Habitat requirements of the seabird tick, Ixodes uriae (Acari: Ixodidae), from the Antarctic Peninsula in relation to water balance characteristics of eggs, nonfed and engorged stages

Worldwide host associations of the tick genus Ixodes suggest relationships based on environmental sharing rather than on co-phylogenetic events

BACKGROUND

This study aims to capture how ticks of the genus Ixodes gained their hosts using network constructs. We propose two alternative hypotheses, namely, an ecological background (ticks and hosts sharing environmentally available conditions) and a phylogenetic one, in which both partners co-evolved, adapting to existing environmental conditions after the association took place.

METHODS

We used network constructs linking all the known pairs of associations between each species and stage of ticks with families and orders of hosts. Faith's phylogenetic diversity was used to evaluate the phylogenetic distance of the hosts of each species and changes occurring in the ontogenetic switch between consecutive stages of each species (or the extent of the changes in phylogenetic diversity of hosts for consecutive stages of the same species).

RESULTS

We report highly clustered associations among Ixodes ticks and hosts, supporting the influence of the ecological adaptation and coexistence, demonstrating a lack of strict tick-host coevolution in most cases, except for a few species. Keystone hosts do not exist in the relationships between Ixodes and vertebrates because of the high redundancy of the networks, further supporting an ecological relationship between both types of partners. The ontogenetic switch of hosts is high for species with enough data, which is another potential clue supporting the ecological hypothesis. Other results suggest that the networks displaying tick-host associations are different according to the biogeographical realms. Data for the Afrotropical region reveal a lack of extensive surveys, while results for the Australasian region are suggestive of a mass extinction of vertebrates. The Palearctic network is well developed, with many links demonstrating a highly modular set of relationships.

CONCLUSIONS

With the obvious exceptions of Ixodes species restricted to one or a few hosts, the results point to an ecological adaptation. Even results on species linked to groups of ticks (such as Ixodes uriae and the pelagic birds or the bat-tick species) are suggestive of a previous action of environmental forces.

Amblyomma mixtum free-living stages: Inferences on dry and wet seasons use, preference, and niche width in an agroecosystem (Yopal, Casanare, Colombia)

The formulation of effective control strategies for any pest species generally involves the study of habitat use and preference and niche width in anthropogenically transformed natural landscapes. We evaluated whether the use, habitat preference, and niche range of the Amblyomma mixtum tick changed between stages, habitats, and seasonality (dry-wet seasons 2019) on a farm in Yopal (Casanare, Colombia). The presence and relative abundance of free-living larvae, nymphs, and adults was quantified in four different habitats according to the type of vegetation cover (Riparian Forest, Cocoa Crop, King Grass Crop, and Star Grass Paddock). Habitat availability was estimated, environmental variables were analyzed, and various indices of habitat use and preference, and niche width were calculated. A. mixtum’s habitat use and preference, and niche width changed between stages, habitat types, and time of the year. The total abundance of A. mixtum was an order of magnitude greater in the dry season than the wet season. In the dry season, all stages used all habitats, while A. mixtum adults used all the habitats in both seasons. In the dry season, nymphs and larvae preferred three out of the four habitats, while adults preferred the King Grass Crop. In the wet season, nymphs and larvae preferred two habitats, whereas the adults preferred the King Grass Crop. The value of the niche width index was high for larvae, nymphs, and adults in the dry season, while it was high only for adults in the wet season. Thus, A. mixtum’s vast environmental tolerance and niche breadth allows the species to use and colonize changing habitats (unstable or temporary) with fluctuating environmental conditions (e.g., King Grass Crop), potentially keeping a stable population over time and making it an extremely resistant species. However, the wet flooding season in Yopal may exceed A. mixtum’s stages’ tolerances.

