Prevalence of 'Candidatus Rickettsia vini' in Ixodes arboricola ticks in the North of Spain, 2011-2013

Hard ticks (Acari: Ixodidae) associated with birds in Europe: Review of literature data

Hard ticks (Acari: Ixodidae) are considered the most important transmitters of pathogens in the temperate zone that covers most of Europe. In the era of climate change tick-borne diseases are predicted to undergo geographical range expansion toward the north through regions that are connected to southern areas of the continent by bird migration. This alone would justify the importance of synthesized knowledge on the association of tick species with avian hosts, yet birds also represent the most taxonomically and ecologically diverse part of urban vertebrate fauna. Birds frequently occur in gardens and near animal keeping facilities, thus playing a significant role in the dispersal of ticks and tick-borne pathogens in synanthropic environments. The primary aim of this review is to provide a comprehensive reference source (baseline data) for future studies, particularly in the context of discovering new tick-host associations after comparison with already published data. The records on the ixodid tick infestations of birds were assessed from nearly 200 papers published since 1952. In this period, 37 hard tick species were reported from 16 orders of avian hosts in Europe. Here we compile a list of these tick species, followed by the English and Latin name of all reported infested bird species, as well as the tick developmental stage and country of origin whenever this information was available. These data allowed a first-hand analysis of general trends regarding how and at which developmental stage of ticks tend to infest avian hosts. Five tick species that were frequently reported from birds and show a broad geographical distribution in the Western Palearctic (Ixodes arboricola, I. frontalis, I. ricinus, Haemaphysalis concinna and Hyalomma marginatum) were also selected for statistical comparisons. Differences were demonstrated between these tick species regarding their association with bird species that typically feed from the ground and those that rarely occur at the soil level. The ecology of these five bird-infesting tick species is also illustrated here according to avian orders, taking into account the ecology (habitat type) and activity (circadian rhythm and feeding level) of most bird species that represent a certain order.

Novel Genotypes of Nidicolous Argas Ticks and Their Associated Microorganisms From Spain

The knowledge of the distribution, richness and epidemiological importance of soft ticks of the genus Argas is incomplete. In Spain, five Argas species have been recorded, including three ornitophilic nidicolous ticks, but their associated microorganisms remain unknown. This study aimed to investigate ticks from bird nests and their microorganisms. Ticks were collected extensively from natural cavities and nest-boxes used by European rollers (Coracias garrulus) and little owls (Athene noctua) in Southeastern and Central Spain. Ticks were morphologically and genetically identified and corresponding DNA/RNA tick extracts were analyzed [individually (n = 150) or pooled (n = 43)] using specific PCR assays for bacteria (Anaplasmataceae, Bartonella, Borrelia, Coxiella/Rickettsiella, and Rickettsia spp.), viruses (Flaviviruses, Orthonairoviruses, and Phenuiviruses), and protozoa (Babesia/Theileria spp.). Six Argas genotypes were identified, of which only those of Argas reflexus (n = 8) were identified to the species level. Two other genotypes were closely related to each other and to Argas vulgaris (n = 83) and Argas polonicus (n = 33), respectively. These two species have not been previously reported from Western Europe. Two additional genotypes (n = 4) clustered with Argas persicus, previously reported in Spain. The remaining genotype (n = 22) showed low sequence identity with any Argas species, being most similar to the African Argas africolumbae. The microbiological screening revealed infection with a rickettsial strain belonging to Rickettsia fournieri and Candidatus Rickettsia vini group in 74.7% of ticks, mainly comprising ticks genetically related to A. vulgaris and A. polonicus. Other tick endosymbionts belonging to Coxiella, Francisella and Rickettsiella species were detected in ten, one and one tick pools, respectively. In addition, one Babesia genotype, closely related to avian Babesia species, was found in one tick pool. Lastly, Anaplasmataceae, Bartonella, Borrelia, and viruses were not detected. In conclusion, five novel Argas genotypes and their associated microorganisms with unproven pathogenicity are reported for Spain. The re-use of nests between and within years by different bird species appears to be ideal for the transmission of tick-borne microorganisms in cavity-nesting birds of semiarid areas. Further work should be performed to clarify the taxonomy and the potential role of soft Argas ticks and their microorganisms in the epidemiology of zoonoses.

