M. P. Pfäffle

The ecology of tick-borne diseases

Zoonotic diseases are major causes of infection related morbidity and mortality worldwide. Of the various arthropods capable of transmitting pathogens that cause such diseases to humans, ticks, which are vectors of more kinds of pathogens than any other group of invertebrate, have become an increasing focus of attention. This is particularly the case in the temperate northern hemisphere where they are a significant vector of human disease. Here, we provide an overview of the complex ecological systems defining the various epidemiological cycles of tick-borne diseases. We highlight the abiotic and biotic factors influencing the establishment and persistence of tick populations and their associated pathogens. Furthermore, we emphasize the dynamic nature of such systems, especially when they are under the influence of both small and large-scale anthropogenic changes to the environment. Although a great deal of work has been done on ticks and the diseases which they transmit, the very dynamism of the system means that new factors are continually arising which shift the epidemiological pattern within specific areas. We therefore consider that more detailed, long-term (i.e. at least 10 years), multidisciplinary studies need to be carried out to define why and how these pattern shifts take place and to determine their public health significance.

Occurrence of different Borrelia burgdorferi sensu lato genospecies including B. afzelii, B. bavariensis, and B. spielmanii in hedgehogs (Erinaceus spp.) in Europe.

In order to determine whether European hedgehogs (Erinaceus europaeus and E. roumanicus) play a role in the epidemiological cycle of Borrelia burgdorferi sensu lato in Central Europe and Great Britain, tissue samples of hedgehogs from Germany (n=211), Austria (n=4), the Czech Republic (n=22), and the U.K. (n=32) were tested for the presence of these tick-borne pathogens. PCR for amplification of the B. burgdorferi s.l.-specific 5S-23S intergenic spacer region as well as the outer surface protein A (ospA) gene were used. B. burgdorferi s.l. DNA was detected in 35 of the 259 E. europaeus and in 2 of 10 E. roumanicus. B. burgdorferi prevalences in E. europaeus ranged from 0% (U.K.) to 37.5% (Czech Republic), for E. roumanicus from 0% (Czech Republic) to 50.0% (Austria). Sequencing revealed the occurrence of 3 different B. burgdorferi genospecies in E. europaeus: B. afzelii was the dominant genospecies, followed by B. bavariensis (previously B. garinii OspA serotype 4) and B. spielmanii, the latter was detected for the first time in Hamburg (Germany). B. afzelii and B. bavariensis were also found in E. roumanicus. Our results suggest that hedgehogs modulate the epidemiology of certain species of the B. burgdorferi s.l. complex, potentially affecting the distribution and abundance of individual B. burgdorferi s.l. genospecies in various habitats. We hypothesise that juvenile or individuals with low immune competence in particular, have a high reservoir potential for the 3 genospecies identified here.

Comparative population dynamics of a generalist (Ixodes ricinus) and specialist tick (I. hexagonus) species from European hedgehogs

Although the population dynamics of the tick Ixodes ricinus are relatively well studied, those of other Western European tick species are largely unknown. Moreover, there is very little information related to the interactions between I. ricinus and other ticks. Such knowledge, however, is of special interest in respect to the epidemiology of tick-borne pathogens such as Borrelia spp. We compared the dynamics of the generalist I. ricinus with the nest-dwelling hedgehog specialist, I. hexagonus. Both species were collected from hedgehogs from a naturally infested experimental population between 2006 and 2008. Ticks were collected once a month from March to October from each hedgehog counted and the life history stage and species determined. All hedgehogs harboured both tick species. Nymphs, females and males of I. ricinus showed clear bimodal seasonal distributions with peaks in spring and autumn, while larvae peaked only in summer. The density of I. hexagonus life stages was low during the whole investigation period and seasonal fluctuations of population density were much weaker compared to I. ricinus. Nymphs and larvae showed comparatively little change in population size and no consistent period of peak density. Females showed a single peak in summer and males were found only occasionally on hedgehogs. We suggest density-dependent mechanisms regulating the population density of the specialist I. hexagonus but not of the generalist I. ricinus.

