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Ticks and Tick-Borne Pathogens
Abstract and Figures
There has been much progress in our understanding of the phylogeny and evolution of ticks, particularly hard ticks, in the past 5 years. Indeed, a consensus about the phylogeny of the hard ticks has emerged. Our current working hypothesis for the phylogeny of ticks is quite different to the working hypothesis of 5 years ago. So that the classification reflects our knowledge of ticks, several changes to the nomenclature of ticks are imminent. One subfamily, the Hyalomminae, will probably be sunk, yet another, the Bothriocrotoninae n. subfamily, will be created. Bothriocrotoninae n. subfamily, and Bothriocroton n. genus, are being created to house an early-diverging ('basal') lineage of endemic Australian ticks that used to be in the genus Aponomma (ticks of reptiles). There has been progress in our understanding of the subfamily Rhipicephalinae. The genus Rhipicephalus is almost certainly paraphyletic with respect to the genus Boophilus. Thus, the genus Boophilus will probably become a subgenus of Rhipicephalus. This change to the nomenclature, unlike other options, will keep the name Boophilus in common usage. Rhipicephalus (Boophilus) microplus may still called B. microplus, and Rhipicephalus (Boophilus) annulatus may still be called B. annulatus, but the nomenclature will have been changed to reflect our knowledge of the phylogeny and evolution of these ticks. New insights into the historical zoogeography of ticks will also be presented.
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... Together with morphological identification, the genetic characterization of ticks has been considered as an important component in understanding tick systematic and evolutionary history [39]. In this study, we employed DNA barcoding for the precise identification of D. marginatus. ...
Simple Summary
Dermacentor ticks have a wide geographic range with an uneven distribution in the globe. They are not scientifically well known because they survive in hard topographic and harsh climatic regions along with elevated mountains. Many mammals serve as a primary host for Dermacentor ticks, like many other tick species. The present study aimed to provide the first morphological and molecular confirmation of Dermacentor marginatus and its related pathogens like Anaplasma marginale and Rickettsia raoultii in Pakistan. In this study, a total of 26 specimens (19 males and 7 females) were collected from goats and morphologically identified. A subset of 18 specimens were subjected for the molecular characterization of ticks and associated pathogen detection. In the BLAST and phylogenetic analyses, D. marginatus and their associated pathogen sequences showed close resemblance with their corresponding species. In the present study, we reported the first genetic characterization of D. marginatus and associated A. marginale and R. raoultii in Pakistan. Due to the difficult access and harsh climate, it is important to investigate the ticks and related pathogens in the northern parts of Pakistan due to their zoonotic threats.
Abstract
Ticks of the genus Dermacentor Koch, 1844 (Acari: Ixodidae) are poorly known systematically due to their habitation in harsh topographic environments and high mountains. Dermacentor ticks are diversely distributed in the Palearctic, Nearctic, and Oriental regions. There is no available information on the occurrence of Dermacentor marginatus in Pakistan; thus, the current investigation aimed the first morphological and molecular confirmation of this species and associated Anaplasma marginale and Rickettsia raoultii. Ticks were collected from goats (Capra hircus) and morphologically identified. Genomic DNA was extracted from 18/26 (69.23%) tick specimens, including 11 males and 7 females (1 unfed and 6 fed females). Extracted DNA was subjected to PCR for the amplification of genetic markers like 16S rDNA and cox1 for ticks, 16S rDNA for Anaplasma spp., and gltA and ompB for Rickettsia spp. A total of 26 D. marginatus ticks composed of 19 males (73.07%) and 7 females (26.9%) [1 (3.84%) unfed and 6 (23.07%) fed females] were collected from goats. According to amplicons via BLAST analysis, the 16S rDNA sequence showed 97.28–98.85% identity and the cox1 sequence showed 95.82–98.03% identity with D. marginatus. Additionally, the 16S rDNA sequence for Anaplasma sp. was detected in D. marginatus that showed 100% identity with Anaplasma marginale. Rickettsial gltA and ompB sequences for Rickettsia sp. showed 100% identity with Rickettsia raoultii. In phylogenetic analysis, ticks’ 16S rDNA and cox1 sequences clustered with the same species. In phylogenetic analysis, A. marginale based on 16 rDNA clustered with A. marginale, while gltA and ompB sequences clustered with R. raoultii. This is the first study on the genetic characterization of D. marginatus and associated A. marginale and R. raoultii in Pakistan. The northern areas of Pakistan, which need to be explored in terms of ticks and associated pathogens due to their zoonotic threats, have been neglected due to the inaccessible climatic conditions.
