Emergence Of Vector-borne Diseases Research Articles

How climate, species interactions, and global change drive infectious disease dynamics

Understanding the climatic conditions that drive vector-borne disease emergence and spread is critically important for understanding current infectious disease dynamics and predicting how they may shift with climate change. Temperature, rainfall, and humidity can influence vector abundance, distribution, and vectorial capacity (the number of infectious vector bites per person) by affecting a variety of vector traits, including survival, reproduction, and development. Using dengue and chikungunya as examples, I will discuss how climate factors impact the abundance of the Aedes aegypti mosquito vector and disease transmission. Often temperature, rainfall, and humidity influence mosquito traits differently across their environmental ranges. For instance, the relationships between temperature and multiple mosquito traits are unimodal, which has led to the prediction of an intermediate optimal temperature for disease transmission, which is lower than previously expected. We are incorporating these climate-driven traits into mathematical models to better understand how climate affects dengue and chikungunya transmission in Africa and South America, using field entomology and epidemiology data from Kenya and Ecuador. These models can help us predict disease transmission in the near future and understand how global climate change is likely to shift transmission in space and time in the longer term. Further, these results have implications for understanding where other Aedes aegypti-vectored diseases could circulate, including currently known diseases of concern such as Zika and yellow fever, as well as emerging pathogens such as Mayaro virus.

WHO bites back rabies pre-travel vaccination schedules – Implications for travel medicine

Disease epidemiology of (re-)emerging infectious diseases is changing rapidly, rendering surveillance of travel-associated illness important.We evaluated travel-related illness encountered at EuroTravNet clinics, the European surveillance sub-network of GeoSentinel, between March 1, 1998 and March 31, 2018.103,739 ill travellers were evaluated, including 11,239 (10.8%) migrants, 89,620 (86.4%) patients seen post-travel, and 2,880 (2.8%) during and after travel. Despite increasing numbers of patient encounters over 20 years, the regions of exposure by year of clinic visits have remained stable. In 5-year increments, greater proportions of patients were migrants or visiting friends and relatives (VFR); business travel-associated illness remained stable; tourism-related illness decreased. Falciparum malaria was amongst the most-frequently diagnosed illnesses with 5,254 cases (5.1% of all patients) and the most-frequent cause of death (risk ratio versus all other illnesses 2.5:1). Animal exposures requiring rabies post-exposure prophylaxis increased from 0.7% (1998–2002) to 3.6% (2013–2018). The proportion of patients with seasonal influenza increased from zero in 1998–2002 to 0.9% in 2013–2018. There were 44 cases of viral haemorrhagic fever, most during the past five years. Arboviral infection numbers increased significantly as did the range of presenting arboviral diseases, dengue and chikungunya diagnoses increased by 2.6% and 1%, respectively.Travel medicine must adapt to serve the changing profile of travellers, with an increase in migrants and persons visiting relatives and friends and the strong emergence of vector-borne diseases, with potential for further local transmission in Europe.This project was supported by a cooperative agreement (U50CK00189) between the Centers for Disease Control and Prevention to the International Society of Travel Medicine (ISTM) and funding from the ISTM and the Public Health Agency of Canada.

Emergence of tick-borne diseases at northern latitudes in Europe: a comparative approach

The factors that drive the emergence of vector-borne diseases are difficult to identify due to the complexity of the pathogen-vector-host triad. We used a novel comparative approach to analyse four long-term datasets (1995–2015) on the incidence of tick-borne diseases in humans and livestock (Lyme disease, anaplasmosis and babesiosis) over a geographic area that covered the whole of Norway. This approach allowed us to separate general (shared vector) and specific (pathogen reservoir host) limiting factors of tick-borne diseases, as well as the role of exposure (shared and non-shared pathogens in different hosts). We found broadly similar patterns of emergence across the four tick-borne diseases. Following initial increases during the first decade of the time series, the numbers of cases peaked at slightly different years and then stabilized or declined in the most recent years. Contrasting spatial patterns of disease incidence were consistent with exposure to ticks being an important factor influencing disease incidence in livestock. Uncertainty regarding the reservoir host(s) of the pathogens causing anaplasmosis and babesiosis prevented a firm conclusion regarding the role of the reservoir host-pathogen distribution. Our study shows that the emergence of tick-borne diseases at northern latitudes is linked to the shared tick vector and that variation in host-pathogen distribution and exposure causes considerable variation in emergence.

