Jolyon M. Medlock

Driving forces for changes in geographical distribution of Ixodes ricinus ticks in Europe

Many factors are involved in determining the latitudinal and altitudinal spread of the important tick vector Ixodes ricinus (Acari: Ixodidae) in Europe, as well as in changes in the distribution within its prior endemic zones. This paper builds on published literature and unpublished expert opinion from the VBORNET network with the aim of reviewing the evidence for these changes in Europe and discusses the many climatic, ecological, landscape and anthropogenic drivers. These can be divided into those directly related to climatic change, contributing to an expansion in the tick’s geographic range at extremes of altitude in central Europe, and at extremes of latitude in Scandinavia; those related to changes in the distribution of tick hosts, particularly roe deer and other cervids; other ecological changes such as habitat connectivity and changes in land management; and finally, anthropogenically induced changes. These factors are strongly interlinked and often not well quantified. Although a change in climate plays an important role in certain geographic regions, for much of Europe it is non-climatic factors that are becoming increasingly important. How we manage habitats on a landscape scale, and the changes in the distribution and abundance of tick hosts are important considerations during our assessment and management of the public health risks associated with ticks and tick-borne disease issues in 21st century Europe. Better understanding and mapping of the spread of I. ricinus (and changes in its abundance) is, however, essential to assess the risk of the spread of infections transmitted by this vector species. Enhanced tick surveillance with harmonized approaches for comparison of data enabling the follow-up of trends at EU level will improve the messages on risk related to tick-borne diseases to policy makers, other stake holders and to the general public.

A review of the invasive mosquitoes in Europe: Ecology, public health risks, and control options

There has been growing interest in Europe in recent years in the establishment and spread of invasive mosquitoes, notably the incursion of Aedes albopictus through the international trade in used tires and lucky bamboo, with onward spread within Europe through ground transport. More recently, five other non-European aedine mosquito species have been found in Europe, and in some cases populations have established locally and are spreading. Concerns have been raised about the involvement of these mosquito species in transmission cycles of pathogens of public health importance, and these concerns were borne out following the outbreak of chikungunya fever in Italy in 2007, and subsequent autochthonous cases of dengue fever in France and Croatia in 2010. This article reviews current understanding of all exotic (five introduced invasive and one intercepted) aedine species in Europe, highlighting the known import pathways, biotic and abiotic constraints for establishment, control strategies, and public health significance, and encourages Europe-wide surveillance for invasive mosquitoes.

Potential Impact of Antiviral Drug Use during Influenza Pandemic

Impact of different antiviral treatment strategies on hospitalizations during an influenza pandemic is evaluated.

Suitability of European climate for the Asian tiger mosquito Aedes albopictus: recent trends and future scenarios

The Asian tiger mosquito (Aedes albopictus) is an invasive species that has the potential to transmit infectious diseases such as dengue and chikungunya fever. Using high-resolution observations and regional climate model scenarios for the future, we investigated the suitability of Europe for A. albopictus using both recent climate and future climate conditions. The results show that southern France, northern Italy, the northern coast of Spain, the eastern coast of the Adriatic Sea and western Turkey were climatically suitable areas for the establishment of the mosquito during the 1960–1980s. Over the last two decades, climate conditions have become more suitable for the mosquito over central northwestern Europe (Benelux, western Germany) and the Balkans, while they have become less suitable over southern Spain. Similar trends are likely in the future, with an increased risk simulated over northern Europe and slightly decreased risk over southern Europe. These distribution shifts are related to wetter and warmer conditions favouring the overwintering of A. albopictus in the north, and drier and warmer summers that might limit its southward expansion.

Potential transmission of West Nile virus in the British Isles: an ecological review of candidate mosquito bridge vectors

Abstract.  West Nile virus (WNV) transmitted by mosquitoes (Diptera: Culicidae) infects various vertebrates, being pathogenic for birds, horses and humans. After its discovery in tropical Africa, sporadic outbreaks of WNV occurred during recent decades in Eurasia, but not the British Isles * . WNV reached New York in 1999 and spread to California by 2003, causing widespread outbreaks of West Nile encephalitis across North America, transmitted by many species of mosquitoes, mainly Culex spp. The periodic reappearance of WNV in parts of continental Europe (from southern France to Romania) gives rise to concern over the possibility of WNV invading the British Isles.

