Evidence for changes in the occurrence, frequency or severity of human health impacts resulting from exposure to alien species in Europe: a systematic map
© The Author(s) 2017
Received: 17 January 2017
Accepted: 27 July 2017
Published: 22 August 2017
Alien species are frequently considered a serious environmental threat but negative impacts on human health through injury, allergy, or as vectors of disease sometimes have the most dire consequences for human livelihoods. Climate change and the increasing magnitude and frequency of introductions of species across geographic barriers as a result of international trade are likely to change their establishment, spread, abundance, physiology or phenology, potentially also altering their human health impacts. Yet despite receiving increasing attention in the scientific literature, there have been few attempts to quantify recent changes in human health impacts. Here we report the findings from a systematic map of the literature identifying evidence of any change in the occurrence, frequency or severity of impacts of alien species on human health in Europe over the last 25 years.
We conducted a systematic search of the ecological and medical literature using English language search terms to identify potentially relevant studies. Search results were assessed against inclusion criteria published in an a priori protocol at title, abstract and full-text to determine their suitability for inclusion in the review. Repeatability was checked at each stage by comparing a subset between reviewers and testing for inter-rater agreement using Cohen’s kappa test. Studies deemed relevant at full text were coded against bibliographic, inclusion and study design criteria to create a searchable database of evidence.
Searches retrieved over 15,700 results yet only sixteen cases met criteria for inclusion in the systematic map. Most of this evidence represents first records of impacts from different areas, and in particular first reports of transmission of exotic diseases by introduced mosquito species.
There is currently limited published evidence demonstrating a change in the occurrence, frequency or severity of human health impacts caused by alien species in Europe over the last 25 years. Relevant studies relate to only a few species, often report specific cases and rarely link health impacts with ecology, distribution or spread of the species. Difficulties in attributing human health impacts, such as stings or allergies, to a specific alien species likely complicate attempts to measure changes, as may differences in professional interests between the environmental and health professions. Future studies could helpfully compare spread or abundance with reported, rather than potential, health impacts. Better cooperation between invasion ecologists and health professionals working in affected areas are likely to be necessary to improve the evidence base on this topic for the future.
Types of health impacts associated with contact with alien plants and animals considered within the remit of this systematic map
Type of contact
Example impacts associated with alien plant species
Example impacts associated with alien animal species
Impacts arising from direct contact
Skin blistering resulting from contact with Heracleum mantegazzianum sap
Bites e.g. from Aedes albopictus; stings from Vespa velutina
Impacts arising from indirect contact
Allergic rhinitis resulting from contact with pollen from Ambrosia artemisiifolia
Pseudo allergic reaction to urticating setae produced by Thaumetopoea processionea
Impacts arising from the transmission of pests or pathogens by the alien species
Malaria from introduced mosquito bites; Lyme disease transmitted by ticks spread by Eutamias sibiricus
To date, there have been few attempts to systematically identify or quantify the extent of alien species impacts on human health. A recent review by Schindler et al.  found that most articles describe the types of health impacts without quantitative assessment of numbers of people affected. Further, research on this topic appears biased towards a few species, hindering a balanced understanding of the scale, patterns and trends of these impacts [1, 3]. This bias towards a small number of species is problematic as the information may not be generalisable to other species, meaning that emerging risks to public health may not be fully recognised . Without this information, it will prove challenging to prepare appropriate and timely environmental or public health responses to emerging threats in the face of climate change.
Despite receiving increasing attention in the scientific literature, there have been few attempts to quantify recent changes in the human health impacts of alien species. To address this, we report the findings from a systematic mapping of the literature identifying evidence of any change in the occurrence, frequency or severity of impacts of alien species on human health in Europe over the last 25 years.
Objective of the review
- Primary question::
What evidence exists for changes in the occurrence, severity or frequency of human health impacts resulting from exposure to alien species in Europe?
