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Background: Zika is of great medical relevance due to its rapid geographical spread in 2015 and 2016 in South America and its serious implications, for example, certain birth defects. Recent epidemics urgently require a better understanding of geographic patterns of the Zika virus transmission risk. This study aims to map the Zika virus transmission risk in South and Central America. We applied the maximum entropy approach, which is common for species distribution modelling, but is now also widely in use for estimating the geographical distribution of infectious diseases.
Methods: As predictor variables we used a set of variables considered to be potential drivers of both direct and indirect effects on the emergence of Zika. Specifically, we considered (a) the modelled habitat suitability for the two main vector species Aedes aegypti and Ae. albopictus as a proxy of vector species distributions; (b) temperature, as it has a great influence on virus transmission; (c) commonly called evidence consensus maps (ECM) of human Zika virus infections on a regional scale as a proxy for virus distribution; (d) ECM of human dengue virus infections and, (e) as possibly relevant socio-economic factors, population density and the gross domestic product.
Results: The highest values for the Zika transmission risk were modelled for the eastern coast of Brazil as well as in Central America, moderate values for the Amazon basin and low values for southern parts of South America. The following countries were modelled to be particularly affected: Brazil, Colombia, Cuba, Dominican Republic, El Salvador, Guatemala, Haiti, Honduras, Jamaica, Mexico, Puerto Rico and Venezuela. While modelled vector habitat suitability as predictor variable showed the highest contribution to the transmission risk model, temperature of the warmest quarter contributed only comparatively little. Areas with optimal temperature conditions for virus transmission overlapped only little with areas of suitable habitat conditions for the two main vector species. Instead, areas with the highest transmission risk were characterised as areas with temperatures below the optimum of the virus, but high habitat suitability modelled for the two main vector species.
Conclusion: Modelling approaches can help estimating the spatial and temporal dynamics of a disease. We focused on the key drivers relevant in the Zika transmission cycle (vector, pathogen, and hosts) and integrated each single component into the model. Despite the uncertainties generally associated with modelling, the approach applied in this study can be used as a tool and assist decision making and managing the spread of Zika.
Tick-borne diseases are a major health problem worldwide and could become even more important in Europe in the future. Due to changing climatic conditions, ticks are assumed to be able to expand their ranges in Europe towards higher latitudes and altitudes, which could result in an increased occurrence of tick-borne diseases.
There is a great interest to identify potential (new) areas of distribution of vector species in order to assess the future infection risk with vector-borne diseases, improve surveillance, to develop more targeted monitoring program, and, if required, control measures.
Based on an ecological niche modelling approach we project the climatic suitability for the three tick species Ixodes ricinus, Dermacentor reticulatus and Dermacentor marginatus under current and future climatic conditions in Europe. These common tick species also feed on humans and livestock and are vector competent for a number of pathogens.
For niche modelling, we used a comprehensive occurrence data set based on several databases and publications and six bioclimatic variables in a maximum entropy approach. For projections, we used the most recent IPCC data on current and future climatic conditions including four different scenarios of socio-economic developments.
Our models clearly support the assumption that the three tick species will benefit from climate change with projected range expansions towards north-eastern Europe and wide areas in central Europe with projected potential co-occurrence.
A higher tick biodiversity and locally higher abundances might increase the risk of tick-borne diseases, although other factors such as pathogen prevalence and host abundances are also important.
Background: Worldwide, the number of recorded human hantavirus infections as well as the number of affected countries is on the rise. In Europe, most human hantavirus infections are caused by the Puumala virus (PUUV), with bank voles (Myodes glareolus) as reservoir hosts. Generally, infection outbreaks have been related to environmental conditions, particularly climatic conditions, food supply for the reservoir species and land use. However, although attempts have been made, the insufficient availability of environmental data is often hampering accurate temporal and spatially explicit models of human hantavirus infections.
Methods: In the present study, dynamics of human PUUV infections between 2001 and 2015 were explored using ArcGIS in order to identify spatio-temporal patterns.
Results: Percentage cover of forest area was identified as an important factor for the spatial pattern, whereas beech mast was found explaining temporal patterns of human PUUV infections in Germany. High numbers of infections were recorded in 2007, 2010 and 2012 and areas with highest records were located in Baden-Wuerttemberg (southwest Germany) and North Rhine-Westphalia (western Germany).
Conclusion: More reliable data on reservoir host distribution, pathogen verification as well as an increased awareness of physicians are some of the factors that should improve future human infection risk assessments in Germany.