Climate change and the emergence of vector-borne diseases in Europe: case study of dengue fever.

BackgroundDengue fever is the most prevalent mosquito-borne viral disease worldwide. Dengue transmission is critically dependent on climatic factors and there is much concern as to whether climate change would spread the disease to areas currently unaffected. The occurrence of autochthonous infections in Croatia and France in 2010 has raised concerns about a potential re-emergence of dengue in Europe. The objective of this study is to estimate dengue risk in Europe under climate change scenarios.MethodsWe used a Generalized Additive Model (GAM) to estimate dengue fever risk as a function of climatic variables (maximum temperature, minimum temperature, precipitation, humidity) and socioeconomic factors (population density, urbanisation, GDP per capita and population size), under contemporary conditions (1985–2007) in Mexico. We then used our model estimates to project dengue incidence under baseline conditions (1961–1990) and three climate change scenarios: short-term 2011–2040, medium-term 2041–2070 and long-term 2071–2100 across Europe. The model was used to calculate average number of yearly dengue cases at a spatial resolution of 10 × 10 km grid covering all land surface of the currently 27 EU member states. To our knowledge, this is the first attempt to model dengue fever risk in Europe in terms of disease occurrence rather than mosquito presence.ResultsThe results were presented using Geographical Information System (GIS) and allowed identification of areas at high risk. Dengue fever hot spots were clustered around the coastal areas of the Mediterranean and Adriatic seas and the Po Valley in northern Italy.ConclusionsThis risk assessment study is likely to be a valuable tool assisting effective and targeted adaptation responses to reduce the likely increased burden of dengue fever in a warmer world.Electronic supplementary materialThe online version of this article (doi:10.1186/1471-2458-14-781) contains supplementary material, which is available to authorized users.

Evaluation of a Continuous Indicator for Syndromic Surveillance through Simulation. Application to Vector Borne Disease Emergence Detection in Cattle Using Milk Yield

Two vector borne diseases, caused by the Bluetongue and Schmallenberg viruses respectively, have emerged in the European ruminant populations since 2006. Several diseases are transmitted by the same vectors and could emerge in the future. Syndromic surveillance, which consists in the routine monitoring of indicators for the detection of adverse health events, may allow an early detection. Milk yield is routinely measured in a large proportion of dairy herds and could be incorporated as an indicator in a surveillance system. However, few studies have evaluated continuous indicators for syndromic surveillance. The aim of this study was to develop a framework for the quantification of both disease characteristics and model predictive abilities that are important for a continuous indicator to be sensitive, timely and specific for the detection of a vector-borne disease emergence. Emergences with a range of spread characteristics and effects on milk production were simulated. Milk yields collected monthly in 48 713 French dairy herds were used to simulate 576 disease emergence scenarios. First, the effect of disease characteristics on the sensitivity and timeliness of detection were assessed: Spatio-temporal clusters of low milk production were detected with a scan statistic using the difference between observed and simulated milk yields as input. In a second step, the system specificity was evaluated by running the scan statistic on the difference between observed and predicted milk yields, in the absence of simulated emergence. The timeliness of detection depended mostly on how easily the disease spread between and within herds. The time and location of the emergence or adding random noise to the simulated effects had a limited impact on the timeliness of detection. The main limitation of the system was the low specificity i.e. the high number of clusters detected from the difference between observed and predicted productions, in the absence of disease.

