Tracking Asian tiger mosquito introductions in the Netherlands using Nextstrain

The Asian tiger mosquito Aedes albopictus is an undesirable invasive mosquito species that causes considerable nuisance through its biting behaviour, and has been proven to transmit more than 22 different viruses under laboratory conditions. Human-aided transportation, the capacity of winter diapause, and possibly global warming have contributed to the global invasion of Ae. albopictus. The species was found for the first time in the Netherlands in 2005, and since 2010 has been found introduced at many locations throughout the country. Elucidating the origin of these introduced mosquitoes could help the authorities on the planning and evaluation of the risk-based surveillance of Aedes invasive mosquitoes. This study aims to determine the genomic diversity of Ae. albopictus that is represented within and between collection sites with a database consisting of Ae. albopictus specimens from past introductions in the Netherlands, specimens from populations from other regions in the world, and data from specimens present in databases. In this study, complete mitochondrial genomes were sequenced, a recommended marker for phylogeography analysis of Ae. albopictus. Metadata is presented in a Nextstrain build containing 254 Ae. albopictus genomes up to October 2020. Overall, the phylogeny results of the Nextstrain build reveals a low mitogenomic diversity within Ae. albopictus. Genomic diversity of Ae. albopictus specimens found in the Netherlands fall within one main cluster which is hypothesised to represent the globally invasive strain of the species. Other organisations are stimulated to share data or materials for inclusion and improvement of the Nextstrain build, which can be accessed at https://nextstrain.nrcnvwa.nl/Aedes/20210728.info:eu-repo/semantics/publishedVersio

AIMSurv: First pan-European harmonized surveillance of Aedes invasive mosquito species of relevance for human vector-borne diseases

Human and animal vector-borne diseases, particularly mosquito-borne diseases, are emerging or re-emerging worldwide. Six Aedes invasive mosquito (AIM) species were introduced to Europe since the 1970s: Aedes aegypti, Ae. albopictus, Ae. japonicus, Ae. koreicus, Ae. atropalpus and Ae. triseriatus. Here, we report the results of AIMSurv2020, the first pan-European surveillance effort for AIMs. Implemented by 42 volunteer teams from 24 countries. And presented in the form of a dataset named “AIMSurv Aedes Invasive Mosquito species harmonized surveillance in Europe. AIM-COST Action. Project ID: CA17108”. AIMSurv2020 harmonizes field surveillance methodologies for sampling different AIMs life stages, frequency and minimum length of sampling period, and data reporting. Data include minimum requirements for sample types and recommended requirements for those teams with more resources. Data are published as a Darwin Core archive in the Global Biodiversity Information Facility- Spain, comprising a core file with 19,130 records (EventID) and an occurrences file with 19,743 records (OccurrenceID). AIM species recorded in AIMSurv2020 were Ae. albopictus, Ae. japonicus and Ae. koreicus, as well as native mosquito species

Anopheles maculipennis Complex in The Netherlands: First Record of Anopheles daciae (Diptera: Culicidae)

Despite their past importance as vectors of indigenous malaria, the species composition and spatial distribution of the members of the Anopheles maculipennis complex have been studied to a limited extent in the Netherlands. Therefore, this investigation focuses on the distribution of the members of this complex in the Netherlands, including Anopheles daciae, which has recently been found in countries bordering the Netherlands. In the framework of a national mosquito surveillance between 2010 and 2021, a total of 541 specimens of An. maculipennis s.l. were analyzed from 161 locations covering the entire territory. In addition, 89 specimens were analyzed from overwintering sites during the winter of 2020/2021. All individual mosquitoes were identified to species-level using Sanger sequencing of the ribosomal internal transcribed spacer 2. To characterize the habitat of An. maculipennis s.l. in the Netherlands, land cover use data was extracted in a 1 km buffer area around each finding location. For populations collected in summers between 2010 and 2021, the most frequent species was An. messeae, present in 88.19% of the locations, followed by An. maculipennis s.s. (11.80%), An. atroparvus (3.72%) and An. daciae (3.72%). Anopheles daciae was found in the southern inland areas of the country. Furthermore, An. messeae and An. daciae occurred in sympatry at overwintering sites. This study provides relevant information on the occurrence of species of the Anopheles maculipennis complex in the Netherlands, contributing to a better estimation of the risk of mosquito-borne disease in the country

Modelling the potential spatial distribution of mosquito species using three different techniques

Background: Models for the spatial distribution of vector species are important tools in the assessment of the risk of establishment and subsequent spread of vector-borne diseases. The aims of this study are to define the environmental conditions suitable for several mosquito species through species distribution modelling techniques, and to compare the results produced with the different techniques. Methods: Three different modelling techniques, i.e., non-linear discriminant analysis, random forest and generalised linear model, were used to investigate the environmental suitability in the Netherlands for three indigenous mosquito species (Culiseta annulata, Anopheles claviger and Ochlerotatus punctor). Results obtained with the three statistical models were compared with regard to: (i) environmental suitability maps, (ii) environmental variables associated with occurrence, (iii) model evaluation. Results: The models indicated that precipitation, temperature and population density were associated with the occurrence of Cs. annulata and An. claviger, whereas land surface temperature and vegetation indices were associated with the presence of Oc. punctor. The maps produced with the three different modelling techniques showed consistent spatial patterns for each species, but differences in the ranges of the predictions. Non-linear discriminant analysis had lower predictions than other methods. The model with the best classification skills for all the species was the random forest model, with specificity values ranging from 0.89 to 0.91, and sensitivity values ranging from 0.64 to 0.95. Conclusions: We mapped the environmental suitability for three mosquito species with three different modelling techniques. For each species, the maps showed consistent spatial patterns, but the level of predicted environmental suitability differed; NLDA gave lower predicted probabilities of presence than the other two methods. The variables selected as important in the models were in agreement with the existing knowledge about these species. All model predictions had a satisfactory to excellent accuracy; best accuracy was obtained with random forest. The insights obtained can be used to gain more knowledge on vector and non-vector mosquito species. The output of this type of distribution modelling methods can, for example, be used as input for epidemiological models of vector-borne diseases