... The phylogenetic relationships among tick species (Acari: Ixodidae) have been discussed for decades by several authors based on morphological, physiological, and ecological variation studies, as well as reviews based on molecular systematics and biogeographical patterns (Hoogstraal and Aeschlimann 1982;Black et al. 1997; Barker and Murrell 2002;Burger et al. 2012;Nava et al. 2017;Zemtsova et al. 2016). Hard ticks (Acari: Ixodidae) display cryptic species complexes; for example, the Amblyomma cajennense sensu lato complex, which until recently was considered a single tick species in the New World and is distributed from the southern United States to northern Argentina (Estrada-Peña et al. 2014). ...
The systematics of several ticks species (Acari: Ixodidae) remains controversial. Many species, including those of the Amblyomma
cajennense complex and Rhipicephalus sanguineus s.l., are given special attention since they are cryptic species complexes and are
also important in human and veterinary medicine. The A. cajennense complex was recently reorganized into six valid species,
among which Amblyomma patinoi and Amblyomma mixtum have been confirmed in Colombia. On the other hand, the taxonomic
status of R. sanguineus s.l. is controversial since it is a cosmopolitan cryptic species complex with a high reproductive capacity and a
broad range of hosts (includingman). To address this challenge, the germ cells ofmale ticks display a diversemorphology that offers
novel opportunities for taxonomy. This study describes the events of spermatogenesis in A. mixtum and R. sanguineus s.l. individuals
collected during active feeding on domestic hosts in the department of Caldas, Colombia. The individuals were identified using
dichotomous keys and through PCR amplification of a fragment of the mitochondrial 16S ribosomal DNA gene. The male
reproductive systems of A. mixtum and R. sanguineus s.l. were fixed in 2.5% glutaraldehyde for 48 h and dehydrated in increasing
dilutions of ethanol. The samples were then embedded andmounted in historesin to obtain sections of 3 μm that were stained with
hematoxylin-eosin (HE), photographed, and visualized through optical microscopy. The results show that the morphology of mature
germ cells displays excellent diagnostic traits that can be used for tick taxonomy.
Nuttalliella namaqua Bedford, 1931 is the sole extant tick species that belongs to the genus and family Nuttalliella and Nuttalliellidae respectively. With the characteristics that are respectively distinctive to hard and soft ticks, it is regarded as the species closest to the ancestral lineage of ticks as well as the missing link between the Argasidae and Ixodidae families. In this review, literature search of the articles reporting on N. namaqua was done in Google Scholar and PubMed databases. After relevance and eligibility screening, 12 articles were deemed eligible and appraised. The results showed that N. namaqua was respectively distinct to limited regions of Africa such as Botswana, Namibia, Mozambique, South Africa and Tanzania. The review also indicated that N. namaqua was collected from murid rodents, African Savanna hare, scrub hare, elephant shrews, rock hyraxes, black backed jackal, lizards and off-host in locations that include under a stone, rock crevices, on a rock wall and respectively in the nests of an eagle and a lesser striped swallow. Irrespective of all the reports, natural hosts of the nymphs are still not clearly defined. Numerous phylogeny studies have reported Nuttalliellidae as the sister-lineage to Argasidae and Ixodidae tick families. Moreover, a recent report indicated that the similarities between Nuttalliellidae and the fossil families Deinocrotonidae and Legionaris award them to be merged into one family, preferably Nuttalliellidae Thus, further research on this family, will perhaps provide more knowledge about its unclear distribution, life cycle as well as the evolution of ticks in general.
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.
Graphical Abstract
Widespread and increasing resistance to most available acaracides threatens both global livestock industries and public health. This necessitates better understanding of ticks and the diseases they transmit in the development of new control strategies. Ticks: Biology, Disease and Control is written by an international collection of experts and covers in-depth information on aspects of the biology of the ticks themselves, various veterinary and medical tick-borne pathogens, and aspects of traditional and potential new control methods. A valuable resource for graduate students, academic researchers and professionals, the book covers the whole gamut of ticks and tick-borne diseases from microsatellites to satellite imagery and from exploiting tick saliva for therapeutic drugs to developing drugs to control tick populations. It encompasses the variety of interconnected fields impinging on the economically important and biologically fascinating phenomenon of ticks, the diseases they transmit and methods of their control.