Any human population resident in Europe
Contact with species alien to all or part of Europe
No contact or more/less frequent or severe contact
Change in the occurrence, frequency or severity of health impacts in human populations since 1990
This systematic map was conducted in accordance with the CEE Guidelines for Systematic Review and Evidence Synthesis in Environmental Management Version 4.2  to methods specified a priori in a previously published protocol . Following publication of the protocol, study inclusion criteria were subsequently refined to improve consistency in reviewer screening, as detailed in the Study inclusion criteria section below.
A comprehensive search of multiple information sources attempted to capture an un-biased sample of both published and grey literature, using terms and sources identified during scoping and tested for comprehensiveness using a sample of relevant known studies . All searches were conducted in 2015 by HB, MA and SS. Full details of all of the searches, including dates, sources, platforms, terms, numbers of results generated and destination of retrieved records are reported in Additional file 1.
Search terms relating to both alien species and their human health impacts were used to identify potentially relevant studies. Due to the different search functionalities of the sources used the exact search strings deployed varied across databases. Full details of each search string, including any wildcards, Boolean operators (e.g. AND or OR), nesting (brackets), phrase searching and limits used, are provided in Additional file 1. Exposure search terms included in combination: “invasive species”; alien; “non-native”; exotic; “introduced species”; “non-indigenous” and weed. Outcome search terms included in combination: allerg*; hay-fever; asthma; dermatitis; bite; biting; sting*; toxic*; poison*; venom*; irrita*; disease; outbreak; epidemic; parasit*; vector; host; reservoir; “human health” and “public health”. Although the use of subject headings such as MeSH was considered, they were not used during the searches for this systematic map. However, this could be addressed in future updates or in other maps using similar search sources.
The systematic map searches encompassed eight online bibliographic databases (Web of Science; MEDLINE; CINAHL; CAB Direct including CAB Abstracts and Global Health; EMBASE; SCOPUS; TOXNET including DART (Developmental and Reproductive Toxicology); Armed Forces Pest Management Board Literature Retrieval System), Google Scholar to help identify grey or recently published literature, and a range of specialist sources relating to either health or alien species (see Additional file 1 for full details of all sources searched). Alien species databases were searched using the species names identified in the protocol and cited references screened for potentially relevant articles.
In addition, recent issues of three alien species journals not yet indexed in Web of Science (NeoBiota, Management of Biological Invasions and Bioinvasion Records) were hand searched by screening at title all articles to identify any potentially relevant to the systematic map topic. Online early articles (prior to allocation in an issue) as well as the most recent three issues of two other journals (Biological Invasions and Aquatic Invasions) were also hand screened to account for time lags in articles being indexed in the bibliographic databases.
References contained within review articles identified either during scoping or during the screening of the systematic map search results were checked for additional relevant studies that may have been missed.
Reference management and recording
Results of the bibliographic database searches and the first 100 hits from the Google Scholar searches were exported into RefWorks reference management software. Search results were later transferred to EndNote referencing software to allow for offline screening and enhanced sharing of files between the project team. All other search results were screened online at title and any potentially relevant results were recorded in a spreadsheet.
Study inclusion criteria
Any human population resident in Europe.
Contact with species alien to Europe or being native in parts of Europe but alien to others that cause negative impacts on human health. Here we define alien species as species transported by direct or indirect human agency beyond the biogeographic limits of their past or present geographic ranges into areas in which they do not naturally occur [11, 12]. For the purposes of this map, we included alien vector species (e.g. mosquitos, ticks, sandflies), which may carry and transmit infectious pathogens to humans, and alien reservoir species (e.g. mammals, birds and reptiles), which are intermediate or long-term hosts of pathogens of infectious diseases (categories 1b, 2a, 2b and 2c under the framework identified by ). We excluded pathogens, pets, domestic or exotic animals that have direct impacts (e.g. bites from exotic snakes in captivity) or that serve as vectors or reservoirs, poisonous species imported for consumption and European species that do not fall under the definition of alien species above.
No contact or less frequent or severe contact. Any time series or spatial comparison.
