we provide valuable information for modelling the impact of future climate scenarios.

Climate change and Trypanosoma cruzi transmission in North and central America

Trypanosoma cruzi is a protozoan parasite that causes Chagas disease in humans. Transmission of T cruzi by triatomine vectors is dependent on diverse environmental and socioeconomic factors. Climate change, which is disrupting patterns of human habitation and land use, can affect the epidemiology of Chagas disease by influencing the distribution of vector and host species. We conducted a review using triatomine distribution as a proxy for T cruzi transmission in North America (Canada, Mexico, and the USA) and central America (Belize, Costa Rica, El Salvador, Guatemala, Honduras, Nicaragua, and Panama) and investigated the association of T cruzi transmission with climate change, identifying 12 relevant studies. Most studies (n=9) modelled the effect of the scenario of climate change on the distribution of relevant vector species and found that global warming could sometimes favour and sometimes hinder triatomine distribution. There is a need for more research in parasite biology and social sciences to further understand how climate change and socioeconomic factors can affect the epidemiology of this neglected tropical disease.

Usutu virus, an emerging arbovirus with One Health importance

Usutu virus (USUV, Flaviviridae) is an emerging arbovirus that has led to epizootic outbreaks in birds and numerous human neuroinvasive disease cases in Europe. It is maintained in an enzootic cycle with Culex mosquitoes and passerine birds, a transmission cycle that is shared by West Nile virus (WNV) and St. Louis encephalitis virus (SLEV), two flaviviruses that are endemic in the United States. USUV and WNV co-circulate in Africa and Europe, and SLEV and WNV co-circulate in North America. These three viruses are prime examples of One Health issues, in which the interactions between humans, animals, and the environments they reside in can have important health impacts. The three facets of One Health are interwoven throughout this article as we discuss the mechanisms of flavivirus transmission and emergence. We explore the possibility of USUV emergence in the United States by analyzing the shared characteristics among USUV, WNV, and SLEV, including the role that flavivirus co-infections and sequential exposures may play in viral emergence. Finally, we provide insights on the importance of integrated surveillance programs as One Health tools that can be used to mitigate USUV emergence and spread.

Space-time dynamics of the dengue epidemic in Brazil, 2024: an insight for decision making

BACKGROUND

Dengue is a vector-borne viral infection caused by the dengue virus transmitted to humans primarily by Aedes aegypti. The year 2024 has been a historic year for dengue in Brazil, with the highest number of probable cases ever registered. Herein, we analyze the temporal trend and spatio-temporal dynamics of dengue cases in Brazil during the first nine epidemiological weeks (EW) of 2024.

METHODS

This is an ecological study, including all probable cases of dengue in Brazil during the period, carried out in two steps: time series analysis to assess the temporal trend and spatial analysis to identify high-risk clusters.

RESULTS

1,345,801 probable cases of dengue were reported. The regions with the highest increasing trend were the Northeast with an average epidemiologic week percent change (AEPC) of 52.4 (95% CI: 45.5-59.7; p < 0.001) and the South with 35.9 (95% CI: 27.7-44.5; p < 0.001). There was a statistically significant increasing trend in all states, except Acre (AEPC = -4.1; 95% CI: -16.3-10; p = 0.55), Amapá (AEPC = 1.3; 95% CI: -16.2-22.3; p = 0.9) and Espírito Santo (AEPC = 8.9; 95% CI: -15.7-40.6; p = 0.5). The retrospective space-time analysis showed a cluster within the Northeast, Central-West and Southeast regions, with a radius of 515.3 km, in which 1,267 municipalities and 525,324 of the cases were concentrated (RR = 6.3; p < 0.001). Regarding the spatial variation of the temporal trend, 21 risk areas were found, all of them located in Southeast or Central-West states. The area with the highest relative risk was Minas Gerais state, where 5,748 cases were concentrated (RR = 8.1; p < 0.001). Finally, a purely spatial analysis revealed 25 clusters, the one with the highest relative risk being composed of two municipalities in Acre (RR = 6.9; p < 0.001).

CONCLUSIONS

We described a detailed temporal-spatial analysis of dengue cases in the first EWs of 2024 in Brazil, which were mainly concentrated in the Southeast and Central-West regions. Overall, it is recommended that governments adopt public policies to control the the vector population in high-risk areas, as well as to prevent the spread of dengue fever to other areas of Brazil.