Cold hardening improves larval tick questing under low temperatures at the expense of longevity

Questing in ticks is essential for locating a host, and this behavioral response can occur at regionally specific low temperatures for most tick species. Little is known about the dynamics between tick questing behavior and temperature in ticks, specifically how this may impact other aspects of tick biology. Here, we examine whether cold hardening increases questing in three larval tick species (Ixodes uriae, Dermacentor variabilis, and Amblyomma americanum) at low temperatures and whether cold hardening impacts longevity. Rapid cold hardening and prolonged cold acclimation benefitted ticks by decreasing the temperature of chill coma onset, and increased survival, activity, and questing in ticks at low temperatures. Oxygen consumption increased at low temperatures following acclimation in larvae, suggesting this process has a distinct metabolic expense. This increased metabolism associated with hardening led to a substantial reduction in larval longevity as nutrient reserves are limited and cannot be replenished until a host is located. These studies suggest that tick larvae, and likely other developmental stages, require a delicate balance between the need for questing at low temperatures and survival until the first blood meal.

The Impacts of Climate Change on Ticks and Tick-Borne Disease Risk

Ticks exist on all continents and carry more zoonotic pathogens than any other type of vector. Ticks spend most of their lives in the external environment away from the host and are thus expected to be affected by changes in climate. Most empirical and theoretical studies demonstrate or predict range shifts or increases in ticks and tick-borne diseases, but there can be a lot of heterogeneity in such predictions. Tick-borne disease systems are complex, and determining whether changes are due to climate change or other drivers can be difficult. Modeling studies can help tease apart and understand the roles of different drivers of change. Predictive models can also be invaluable in projecting changes according to different climate change scenarios. However, validating these models remains challenging, and estimating uncertainty in predictions is essential. Another focus for future research should be assessing the resilience of ticks and tick-borne pathogens to climate change.

Questing by Tick Larvae (Acari: Ixodidae): A Review of the Influences That Affect Off-Host Survival

Questing is a host-seeking behavior in which ticks ascend plants, extend their front legs, and wait poised for a chance to attach to a passing host. Hard ticks are ectoparasites of terrestrial vertebrates and because some species vector disease, they are among the most medically important of arthropod pests. All ixodid ticks require blood to survive and reproduce with the number of blood-hosts needed to complete their life cycle varying among species. The vast majority are three-host ticks requiring a different host for each developmental stage: larva, nymph, and adult. A few, including some of the most economically important species, are one-host ticks, that quest only in the larval stage. Questing is a rate-limiting behavior critical to tick survival and disease transmission. For the off-host larval stage, survival is highly dependent on ecological and physiological factors. Yet, off-host larval ecophysiology is often overlooked for the more obvious adult and nymphal tick-host interactions. This review summarizes the literature on ixodid larval questing with emphasis on how specific biotic and abiotic factors affect off-host survival.

Evaluating Functional Dispersal in a Nest Ectoparasite and Its Eco-Epidemiological Implications

Functional dispersal (between-site movement, with or without subsequent reproduction) is a key trait acting on the ecological and evolutionary trajectories of a species, with potential cascading effects on other members of the local community. It is often difficult to quantify, and particularly so for small organisms such as parasites. Understanding this life history trait can help us identify the drivers of population dynamics and, in the case of vectors, the circulation of associated infectious agents. In the present study, functional dispersal of the soft tick Ornithodoros maritimus was studied at a small scale, within a colony of yellow-legged gulls (Larus michahellis). Previous work showed a random distribution of infectious agents in this tick at the within-colony scale, suggesting frequent tick movement among nests. This observation contrasts with the presumed strong endophilic nature described for this tick group. By combining an experimental field study, where both nest success and tick origin were manipulated, with Capture-Mark-Recapture modeling, dispersal rates between nests were estimated taking into account tick capture probability and survival, and considering an effect of tick sex. As expected, tick survival probability was higher in successful nests, where hosts were readily available for the blood meal, than in unsuccessful nests, but capture probability was lower. Dispersal was low overall, regardless of nest state or tick sex, and there was no evidence for tick homing behavior; ticks from foreign nests did not disperse more than ticks in their nest of origin. These results confirm the strong endophilic nature of this tick species, highlighting the importance of life cycle plasticity for adjusting to changes in host availability. However, results also raise questions with respect to the previously described within-colony distribution of infectious agents in ticks, suggesting that tick dispersal either occurs over longer temporal scales and/or that transient host movements outside the breeding period result in vector exposure to a diverse range of infectious agents.