Habitat suitability modelling to assess the introductions of Aedes albopictus (Diptera: Culicidae) in the Netherlands

Background In the Netherlands, Aedes albopictus has been found each year since 2010 during routine exotic mosquito species surveillance at companies that import used tires. We developed habitat suitability models to investigate the potential risk of establishment and spread of this invasive species at these locations. Methods We used two methodologies: first, a species distribution model based on the maximum entropy modelling approach (MaxEnt) taking into consideration updated occurrence data of the species in Europe, and secondly, a spatial logic conditional model based on the temperature requirements of the species and using land surface temperature data (LST model). Results Suitability assessment obtained with the MaxEnt model at European level accurately reflect the current distribution of the species and these results also depict moderately low values in parts of the Netherlands, Belgium, Denmark, the British islands and southern parts of Scandinavia. Winter temperature was the variable that contributed most to the performance of the model (47.3%). The results of the LST model showed that: (i) coastal areas are suitable for overwintering of eggs; (ii) large areas in the northern part of the country have a low suitability for adult survival; and (iii) the entire country is suitable for successful completion of the life-cycle if the species is introduced after the winter months. Results of the LST model revealed that temperatures in 2012 and 2014 did not limit the overwintering of eggs or survival of adults at the locations where the species was found. By contrast, for the years 2010, 2011 and 2013, overwintering of eggs at these locations is considered unlikely. Conclusions Results using two modelling methodologies show differences in predicted habitat suitability values. Based on the results of both models, the climatic conditions could hamper the successful overwintering of eggs of Ae. albopictus and their survival as adults in many areas of the country. However, during warm years with mild winters, many areas of the Netherlands offer climatic conditions suitable for developing populations. Regular updates of the models, using updated occurrence and climatic data, are recommended to study the areas at risk

Assessment of the probability of entry of Rift Valley fever virus into the EU through active or passive movement of vectors

The overall aim of this scientific report is the assessment of the probability of entry of Rift Valley fever virus (RVFV) into the European Union (EU) through active or passive movement of vectors. Two different import pathways were considered in this report, i.e. import through flights and import via cargo on ships. The import through road transport, eggs or immature stages, and wind was not considered in this report as thought to be zero or negligible. In total 39 potential RVFV vectors were identified based on our review. Of the 39 identified potential vectors of RVFV, the five highest ranked based on their distribution in the African at‐risk countries, their potential role as vector, and their behavioural and ecological traits influencing the risk of transportation were: Anopheles pharoensis, Aedes aegypti, Mansonia uniformis, Aedes mcintoshi, and Culex quinquefasciatus. Four of these species were also detected in airports or airplanes in the EU. The estimated probability of entry of RVFV infected mosquito vectors into the EU through the passive movement of mosquito vectors by flights is medium for the Netherlands, France, Germany and Italy. These countries are heavily connected through direct flights from the 14 at‐risk countries in Africa. A low risk of RVFV import was estimated for Spain, Poland, Belgium and Austria and for 16 countries the risk was zero. Overall the risk of RVFV import through ship‐cargo was zero for most of the EU Member States and low for the Netherlands, Spain, Germany and Belgium

Spatial risk analysis for the introduction and circulation of six arboviruses in the Netherlands

BACKGROUND: Arboviruses are a growing public health concern in Europe, with both endemic and exotic arboviruses expected to spread further into novel areas in the next decades. Predicting where future outbreaks will occur is a major challenge, particularly for regions where these arboviruses are not endemic. Spatial modelling of ecological risk factors for arbovirus circulation can help identify areas of potential emergence. Moreover, combining hazard maps of different arboviruses may facilitate a cost-efficient, targeted multiplex-surveillance strategy in areas where virus transmission is most likely. Here, we developed predictive hazard maps for the introduction and/or establishment of six arboviruses that were previously prioritized for the Netherlands: West Nile virus, Japanese encephalitis virus, Rift Valley fever virus, tick-borne encephalitis virus, louping-ill virus and Crimean-Congo haemorrhagic fever virus. METHODS: Our spatial model included ecological risk factors that were identified as relevant for these arboviruses by an earlier systematic review, including abiotic conditions, vector abundance, and host availability.

Bluetongue, Schmallenberg - what is next? Culicoides-borne viral diseases in the 21st Century

In the past decade, two pathogens transmitted by Culicoides biting midges (Diptera: Ceratopogonidae), bluetongue virus and Schmallenberg virus, have caused serious economic losses to the European livestock industry, most notably affecting sheep and cattle. These outbreaks of arboviral disease have highlighted large knowledge gaps on the biology and ecology of indigenous Culicoides species. With these research gaps in mind, and as a means of assessing what potential disease outbreaks to expect in the future, an international workshop was held in May 2013 at Wageningen University, The Netherlands. It brought together research groups from Belgium, France, Germany, Spain, Switzerland, United Kingdom and The Netherlands, with diverse backgrounds in vector ecology, epidemiology, entomology, virology, animal health, modelling, and genetics. Here, we report on the key findings of this workshop