Widespread and increasing resistance to most available acaracides threatens both global livestock industries and public health. This necessitates better understanding of ticks and the diseases they transmit in the development of new control strategies. Ticks: Biology, Disease and Control is written by an international collection of experts and covers in-depth information on aspects of the biology of the ticks themselves, various veterinary and medical tick-borne pathogens, and aspects of traditional and potential new control methods. A valuable resource for graduate students, academic researchers and professionals, the book covers the whole gamut of ticks and tick-borne diseases from microsatellites to satellite imagery and from exploiting tick saliva for therapeutic drugs to developing drugs to control tick populations. It encompasses the variety of interconnected fields impinging on the economically important and biologically fascinating phenomenon of ticks, the diseases they transmit and methods of their control.
Among Chelicerata, larval instars of sea spiders (Pycnogonida) can be parasitic. The oldest putative sea spider from the Cambrian ‘Orsten’ is immature and resembles comparable instars of modern species with a parasitic phase to their life cycle. All other parasitic chelicerates are mites, with several examples in both the Acariformes and Parasitiformes clades. Fossils revealing parasitic behaviour, or belonging to purely parasitic clades, come from various amber sources from the mid-Cretaceous onwards. From Acariformes there are records of Parasitengona, Myobiidae, Pterygosomatoidea, Resinacaridae, Acarophenacidae, Pyemotidae and Apotomelidae. Parasitiformes is represented by several ticks (Ixodida) and potentially Laelapidae from the Mesostigmata. Parasitism appears to have evolved independently within mites on several occasions. Possible transitions to this lifestyle via nest associations and/or phoresy are discussed. Arachnids as victims of parasites include amber records of nematode worms (Mermithidae), erythraeid mites (Erythraeidae), mantid flies (Neuroptera: Mantispidae), ichneumon wasps (Hymenoptera: Ichneumonidae) and spider flies (Diptera: Acroceridae).
Background:
There has recently been a substantial increase in the number of tick species and tick-borne infectious agents in Tanzania. Owing to their impact on human, livestock, and wild animal health, increased knowledge of ticks is needed. So far, no published data on the genetic relationship between hard tick (Ixodidae) sequences collected from cattle are available in Tanzania.
Methods:
Ticks from cattle in the wards, which lie at the border of Mikumi National Park, were collected in the dry season, November to December 2019. Morphological identification of ticks was initially performed at the genus level. To identify ticks at the species level, molecular analysis based on the 16S rRNA gene was performed. Evolutionary relationships and genetic distances between ticks were determined using MaximumLikelihood and Kimura 2-parameter methods, respectively.
Results:
Based on morphology, two genera (Rhipicephalus and Hyalomma) were identified in the 630 adult ticks collected from a total of 252 cattle. Six species (Rhipicephalus microplus, Rhipicephalus evertsi, Hyalomma marginatum, Hyalomma rufipes, Hyalomma truncatum, and Hyalomma turanicum) were confirmed by BLASTn and phylogenetic analyses. Considerable mean and pairwise genetic distances were observed for Rhipicephalus and Hyalomma genera.
Conclusion:
The presence of different phylogenetic clusters and considerable mean and pairwise genetic distances observed reflect possible biological diversity of hard ticks present in the study area. Considering the value of the cattle in the livelihoods and economies of people and the country, the outcomes of this study will be useful in planning integrated control strategies for ticks and tick-borne diseases in Tanzania.
Provides useful information to citizens of Iowa on potential threat of tick-borne diseases in the state.
Ticks are parasitiform mites that are obligate hematophagous ectoparasites of amphibians, reptiles, birds, and mammals. A phylogeny for tick families, subfamilies, and genera has been described based on morphological characters, life histories, and host associations. To test the existing phylogeny, we sequenced approximate to 460 bp from the 3' end of the mitochondrial 16S rRNA gene (rDNA) in 36 hard- and soft-tick species; a mesostigmatid mite, Dermanyssus gallinae, was used as an outgroup. Phylogenies derived using distance; maximum-parsimony, or maximum-likelihood methods were congruent. The existing phylogeny was largely supported with four excep tions. In hard ticks (Ixodidae), members of Haemaphysalinae were monophyletic with the primitive Amblyomminae and members of Hyalomminae grouped within the Rhipicephalinae. In soft ticks (Argasidae), the derived phylogeny failed to support a monophyletic relationship among members of Ornithodorinae and supported placement of Argasinae as basal to the Ixodidae, suggesting that hard ticks may have originated from an Argas-like ancestor. Because most Argus species are obligate bird ectoparasites, this result supports earlier suggestions that hard ticks did not evolve until the late Cretaceous.