Change in the occurrence, frequency or severity of health impacts in human populations since 1990 .
- Study design::
All study designs were included that provided sufficient data to meet the other systematic map inclusion criteria, as long as the study period took place including or since 1990. Studies published after 1990 but completed prior to this date were not included.
Tests for consistency
Tests for consistency between reviewers were conducted at the title, abstract and full text stages of article screening.
A subset of 100 titles randomly generated using the Excel random number generator function were assessed by three reviewers prior to title screening to ensure that the inclusion criteria would be applied consistently (HB, SS and MA). Scores were compared using Cohen’s Kappa test , and inter-reviewer scores were fair-to-moderate (0.232, 0.441 and 0.513 between reviewer-pairs; 56% overall reviewer agreement). All titles without agreement across all three reviewers were discussed to determine which should be included or excluded; disagreements generally resulted from either a difference of opinion as to how generally the criteria should be applied or a difference in reviewer knowledge (for example if a reviewer was unsure of whether a location or a species met the inclusion criteria they might keep in an article for further checking that had been excluded by the other reviewers). This resulted in a refined understanding of the inclusion criteria, as reflected above.
A second set of 100 references, randomly generated in the same way as the first set, were also assessed at title by the same reviewers to measure whether inter-rater agreement had improved following refinement of the criteria. Kappa scores were good (0.658, 0.718 and 0.650) with 82% complete agreement between reviewers, suggesting an improvement in consistency as to how the inclusion criteria were applied.
A further set of 100 randomly selected abstracts were assessed independently by all three reviewers and inter-rater agreement again scored using Cohen’s kappa test. Reviewers were in complete agreement over 63% of the abstracts (either scored Y/Y/Y or N/N/N). Kappa scores were moderate to good (0.518; 0.733 and 0.579 between reviewer-pairs).
All articles selected as meeting the review inclusion criteria at full-text and subjected to study coding were assessed independently by two reviewers to check for consistency and any discrepancies discussed with a third reviewer if agreement could not be reached. Any articles that were identified for full text assessment but were either unavailable to the review team or were excluded for failing to meet the inclusion criteria at full text are listed in Additional file 2, along with reasons for their exclusion. The number of studies included or excluded at each stage of the systematic mapping process were recorded in a flowchart.
Study quality assessment
Included studies were not critically appraised using an existing study quality tool as data resulted from unintentional exposures to the alien species rather than as a result of intentional experimental manipulation. However, details relating to the study that could be used to infer quality (for example, study type, study design, spatial scale, comparators and timescale as applicable) were coded as part of the systematic mapping process. Simple descriptive statistics relating to these details were generated in Excel to provide an overview of the quality of the available evidence.
Data coding strategy
Categories used for coding studies included in the systematic map at full text
Type of data
1. Bibliographic information
a. Publication type
2. Information relating to the inclusion criteria
a. Population i: Human population affected
b. Population ii: Location of exposure
c. Population iii: Location of reported impact
d. Population iv: Activity of population at exposure
e. Exposure i: Taxonomic group of the alien species
f. Exposure ii: Species name (binomial) of the alien species
g. Exposure iii: Biome at location of exposure
h. Exposure iv: Habitat at location of exposure
i. Outcome i: Type of human health impact (disease or pathogen transmission/allergen or irritant)
j. Outcome ii: Specific condition (type of injury, allergy, dermatitis, disease)
k. Outcome iii: Change in human health impact (occurrence/frequency/severity)
3. Information relating to the study
a. Study type (e.g. patient case study, RCT)
b. Study design (sampling size, etc.)
c. Spatial scale of reported impact
f. Other factors affecting the outcome
4. Additional information relating to the species of concern
a. Geographic origin (native range)
b. Pathway(s) of introduction (following the classification of Hulme et al. )
Once relevant studies were assessed, coded and checked by a second reviewer, the data were included in a searchable spreadsheet detailing each of the coded variables. Simple descriptive statistics relating to key trends in the final dataset were generated in Excel for presentation in the final systematic map report.