Public health significance of invasive mosquitoes in Europe

There are currently five invasive Aedes mosquito species known to be established in Europe, namely Aedes albopictus, Aedes aegypti, Aedes japonicus, Aedes atropalpus and Aedes koreicus. Aedes albopictus and Aedes aegypti are the incriminated vectors in the recent outbreaks of chikungunya and dengue fever in Europe. However, both laboratory experiments and field observations indicate that these invasive mosquitoes have a potential to also transmit other pathogens of public health importance. Increasing travel and pathogen introduction, expansion of vector distribution, and both environmental and climatic changes are likely to raise the risk of pathogen transmission by these invasive Aedes mosquitoes. Their vector status and their involvement in pathogen transmission are dynamic processes that shape the future of mosquito-borne disease epidemiology in Europe. Beside vector surveillance, enhanced disease surveillance will enable the early detection of cases and the prompt implementation of control measures.

Analysis of the potential for survival and seasonal activity of Aedes albopictus (Diptera: Culicidae) in the United Kingdom.

ABSTRACT The international trade in used tires, coupled with the ability to lay non-desiccating eggs, has enabled Aedes albopictus (Skuse) (Diptera: Culicidae) to travel and establish on new continents, including North, Central, and South America, the Caribbean, Australasia, Africa, and Europe. Concerns have been raised over its potential role in the transmission of arboviruses and Dirofilaria nematodes. Following importation into northerly latitudes, photoperiodicallyinduced egg diapause enables establishment of Ae. albopictus, and a number of abiotic factors determine the subsequent seasonal activity. The United Kingdom (U.K.) imports over 5 million used tires annually, and this seems the most likely route by which Ae. albopictus would be imported. The anthropophilic and container-breeding nature of Ae. albopictus could cause an urban human biting nuisance and the potential for involvement in (human and veterinary) disease transmission cycles needs to be assessed. This paper addresses the likelihood for importation of Ae. albopictus into the U.K. and assesses, using a Geographic Information Systems (GIS)-based model, the ability for Ae. albopictus to establish, and the likely seasonal activity. It also reviews its possible role as a potential disease vector in the U.K.. The model predicts that abiotic risk factors would permit establishment of Ae. albopictus throughout large parts of lowland U.K., with at least four to five months of adult activity (May–September), being more prolonged in the urban centers around London and the southern coastal ports. Pre-emptive surveillance of possible imported Ae. albopictus, through a targeted approach, could prevent the establishment of this exotic mosquito and mitigate any subsequent human and animal health implications for the U.K., either now or in the future.

Effect of climate change on vector-borne disease risk in the UK

During the early part of the 21st century, an unprecedented change in the status of vector-borne disease in Europe has occurred. Invasive mosquitoes have become widely established across Europe, with subsequent transmission and outbreaks of dengue and chikungunya virus. Malaria has re-emerged in Greece, and West Nile virus has emerged throughout parts of eastern Europe. Tick-borne diseases, such as Lyme disease, continue to increase, or, in the case of tick-borne encephalitis and Crimean-Congo haemorrhagic fever viruses, have changed their geographical distribution. From a veterinary perspective, the emergence of Bluetongue and Schmallenberg viruses show that northern Europe is equally susceptible to transmission of vector-borne disease. These changes are in part due to increased globalisation, with intercontinental air travel and global shipping transport creating new opportunities for invasive vectors and pathogens. However, changes in vector distributions are being driven by climatic changes and changes in land use, infrastructure, and the environment. In this Review, we summarise the risks posed by vector-borne diseases in the present and the future from a UK perspective, and assess the likely effects of climate change and, where appropriate, climate-change adaptation strategies on vector-borne disease risk in the UK. Lessons from the outbreaks of West Nile virus in North America and chikungunya in the Caribbean emphasise the need to assess future vector-borne disease risks and prepare contingencies for future outbreaks. Ensuring that adaptation strategies for climate change do not inadvertently exacerbate risks should be a primary focus for decision makers.

Prevalence of Neoehrlichia mikurensis in ticks and rodents from North-west Europe.

