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Since the beginning of the 1980s, 33 emerging tick-borne agents have been identified in mainland China, including eight species of spotted fever group rickettsiae, seven species in the family Anaplasmataceae, six genospecies in the complex Borrelia burgdorferi sensu lato, 11 species of Babesia, and the virus causing severe fever with thrombocytopenia syndrome. In this Review we have mapped the geographical distributions of human cases of infection. 15 of the 33 emerging tick-borne agents have been reported to cause human disease, and their clinical characteristics have been described. The non-specific clinical manifestations caused by tick-borne pathogens present a major diagnostic challenge and most physicians are unfamiliar with the many tick-borne diseases that present with non-specific symptoms in the early stages of the illness. Advances in and application of modern molecular techniques should help with identification of emerging tick-borne pathogens and improve laboratory diagnosis of human infections. We expect that more novel tick-borne infections in ticks and animals will be identified and additional emerging tick-borne diseases in human beings will be discovered.

Neoehrlichia mikurensis is an intracellular bacterium transmitted in Europe and Asia by ticks of the Ixodes ricinus complex. Interest in this bacterium has increased since it was demonstrated to be responsible for febrile syndromes in patients. To date, most clinical cases have been reported in northern Europe, but case series have also been described in central Europe and China. Notably, thrombotic events occurred during the course of the disease. We investigated the presence of N. mikurensis in 10,885 I. ricinus nymphs in two regions of France (Alsace and Brittany) collected between 2013 and 2020 and in 934 patients suspected of human granulocytic anaplasmosis in Alsace, an endemic area for Lyme borreliosis, using a specific PCR assay. N. mikurensis was detected in 5.42% of the ticks from Alsace, whereas only one (0.03%) tick was found to be positive in Brittany. Spatiotemporal disparities were also noticed within the Alsace region over the four collection sites investigated, and a significant increase in the prevalence of nymphs carrying N. mikurensis was also observed in the last three years of collection. Four out of 934 screened patients were found to be positive for N. mikurensis. Two had malignancies, and the other two were apparently immunocompetent. Superficial thrombosis was noticed in one patient, and long-lasting bacteremia was noted in another patient. These four patients are the first clinical cases of neoehrlichiosis described in France. We suggest including N. mikurensis in the differential diagnosis of post-tick bite febrile syndromes to treat patients and prevent the occurrence of thrombotic complications.

Background Elucidating which wildlife species significantly contribute to the maintenance of Ixodes ricinus populations and the enzootic cycles of the pathogens they transmit is imperative in understanding the driving forces behind the emergence of tick-borne diseases. Here, we aimed to quantify the relative contribution of four mustelid species in the life-cycles of I. ricinus and Borrelia burgdorferi ( sensu lato ) in forested areas and to investigate their role in the transmission of other tick-borne pathogens . Road-killed badgers, pine martens, stone martens and polecats were collected in Belgium and the Netherlands. Their organs and feeding ticks were tested for the presence of tick-borne pathogens. Results Ixodes hexagonus and I. ricinus were found on half of the screened animals ( n = 637). Pine martens had the highest I. ricinus burden, whereas polecats had the highest I. hexagonus burden. We detected DNA from B. burgdorferi ( s.l. ) and Anaplasma phagocytophilum in organs of all four mustelid species ( n = 789), and Neoehrlichia mikurensis DNA was detected in all species, except badgers. DNA from B. miyamotoi was not detected in any of the investigated mustelids. From the 15 larvae of I. ricinus feeding on pine martens ( n = 44), only one was positive for B. miyamotoi DNA, and all tested negative for B. burgdorferi ( s.l. ), N. mikurensis and A. phagocytophilum . The two feeding larvae from the investigated polecats ( n = 364) and stone martens ( n = 39) were negative for all four pathogens. The infection rate of N. mikurensis was higher in feeding nymphs collected from mustelids compared to questing nymphs, but not for B. burgdorferi ( s.l. ), B. miyamotoi or A. phagocytophilum. Conclusions Although all stages of I. ricinus can be found on badgers, polecats, pine and stone martens, their relative contribution to the life-cycle of I. ricinus in forested areas is less than 1%. Consequently, the relative contribution of mustelids to the enzootic cycles of I. ricinus -borne pathogens is negligible, despite the presence of these pathogens in organs and feeding ticks. Interestingly, all four mustelid species carried all stages of I. hexagonus , potentially maintaining enzootic cycles of this tick species apart from the cycle involving hedgehogs as main host species.