Background: In the face of ongoing climate warming, vector-borne diseases are expected to increase in Europe, including tick-borne diseases (TBD). The most abundant tick-borne diseases in Germany are Tick-Borne Encephalitis (TBE) and Lyme Borreliosis (LB), with Ixodes ricinus as the main vector.
Methods: In this study, we display and compare the spatial and temporal patterns of reported cases of human TBE and LB in relation to some associated factors. The comparison may help with the interpretation of observed spatial and temporal patterns.
Results: The spatial patterns of reported TBE cases show a clear and consistent pattern over the years, with many cases in the south and only few and isolated cases in the north of Germany. The identification of spatial patterns of LB disease cases is more difficult due to the different reporting practices in the individual federal states. Temporal patterns strongly fluctuate between years, and are relatively synchronized between both diseases, suggesting common driving factors. Based on our results we found no evidence that weather conditions affect the prevalence of both diseases. Both diseases show a gender bias with LB bing more commonly diagnosed in females, contrary to TBE being more commonly diagnosed in males.
Conclusion: For a further investigation of of the underlying driving factors and their interrelations, longer time series as well as standardised reporting and surveillance system would be required.
Ambrosia artemisiifolia L., native to North America, is a problematic invasive species, because of its highly allergenic pollen. The species is expected to expand its range due to climate change. By means of ecological niche modelling (ENM), we predict habitat suitability for A. artemisiifolia in Europe under current and future climatic conditions. Overall, we compared the performance and results of 16 algorithms commonly applied in ENM. As occurrence records of invasive species may be dominated by sampling bias, we also used data from the native range. To assess the quality of the modelling approaches we assembled a new map of current occurrences of A. artemisiifolia in Europe. Our results show that ENM yields a good estimation of the potential range of A. artemisiifolia in Europe only when using the North American data. A strong sampling bias in the European Global Biodiversity Information Facility (GBIF) data for A. artemisiifolia causes unrealistic results. Using the North American data reflects the realized European distribution very well. All models predict an enlargement and a northwards shift of potential range in Central and Northern Europe during the next decades. Climate warming will lead to an increase and northwards shift of A. artemisiifolia in Europe.
Background: Studies of parasite communities and patterns in the Antarctic are an important knowledge base with the potential to track shifts in ecological relations and study the effects of climate change on host–parasite systems. Endemic Nototheniinae is the dominant fish group found in Antarctic marine habitats. Through their intermediate position within the food web, Nototheniinae link lower to higher trophic levels and thereby also form an important component of parasite life cycles. The study was set out to gain insight into the parasite fauna of Nototheniops larseni, N. nudifrons and Lepidonotothen squamifrons (Nototheniinae) from Elephant Island (Antarctica).
Methods: Sampling was conducted at three locations around Elephant Island during the ANT-XXVIII/4 expedition of the research vessel Polarstern. The parasite fauna of three Nototheniine species was analysed, and findings were compared to previous parasitological and ecological research collated from a literature review.
Results: All host species shared the parasites Neolebouria antarctica (Digenea), Corynosoma bullosum (Acanthocephala) and Pseudoterranova decipiens E (Nematoda). Other parasite taxa were exclusive to one host species in this study. Nototheniops nudifrons was infected by Ascarophis nototheniae (Nematoda), occasional infections of N. larseni with Echinorhynchus petrotschenkoi (Acanthocephala) and L. squamifrons with Elytrophalloides oatesi (Digenea) and larval tetraphyllidean Cestoda were detected.
Conclusion: All examined fish species’ parasites were predominantly euryxenous regarding their fish hosts. The infection of Lepidonotothen squamifrons with Lepidapedon garrardi (Digenea) and Nototheniops larseni with Echinorhynchus petrotschenkoi represent new host records. Despite the challenges and limited opportunities for fishing in remote areas, future studies should continue sampling on a more regular basis and include a larger number of fish species and sampling sites within different habitats.
Aim: Formerly introduced for their presumed value in controlling mosquito-borne diseases, the two mosquitofish Gambusia affinis and G. holbrooki (Poeciliidae) are now among the world's most widespread invasive alien species, negatively impacting aquatic ecosystems around the world. These inconspicuous freshwater fish are, once their presence is noticed, difficult to eradicate. It is, therefore, of utmost importance to assess their geographic potential and to identify their likely ability to persist under novel climatic conditions.
Location Global.