BackgroundNeoehrlichia mikurensis s an emerging and vector-borne zoonosis: The first human disease cases were reported in 2010. Limited information is available about the prevalence and distribution of Neoehrlichia mikurensis in Europe, its natural life cycle and reservoir hosts. An Ehrlichia-like schotti variant has been described in questing Ixodes ricinus ticks, which could be identical to Neoehrlichia mikurensis.MethodsThree genetic markers, 16S rDNA, gltA and GroEL, of Ehrlichia schotti-positive tick lysates were amplified, sequenced and compared to sequences from Neoehrlichia mikurensis. Based on these DNA sequences, a multiplex real-time PCR was developed to specifically detect Neoehrlichia mikurensis in combination with Anaplasma phagocytophilum in tick lysates. Various tick species from different life-stages, particularly Ixodes ricinus nymphs, were collected from the vegetation or wildlife. Tick lysates and DNA derived from organs of wild rodents were tested by PCR-based methods for the presence of Neoehrlichia mikurensis. Prevalence of Neoehrlichia mikurensis was calculated together with confidence intervals using Fishers exact test.ResultsThe three genetic markers of Ehrlichia schotti-positive field isolates were similar or identical to Neoehrlichia mikurensis. Neoehrlichia mikurensis was found to be ubiquitously spread in the Netherlands and Belgium, but was not detected in the 401 tick samples from the UK. Neoehrlichia mikurensis was found in nymphs and adult Ixodes ricinus ticks, but neither in their larvae, nor in any other tick species tested. Neoehrlichia mikurensis was detected in diverse organs of some rodent species. Engorging ticks from red deer, European mouflon, wild boar and sheep were found positive for Neoehrlichia mikurensis.ConclusionsEhrlichia schotti is similar, if not identical, to Neoehrlichia mikurensis. Neoehrlichia mikurensis is present in questing Ixodes ricinus ticks throughout the Netherlands and Belgium. We propose that Ixodes ricinus can transstadially, but not transovarially, transmit this microorganism, and that different rodent species may act as reservoir hosts. These data further imply that wildlife and humans are frequently exposed to Neoehrlichia mikurensis- infected ticks through tick bites. Future studies should aim to investigate to what extent Neoehrlichia mikurensis poses a risk to public health.

Tick surveillance in Great Britain.

The ability for public/veterinary health agencies to assess the risks posed by tick-borne pathogens is reliant on an understanding of the main tick vector species. Crucially, the status, distribution, and changing trends in tick distribution and abundance are implicit requirements of any risk assessment; however, this is contingent on the quality of tick distribution data. Since 2005 the Health Protection Agency has promoted an enhanced tick surveillance program. Through engagement with a variety of public and veterinary health agencies and practitioners (e.g., clinicians and veterinarians), wildlife groups (deer society, zoos, animal refuge centers, and academics), and amateur entomologists, >4000 ticks from 900 separate records across Great Britain have been submitted, representing 14 tick species (Ixodes ricinus, Ixodes hexagonus, Ixodes acuminatus, Ixodes arboricola, Ixodes canisuga, Ixodes frontalis, Ixodes lividus, Ixodes trianguliceps, Ixodes ventalloi, Carios vespertilionis, Dermacentor reticulatus, Haemaphysalis punctata, Hyalomma marginatum, and Amblyomma species). The majority of ticks submitted were I. ricinus (81%), followed by I. hexagonus (10%) and I. frontalis (2.5%). Predominant host groups include companion animals (411 records), humans (198 records), wild birds (111 records), and large wild mammals (88 records), with records also from small/medium wild mammals, livestock, the environment and domestic/aviary birds. The scheme has elucidated the detection of two nonnative tick species, the expansion of previously geographically restricted D. reticulatus and produced ground data on the spread of I. ricinus in southwest England. It has also provided a forum for submission of ticks from the concerned public and particularly those infected with Lyme borreliosis, thus raising awareness among public health agencies of the increased peri-urban tick problem in Britain. Our results demonstrate that it is possible to run a cost-effective nationwide surveillance program to successfully monitor endemic tick species, identify subtle changes in their distribution, and detect the arrival and presence of exotic species.