Morphological descriptions of the nymph and adults of Ornithodoros clarki, the larva and nymph of Ornithodoros rondoniensis, with notes on their phylogenetic relationships

Based on tick specimens collected recently in Mexico, Nicaragua, Panama and Brazil, we provide morphological descriptions of the nymph and adults of Ornithodoros clarki Jones & Clifford, 1972 from the first three countries, and the larva and nymph of Ornithodoros rondoniensis (Labruna, Terassini, Camargo, Brandão, Ribeiro & Estrada-Peña, 2008) from Brazil. Also, an analysis of mitochondrial 16S rDNA sequences was performed to analyze the phylogenetic relationships of these tick species. Adults and nymphs of O. clarki and O. rondoniensis are unique among the Argasidae family by presenting exceptionally large spiracular plates with small goblets, and an integument with smooth polygonal mammillae. However, these two species are morphologically distinct based on specific patterns of coxal folds, idiosomal mammillae and pilosity, and female genital flap. In contrast, the larvae of O. clarki and O. rondoniensis are morphologically identical, except for a general larger size of the former species; this slight difference is corroborated by Principal Component Analysis (PCA) by using 40 morphometric variables. Phylogenetic analyses including 16S rDNA partial sequences of different Ornithodoros taxa from Central and South America indicate that O. rondoniensis from Brazil diverges from O. clarki from Mexico, Nicaragua and Panama. However, phylogenetic distance separating both alleged species is similar or slightly lower than the distances depicted for conspecific populations of a few other Ornithodoros species. Nonetheless, our primary criterion to maintain O. rondoniensis as a valid species is because its adult and nymphal stages do present distinct morphological traits that easily distinguish these postlarval stages from O. clarki.

Ornithodoros cerradoensis n. sp. (Acari: Argasidae), a member of the Ornithodoros talaje (Guérin-Méneville, 1849) group, parasite of rodents in the Brazilian Savannah

Ornithodoros cerradoensis n. sp. is described from field-collected and laboratory reared nymphs, males, females, and larvae parasitizing the rodents Cavia aperea and Thrichomys sp. in the Brazilian Savannah. This new species is morphologically and genetically related with the Ornithodoros talaje group and can be separated from other Neotropical species using the following combination of characters: larva with 18 pairs of setae on dorsum (seven anterolateral, four central and seven posterolateral), hypostome with median dentition 2/2; adults provided with large mammillae; dorsal disks surrounded by bulked marginal ridges delimiting barely pebbled areas; three disks in the anterolateral file, and median disk not merging with the posteromedian file. Feeding assays in the laboratory demonstrated that (1) larvae of O. cerradoensis are slow-feeders (∼6 days), (2) first nymphal instar (N1) molts to second instar (N2) without feeding, and (3) N2 and third nymphal instar (N3) engorge rapidly (minutes). With the exception of Ornithodoros hasei nymphs that depict flattened bodies, O. cerradoensis N1, N2, and N3 highly resemble homologous instars of other species in O. talaje sensu lato, therefore are not suitable for morphological comparisons within the group. In addition to morphological signature of larvae and adults that separate this new species; results of cross-mating attempts between O. cerradoensis and Ornithodoros guaporensis a morphologically and phylogenetically closely related species that also parasitizes rodents in the Brazilian Savannah; a Principal Component Analysis using larval characters; and a phylogenetic analysis using mitochondrial markers, support O. cerradoensis as an independent lineage within the Ornithodorinae.

Description of a new soft tick species (Acari: Argasidae: Ornithodoros) parasite of Octodon degus (Rodentia: Octodontidae) in northern Chile

A new argasid (Argasidae) tick is herein described based on morphology and molecular data obtained from larvae parasitizing Octodon degus and from ticks collected inside burrows in northern Chile. Unfed laboratory-reared larvae were mounted in slides for morphometrical and morphological analyses. Larvae of Ornithodoros octodontus n. sp. share morphological traits with Ornithodoros quilinensis and Ornithodoros xerophylus, two species associated with rodents in the Argentinean Chaco. However, a longer hypostome with two rows of 21 and 22 denticles each one, and conspicuous leaf-shaped anal plates separate O. octodontus. While nymphal stages of O. octodontus lack cheeks and possess a micromammillated dorsal integument, adults have cheeks and exhibit markedly irregular mammillae along their dorsal surface. Phylogenetic analyses of neotropical Argasidae based on mitochondrial 16S rDNA sequences point that O. octodontus forms a monophyletic group with O. xerophylus and an unidentified Ornithodoros sp. from Bolivia, all of them associated with burrow-dweller rodents. Ornithodoros aragaoi and Ornithodoros davisi, two rare species collected once only in the Peruvian Andean Plateau during 1955 are morphologically closely related with adults and nymphs of O. octodontus. Biological observations of O. octodontus revealed autogenic females. For the moment, subgeneric classification of this new species depends on further biological studies. The fauna of ticks occurring in Chile is now represented by 22 species, 11 belonging to the Argasidae family.