Circumpolar diversification of the Ixodes uriae tick virome

Ticks (order: Ixodida) are a highly diverse and ecologically important group of ectoparasitic blood-feeding organisms. One such species, the seabird tick (Ixodes uriae), is widely distributed around the circumpolar regions of the northern and southern hemispheres. It has been suggested that Ix. uriae spread from the southern to the northern circumpolar region millions of years ago and has remained isolated in these regions ever since. Such a profound biographic subdivision provides a unique opportunity to determine whether viruses associated with ticks exhibit the same evolutionary patterns as their hosts. To test this, we collected Ix. uriae specimens near a Gentoo penguin (Pygoscelis papua) colony at Neko harbour, Antarctica, and from migratory birds—the Razorbill (Alca torda) and the Common murre (Uria aalge)—on Bonden island, northern Sweden. Through meta-transcriptomic next-generation sequencing we identified 16 RNA viruses, seven of which were novel. Notably, we detected the same species, Ronne virus, and two closely related species, Bonden virus and Piguzov virus, in both hemispheres indicating that there have been at least two cross-circumpolar dispersal events. Similarly, we identified viruses discovered previously in other locations several decades ago, including Gadgets Gully virus, Taggert virus and Okhotskiy virus. By identifying the same or closely related viruses in geographically disjunct sampling locations we provide evidence for virus dispersal within and between the circumpolar regions. In marked contrast, our phylogenetic analysis revealed no movement of the Ix. uriae tick hosts between the same locations. Combined, these data suggest that migratory birds are responsible for the movement of viruses at both local and global scales.

As host populations diverge, so may those microorganisms, including viruses, that are dependent on those hosts. To examine this key issue in host-microbe evolution we compared the co-phylogenies of the seabird tick, Ixodes uriae, and their RNA viruses sampled from the far northern and southern hemispheres. Despite the huge geographic distance between them, phylogeographic analysis reveals that the same and closely related viruses were found both within and between the northern and southern circumpolar regions, most likely reflecting transfer by virus-infected migratory birds. In contrast, genomic data suggested that the Ix. uriae populations were phylogenetically distinct between the northern and southern hemispheres. This work emphasises the importance of migratory birds and ticks as vectors and sources of virus dispersal and introduction at both the local and global scales.

Sustained RNA virome diversity in Antarctic penguins and their ticks

Despite its isolation and extreme climate, Antarctica is home to diverse fauna and associated microorganisms. It has been proposed that the most iconic Antarctic animal, the penguin, experiences low pathogen pressure, accounting for their disease susceptibility in foreign environments. There is, however, a limited understanding of virome diversity in Antarctic species, the extent of in situ virus evolution, or how it relates to that in other geographic regions. To assess whether penguins have limited microbial diversity we determined the RNA viromes of three species of penguins and their ticks sampled on the Antarctic peninsula. Using total RNA sequencing we identified 107 viral species, comprising likely penguin associated viruses (n = 13), penguin diet and microbiome associated viruses (n = 82), and tick viruses (n = 8), two of which may have the potential to infect penguins. Notably, the level of virome diversity revealed in penguins is comparable to that seen in Australian waterbirds, including many of the same viral families. These data run counter to the idea that penguins are subject to lower pathogen pressure. The repeated detection of specific viruses in Antarctic penguins also suggests that rather than being simply spill-over hosts, these animals may act as key virus reservoirs.

Determinants of external and blood parasite load in African penguins (Spheniscus demersus) admitted for rehabilitation

We investigate the factors associated with the occurrence and abundance of external and blood parasites in African penguins (Spheniscus demersus), an endangered seabird that breeds exclusively on the coasts of Namibia and South Africa. External parasites were collected using the dust-ruffling method from 171 African Penguins admitted at a rehabilitation facility in the Western Cape, South Africa. Additionally, blood smears were obtained upon admission and weekly during rehabilitation and examined for blood parasites. Fleas Parapsyllus longicornis humboldti, ticks Ornithodoros capensis and lice Austrogoniodes demersus were recovered from 93, 63 and 40%, respectively, of the penguins upon admission to the centre. Rescue location and age group were identified as significant determinants of flea abundance, whereas month of admission was a significant determinant of tick abundance. Blood parasites were also common on admission, with Babesia being the most frequent (46% prevalence) whereas Borrelia was recorded sporadically (1.2%) and Plasmodium was recorded once. The prevalence and abundance of ticks on admission was positively associated with Babesia infection on admission. Our findings demonstrate the variability and contributing factor of parasite infections in an endangered species of penguin, and highlight the need for additional research on the parasite-host dynamics involving these potential disease vectors.