Background Ticks are transmitting a wide range of bacterial pathogens that cause substantial morbidity and mortality in domestic animals. The full pathogen burden transmitted by tick vectors is incompletely studied in many geographical areas, and extensive studies are required to fully understand the diversity and distribution of pathogens transmitted by ticks. Results We sampled 824 ticks of 11 species collected in 19 counties in Romania. Ticks were collected mainly from dogs, but also from other domestic and wild animals, and were subjected to molecular screening for pathogens. Rickettsia spp. was the most commonly detected pathogen, occurring in 10.6% (87/824) of ticks. Several species were detected: Rickettsia helvetica , R. raoultii , R. massiliae , R. monacensis , R. slovaca and R. aeschlimannii . A single occurrence of the zoonotic bacterium Bartonella vinsonii berkhoffii was detected in a tick collected from a dog. Anaplasma phagocytophilum occurred in four samples, and sequences similar to Anaplasma marginale/ovis were abundant in ticks from ruminants. In addition, molecular screening showed that ticks from dogs were carrying an Ehrlichia species identical to the HF strain as well as the enigmatic zoonotic pathogen “ Candidatus Neoehrlichia mikurensis”. An organism similar to E. chaffeensis or E. muris was detected in an Ixodes ricinus collected from a fox. Conclusions We describe an abundant diversity of bacterial tick-borne pathogens in ticks collected from animal hosts in Romania, both on the level of species and genotypes/strains within these species. Several findings were novel for Romania, including Bartonella vinsonii subsp. berkhoffii that causes bacteremia and endocarditis in dogs. “ Candidatus Neoehrlichia mikurensis” was detected in a tick collected from a dog. Previously, a single case of infection in a dog was diagnosed in Germany. The results warrant further studies on the consequences of tick-borne pathogens in domestic animals in Romania.

Background Globally, the disease ecology of reptiles remains understudied, even for threatened and iconic species such as the Galápagos marine iguana ( Amblyrhynchus cristatus ). Although marine iguanas are parasitized by distinct species of ticks and mites, research on vector-borne diseases for this species is limited. Methods In this study, we detected 16S ribosomal RNA (rRNA) sequences of Candidatus Allocryptoplasma in transcriptomic data from marine iguana blood samples. These 16S rRNA sequences were further characterized through phylogenetic analysis and a haplotype network. Results Our analysis revealed the first molecular evidence for the infection of marine iguanas with Candidatus Allocryptoplasma, a candidate genus in the family Anaplasmataceae with unknown pathogenic potential, likely transmitted by ticks. Phylogenetic analysis of the novel 16S rRNA sequences together with available Anaplasmataceae sequences confirmed their assignment to this candidate genus. A haplotype network analysis indicated that the agent infecting the marine iguana represents a distinct lineage within the known Ca . Allocryptoplasma diversity. Conclusions Candidatus Allocryptoplasma had a high prevalence within marine iguanas, infecting individuals across most of the geographical range of this species. To elucidate the transmission dynamics of this bacterium in the Galápagos ecosystem, ectoparasites of the marine iguana and shared vertebrate hosts should be screened for infection with Ca . Allocryptoplasma. Graphical Abstract