Pathogenic microorganisms in ticks removed from Slovakian residents over the years 2008-2018

A total of 750 ticks feeding on humans were collected during the years 2008-2018. The majority of ticks (94.8 %) came from Slovakia, with 3.5 % from the Czech Republic, 0.9 % from Austria, and 0.3 % from Hungary. Travellers from Ukraine, Croatia, France, and Cuba also brought one tick from each of these countries. The majority of the analysed ticks were identified as Ixodes ricinus (94.3 %). Dermacentor reticulatus (0.93 %), Haemaphysalis concinna (0.1 %), Haemaphysalis sp. (0.1 %), Ixodes arboricola (0.1 %), and Rhipicephalus sp. (0.1 %) were also encountered. The most frequently found stage of I. ricinus was the nymph (69.9 %) followed by adult females (20.4 %) and larvae (8.3 %). Ticks were predominantly found on children younger than 10 years (46.3 %) and adults between 30-39 years (21.4 %). In children younger than 10 years, the ticks were usually found on the head, while in other age categories, the ticks were predominantly attached to legs. Ticks were further individually analysed for the presence of Rickettsia spp., Coxiella burnetii, Borrelia burgdorferi sensu lato, Anaplasma phagocytophilum, Neoehrlichia mikurensis, Bartonella spp. and Babesia spp. The overall prevalences of tick-borne bacteria assessed in I. ricinus ticks acquired in Slovakia were: rickettsiae 25.0 % (95 % CI: 21.7-28.2), B. burgdorferi s.l. 20.5 % (95 % CI: 17.4-23.5), A. phagocytophilum 13.5 % (95 % CI: 10.9-16.0), Babesia spp. 5.2 % (95 % CI: 3.5-6.9), C. burnetii 3.0 % (95 % CI: 1.5-4.6), and N. mikurensis 4.4 % (95 % CI: 2.0-6.8). Pathogenic species Rickettsia raoultii, Rickettsia helvetica, Rickettsia monacensis, A. phagocytophilum, Borrelia garinii, Borrelia afzelii, Borrelia valaisiana, Babesia microti, and Babesia divergens were identified in D. reticulatus and I. ricinus ticks.

Isolation of Candidatus Rickettsia vini from Belgian Ixodes arboricola ticks and propagation in tick cell lines

Candidatus Rickettsia vini was originally detected in Ixodes arboricola ticks from Spain, and subsequently reported from several other Western Palearctic countries including Belgium. Recently, the bacterium was isolated in mammalian (Vero) cell culture from macerated male I. arboricola from Czech Republic, but there have been no reports of propagation in tick cells. Here we report isolation in a tick cell line of three strains of Ca. R. vini from I. arboricola collected from nests of great tits (Parus major) in Belgium. Internal organs of one male and two engorged female ticks were dissected aseptically, added to cultures of the Rhipicephalus microplus cell line BME/CTVM23 and incubated at 28 °C. Rickettsia-like bacteria were first seen in Giemsa-stained cytocentrifuge smears between 2 and 15 weeks later. Two of the isolates grew rapidly, destroying the tick cells within 2–4 weeks of onward passage in BME/CTVM23 cells, while the third isolate grew much more slowly, only requiring subculture at 4−5-month intervals. PCR amplification of bacterial 16S rRNA and Rickettsia gltA, sca4, ompB, ompA and 17-kDa genes revealed that all three isolates were Ca. R. vini, with 100 % identity to each other and to published Ca. R. vini sequences from other geographical locations. Transmission electron microscopy revealed typical single Rickettsia bacteria in the cytoplasm of BME/CTVM23 cells. The Ca. R. vini strain isolated from the male I. arboricola tick, designated Boshoek1, was tested for ability to grow in a panel of Ixodes ricinus, Ixodes scapularis and R. microplus cell lines and in Vero cells. The Boshoek1 strain grew rapidly, causing severe cytopathic effect, in the R. microplus line BME26, the I. ricinus line IRE11 and Vero cells, more slowly in the I. ricinus line IRE/CTVM19, possibly established a low-level infection in the I. ricinus line IRE/CTVM20, and failed to infect cells of any of four I. scapularis lines over a 12-week observation period. This study confirmed the applicability of the simple tick organ-cell line co-cultivation technique for isolation of tick-borne Rickettsia spp. using BME/CTVM23 cells.