An internal transcribed spacer (ITS2) sequence between the 5.8S and 28S rRNA genes was used to estimate the phyletic relationships among Ixodes spp. tick vectors of Lyme disease-causing Borrelia spirochetes. Analysis indicates that Borrelia burgdorferi sensu lato species associated with Lyme disease are found mainly in ticks of the Ixodes ricinus species complex. Other closely related tick species are not known to transmit the Borrelia-that cause Lyme disease in humans, but they appear to have a specific association with other closely related Borrelia species. There is a high degree of concordance in the phylogenetics of Borrelia taxa and the phylogenetic relationships among Ixodes ticks.
A larval argasid tick (Acari: Ixodida: Argasidae) is described from a single specimen preserved in amber from New Jersey. The amber is dated as Turonian, 90-94 mya, and thereby doubles the age of the oldest fossil in the mite order Parasitiformes. The specimen shows general characteristics of the genus Carios, but is unique because of its pattern of dorsal setae, featuring a double row of posterior marginal setae. Earlier hypotheses that Carios arose after the isolation of South America are challenged but not rejected by the discovery of this fossil. Salvaging these hypotheses seems most compatible with dispersal on birds, an idea consistent with the presence of a small feather in the same outcrop in which the tick fossil was found.
The bacterial genus Rickettsia is traditionally divided into three biotypes, the spotted fever group (SFG), the typhus group (TG), and the scrub typhus group (STG) based on vector host and antigenic cross-reactivity. DNA sequence data were gathered from the 16S ribosomal RNA gene of several SFG and TG species. Comparative sequence analysis shows that: i) all species of Rickettsia are closely related, exhibiting 0.3–2.6% sequence divergence; ii) although there are identifiable clusters corresponding to the SFG and TG, species of Rickettsia fall into more than two distinct phylogenetic groups; iii) the tick-borne species Rickettsia bellii and Rickettsia canada diverged prior to the schism between the spotted fever and typhus groups; iv) the newly described AB bacterium is clearly a member of Rickettsia, but its phylogenetic placement within the genus is problematic; v) the mite-borne Rickettsia akari, the tick-borne Rickettsia australis and the recently described flea-borne ELB agent form a loose cluster that cannot be definitively associated with either the TG or the traditional SFG cluster. This latter Glade may represent a unique group(s) distinct from the main cluster of spotted fever and typhus group species. The divergence of Rickettsia was an ancient event within the α-subclass of the proteobacteria. The sequence divergence between Rickettsia and Ehrlichia, the closest known genus to Rickettsia, is nearly equal to the sequence divergence between Rickettsia and all other α-subclass proteobacterial taxa included in the analysis. When Rickettsia was compared to a representative group of the α-subclass, twenty-eight nucleotide sites were identified which uniquely characterize the 16S rRNA sequences of all species of Rickettsia. The approximate time of divergence between the various species of Rickettsia, estimated from the bacterial 16S rRNA molecular clock, coincides with the approximate divergence time of the hard body ticks which are the arthropod hosts of many Rickettsia. Thus, the possibility of coevolution between these intracellular bacteria and their tick hosts exists.
Based on laboratory observations of three species of Allothyrus (Parasitiformes: Holothyrida: Allothyridae) from south east Queensland and gut content analysis of 62 individuals representing 11 species of Allothyrus from eastern Australia, we determined that Australian Allothyridae are scavengers that ingest fluids only. Living arthropods, nematodes, snails and annelids were ignored, but dead arthropods were readily fed upon and were sufficient to maintain adults and nymphs for many months. The adults were sluggish, timid animals that relied on armour, thanatosis and probably on noxious chemicals for protection: the juveniles produced secretions from idiosomal glands. In contrast, most early derivative Mesostigmata that we tested (Sejina, species of Sejus and Uropodella; Uropodina, Polyaspis sp. and Cercomegistina, an undescribed Asternoseiidae) were aggressive predators of small invertebrates and ingested fluids only; however, two species of Asternolaelaps (Sejina) had solid fungal and animal material in their guts. Similarly, the early derivative acariform (Palaeosomata, species of Stomacarus and Loftacarus) and opilioacariform mites (an undescribed Opilioacarida from Australia) that we examined all ingested particulate foods, including fungal and animal material. These observations are consistent with the hypothesis that the earliest mites were scavengers and opportunistic predators that ingested solid foods and that fluid feeding is a derived condition linking the three orders of Parasitiformes (Holothyrida, Ixodida and Mesostigmata).