Methods We build species distribution models using occurrence data from the native and introduced distribution ranges to identify putative niche shifts and further ascertain the areas climatically suitable for the establishment and possible spread of mosquitofish.
Results We found significant niche expansions into climatic regions outside their natural climatic conditions, emphasizing the importance of integrating climatic niches of both native and invasive ranges into projections. In particular, there was a marked shift toward tropical regions in Asia and a clear niche shift of European G. holbrooki. This ecological flexibility partly explains the massive success of the two species, and substantially increases the risk for further range expansion. We also showed that the potential for additional expansion resulting from climate change is enormous—especially in Europe.
Main conclusions Despite the successful invasion history and ongoing range expansions, many countries still lack proper preventive measures. Thus, we urge policy makers to carefully evaluate the risk both mosquitofish pose to a particular area and to initiate appropriate management strategies.
Biological invasions have been associated with niche changes; however, their occurrence is still debated. We assess whether climatic niches between native and non-native ranges have changed during the invasion process using two globally spread mosquitoes as model species, Aedes albopictus and Aedes aegypti. Considering the different time spans since their invasions (>300 vs. 30–40 years), niche changes were expected to be more likely for Ae. aegypti than for Ae. albopictus. We used temperature and precipitation variables as descriptors for the realized climatic niches and different niche metrics to detect niche dynamics in the native and non-native ranges. High niche stability, therefore, no niche expansion but niche conservatism was revealed for both species. High niche unfilling for Ae. albopictus indicates a great potential for further expansion. Highest niche occupancies in non-native ranges occurred either under more temperate (North America, Europe) or tropical conditions (South America, Africa). Aedes aegypti has been able to fill its native climatic niche in the non-native ranges, with very low unfilling. Our results challenge the assumption of rapid evolutionary change of climatic niches as a requirement for global invasions but support the use of native range-based niche models to project future invasion risk on a large scale.
Background: More than 170 species of tabanids are known in Europe, with many occurring only in limited areas or having become very rare in the last decades. They continue to spread various diseases in animals and are responsible for livestock losses in developing countries. The current monitoring and recording of horseflies is mainly conducted throughout central Europe, with varying degrees of frequency depending on the country. To the detriment of tabanid research, little cooperation exists between western European and Eurasian countries.
Methods: For these reasons, we have compiled available sources in order to generate as complete a dataset as possible of six horsefly species common in Europe. We chose Haematopota pluvialis, Chrysops relictus, C. caecutiens, Tabanus bromius, T. bovinus and T. sudeticus as ubiquitous and abundant species within Europe. The aim of this study is to estimate the distribution, land cover usage and niches of these species. We used a surface-range envelope (SRE) model in accordance with our hypothesis of an underestimated distribution based on Eurocentric monitoring regimes.
Results: Our results show that all six species have a wide range in Eurasia, have a broad climatic niche and can therefore be considered as widespread generalists. Areas with modelled habitat suitability cover the observed distribution and go far beyond these. This supports our assumption that the current state of tabanid monitoring and the recorded distribution significantly underestimates the actual distribution. Our results show that the species can withstand extreme weather and climatic conditions and can be found in areas with only a few frost-free months per year. Additionally, our results reveal that species prefer certain land-cover environments and avoid other land-cover types.
Conclusions: The SRE model is an effective tool to calculate the distribution of species that are well monitored in some areas but poorly in others. Our results support the hypothesis that the available distribution data underestimate the actual distribution of the surveyed species.
Environmental niche modelling is an acclaimed method for estimating species’ present or future distributions. However, in marine environments the assembly of representative data from reliable and unbiased occurrences is challenging. Here, we aimed to model the environmental niche and distribution of marine, parasitic nematodes from the Pseudoterranova decipiens complex using the software Maxent. The distribution of these potentially zoonotic species is of interest, because they infect the muscle tissue of host species targeted by fisheries. To achieve the best possible model, we used two different approaches. The land distance (LD) model was based on abiotic data, whereas the definitive host distance (DHD) model included species-specific biotic data. To assess whether DHD is a suitable descriptor for Pseudoterranova spp., the niches of the parasites and their respective definitive hosts were analysed using ecospat. The performance of LD and DHD was compared based on the variables’ contribution to the model. The DHD-model clearly outperformed the LD-model. While the LD-model gave an estimate of the parasites’ niches, it only showed the potential distribution. The DHD-model produced an estimate of the species’ realised distribution and indicated that biotic variables can help to improve the modelling of data-poor, marine species.