Comparative vector competence of the Afrotropical soft tick Ornithodoros moubata and Palearctic species, O. erraticus and O. verrucosus, for African swine fever virus strains circulating in Eurasia

African swine fever (ASF) is a lethal hemorrhagic disease in domestic pigs and wild suids caused by African swine fever virus (ASFV), which threatens the swine industry globally. In its native African enzootic foci, ASFV is naturally circulating between soft ticks of the genus Ornithodoros, especially in the O. moubata group, and wild reservoir suids, such as warthogs (Phacochoerus spp.) that are bitten by infected soft ticks inhabiting their burrows. While the ability of some Afrotropical soft ticks to transmit and maintain ASFV is well established, the vector status of Palearctic soft tick species for ASFV strains currently circulating in Eurasia remains largely unknown. For example, the Iberian soft tick O. erraticus is a known vector and reservoir of ASFV, but its ability to transmit different ASFV strains has not been assessed since ASF re-emerged in Europe in 2007. Little is known about vector competence for ASFV in other species, such as O. verrucosus, which occurs in southern parts of Eastern Europe, including Ukraine and parts of Russia, and in the Caucasus. Therefore, we conducted transmission trials with two Palearctic soft tick species, O. erraticus and O. verrucosus, and the Afrotropical species O. moubata. We tested the ability of ticks to transmit virulent ASFV strains, including one of direct African origin (Liv13/33), and three from Eurasia that had been involved in previous (OurT88/1), and the current epizooties (Georgia2007/1 and Ukr12/Zapo). Our experimental results showed that O. moubata was able to transmit the African and Eurasian ASFV strains, whereas O. erraticus and O. verrucosus failed to transmit the Eurasian ASFV strains. However, naïve pigs showed clinical signs of ASF when inoculated with homogenates of crushed O. erraticus and O. verrucosus ticks that fed on viraemic pigs, which proved the infectiousness of ASFV contained in the ticks. These results documented that O. erraticus and O. verrucosus are unlikely to be capable vectors of ASFV strains currently circulating in Eurasia. Additionally, the persistence of infection in soft ticks for several months reaffirms that the infectious status of a given tick species is only part of the data required to assess its vector competence for ASFV.

Description of Ornithodoros montensis n. sp. (Acari, Ixodida: Argasidae), a parasite of the toad Rhinella arenarum (Amphibia, Anura: Bufonidae) in the Monte Desert of Argentina

A new tick species of the genus Ornithodoros (Acari: Argasidae) was described from larvae collected on the toad Rhinella arenarum in a locality from Argentina belonging to the Monte Biogeographic Province. Ornithodoros montensis n. sp. was described based on morphological traits and sequences of the mitochondrial 16S rRNA gene. The diagnostic characters for this species are a combination of idiosoma oval, dorsal plate pyriform with posterior margin slightly concave, dorsal surface with 17 pairs of setae (7 anterolateral, 4 to 5 central and 5 to 6 posterolateral), ventral surface with 6 pairs of setae and 1 pair on anal valves, three pairs of sternal setae, postcoxal setae absent, and hypostome pointed apically with dental formula 3/3 in the anterior half and 2/2 posteriorly almost to base. Phylogenetic analysis of 16S rDNA sequences and a principal component analysis based on morphometric characters provided additional support to the description of O. montensis as an independent lineage within the genus Ornithodoros. Larvae of O. montensis are phylogenetically closely related to O. puertoricensis, O. rioplatensis, O. talaje s.s., O. guaporensis, O. hasei and O. atacamensis, all of them belonging to the "O. talaje group".

A survey of argasid ticks and tick-associated pathogens in the Peripheral Oases around Tarim Basin and the first record of Argas japonicus in Xinjiang, China

Argasid ticks (Acari: Argasidae) carry and transmit a variety of pathogens of animals and humans, including viruses, bacteria and parasites. There are several studies reporting ixodid ticks (Acari: Ixodidae) and associated tick-borne pathogens in Xinjiang, China. However, little is known about the argasid ticks and argasid tick-associated pathogens in this area. In this study, a total of 3829 adult argasid ticks infesting livestock were collected at 12 sampling sites of 10 counties in the Peripheral Oases, which carry 90% of the livestock and humans population, around the Tarim Basin (southern Xinjiang) from 2013 to 2016. Tick specimens were identified to two species from different genera by morphology and sequences of mitochondrial 16S rRNA and 12S rRNA were derived to confirm the species designation. The results showed that the dominant argasid ticks infesting livestock in southern Xinjiang were Ornithodoros lahorensis (87.86%, 3364/3829). Ornithodoros lahorensis was distributed widely and were collected from 10 counties of southern Xinjiang. Argas japonicus was collected from Xinjiang for the first time. In addition, we screened these ticks for tick-associated pathogens and showed the presence of DNA sequences of Rickettsia spp. of Spotted fever group and Anaplasma spp. in the argasid ticks. This finding suggests the potential role for Argas japonicus as a vector of pathogens to livestock and humans.