Predicting ectotherm disease vector spread—benefits from multidisciplinary approaches and directions forward

The occurrence of ectotherm disease vectors outside of their previous distribution area and the emergence of vector-borne diseases can be increasingly observed at a global scale and are accompanied by a growing number of studies which investigate the vast range of determining factors and their causal links. Consequently, a broad span of scientific disciplines is involved in tackling these complex phenomena. First, we evaluate the citation behaviour of relevant scientific literature in order to clarify the question "do scientists consider results of other disciplines to extend their expertise?" We then highlight emerging tools and concepts useful for risk assessment. Correlative models (regression-based, machine-learning and profile techniques), mechanistic models (basic reproduction number R0) and methods of spatial regression, interaction and interpolation are described. We discuss further steps towards multidisciplinary approaches regarding new tools and emerging concepts to combine existing approaches such as Bayesian geostatistical modelling, mechanistic models which avoid the need for parameter fitting, joined correlative and mechanistic models, multi-criteria decision analysis and geographic profiling. We take the quality of both occurrence data for vector, host and disease cases, and data of the predictor variables into consideration as both determine the accuracy of risk area identification. Finally, we underline the importance of multidisciplinary research approaches. Even if the establishment of communication networks between scientific disciplines and the share of specific methods is time consuming, it promises new insights for the surveillance and control of vector-borne diseases worldwide.

Analysis of the El Niño/La Niña-Southern Oscillation variability and malaria in the Estado Sucre, Venezuela

The last decade has seen an unprecedented, worldwide acceleration of environmental and climate changes. These processes impact the dynamics of natural systems, which include components associated with human communities such as vector-borne diseases. The dynamics of environmental and climate variables, altered by global change as reported by the Intergovernmental Panel on Climate Change, affect the distribution of many tropical diseases. Complex systems, e.g. the El Niño/La Niña-Southern Oscillation (ENSO), in which environmental variables operate synergistically, can provoke the reemergence and emergence of vector-borne diseases at new sites. This research investigated the influence of ENSO events on malaria incidence by determining the relationship between climate variations, expressed as warm, cold and neutral phases, and their relation to the number of malaria cases in some north-eastern municipalities of Venezuela (Estado Sucre) during the period 1990-2000. Significant differences in malaria incidence were found, particularly in the La Niña ENSO phases (cold) of moderate intensity. These findings should be taken into account for surveillance and control in the future as they shed light on important indicators that can lead to reduced vulnerability to malaria.

Dryland salinity and vector-borne disease emergence in southwestern Australia

Broad-scale clearing of native vegetation for agriculture in southwestern Australia has resulted in severe ecosystem degradation, which has been compounded by the subsequent development of large areas of dryland salinity; decreased transevaporation allows the water table to rise, dissolving ancient aeolian salt deposits and creating saline surface pools. The mosquito-borne disease Ross River virus has been noted as a potential adverse human health outcome in salinity-affected regions because the principal vector, Aedes camptorhynchus, is salt tolerant and thrives preferentially in such systems. To understand the geology and ecology underlying the relationship between land clearing and disease emergence, we examine the relationship between dryland salinity processes that determine the dissolved solids profile of saline pools in affected areas, the mosquito vectors and interactions with the human population within the disease cycle. Aedes camptorhynchus is able to survive in a wide range of salinities in pools created by dryland salinity processes. The link with disease emergence is achieved where population distribution and activity overlaps with the convergence of environmental and ecological conditions that enhance disease transmission.

Quantitative genetics of Aedes aegypti vector competence for dengue viruses: towards a new paradigm?

Similar to many other host-pathogen interactions, the vector competence of Aedes aegypti for dengue viruses appears to be determined by genotype-by-genotype interactions, whereby the outcome of infection depends on the specific combination of mosquito and virus genotypes. This can complicate efforts to dissect the genetic basis of vector competence in nature because it obscures mapping between genotype and phenotype and brings into question the notion of universal mosquito resistance or susceptibility. Conversely, it offers novel opportunities to better define compatible vector-pathogen associations based on integration of both vector and pathogen genomics, which should eventually improve understanding of pathogen transmission dynamics and the risk of vector-borne disease emergence.