Molecular Detection of Anaplasma phagocytophilum in the European Hedgehog (Erinaceus europaeus) and its Ticks

The European hedgehog (Erinaceus europaeus) is a common wild mammal in Central Europe that shares habitats with humans in urban, peri-urban, and rural areas. Thus, this species may play a role in human contact with zoonotic diseases. Here we report the presence of the pathogen Anaplasma phagocytophilum in hedgehogs and their ticks in Germany.

Analysis of the Population Structure of Anaplasma phagocytophilum Using Multilocus Sequence Typing

Anaplasma phagocytophilum is a Gram-negative obligate intracellular bacterium that replicates in neutrophils. It is transmitted via tick-bite and causes febrile disease in humans and animals. Human granulocytic anaplasmosis is regarded as an emerging infectious disease in North America, Europe and Asia. However, although increasingly detected, it is still rare in Europe. Clinically apparent A. phagocytophilum infections in animals are mainly found in horses, dogs, cats, sheep and cattle. Evidence from cross-infection experiments that A. phagocytophilum isolates of distinct host origin are not uniformly infectious for heterologous hosts has led to several approaches of molecular strain characterization. Unfortunately, the results of these studies are not always easily comparable, because different gene regions and fragment lengths were investigated. Multilocus sequence typing is a widely accepted method for molecular characterization of bacteria. We here provide for the first time a universal typing method that is easily transferable between different laboratories. We validated our approach on an unprecedented large data set of almost 400 A. phagocytophilum strains from humans and animals mostly from Europe. The typability was 74% (284/383). One major clonal complex containing 177 strains was detected. However, 54% (49/90) of the sequence types were not part of a clonal complex indicating that the population structure of A. phagocytophilum is probably semiclonal. All strains from humans, dogs and horses from Europe belonged to the same clonal complex. As canine and equine granulocytic anaplasmosis occurs frequently in Europe, human granulocytic anaplasmosis is likely to be underdiagnosed in Europe. Further, wild boars and hedgehogs may serve as reservoir hosts of the disease in humans and domestic animals in Europe, because their strains belonged to the same clonal complex. In contrast, as they were only distantly related, roe deer, voles and shrews are unlikely to harbor A. phagocytophilum strains infectious for humans, domestic or farm animals.

Tick-induced blood loss leads to regenerative anaemia in the European hedgehog ( Erinaceus europaeus).

Although there is an increasing understanding of the role of parasites in their host dynamics, accurate, quantitative estimates of parasite caused morbidity in wild animals are rare. Here, we examine the possible impact of 2 tick species (Ixodes ricinus, I. hexagonus) on the condition of the European hedgehog (Erinaceus europaeus). For this, we tested for correlations between blood parameters of 36 adult hedgehogs from an experimental population enclosed in a natural habitat and their tick infestation over a period of 8 months (March-October 2007). We found correlations between the tick infestation and the concentration of red blood cells, haemoglobin, haematocrit, MCH, MCHC, thrombocytes, lymphocytes and neutrophils. These results indicate that ticks can induce anaemia in the hedgehog. The peripheral blood characteristics and the erythrocyte indices characterize this anaemia as haemorrhagic and regenerative. During the course of our study the hedgehogs of our population showed below normal mortality but morbidity was found to be high resulting from the blood loss caused by the feeding activity of the ticks.

The avian acanthocephalan Plagiorhynchus cylindraceus (Palaeacanthocephala) parasitizing the European hedgehog (Erinaceus europaeus) in Europe and New Zealand.