Mean daily temperatures can predict the thermal limits of malaria transmission better than rate summation

Temperature shapes the distribution, seasonality, and magnitude of mosquito-borne disease outbreaks. Mechanistic models predicting transmission often use mosquito and pathogen thermal responses from constant temperature experiments. However, mosquitoes live in fluctuating environments. Rate summation (nonlinear averaging) is a common approach to infer performance in fluctuating environments, but its accuracy is rarely validated. We measured three mosquito traits that impact transmission (bite rate, survival, fecundity) in a malaria mosquito (Anopheles stephensi) across temperature gradients with three diurnal temperature ranges (0, 9 and 12°C). We compared thermal suitability models with temperature-trait relationships observed under constant temperatures, fluctuating temperatures, and those predicted by rate summation. We mapped results across An. stephenesi's native Asian and invasive African ranges. We found: 1) daily temperature fluctuation significantly altered trait thermal responses; 2) rate summation partially captured decreases in performance near thermal optima, but also incorrectly predicted increases near thermal limits; and 3) while thermal suitability characterized across constant temperatures did not perfectly capture suitability in fluctuating environments, it was more accurate for estimating and mapping thermal limits than predictions from rate summation. Our study provides insight into methods for predicting mosquito-borne disease risk and emphasizes the need to improve understanding of organismal performance under fluctuating conditions.

The Alligator and the Mosquito: North American Crocodilians as Amplifiers of West Nile Virus in Changing Climates

In an age of emerging zoonoses, it is important to understand the intricate system of vectors and reservoirs, or hosts, and their relation to humans. West Nile Virus (WNV) has been detected in a myriad of nonhuman hosts. Transmission of the virus to humans is reliant on amplified seroprevalence within the host, which occurs primarily in birds. However, recent studies have found that other animal groups, including crocodilians, can obtain seroprevalence amplification to levels that make them competent hosts able to transmit WNV to mosquitoes, which can then transmit to humans. Climate change could exacerbate this transmission risk by shifting the distributions of mosquito vectors towards novel geographic ranges. Here, we use maximum entropy models to map the current and future distributions of three mosquito vector species and four crocodilian species in North America to determine the emerging risk of WNV outbreaks associated with changing climates and WNV associated with crocodilians in North America. From our models, we determined that one mosquito species in particular, Culex quinquefasciatus, will increase its distribution across the ranges of all crocodilian species in all tested climate change scenarios. This poses a potential risk to public health for people visiting and living near crocodilian farms and high-density natural crocodilian populations.

Warmer environmental temperature accelerates aging in mosquitoes, decreasing longevity and worsening infection outcomes

BACKGROUND

Most insects are poikilotherms and ectotherms, so their body temperature is predicated by environmental temperature. With climate change, insect body temperature is rising, which affects how insects develop, survive, and respond to infection. Aging also affects insect physiology by deteriorating body condition and weakening immune proficiency via senescence. Aging is usually considered in terms of time, or chronological age, but it can also be conceptualized in terms of body function, or physiological age. We hypothesized that warmer temperature decouples chronological and physiological age in insects by accelerating senescence. To investigate this, we reared the African malaria mosquito, Anopheles gambiae, at 27 °C, 30 °C and 32 °C, and measured survival starting at 1-, 5-, 10- and 15-days of adulthood after no manipulation, injury, or a hemocoelic infection with Escherichia coli or Micrococcus luteus. Then, we measured the intensity of an E. coli infection to determine how the interaction between environmental temperature and aging shapes a mosquito's response to infection.

RESULTS

We demonstrate that longevity declines when a mosquito is infected with bacteria, mosquitoes have shorter lifespans when the temperature is warmer, older mosquitoes are more likely to die, and warmer temperature marginally accelerates the aging-dependent decline in survival. Furthermore, we discovered that E. coli infection intensity increases when the temperature is warmer and with aging, and that warmer temperature accelerates the aging-dependent increase in infection intensity. Finally, we uncovered that warmer temperature affects both bacterial and mosquito physiology.

CONCLUSIONS

Warmer environmental temperature accelerates aging in mosquitoes, negatively affecting both longevity and infection outcomes. These findings have implications for how insects will serve as pollinators, agricultural pests, and disease vectors in our warming world.