Review descriptive statistics
Mapping the quantity of papers relevant to the question
Summary of studies demonstrating a change in the occurrence, frequency or severity of human health impacts resulting from exposure to alien species in Europe
Disease transmission—dengue fever
Outbreak with 1891 cases of dengue fever in 2012 following introduction of A. aegypti in 2005
Disease transmission—dengue fever
Two cases of Dengue fever presented in adult males in France with no recent history of international travel. A. albopictus has been established since 2004
Disease transmission—dengue fever
Two cases of dengue fever in Croatia, one in a German tourist and a second in a local resident, were identified in 2010. Serological assessment suggested at least seven other recent cases. A. albopictus was first recorded in Croatia in 2004
Disease transmission—Chikungunya virus
Over 200 cases in two contiguous villages in Italy. In most cases the disease was fairly mild, with one reported death. The virus was identified in A. albopictus suggesting local transmission
Disease transmission—Chikungunya virus
Two female children developed Chikungunya after being bitten at a sleep over near to an imported case, suggesting local transmission
Several reports of biting and nuisance behaviour identified as recently established A. japonicus
Of 13,719 atopic patients diagnosed between 1997 and 2007, the frequency of ragweed pollen sensitization increased from 8.5% in 1997 to 17.5% in 2007
Increase in the proportion of patients aged <20 years becoming allergic to ragweed was observed in a study of 665 patients over 15 years, from 0% 1990–1996 to 18% during the last 10 years
Twenty A. artemisiifolia scouts (tasked with finding and eliminating the weed) were assessed, and despite close contact to A. artemisiifolia over a median of 13.8 months, none of the participants became sensitized or allergic to it
No evidence of nuisance biting attributable to alien mosquitoes over a 10 year period according to a survey of local authorities
Respiratory problems and skin irritation
First cases reported in 2003/2004, in 2005 around 200 people affected by respiratory symptoms resulting from exposure to sea spray containing toxins from O. ovata
* after 
Respiratory problems and skin irritation
Multiple cases resulting from exposure to O. ovata toxins
Respiratory problems and skin irritation
Five out of nine recorded blooms between 2006 and 2009 led to symptoms in divers, swimmers, and shoreline inhabitants, with a total of 47 patients presenting symptoms
Numerous cases of itchy rashes reported to the environmental health officer associated with T. processionea caterpillars on nearby oak trees
A survey of French poison centres in 20 Departments showed no increase in the number of reported hymenoptera stings following the introduction of V. velutina
One case report where a patient suffered severe symptoms after being stung by V. velutina 12 times on the head
Evidence also suggests that harmful blooms of alien unicellular algae such as Ostreopsis species are causing significant health impacts along European coasts, with cases reported from Italy [21, 22], Spain and France [23, 24]. Numbers affected ranged from only a handful of cases to over two hundred depending on the outbreak. Those affected were beach users involved in a range of recreational activities including swimming and diving, and suffered from both respiratory problems and skin irritations following contact that regressed over time .
Not all studies present first reports of impacts. Several large-scale long term studies of individuals with allergic symptoms demonstrate changes in sensitisation levels to Ambrosia artemisiifolia among the general population across Europe, indicating that levels of sensitisation are rising and the proportion of young people sensitised is increasing [25, 26]. However, Brandt et al.  found no sensitisation or allergy development in a sample of 20 ragweed workers resulting from exposure to A. artemisiifolia.
Other studies demonstrated no significant change in impacts over time. De Haro et al.  reported no increase in the number of hospitalisations resulting from envenomations following the introduction of Vespa velutina to France, although evidence that at least one envenomation has occurred exists, and similarly, Medlock et al.  reported no calls to local authorities resulting from nuisance biting caused by non-native mosquito species in England (all calls were for native species). However, in Switzerland, reports of nuisance biting from the mosquito Aedes japonicus were reported following introduction .