Avian Malaria Parasites Share Congeneric Mosquito Vectors

Assessing parasite specificity to vector is crucial to understanding the emergence of vector-borne diseases and the evolution of parasite diversity. Avian malaria parasites have a cosmopolitan distribution and broad avian host range, which together predict they are vector generalists, but little is known about parasite-vector associations in the wild. We tested this prediction by asking if 5 different mosquito species, known to feed on birds and abundant in the northeastern United States, were naturally infected in the field with identical avian Plasmodium spp. lineages. Mosquitoes were not pooled but rather analyzed individually, and, possibly as a result, lineage diversity was higher than reported in previous avian malaria vector studies. Plasmodium spp. lineages were rare in Aedes canadensis and absent in Aedes aurifer and Culiseta melanura. We sequenced a standard Plasmodium cytochrome b marker from Culex pipiens pipiens, Culex restuans, and Ae. canadensis. Most Plasmodium clades were shared by Cx. pipiens and Cx. restuans. In addition, 4 individual lineages were shared by both mosquito species, including the most common lineage. One Plasmodium clade, however, was only found in Cx. restuans. We therefore found limited support for our prediction that avian Plasmodium spp. vector breadth accompanies host breadth. The association of both Culex species with most Plasmodium clades, and the presence of a single parasite lineage in 3 mosquito species representing 2 genera, suggests that avian Plasmodium species are not tightly coevolved with vector species.

Seasonal Variation of Potential Flavivirus Vectors in an Urban Biological Reserve in Northeastern Brazil

Although yellow fever (YF) has not been reported on the eastern coast of Brazil since 1942, there was a reemergence of dengue fever in Brazil in 1987 due to the reintroduction of Aedes aegypti (L.). To assess areas of potential risk for transmission of vector-borne diseases, a surveillance system was placed in a large Atlantic Forest reserve in Natal, Rio Grande do Norte, Brazil, where in 2004 unexplained epizootics were reported among marmosets. The etiologic agent causing the mortality in marmosets has not been identified. Wyeomyia bourrouli Lutz, Haemagogus leucocelaenus Dyar & Shannon, Ae. aegypti, Aedes albopictus (Skuse), Ochlerotatus scapularis Rondani, Ochlerotatus serratus Theobald, Ochlerotatus taeniorhynchus Wiedemann, Culex quinquefasciatus Say, and Limatus durhami Theobald were collected in the park and in the proximity of the households adjacent to the park. Seasonal abundance fluctuation was significant for Ae. aegypti, Ae. albopictus, Ochlerotatus scapularis (Rondani), and Hg. leucocelaenus. Eggs of Ae. aegypti, Ae. albopictus, and Hg. leucocelaenus were more frequently found at the conclusion of the rainy season. A significant negative correlation between the number ofAe. albopictus collected and temperature was observed (r = -0.50), i.e., for each 10C increase in temperature, the number of specimens collected decreased eight-fold. The findings reported herein reinforce the need for a sustainable arboviral surveillance program in this area to decrease the potential risk of emergence of vector borne diseases as YF.

Food Security and Emerging Infectious Diseases: The Unsustainable Case of the Andes-Amazon Region, due to Large Scale Crop Production and Global Trade Policies

ISEE-0704 Background and Objectives: Food security embraces, among other dimensions, food production and distribution, which are related to changes in land-use and cover and biodiversity, therefore in the epidemiology of infectious diseases. The ongoing infrastructure development policies for the region, allowing increasing international commerce (especially the exportation of Soya-bean from Brazil to Asia), include the paving of the 1,000 miles “Pacific Highway”, as well as the resulting 2,500 miles of hydro-ways from the building of hydroelectric dams. The vicious cycle (roads and dams building–LUCC through logging/forest fires–biodiversity loss) affect vectors’ ecology and bring people, vectors, and wild reservoirs into overlapping areas, fostering the (re)emergence of vector-borne diseases. This work was aimed at assessing these linkages and understanding this complex process to help breaking this vicious cycle. Methods: Case Study methodology enabled the investigation to retain the characteristics of real-life events and coped with the situation in which there were multiple variables of interest and sources of evidence – such as documentary sources, interviews, analysis of changes in land use and cover and in the region’s epidemiology – while assessing what can be learned to mitigate societal suffering and environmental loss when developmental policies are aimed at promoting food production and trade. Results: The (re)emergence of American Cutaneous Leishmaniasis and Bartonellosis (Carrion Disease) are two seminal examples of how infectious diseases in the Andes-Amazon Region can be linked to LUCC and to biodiversity loss from deforestation, road paving and dams building, fostered by distant food production and distribution. Conclusion: It is fundamental to make explicit the linkages between “development” policies, LUCC, forest and biodiversity losses, and, ultimately, food security, if we are to increase the awareness about ecosystem services to regulate the (re)emergence of infectious diseases.