The impact of ectoparasitism on thermoregulation in Yarrow’s Spiny Lizards (Sceloporus jarrovii)

Parasites are ubiquitous and can have large impacts on the fitness of their hosts. The effects of ectoparasites on physiology, behaviour, and immune function suggest that they could be part of the factors which impact thermoregulation. We tested the hypothesis that ectoparasites impact thermoregulation in Yarrow’s Spiny Lizards (Sceloporus jarrovii Cope in Yarrow, 1875) living along an elevational gradient. We predicted a positive association between ectoparasite load and body temperature (Tb), and a negative association between ectoparasite load and effectiveness of thermoregulation (de – db index). We also predicted that the impacts of ectoparasites would be greatest at high elevation where thermal quality of the environment is low because the costs of thermoregulation increase with elevation and these costs can impact thermal immune responses. We found a significant association between the number of chiggers (Trombiculoidea) harboured by lizards and Tb that depended on elevation, but no association between ectoparasite load and de – db index. The mean chigger infection rate was associated with a ΔTb of +0.18 °C at low elevation (consistent with fever) and of –1.07 °C at high elevation (consistent with hypothermia). These findings suggest that parasitism by chiggers impacts lizard Tb in a way that depends on environmental thermal quality.

Climate change, biodiversity, ticks and tick-borne diseases: The butterfly effect

We have killed wild animals for obtaining food and decimated forests for many reasons. Nowadays, we are burning fossil fuels as never before and even exploring petroleum in deep waters. The impact of these activities on our planet is now visible to the naked eye and the debate on climate change is warming up in scientific meetings and becoming a priority on the agenda of both scientists and policy decision makers. On the occasion of the Impact of Environmental Changes on Infectious Diseases (IECID) meeting, held in the 2015 in Sitges, Spain, I was invited to give a keynote talk on climate change, biodiversity, ticks and tick-borne diseases. The aim of the present article is to logically extend my rationale presented on the occasion of the IECID meeting. This article is not intended to be an exhaustive review, but an essay on climate change, biodiversity, ticks and tick-borne diseases. It may be anticipated that warmer winters and extended autumn and spring seasons will continue to drive the expansion of the distribution of some tick species (e.g., Ixodes ricinus) to northern latitudes and to higher altitudes. Nonetheless, further studies are advocated to improve our understanding of the complex interactions between landscape, climate, host communities (biodiversity), tick demography, pathogen diversity, human demography, human behaviour, economics, and politics, also considering all ecological processes (e.g., trophic cascades) and other possible interacting effects (e.g., mutual effects of increased greenhouse gas emissions and increased deforestation rates). The multitude of variables and interacting factors involved, and their complexity and dynamism, make tick-borne transmission systems beyond (current) human comprehension. That is, perhaps, the main reason for our inability to precisely predict new epidemics of vector-borne diseases in general.

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Human development affects the environment and the climate.

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Environmental and climate changes impacts on biodiversity.

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Environmental and climate changes alter tick population dynamics.

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Biodiversity loss affects tick-borne pathogen transmission.

The tick Ixodes uriae (Acari: Ixodidae): Hosts, geographical distribution, and vector roles

The seabird tick Ixodes uriae White 1852, has the most extensive geographical distribution of all tick species, including Afrotropical, Australasian, Nearctic, Neotropical and Palearctic Zoogeographic Regions. Additionally, this tick species parasitizes a wide range of seabirds and constitutes a host for several viral and bacterial agents. Considering the current biological knowledge about this tick species, in this article we list localities, hosts, tick-borne microorganisms and viruses transmitted by I. uriae described in the literature and include new geographical records.