The main pathways of arrival of the alien species with health impacts included in this map are as contaminants or as stowaways, originating from Asia, North America and Africa.
Mapping the quality of papers relevant to the question
Most papers included in the systematic map present numbers of patients affected by an illness or outbreak resulting from environmental exposure to an alien species and so many of the features associated with a well-designed scientific experiment are lacking. For example, temporal and geographical scales tend to reflect the extent of the outbreak and comparators are rarely reported. Studies that assess longer term impacts (e.g. Ambrosia [25, 26]) tend to report longer time periods and larger geographic areas but are still reliant on recorded data of impacts. These data reflect only those individuals contacting relevant agencies or reporting symptoms (e.g. to allergy centres), and so anyone affected that did not seek medical attention, or conversely, anyone exposed who did not experience symptoms, will not be represented. Many studies were excluded because there was no attempt to include a temporal comparator.
Perhaps the greatest threat to human health in Europe currently posed by alien species is the transmission of exotic diseases by non-native arthropods. Some pathogens have the potential to significantly affect large numbers of citizens within relatively short time frames, as demonstrated for example by the outbreak of Chikungunya fever in Italy (e.g. ). Despite a relative lack of evidence within this map on allergenic plant species, sensitivity to A. artemisiifolia appears to be increasing in Europe. There is much data available in the literature (for example on pollen loads and season lengths) that suggests the spread of this allergenic species will continue to increase the burden on health care systems resulting from the treatment of long-term allergic conditions. Other health impacts are likely to result from either potentially high contact but temporally and geographically restricted events associated with seasonal abundance of species with cyclic populations, or ad hoc events resulting from random encounters such as envenomations by V. velutina. Increased monitoring and reporting is critical to establish baselines in impact data and identify any geographic and temporal trends.
For many health-relevant alien species, knowledge gaps must be interpreted as lack of accessible data rather than providing evidence of no impact. It may be the case that evidence exists but it is not accessible using standard systematic reviewing or mapping methodologies, and that alternative methods (for example, compiling data from press reports or accessing national medical records or databases) must be used to increase the information available in this area. For many alien species, existing evidence of health impacts did not fit the inclusion criteria for this map (for example ad hoc case reports referring to injuries sustained following contact with H. mantegazzianum as mentioned above) and this may be a suitable topic for a future evidence map to help quantify the health impacts of alien species. Regardless, a lack of baseline data on the health impacts of alien species is concerning as without this evidence it is difficult to establish how much of a risk these species pose to human health currently and in the foreseeable future and therefore to determine an appropriate management response. Further, without a better understanding of which species pose a tangible threat and where, it is difficult to justify or target awareness raising measures for relevant primary care workers, meaning that patients may not receive an accurate or as rapid diagnosis as possible.
Individual case reports. Although these case reports provide valuable evidence that a given species is having an impact (e.g. ), they do not represent the magnitude of effects or whether changes are occurring, and as ad hoc events do not provide an accurate baseline against which to measure future changes. An exception is where a case report represents the first report of an impact from a new area as it shows that the alien species is present where it previously was not. This information was included in the map.
Studies looking at vector competence. Evidence that specific species can carry and transmit particular diseases (or evidence for feeding on different hosts) is likely to be valuable when assessing the potential risks posed by introduced vector species but does not provide evidence of an impact and so has not been included here.
Studies looking at levels of sensitivity or reactivity to allergenic substances without a comparator. For example, studies showing the prevalence of sensitivity to A. artemisiifolia would not be included unless there was evidence that levels of sensitivity had changed over time or due to exposure.
Studies on captive animals. There are studies providing data on the human health risks associated with captive animals, and predominantly exotic pets, for example salmonella transmission (e.g. ) or snake bites (e.g. ). However, the circumstances under which health may be affected when dealing with a captive animal may be very different from the circumstances in which the species may be encountered in the wild, meaning that the risk of injury or disease transmission is likely to be different.