Discarded vehicle tires and their association with mosquito vector abundance across socioenvironmental gradients in New Orleans, LA

Discarded vehicle tires serve as habitat for mosquito vectors. In New Orleans, Louisiana, discarded tires are an increasingly important public concern, especially considering that the city is home to many medically important mosquito species. Discarded tires are known to be associated with mosquito abundance, but how their presence interacts with other socioenvironmental gradients to influence mosquito ecology is poorly understood. Here, we ask whether discarded tire distribution could be explained by social factors, particularly median income, home vacancy and human population density, and whether these factors interact with urban heat islands (UHI) to drive mosquito vector assemblages. We surveyed tire piles across the city and adult mosquitoes in 12 sites, between May and October of 2020. We compared this data with the social indicators selected and UHI estimates. Our results show that median income and human population density were inversely related to tire abundance. Tire abundance was positively associated with Aedes albopictus abundance in places of low heat (LS) severity. Heat was the only predictor for the other monitored species, where high heat corresponded to higher abundance of Aedes aegypti, and LS to higher abundance of Culex quinquefasciatus. Our results suggest that low-income, sparsely populated neighborhoods of New Orleans may be hotspots for discarded vehicle tires, and are associated with higher abundances of at least one medically important mosquito (Ae. albopictus). These findings suggest potential locations for prioritizing source reduction efforts to control mosquito vectors and highlight discarded tires as a potential exposure pathway to unequal disease risk for low-income residents.

Role of vector phenotypic plasticity in disease transmission as illustrated by the spread of dengue virus by Aedes albopictus

The incidence of vector-borne disease is on the rise globally, with burdens increasing in endemic countries and outbreaks occurring in new locations. Effective mitigation and intervention strategies require models that accurately predict both spatial and temporal changes in disease dynamics, but this remains challenging due to the complex and interactive relationships between environmental variation and the vector traits that govern the transmission of vector-borne diseases. Predictions of disease risk in the literature typically assume that vector traits vary instantaneously and independently of population density, and therefore do not capture the delayed response of these same traits to past biotic and abiotic environments. We argue here that to produce accurate predictions of disease risk it is necessary to account for environmentally driven and delayed instances of phenotypic plasticity. To show this, we develop a stage and phenotypically structured model for the invasive mosquito vector, Aedes albopictus, and dengue, the second most prevalent human vector-borne disease worldwide. We find that environmental variation drives a dynamic phenotypic structure in the mosquito population, which accurately predicts global patterns of mosquito trait-abundance dynamics. In turn, this interacts with disease transmission to capture historic dengue outbreaks. By comparing the model to a suite of simpler models, we reveal that it is the delayed phenotypic structure that is critical for accurate prediction. Consequently, the incorporation of vector trait relationships into transmission models is critical to improvement of early warning systems that inform mitigation and control strategies.

Climate change impacts on dengue transmission areas in Espírito Santo state, Brazil

Espírito Santo state, in Brazil, is a dengue-endemic region predicted to suffer from an increase in temperature and drought due to climate change, which could affect the areas with active dengue virus transmission. The study objective was modeling climatic factors and climate change effects in zones suitable for dengue virus transmission in Espírito Santo state, Brazil. Data on dengue reports from 2022 were used to determine climatic variables related to spatial distribution. The climate change projections were generated for the 2030s, 2050s, 2070s, and 2090s for three distinct Shared Socioeconomic Pathways: SSP1-2.6, SSP2-4.5 and SSP5-8.5. A maximum entropy algorithm was used to construct the three models and projections, and the results were used to calculate the ensemble mean. Isothermality, the maximum temperature of the warmest month, precipitation of the wettest month, precipitation of the warmest quarter, and annual precipitation impacted the model. Projections indicated a change in areas suitable for dengue virus transmission, varying from -30.44% in the 2070s (SSP1-2.6) to +13.07% in the 2070s (SSP5-8.5) compared to 2022. The coastal regions were consistently suitable in all scenarios. Urbanized and highly populated areas were predicted to persist with active dengue transmission in Espírito Santo state, posing challenges for public health response.

The Impacts of Climate Change on the Emergence and Reemergence of Mosquito-Borne Diseases in Temperate Zones: An Umbrella Review Protocol

INTRODUCTION

Mosquito-borne diseases represent a global public health concern and are responsible for over 700 000 deaths globally every year. Additionally, many mosquito species have undergone a dramatic global expansion due to various factors, including climate change, and forecasts indicate that mosquito populations will persist in dispersing beyond their present geographic range, namely in temperate climates. The research literature on this topic has grown in recent years, including some systematic evidence synthesis. However, to provide a comprehensive overview of this growing literature needed for policy action, a summary of this evidence, including existing systematic reviews, is required. This study aims to undertake an umbrella review that explores the impacts of climate change on the emergence and reemergence of diseases transmitted by mosquitoes in temperate zones and the publication of the protocol is a fundamental step to ensure the credibility, transparency and reproducibility of this research.