New record of Rickettsia vini in Ixodes lividus ticks from Lithuania

Ixodes lividus Koch, 1844 (Ixodida: Ixodidae) ticks are parasites specific to the sand martin (Riparia riparia). The distribution range of I. lividus covers Europe and Asia and they are found wherever sand martins nest. Borrelia burgdorferi sensu stricto, Borrelia garinii and Rickettsia vini have recently been detected in I. lividus ticks in Central Europe. The aim of this study was to investigate the presence of Rickettsia spp. (Rickettsiales: Rickettsiaceae) and Borrelia spp. (Spirochaetales: Spirochaetaceae) in I. lividus ticks in Lithuania. A total of 2622 non-engorged I. lividus from two different colonies comprising 40 sand martin nests were collected in Lithuania in 2013 and 2015. Rickettsial DNA was detected in 106 of the 117 pooled larvae samples, in all examined seven nymphs, four females and one male specimen. Sequence analysis of partial gltA, ompA and htrA genes showed 99-100 % identity with the corresponding R. vini sequences deposited in GenBank. None of I. lividus tested was infected with Borrelia burgdorferi sensu lato. This is the first time that the presence of R. vini has been reported in Lithuania.

Prevalence and diversity of Rickettsia species in ectoparasites collected from small rodents in Lithuania

BACKGROUND

Rickettsiae are emerging pathogens causing public health problems in many countries around the world. Rickettsia spp. are found in association with a wide range of arthropods which feed on different species of animals. However, the distribution and natural cycle of Rickettsia species and their association with different arthropod vectors are not fully established. The aim of this study was to investigate the presence and prevalence of Rickettsia spp. in ticks, mites and fleas parasitizing different species of small mammals in Lithuania and to molecularly characterize the Rickettsia spp. obtained from different ectoparasites.

RESULTS

A total of 1261 ectoparasites (596 Ixodes ricinus ticks, 550 mites of five species and 115 fleas of eight species) collected from 238 rodents in Lithuania during 2013-2014 were investigated for the presence of Rickettsia pathogens. Infection rates were calculated as the maximum likelihood estimation (MLE) with 95% confidence intervals (CI). The infection rate varied among ectoparasites and was found highest in fleas 43.5%, followed by I. ricinus ticks (MLE = 26.5%; 95% CI: 22.2-31.3%) and then mites (MLE = 9.3%; 95% CI: 7.0-12.2%). Sequence analysis of partial gltA and 17kDa genes revealed the presence of Rickettsia helvetica, R. felis, R. monacensis, Rickettsia sp. and rickettsial endosymbionts. Four Rickettsia spp. were identified in fleas, while three Rickettsia spp. were identified in Laelapidae mites and only one (R. helvetica) in I. ricinus ticks.

CONCLUSIONS

To our knowledge, this is the first report of the occurrence and molecular characterization of Rickettsia spp. in 11 species of ectoparasites of small rodents in Lithuania. The present data extend the knowledge on the distribution of Rickettsia spp. and their association with different arthropod vectors. Prior to our study, R. felis had never been identified in Lithuania. To our knowledge, this is also the first report of R. felis in L. agilis and H. microti mites and in Ct. agyrtes and H. talpae fleas, as well as the first detection of R. monacensis in Ct. agyrtes fleas.