Impacts caused by exotic diseases that have been contracted by humans returning from endemic areas, unless there appears to have been subsequent local spread by alien species (e.g. ).
Impacts resulting from the introduction of free-living microorganisms that may pose a threat to human health when accidentally imported. For example, a number of harmful microorganisms have been transported internationally in ballast water (e.g. [36, 37]).
Impacts resulting from intentional ingestion of alien species. For example, Datura stramonium is sometimes consumed recreationally for its hallucinogenic effects, and has been implicated in hospitalisations both within Europe  and elsewhere (e.g. [39, 40]). Although the number of voluntary poisonings resulting from D. stramonium consumption in France appears to be increasing , the reasons for this are complex and may relate to increasing popularity among recreational drug users rather than abundance in the wild.
Studies that deal with health-relevant alien species, but not with their explicit health impacts, even if some covered topics such as management costs or impacts of global change.
Given the limited evidence base available, it is difficult to currently assess the extent of the impacts of alien species on human health, let alone determine whether global change is driving changes in the occurrence, frequency or severity of human health impacts and, if so, in which directions. Better linking between data on spread/abundance and human health impacts over time (and ideally from the point of introduction onwards for species that are not yet established or still spreading) are required to explore this issue further, and are likely to require collaborative approaches between the environmental and the health communities. The taxonomic and geographical biases in the available data make it difficult to draw broader conclusions about changes in health impacts as they may not transfer across species or regions. For established alien species that are widespread, studies correlating health impacts against abundance or comparing different climatic conditions (such as annual rainfall) or management regimes on health outcomes may be valuable in helping to determine their impacts. For more recently introduced species, studies mapping health impacts may help to monitor spread, focus awareness raising activities aimed at minimising exposure, and provide justification for action aimed at containing the species within a restricted area if eradication is not possible. However, this research suggests that these types of studies are still relatively rare in the scientific literature.
Limitations of the map
Systematic reviews and maps aim to undertake comprehensive searches using bibliographic databases, but it is impossible to undertake exhaustive searches of all potentially relevant sources due to resourcing and language constraints. Even within the results retrieved for this systematic map, there are a number of studies that were unobtainable or published in languages other than English, and so have not been included in the final evidence base. As with any systematic review or map, it is also possible that some relevant studies may have been missed during the searching or screening processes as a result of human error, unclear reporting by the primary authors or use of different terminology from that used here. Further, studies in which relevant species are grouped generally with other (native) species are unlikely to have been detected without specific reference to the search terms identified here. However, this map provides the most comprehensive collection of evidence on this topic to date, and highlights some important limitations that need to be addressed to develop this evidence base in the future.
Revisiting the conceptual model
We believe the conceptual model originally presented in our protocol, although simplistic, to be generally correct. However, we expand it out to include the different types of data that relate to each of the components (Fig. 3) and highlight knowledge gaps and opportunities for future research. The topic of this systematic map (in red in Fig. 3) suggests that there have been relatively few studies directly linking either changes in the abundance or spread of alien species with the human health impacts with which they are associated. However, other areas identified within our conceptual diagram—effectiveness of management of either species or health impacts—are potential topics for further study. For example, data exist on the effectiveness of management of A. artemisiifolia (e.g. [41–43]) and on the effectiveness of treatments for allergies caused by Ambrosia pollen and may prove valuable areas to pursue in future systematic reviews.
Future updating of the map
Now that the first systematic map on this topic has been completed, future updates to the map should be relatively straightforward. However, given the lack of suitable data identified on this topic at the current time, there are no plans to conduct an update in the near future. Running and title screening the searches in the core databases over a restricted time period should provide an idea as to whether there is much potential evidence being published and should be undertaken before an update is commenced.