Combined Sewage Overflow Enhances Oviposition ofCulex quinquefasciatus(Diptera: Culicidae) in Urban Areas

Ecosystem changes caused by anthropogenic activities have modified the environment in ways that at times promote the emergence of vector-borne diseases. Here, we study the effects of combined sewage overflows (CSOs) from urban streams in Atlanta, GA, on oviposition site selection by Culex quinquefasciatus under seminatural field conditions. Counting egg rafts was a reliable indicator of oviposition preferences, and CSO water quality, especially when enriched, was a more attractive oviposition substrate than nonenriched water. Therefore, environmentally sound management of municipal waste water systems has the potential to diminish the risk of Culex-borne diseases in urban areas.

Using remote sensing to map larval and adult populations of Anopheles hyrcanus (Diptera: Culicidae) a potential malaria vector in Southern France

BackgroundAlthough malaria disappeared from southern France more than 60 years ago, suspicions of recent autochthonous transmission in the French Mediterranean coast support the idea that the area could still be subject to malaria transmission. The main potential vector of malaria in the Camargue area, the largest river delta in southern France, is the mosquito Anopheles hyrcanus (Diptera: Culicidae). In the context of recent climatic and landscape changes, the evaluation of the risk of emergence or re-emergence of such a major disease is of great importance in Europe. When assessing the risk of emergence of vector-borne diseases, it is crucial to be able to characterize the arthropod vector's spatial distribution. Given that remote sensing techniques can describe some of the environmental parameters which drive this distribution, satellite imagery or aerial photographs could be used for vector mapping.ResultsIn this study, we propose a method to map larval and adult populations of An. hyrcanus based on environmental indices derived from high spatial resolution imagery. The analysis of the link between entomological field data on An. hyrcanus larvae and environmental indices (biotopes, distance to the nearest main productive breeding sites of this species i.e., rice fields) led to the definition of a larval index, defined as the probability of observing An. hyrcanus larvae in a given site at least once over a year. Independent accuracy assessments showed a good agreement between observed and predicted values (sensitivity and specificity of the logistic regression model being 0.76 and 0.78, respectively). An adult index was derived from the larval index by averaging the larval index within a buffer around the trap location. This index was highly correlated with observed adult abundance values (Pearson r = 0.97, p < 0.05). This allowed us to generate predictive maps of An. hyrcanus larval and adult populations from the landscape indices.ConclusionThis work shows that it is possible to use high resolution satellite imagery to map malaria vector spatial distribution. It also confirms the potential of remote sensing to help target risk areas, and constitutes a first essential step in assessing the risk of re-emergence of malaria in southern France.

Epidemiological processes involved in the emergence of vector-borne diseases : West Nile fever, Rift Valley fever, Japanese encephalitis and Crimean-Congo haemorrhagic fever

Over the past few decades, the geographical distribution of arthropod-borne zoonoses has dramatically expanded. The influence of human-induced or ecological changes on the risk of disease outbreaks is undeniable. However, few hypotheses have been proposed which address the re-emergence of these diseases, the spread of these viruses to previously uninfected areas and their establishment therein. Host and vector movements play an important role in the dissemination of pathogens, and the ability of these diseases to colonise previously uninfected areas may be explained by the diversity of hosts and vectors, the presence of favourable ecological conditions, and the successful adaptations of vectors or pathogens to new ecosystems. The objective of this paper is to describe the epidemiological processes of the vector-borne diseases Rift Valley fever, West Nile fever, Japanese encephalitis and Crimean-Congo haemorrhagic fever.