Isolated populations of Ixodes lividus ticks in the Czech Republic and Belgium host genetically homogeneous Rickettsia vini

In the last two decades, the advent of molecular methods has revealed a remarkable diversity of rickettsiae (Rickettsiales: Rickettsiaceae) in invertebrates. Several species of these obligate intracellular bacteria are known to cause human infections, hence more attention has been directed towards human-biting ectoparasites. A spotted fever group Rickettsia sp. was previously detected in Ixodes lividus ticks (Ixodidae) associated with sand martins (Hirundinidae: Riparia riparia). In order to identify whether this rickettsia varies among isolated tick populations, a total of 1758 I. lividus ticks and five Ixodes ricinus ticks (Ixodidae) were collected in the Czech Republic and 148 I. lividus ticks were collected in Belgium, from nests of sand martins, European bee-eaters (Meropidae: Merops apiaster), Eurasian tree sparrows (Passeridae: Passer montanus), and from captured sand martins. We screened 165 and 78 I. lividus ticks (from the Czech Republic and Belgium, respectively) and all five I. ricinus ticks for the presence of rickettsial DNA. Only I. lividus samples were positive for Rickettsia vini, a spotted fever group rickettsia that commonly infects the tree-hole tick Ixodes arboricola (Ixodidae). Maximum likelihood analysis of the rickettsial sequences showed that the most closely related organism to R. vini corresponds to an uncharacterized rickettsia detected in Argas lagenoplastis (Argasidae), a nidicolous soft tick of the fairy martin (Hirundinidae: Petrochelidon ariel) in Australia. The observed variability of R. vini sequences from isolated tick populations was low; all 85 sequenced samples were identical to each other in five out of six partial rickettsial genes, except for the sca4 sequence (99.9% identity, 808/809 nt) that differed in I. lividus ticks from two sampling sites in the Czech Republic.

Seasonal infestation of birds with immature stages of Ixodes ricinus and Ixodes arboricola

This study assessed the parasitization of cavity-nesting birds and ground-nesting/foraging birds with larvae and nymphs of two Ixodes species, Ixodes ricinus and Ixodes arboricola. Totals of 679 (52.3%) I. ricinus and 619 (47.7%) I. arboricola ticks were collected from 15 species of passerine birds which were caught during the nesting and non-nesting periods of 2003-2006, in the south-eastern part of the Czech Republic, the Drahanská Vrchovina Uplands. In the non-nesting period from October to March, 6.8% (101/1492) of birds were infested with ticks, mainly with I. arboricola larvae. In the non-nesting period, the average intensity of infestation by I. arboricola and I. ricinus was 8.5 and 1.5 individuals per infested bird, respectively. In the nesting period from April to June, 21.6% (50/232) of birds were infested by both tick species but mainly with I. ricinus nymphs. The average intensity of infestation by I. ricinus and I. arboricola was 13.3 and 10.8 individuals per infested bird, respectively. Altogether, 23.2% of the infested birds were parasitized by both immature life stages of one or both tick species. From an enzootic perspective, co-feeding and co-infestation of I. ricinus and I. arboricola subadults on passerine birds might happen and may be important for the dissemination of tick-borne agents.

Characterization of rickettsiae in ticks in northeastern China

Background

Tick-borne rickettsioses are considered important emerging zoonoses worldwide, but their etiological agents, rickettsiae, remain poorly characterized in northeastern China, where many human cases have been reported during the past several years. Here, we determined the characteristics of Rickettsia spp. infections in ticks in this area.

Methods

Ticks were collected by flagging vegetation from Jilin and Heilongjiang provinces of northeastern China followed by morphological identification. The presence of Rickettsia spp. in ticks was detected by PCR targeting the 23S-5S ribosomal RNA intergenic spacer, citrate synthase (gltA) gene, and 190-kDa outer membrane protein gene (ompA). The newly-generated sequences were subjected to phylogenetic analysis using the software MEGA 6.0.