Biology, ecology and distribution of the tick, Haemaphysalis longicornis Neumann (Acari: Ixodidae) in New Zealand

Haemaphysalis longicornis is the only tick in New Zealand that infests livestock. Throughout its range H. longicornis is exposed to and exhibits tolerance to a wide range of environmental conditions, although it flourishes more in moist, warm-temperate environments. This review examines aspects of the biology, physiology and ecology of H. longicornis that determine its distribution and seasonal activity in New Zealand, based on laboratory and field studies. Examples are also drawn from studies outside New Zealand for comparative purposes, especially in the context of seasonal activity as seen in less temperate latitudes. The tick is able to withstand a wide range of temperature, from its developmental threshold of ∼12°C to nearly 40°C at its lethal limit, but its tolerance of dehydration is less wide, especially in the larva and adult, the former especially being the stage that largely determines suitable biotopes for the tick and its present distributional limits. The importance of H. longicornis to the New Zealand livestock industry has recently increased through the establishment and spread of Theileria orientalis Ikeda among dairy and beef cattle, although the tick has always posed production-limiting problems for cattle, deer and to a lesser extent, sheep. The tick's role as a vector of theileriosis and how aspects of the tick's biology affect the spread and maintenance of this disease are discussed. It is proposed that, of available wildlife hosts, the brown hare with its wide-ranging habits, is an important disseminator of ticks. Currently control of ticks is difficult partly because of their wide host range, overlapping activity periods of stadia, and also because the greater part of their annual cycle is spent on pasture. This means that acaricides alone do not satisfactorily reduce tick populations or provide comprehensive protection to stock, so integrated management combining pasture management with good husbandry and chemical prophylaxis is advocated.

First survey of hard ticks (Acari: Ixodidae) on cattle, sheep and goats in Boeen Zahra and Takistan counties, Iran

OBJECTIVE

To carry out the distribution survey of hard ticks of livestock in Boeen Zahra and Takistan counties of Qazvin province from April 2010 to September 2010.

METHODS

Nearly about 2 638 sheep, 461 goats and 318 cattle of 38 herds in different geographical areas were searched for tick infestation.

RESULTS

The species compositions collected from the livestock of Boeen Zahra and Takistan were Haemaphysalis concinna (0.63%), Haemaphysalis sulcata (12.66%), Hyalomma anatolicum (3.80%), Hyalomma asiaticum (3.16%), Hyalomma detritum (5.70%), Hyalomma dromedarii (28.48%), Hyalomma marginatum (13.29%), Hyalomma schulzei (1.89%), Rhipicephalus bursa (3.16%) and Rhipicephalus sanguineus (3.16%), and for Takistan's livestock were Hyalomma dromedarii (9.86%), Hyalomma marginatum (13.29%), Hyalomma schulzei (1.89%) and Rhipicephalus sanguineus (3.16%), respectively. Hard ticks compositions in different topographic areas were different. Hyalomma species had the most prevalence in the areas.

CONCLUSIONS

The veterinary and public health investigation of the above species should be taken.

An experimental test of host specialization in a ubiquitous polar ectoparasite: a role for adaptation?

The evolution of host specificity is considered to be an essential mechanism driving parasite diversity. It may be governed by adaptive constraints that lead to host-dependent fitness trade-offs. Alternatively, specificity may arise via transmission constraints that isolate parasite populations, without necessarily involving adaptation per se. Here, we ask whether the repeated observation of host-associated genetic races across the worldwide distribution of the seabird ectoparasite Ixodes uriae is associated with host adaptation. We conducted a field-based experiment to test for adaptive specialisation in host races of I. uriae. We transferred unengorged ticks of two life stages (nymphs and adults) originating from three host species (black-legged kittiwake, common guillemot and Atlantic puffin) onto young kittiwake nestlings and followed attraction and attachment rates, engorgement times and feeding success of the transplanted ticks. All ticks were also typed genetically to match exploitation patterns with genetic differences among races. Ticks from atypical hosts were significantly less attracted to nestlings than ticks from the typical host, and showed lower feeding success and higher mortality. The degree of host specificity matched patterns of neutral genetic variation among races, with puffin ticks being more specific than guillemot ticks. Differences in specificity were also apparent among tick life stages, suggesting that nymphal ticks may be less discriminating of host type than adult ticks. Our results indicate that the genetic divergence previously observed among sympatric I. uriae host races is at least partially linked to adaptive specialisation to the host species and not simply to host-mediated transmission. They also suggest that the adaptation process may evolve differently in different life stages based on trade-offs with physiological constraints. The identification of the selective forces acting in host specialization will now be necessary to better characterize these patterns and to understand how transmission interacts with the adaptation process to generate parasite biodiversity.