METHODS AND ANALYSIS

Studies published in scientific journals indexed by PubMed, EMBASE, Cochrane Library, Epistemonikos, and Web of Science Core Collection to be included in this umbrella review will meet the following criteria: the topic of study (climate change and mosquito-borne diseases), regions (temperate zones), study designs (systematic reviews and meta-analysis), language (any) and date (since inception until December 31st, 2023). Titles and abstracts from selected articles will be evaluated by two authors independently and any discrepancy will be resolved through consensus or, if not possible, through a third author. The data will be extracted, and the risk of bias will be evaluated. The quality of the methodology of the included reviews will be assessed using AMSTAR 2. A narrative synthesis will examine the included systematic reviews. The quality of evidence for all outcomes will be judged using the Grading of Recommendations Assessment, Development and Evaluation working group methodology.

Spatiotemporally Explicit Epidemic Model for West Nile Virus Outbreak in Germany: An Inversely Calibrated Approach

Since the first autochthonous transmission of West Nile Virus was detected in Germany (WNV) in 2018, it has become endemic in several parts of the country and is continuing to spread due to the attainment of a suitable environment for vector occurrence and pathogen transmission. Increasing temperature associated with a changing climate has been identified as a potential driver of mosquito-borne disease in temperate regions. This scenario justifies the need for the development of a spatially and temporarily explicit model that describes the dynamics of WNV transmission in Germany. In this study, we developed a process-based mechanistic epidemic model driven by environmental and epidemiological data. Functional traits of mosquitoes and birds of interest were used to parameterize our compartmental model appropriately. Air temperature, precipitation, and relative humidity were the key climatic forcings used to replicate the fundamental niche responsible for supporting mosquito population and infection transmission risks in the study area. An inverse calibration method was used to optimize our parameter selection. Our model was able to generate spatially and temporally explicit basic reproductive number (R0) maps showing dynamics of the WNV occurrences across Germany, which was strongly associated with the deviation from daily means of climatic forcings, signaling the impact of a changing climate in vector-borne disease dynamics. Epidemiological data for human infections sourced from Robert Koch Institute and animal cases collected from the Animal Diseases Information System (TSIS) of the Friedrich-Loeffler-Institute were used to validate model-simulated transmission rates. From our results, it was evident that West Nile Virus is likely to spread towards the western parts of Germany with the rapid attainment of environmental suitability for vector mosquitoes and amplifying host birds, especially short-distance migratory birds. Locations with high risk of WNV outbreak (Baden-Württemberg, Bavaria, Berlin, Brandenburg, Hamburg, North Rhine-Westphalia, Rhineland-Palatinate, Saarland, Saxony-Anhalt and Saxony) were shown on R0 maps. This study presents a path for developing an early warning system for vector-borne diseases driven by climate change.

Temperature dependence of mosquitoes: Comparing mechanistic and machine learning approaches

Mosquito vectors of pathogens (e.g., Aedes, Anopheles, and Culex spp. which transmit dengue, Zika, chikungunya, West Nile, malaria, and others) are of increasing concern for global public health. These vectors are geographically shifting under climate and other anthropogenic changes. As small-bodied ectotherms, mosquitoes are strongly affected by temperature, which causes unimodal responses in mosquito life history traits (e.g., biting rate, adult mortality rate, mosquito development rate, and probability of egg-to-adult survival) that exhibit upper and lower thermal limits and intermediate thermal optima in laboratory studies. However, it remains unknown how mosquito thermal responses measured in laboratory experiments relate to the realized thermal responses of mosquitoes in the field. To address this gap, we leverage thousands of global mosquito occurrences and geospatial satellite data at high spatial resolution to construct machine-learning based species distribution models, from which vector thermal responses are estimated. We apply methods to restrict models to the relevant mosquito activity season and to conduct ecologically plausible spatial background sampling centered around ecoregions for comparison to mosquito occurrence records. We found that thermal minima estimated from laboratory studies were highly correlated with those from the species distributions (r = 0.87). The thermal optima were less strongly correlated (r = 0.69). For most species, we did not detect thermal maxima from their observed distributions so were unable to compare to laboratory-based estimates. The results suggest that laboratory studies have the potential to be highly transportable to predicting lower thermal limits and thermal optima of mosquitoes in the field. At the same time, lab-based models likely capture physiological limits on mosquito persistence at high temperatures that are not apparent from field-based observational studies but may critically determine mosquito responses to climate warming. Our results indicate that lab-based and field-based studies are highly complementary; performing the analyses in concert can help to more comprehensively understand vector response to climate change.