Results

The overall infection rate of Rickettsia spp. was 6.12 %. Phylogenetic analyses based on the partial gltA and ompA genes demonstrated that rickettsiae detected in the ticks belong to four species, including “Candidatus Rickettsia tarasevichiae”, Rickettsia heilongjiangensis, Rickettsia raoultii, and a potential new species isolate. The associated tick species were also identified, i.e. Dermacentor nuttalli and Dermacentor silvarum for R. raoultii, Haemaphysalis concinna and Haemaphysalis longicornis for R. heilongjiangensis, and Ixodes persulcatus for “Ca. R. tarasevichiae”. All Rickettsia spp. showed significantly high infection rates in ticks from Heilongjiang when compared to Jilin Province.

Conclusion

Rickettsia heilongjiangensis, R. raoultii and “Ca. R. tarasevichiae” are widely present in the associated ticks in northeastern China, but more prevalent in Heilongjiang Province. The data of this study increase the information on the distribution of Rickettsia spp. in northeastern China, which have important public health implications in consideration of their recent association with human diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s13071-016-1764-2) contains supplementary material, which is available to authorized users.

Rickettsia vini n. sp. (Rickettsiaceae) infecting the tick Ixodes arboricola (Acari: Ixodidae)

BACKGROUND

Recently, a new rickettsia named 'Candidatus Rickettsia vini' belonging to the spotted fever group has been molecularly detected in Ixodes arboricola ticks in Spain, the Czech Republic, Slovakia and Turkey, with prevalence reaching up to 100 %. The aim of this study was to isolate this rickettsia in pure culture, and to describe it as a new Rickettsia species.

METHODS

A total of 148 ornitophilic nidicolous ticks Ixodes arboricola were collected in a forest near Breclav (Czech Republic) and examined for rickettsiae. Shell vial technique was applied to isolate rickettsiae in Vero cells. Rickettsial isolation was confirmed by optical microscopy and sequencing of partial sequences of the rickettsial genes gltA, ompA, ompB, and htrA. Laboratory guinea pigs and chickens were used for experimental infestations and infections. Animal blood sera were tested by immunofluorescence assay employing crude antigens of various rickettsiae.

RESULTS

Rickettsia vini n. sp. was successfully isolated from three males of I. arboricola. Phylogenetic analysis of fragments of 1092, 590, 800, and 497 nucleotides of the gltA, ompA, ompB, and htrA genes, respectively, showed closest proximity of R. vini n. sp. to Rickettsia japonica and Rickettsia heilongjiangensis belonging to the spotted fever group. Experimental infection of guinea pigs and chickens with R. vini led to various levels of cross-reactions of R. vini-homologous antibodies with Rickettsia rickettsii, Rickettsia parkeri, 'Candidatus Rickettsia amblyommii', Rickettsia rhipicephali, Rickettsia bellii, and Rickettsia felis. Laboratory infestations by R. vini-infected I. arboricola larvae on chickens led to no seroconversion to R. vini n. sp., nor cross-reactions with R. rickettsii, R. parkeri, 'Ca. R. amblyommii', R. rhipicephali, R. bellii or R. felis.

CONCLUSIONS

Our results suggest that R. vini n. sp. is possibly a tick endosymbiont, not pathogenic for guinea pigs and chickens. Regarding specific phenotypic characters and significant differences of DNA sequences in comparison to the most closely related species (R. japonica and R. heilongjiangensis), we propose to classify the isolate as a new species, Rickettsia vini.

New tools, new tick-borne diseases?

Tick-borne diseases (TBDs) are a major public health concern that has increased in the past three decades. Nevertheless, emerging or reemerging TBDs may be still misdiagnosed. Molecular biology techniques for the screening of ticks, use of “Omics” approaches and the incorporation of analytical methods such as mass spectrometry or nuclear magnetic resonance, to the study of ticks and their associated pathogens or potential pathogens are promising tools for a more accurate differential diagnosis of TBDs. However, this huge amount of data needs to be carefully interpreted before being incorporated to the routine of clinical practice. In the meantime, a clinical approach and high level of suspicion keep being essential for the diagnosis and proper handling of TBDs.