Understanding the evolutionary structural variability and target specificity of tick salivary Kunitz peptides using next generation transcriptome data

BACKGROUND

Ticks are blood-sucking arthropods and a primary function of tick salivary proteins is to counteract the host's immune response. Tick salivary Kunitz-domain proteins perform multiple functions within the feeding lesion and have been classified as venoms; thereby, constituting them as one of the important elements in the arms race with the host. The two main mechanisms advocated to explain the functional heterogeneity of tick salivary Kunitz-domain proteins are gene sharing and gene duplication. Both do not, however, elucidate the evolution of the Kunitz family in ticks from a structural dynamic point of view. The Red Queen hypothesis offers a fruitful theoretical framework to give a dynamic explanation for host-parasite interactions. Using the recent salivary gland Ixodes ricinus transcriptome we analyze, for the first time, single Kunitz-domain encoding transcripts by means of computational, structural bioinformatics and phylogenetic approaches to improve our understanding of the structural evolution of this important multigenic protein family.

RESULTS

Organizing the I. ricinus single Kunitz-domain peptides based on their cysteine motif allowed us to specify a putative target and to relate this target specificity to Illumina transcript reads during tick feeding. We observe that several of these Kunitz peptide groups vary in their translated amino acid sequence, secondary structure, antigenicity, and intrinsic disorder, and that the majority of these groups are subject to a purifying (negative) selection. We finalize by describing the evolution and emergence of these Kunitz peptides. The overall interpretation of our analyses discloses a rapidly emerging Kunitz group with a distinct disulfide bond pattern from the I. ricinus salivary gland transcriptome.

CONCLUSIONS

We propose a model to explain the structural and functional evolution of tick salivary Kunitz peptides that we call target-oriented evolution. Our study reveals that combining analytical approaches (transcriptomes, computational, bioinformatics and phylogenetics) improves our understanding of the biological functions of important salivary gland mediators during tick feeding.

Host specialization in ticks and transmission of tick-borne diseases: a review

Determining patterns of host use, and the frequency at which these patterns change, are of key importance if we are to understand tick population dynamics, the evolution of tick biodiversity, and the circulation and evolution of associated pathogens. The question of whether ticks are typically host specialists or host generalists has been subject to much debate over the last half-century. Indeed, early research proposed that morphological diversity in ticks was linked to host specific adaptations and that most ticks were specialists. Later work disputed this idea and suggested that ticks are largely limited by biogeographic conditions and tend to use all locally available host species. The work presented in this review suggests that the actual answer likely lies somewhere between these two extremes. Although recent observational studies support the view that phylogenetically diverse host species share ticks when found on similar ecological ranges, theory on host range evolution predicts that host specialization should evolve in ticks given their life history characteristics. Contemporary work employing population genetic tools to examine host-associated population structure in several tick systems support this prediction and show that simple species records are not enough to determine whether a parasite is a true host generalist; host specialization does evolve in ticks at local scales, but may not always lead to speciation. Ticks therefore seem to follow a pattern of being global generalists, local specialists. Given this, the notion of host range needs to be modified from an evolutionary perspective, where one simply counts the number of hosts used across the geographic distribution, to a more ecological view, where one considers host use at a local scale, if we are to better understand the circulation of tick-borne pathogens and exposure risks for humans and livestock.

Global ecology and epidemiology of Borrelia garinii spirochetes

Lyme borreliosis (LB) is a tick-transmitted infectious disease caused by Borrelia burgdorferi sensu lato (s. l.). In Europe, three different Borrelia species are the main causative agents of LB: B. burgdorferi sensu stricto (s.s.), Borrelia afzelii, and Borrelia garinii. The latter depends heavily on birds as its main reservoir hosts. In fact, birds can act both as biological carriers of Borrelia and transporters of infected ticks. The seasonal migration of many bird species not only aid in the spread of B. garinii to new foci but also influence the high level of diversity found within this species. B. garinii have been isolated not only from terrestrial birds in Europe, but also from seabirds worldwide, and homology between isolates in these two different infection cycles suggests an overlap and exchange of strains. In addition, it has been shown that birds can maintain and spread B. garinii genotypes associated with LB in humans. This review article discusses the importance of birds in the ecology and epidemiology of B. garinii spirochetes.