A morphological and phylogenetic analysis of Ornithodoros marinkellei (Acari: Argasidae), with additional notes on habitat and host usage

Ornithodoros marinkellei was described from larvae collected on Pteronotus spp. bats in Colombia and Panama. More recently, this tick was reported in the Brazilian Amazon. Because some morphometric differences were observed between O. marinkellei larvae from Colombia and Brazil, it was proposed that further investigations were needed to assess whether the differences could be attributed to intra- or inter-specific polymorphism. Herein, we collected O. marinkellei specimens in the type locality of Colombia, in Brazil, and in a new locality in Nicaragua, expanding the distribution of the species to Nicaragua. Morphometric analysis of larvae and adults, corroborated by a principal component analysis (PCA), indicated that the Brazilian specimens were larger than specimens from Colombia and Nicaragua. Phylogenetic analysis inferred from the mitochondrial 16S rRNA gene showed ticks from Colombia and Nicaragua more genetically related than any of them with ticks from Brazil, although ticks from the three countries grouped in a clade sister to a major clade containing sequences of various Neotropical Ornithodoros species. We concluded that ticks identified as O. marinkellei from Colombia, Nicaragua, and Brazil represent the same taxon, and that the genetic and morphological differences between them are likely to have a geographical bias. We redescribed the nymph of O. marinkellei, which has a vestigial hypostome, probably incompatible with blood feeding. We also report human infestation by O. marinkellei adults. As all reports of O. marinkellei adults have been from hot caves (temperature > 35 °C), this abiotic condition could be a limiting factor for the occurrence of this tick species.

Molecular evidence and additional morphological characters to distinguish Ornithodoros brodyi and Ornithodoros yumatensis (Ixodida: Argasidae) in their different developmental stages

Ornithodoros brodyi and Ornithodoros yumatensis are two species distributed in the Americas and associated with bats and caves. Both species have similar morphology, and the diagnostic traits of adults have not been detailed or illustrated accurately. In this study, the independence of both species is validated on the basis of molecular evidence (using partial sequences of 16S rDNA gene), and the morphological differences between them (dentition of the hypostome and traits of individual mammillae) are confirmed through light and scanning electron microscopy. In addition to the above characteristics, we observed other traits that may serve to differentiate both species: dorsal setae are short and thick in O. yumatensis and are thin and moderate in size in O. brodyi. We also observed a conspicuous hood in O. brodyi, which was absent in O. yumatensis. Another characteristic observed is a line of setae, near the end of Tarsi II-IV, which in O. brodyi is formed by less than five setae and in O. yumatensis by more than five. The main morphological difference between larvae of the 2 species is the number of ventral setae [9 (4 circumanal pairs) in O. brodyi and 8 (3 circumanal pairs) in O. yumatensis]. The genetic divergence in 16S rDNA sequences between these two species ranges from 9.7 to 10.6%.

Two new species of Ornithodoros (Ixodida; Argasidae) from the Southern Cone of South America

Two new species of the genus Ornithodoros were described from larvae collected in Argentina and Chile. Ornithodoros xerophylus n. sp. was described from specimens collected on the small rodent Graomys centralis in Argentina. The diagnostic characters for this species are a combination of dorsal plate slightly oval with a length of approximately 250 µm, 16 pairs of dorsal setae, hypostome with apex rounded and dental formula 2/2 in most rows, 3/3 apically, and capsule of the Haller's organ oval in shape without reticulations. Larvae of Ornithodoros lahillei n. sp. were collected on the reptiles Philodryas chamissonis and Callopistes maculatus in Chile. The diagnostic characters for O. lahillei are a combination of dorsal plate subtriangular with margins corrugated and posterior margin convex, dorsal surface with 14 pairs of setae, absence of postcoxal setae, and hypostome with apex pointed and dental formula 3/3 in anterior third and 2/2 in the middle and basal portion. Phylogenetic analysis of 16S rDNA sequences and a Principal Component Analysis based on morphometric characters provided additional support to the description of O. lahillei and O. xerophylus as two independent lineages within the genus Ornithodoros.