The palaeacanthocephalan Plagiorhynchus cylindraceus is a common intestinal parasite of passerine birds, which can also occur parenterally or in the intestinal tract of mammals, often as an invading species in many countries worldwide. In this survey, introduced hedgehogs (Erinaceus europaeus, n = 183) killed in New Zealand during a biocontrol campaign and conspecifics (n = 174) that had died in hedgehog rehabilitation centers in Germany and Britain were examined for this parasite. In New Zealand, P. cylindraceus is recorded for the first time here, in the vicinity of Auckland. In Europe, prevalences ranged from 4.2% up to 47.6%, while in New Zealand, only 1.6% (Auckland 7.9%). Most of the worms occurred inside the peritoneal cavity where they had partly degenerated. Since hedgehogs are seldom preyed upon in continental Europe but often become traffic victims, we hypothesize that the worms inside them, whether extra- or intraperitoneally, contribute to the abundance and persistence of the parasite by being ingested by scavenging birds. Accordingly, we consider P. cylindraceus as a “modern parasite” taking advantage of two aspects of global change: anthropogenic promoted transmission (road kills) and the transcontinental spread of infected intermediate and/or final hosts caused by humans.

Detection of Rickettsia helvetica in ticks collected from European hedgehogs (Erinaceus europaeus, Linnaeus, 1758).

The role of wild mammals in the dissemination and maintenance of Rickettsia in nature is still under investigation. European hedgehogs (Erinaceus europaeus) are often heavily infested by tick and flea species that are known to harbor and transmit different Rickettsia spp. We investigated ixodid ticks sampled from European hedgehogs for the presence of Rickettsia. A total of 471 Ixodes ricinus and 755 I. hexagonus were collected from 26 German and 7 British European hedgehogs. These were tested by a genus-specific real-time PCR assay targeting the citrate synthase gene (gltA). The rickettsia minimum infection rate was 11.7% with an increase detected with each parasitic tick stage. No significant difference in Rickettsia prevalence in the 2 Ixodes species was detected. Using sequencing of partial ompB, Rickettsia helvetica was the only species identified. More than half of the hedgehogs carried Rickettsia-positive ticks. In addition, tissue samples from 2/5 hedgehogs (where tissue DNA was available) were PCR-positive. These results show that European hedgehogs are exposed to R. helvetica via infected ticks and might be involved in the natural transmission cycle of this Rickettsia species.

Host preferences of immature Dermacentor reticulatus (Acari: Ixodidae) in a forest habitat in Germany.

Dermacentor reticulatus is widespread throughout Europe and is expanding its range in several European countries. It is associated with a number of different pathogens. Its role in the transmission of disease to humans is currently small; however, it might play an important role in the maintenance of pathogens in enzootic cycles. The ecology of D. reticulatus, especially of the immatures, is not well known. In this study, ticks from small mammals, caught in a capture-mark-release study between May 2012 and October 2014 in a unique woodland area close to Karlsruhe, Germany, were collected. The main host species trapped were the yellow-necked mouse (Apodemus flavicollis) and the bank vole (Myodes glareolus). Small mammal populations showed high variability in their density between the study years, which is probably due to harsh winter conditions in 2012/2013 and missing mast leading to high winter mortality. Larvae and nymphs of D. reticulatus were predominantly found in July and August, respectively, and the infestation rates among the different small mammal species suggest a host preference of D. reticulatus for M. glareolus.

Ixodoidea of the Western Palaearctic: A review of available literature for identification of species

We aim to produce a review of the most important literature references necessary for the identification of ticks of the families Ixodidae and Argasidae in Europe and northern Africa (i.e. the Western Palaearctic region). The purpose of this paper is to pinpoint a set of critically selected papers that contain reliable information on morphology, taxonomic keys, and comparative discussions which are critical for the identification of the ticks reported in the target region. When necessary, comments are provided on the systematic position of a species, or on suitable papers already addressing the issue. This review includes a list of 216 references which cover all Ixodoidea species reported as permanent residents of the Western Palaearctic, namely 28 species of the genus Ixodes, two Dermacentor, seven Haemaphysalis, nine Hyalomma, eight Rhipicephalus, five Argas and about seven species of Ornithodoros.