Meeting the challenges of on-host and off-host water balance in blood-feeding arthropods

In this review, we describe water balance requirements of blood-feeding arthropods, particularly contrasting dehydration tolerance during the unfed, off-host state and the challenges of excess water that accompany receipt of the bloodmeal. Most basic water balance characteristics during the off-host stage are applicable to other terrestrial arthropods, as well. A well-coordinated suite of responses enable arthropods to conserve water resources, enhance their desiccation tolerance, and increase their water supplies by employing a diverse array of molecular, structural and behavioral responses. Water loss rates during the off-host phase are particularly useful for generating a scheme to classify vectors according to their habitat requirements for water, thus providing a convenient tool with potential predictive power for defining suitable current and future vector habitats. Blood-feeding elicits an entirely different set of challenges as the vector responds to overhydration by quickly increasing its rate of cuticular water loss and elevating the rate of diuresis to void excess water and condense the bloodmeal. Immature stages that feed on blood normally have a net increase in water content at the end of a blood-feeding cycle, but in adults the water content reverts to the pre-feeding level when the cycle is completed. Common themes are evident in diverse arthropods that feed on blood, particularly the physiological mechanisms used to respond to the sudden influx of water as well as the mechanisms used to counter water shortfalls that are encountered during the non-feeding, off-host state.

Worldwide distribution and diversity of seabird ticks: implications for the ecology and epidemiology of tick-borne pathogens

The ubiquity of ticks and their importance in the transmission of pathogens involved in human and livestock diseases are reflected by the growing number of studies focusing on tick ecology and the epidemiology of tick-borne pathogens. Likewise, the involvement of wild birds in dispersing pathogens and their role as reservoir hosts are now well established. However, studies on tick-bird systems have mainly focused on land birds, and the role of seabirds in the ecology and epidemiology of tick-borne pathogens is rarely considered. Seabirds typically have large population sizes, wide geographic distributions, and high mobility, which make them significant potential players in the maintenance and dispersal of disease agents at large spatial scales. They are parasitized by at least 29 tick species found across all biogeographical regions of the world. We know that these seabird-tick systems can harbor a large diversity of pathogens, although detailed studies of this diversity remain scarce. In this article, we review current knowledge on the diversity and global distribution of ticks and tick-borne pathogens associated with seabirds. We discuss the relationship between seabirds, ticks, and their pathogens and examine the interesting characteristics of these relationships from ecological and epidemiological points of view. We also highlight some future research directions required to better understand the evolution of these systems and to assess the potential role of seabirds in the epidemiology of tick-borne pathogens.

An endosymbiotic conidial fungus, Scopulariopsis brevicaulis, protects the American dog tick, Dermacentor variabilis, from desiccation imposed by an entomopathogenic fungus

The functional role of an endosymbiotic conidial fungus (Scopulariopsis brevicaulis) prevalent within the integumental glands and hemocoel of the American dog tick (Dermacentor variabilis) was investigated to explore the nature of this tick/fungus association. D. variabilis is normally highly resistant to Metarhizium anisopliae, a widely-distributed entomopathogenic fungus, but when mature female ticks harboring S. brevicaulis were fed a solution containing a mycotoxin (Amphotericin B) to purge this mycobiont internally, the ticks inoculated with M. anisopliae displayed classic signs of pathogenicity, as evidenced by recovery of M. anisopliae from ticks by internal fungus culture, greatly accelerated net transpiration water loss rates (nearly 3x faster than ticks containing S. brevicaulis naturally) and elevation of critical equilibrium humidity (CEH) closer to saturation, implying a reduced capacity to absorb water vapor and disruption of water balance (water gain not equal water loss) that resulted in tick death. The presence of S. brevicaulis within the tick was previously puzzling: the fungus is transmitted maternally and there is no apparent harm inflicted to either generation. This study suggests that S. brevicaulis provides protection to D. variabilis ticks against M. anisopliae. Thus, the S. brevicaulis/tick association appears to be mutualistic symbiosis. Given that both organisms are of medical-veterinary importance, disruption of this symbiosis has potential for generating novel tools for disease control.