The epidemiology and geographic distribution of relapsing fever borreliosis in West and North Africa, with a review of the Ornithodoros erraticus complex (Acari: Ixodida)

BACKGROUND

Relapsing fever is the most frequent bacterial disease in Africa. Four main vector / pathogen complexes are classically recognized, with the louse Pediculus humanus acting as vector for B. recurrentis and the soft ticks Ornithodoros sonrai, O. erraticus and O. moubata acting as vectors for Borrelia crocidurae, B. hispanica and B. duttonii, respectively. Our aim was to investigate the epidemiology of the disease in West, North and Central Africa.

METHODS AND FINDINGS

From 2002 to 2012, we conducted field surveys in 17 African countries and in Spain. We investigated the occurrence of Ornithodoros ticks in rodent burrows in 282 study sites. We collected 1,629 small mammals that may act as reservoir for Borrelia infections. Using molecular methods we studied genetic diversity among Ornithodoros ticks and Borrelia infections in ticks and small mammals. Of 9,870 burrows investigated, 1,196 (12.1%) were inhabited by Ornithodoros ticks. In West Africa, the southern and eastern limits of the vectors and Borrelia infections in ticks and small mammals were 13°N and 01°E, respectively. Molecular studies revealed the occurrence of nine different Ornithodoros species, including five species new for science, with six of them harboring Borrelia infections. Only B. crocidurae was found in West Africa and three Borrelia species were identified in North Africa: B. crocidurae, B. hispanica, and B. merionesi.

CONCLUSIONS

Borrelia Spirochetes responsible for relapsing fever in humans are highly prevalent both in Ornithodoros ticks and small mammals in North and West Africa but Ornithodoros ticks seem absent south of 13°N and small mammals are not infected in these regions. The number of Ornithodoros species acting as vector of relapsing fever is much higher than previously known.

Ornithodoros peruvianus Kohls, Clifford & Jones (Ixodoidea: Argasidae) in Chile: a tentative diagnosis

Three argasid tick larvae were collected on April 2, 2010, from a common vampire bat, Desmodus rotundus, captured in the Parque Nacional Pan de Azúcar (26°09' S, 70°41' W), Region of Atacama, Chile. The larvae were diagnosed as Ornithodoros, and further comparative analysis showed them to be Ornithodoros peruvianus Kohls, Clifford & Jones or a species close to it. Phylogenetic analysis based on 16S mitochondrial rRNA gene sequences of Ornithodoros species plus four Argas species was carried out to clarify the taxonomic position of the larvae. This is the first finding of ticks parasitizing D. rotundus in Chile.

Ectoparasite associations of bats from central Pennsylvania

Between April and October 1997, 689 bats representing seven species were captured at Pennsylvania's Canoe Creek State Park. Each bat was sampled for ectoparasitic arthropods, and four species were collected from 13.2% of the host individuals. Ectoparasites include the bat flea Myodopsylla insignis (Rothschild), the wing mite Spinturnix americanus (Banks), the bed bug Cimex adjunctus Barber, and the soft tick Ornithodoros kelleyi Cooley & Kohls. Prevalence, relative density, and mean intensity were calculated for ectoparasites of Myotis lucifugus (Le Conte), which harbored all four ectoparasite species and was the most commonly captured host. Patterns of ectoparasite associations were examined with respect to host sex and habitat (roost characteristics). Female M. lucifugus hosted higher densities of ectoparasites than did males. Moreover, relative densities of ectoparasites from M. lucifugus were dependent on the proximate roost; hosts captured near Bat Church were more heavily parasitized than those captured near Hartman Mine. Two other bat species were infested with at least one ectoparasite, but sample sizes were too small to analyze statistically. These bat species included Myotis septentrionalis (Trouessart), harboring M. insignis, S. americanus, and O. kelleyi, and Eptesicus fuscus (Beauvois), which harbored M. insignis and O. kelleyi.

Antibacterial peptide defensin is involved in midgut immunity of the soft tick, Ornithodoros moubata

Two defensin genes A and B were previously demonstrated to be up-regulated by blood feeding in the soft tick, Ornithodoros moubata [Nakajima et al. (2001) Two isoforms of a member of the arthropod defensin family from the soft tick, Ornithodoros moubata (Acari: Argasidae). Insect Biochem Mol Biol 31: 747-751]. In this study, two defensin isoforms C and D similar to defensins A and B were newly cloned. A total of four defensins have been identified in O. moubata. All four Ornithodoros defensins are coded as prepro-defensins. Ornithodoros defensin genes consist of four exons and three introns, an organization reported in mussel defensins but not insect defensins. Ornithodoros defensin C and D genes are predominantly expressed in the midgut and up-regulated in response to blood feeding. The mature peptide of the previously cloned Ornithodoros defensin A was purified from the midgut lumen, indicating defensin is secreted into the midgut. These findings confirm the involvement of Ornithodoros defensin in midgut immunity.