There is some evidence for changes in the human health impacts of alien species within Europe over the last 25 years. However, compared to the relevance of the topic for human well-being (e.g. ), there are few studies demonstrating changes in health impacts over time mapped to changing spread or abundance of the alien species. Relevant studies relate to only a few species, often report specific cases or outbreaks, and rarely link health impacts with ecology, distribution or spread of the species, or with public health. Difficulties in attributing human health impacts such as stings or allergies to a specific species likely complicate attempts to measure changes, as do different research interests between ecologists and health professionals. Better cooperation between invasion ecologists, health professionals and others working in affected areas are likely to be necessary to improve the evidence base on this topic for the future.
Implications for policy/management
There is a clear need for better recording/reporting of impacts to determine whether particular alien species present a human health issue or not, to identify any trends (such as changes in impacts) and to inform policy and management appropriately. We recommend that a precautionary approach is adopted towards species likely to pose a threat to human health, and particularly for those species with demonstrable health impacts noted elsewhere. Prevention, detection and rapid response should be prioritised for species of highest concern and risk not yet present and preparations made to raise awareness among relevant professionals (e.g. doctors, environmental managers) and publics most likely to encounter the species (e.g. swimmers, gardeners as appropriate) to facilitate identification and minimise impacts resulting from exposure. For species already present in an area, more thorough assessment of the scale of impacts to date would be valuable in justifying the case for management (or otherwise), and in helping to inform other areas not yet affected by the potential impacts. Depending on the species of concern, alternative forms of data such as vector competence or population sensitivity may be necessary to underpin prioritisation or management decisions until suitable evidence regarding absolute trends in health impacts have been established.
Implications for health professionals
Better awareness of the issue of alien species with potential health impacts among health professionals may be desirable to aid in diagnosing and, in relevant cases, reporting. In particular, knowledge of emerging threats from species that have been recently introduced or are likely to arrive (so called ‘alert species’) could aid in tracking spread, assessing impacts and prioritising management. Understanding seasonal, temporal and geographical changes in the frequency or severity of symptoms associated with specific species (if possible to determine) could also aid in diagnosis and appropriate treatment. This may require a mechanism by which impacts can be reported and recorded to contribute to an evidence base in this area, similar to those used for notifiable diseases. For now, we strongly advocate that health professionals report unusual health impacts relating to alien species in the scientific literature.
Implications for research
Researchers could helpfully aim to link reported human health impacts with ecological aspects to expand the evidence base on this potentially important topic, rather than studying one or the other in isolation—in particular studies matching data on spread or abundance over time to recorded health impacts would be beneficial (i.e. linking data contained within the red box in Fig. 3), rather than using proxy measures or inferring links. Longer term datasets will prove important in assessing any potential changes in impacts, even if just to compare levels of sensitisation or impact on the population. For example, studies reporting sensitisation rates to Ambrosia or impacts resulting from exposure to harmful algal blooms could usefully include data from multiple years to see whether levels change over time. Also, related areas (for example vector competence) may provide a useful tool for assessing risk but a better understanding of how these translate into actual health impacts is necessary, particularly where actual impacts may differ due to different physical, environmental or climatic conditions between different parts of the affected range. This requires collaborative working between both research communities but may also open up new funding avenues for researchers wishing to conduct studies at the interface between ecology or biogeography and human health.
HB, SS, AP, FE and WR developed the review protocol. HB and MA conducted the searches. HB, SS and MA screened the search results, undertook full text assessment and coded relevant studies for inclusion in the map. HB, SS and AP drafted the review manuscript with input from MA, FE and WR. All authors read and approved the final manuscript.
We thank Hans-Peter Hutter and Peter Wallner and two anonymous referees for comments that informed the review methodology and Bethan O’Leary for assistance with the database searches and Irene Oberleitner for her support in finding full text articles. We thank two referees for their comments that helped refine the final manuscript.
The authors declare that they have no competing interests.
Availability of data and materials
Data generated or analysed during this study are included in this published article and its additional information files. A file containing all 15,776 detected articles is available from the corresponding author on request.
Sources of support
This study was funded under the Austrian Climate and Energy Fund within the Framework of the ACRP Program (Project Number KR13AC6K11141).
Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.
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