Neoehrlichia mikurensis is vector-borne gram-negative intracellular bacteria that has a wide range of hosts, and are recognized as emerging human pathogens. This study aimed to investigate the prevalence and genetic characteristics of N. mikurensis infections in rodents from central and southern of Shanxi Province, China. The rodents were captured, and the liver, spleen and kidney were collected for N . mikurensis detection and identification by 16 S rRNA and groEL genes sequencing. N . mikurensis was detected in Apodemus agrarius from Yangquan and Eothenomys inez from Yuncheng, with a positivity rate of 0.66% (2/301). Phylogenetic analysis based on 16 S rRNA and groEL genes revealed that the sequences in this study formed distinct branches separate from reported clusters (Clusters I-IV), clustered near Clusters III and IV, which the pathogenicity was unclear. Analysis of groEL gene polymorphism identified 12 haplotypes (Hap-1 to Hap-12) among 64 sequences (one novel sequence from this study and 63 from GenBank), with high haplotype diversity (Hd = 0.770 ± 0.030). Dominant haplotypes (Hap-2, Hap-3, Hap-4; 82.8% of sequences) exhibited distinct geographic specific patterns. In addition, Asian sequences exhibited greater diversity than European sequences, and human-derived sequences showed the higher genetic diversity than rodent- and tick-derived sequences. Overall, the detection of N . mikurensis in rodents in Shanxi Province expands its known distribution and provides novel insights into the genetic diversity in different regions and hosts.

Argasid ticks (soft ticks) are blood-feeding arthropods that can parasitize rodents, birds, humans, livestock and companion animals. Ticks of the Ornithodoros genus are known to be vectors of relapsing fever borreliosis in humans. In Algeria, little is known about relapsing fever borreliosis and other bacterial pathogens transmitted by argasid ticks. Between May 2013 and October 2015, we investigated the presence of soft ticks in 20 rodent burrows, 10 yellow-legged gull (Larus michahellis) nests and animal shelters in six locations in two different bioclimatic zones in Algeria. Six species of argasid ticks were identified morphologically and through 16S rRNA gene sequencing. The presence and prevalence of Borrelia spp., Bartonella spp., Rickettsia spp. and Anaplasmataceae was assessed by qPCR template assays in each specimen. All qPCR-positive samples were confirmed by standard PCR, followed by sequencing the amplified fragments. Two Borrelia species were identified: Borrelia hispanica in Ornithodoros occidentalis in Mostaganem, and Borrelia cf. turicatae in Carios capensis in Algiers. One new Bartonella genotype and one new Anaplasmataceae genotype were also identified in Argas persicus. The present study highlights the presence of relapsing fever borreliosis agents, although this disease is rarely diagnosed in Algeria. Other bacteria of unknown pathogenicity detected in argasid ticks which may bite humans deserve further investigation.

Studies on the ecology of microbial parasites and their hosts are predicated on understanding the assemblage of and relationship among the species present. Changes in organismal morphology and physiology can have profound effects on host-parasite interactions and associated microbial community structure. The marine rickettsial organism, \"Candidatus Xenohaliotis californiensis\" (WS-RLO), that causes withering syndrome of abalones has had a consistent morphology based on light and electron microscopy. However, a morphological variant of the WS-RLO has recently been observed infecting red abalone from California. We used light and electron microscopy, in situ hybridization and 16S rDNA sequence analysis to compare the WS-RLO and the morphologically distinct RLO variant (RLOv). The WS-RLO forms oblong inclusions within the abalone posterior esophagus (PE) and digestive gland (DG) tissues that contain small rod-shaped bacteria; individual bacteria within the light purple inclusions upon hematoxylin and eosin staining cannot be discerned by light microscopy. Like the WS-RLO, the RLOv forms oblong inclusions in the PE and DG but contain large, pleomorphic bacteria that stain dark navy blue with hematoxylin and eosin. Transmission electron microscopy (TEM) examination revealed that the large pleomorphic bacteria within RLOv inclusions were infected with a spherical to icosahedral-shaped putative phage hyperparasite. TEM also revealed the presence of rod-shaped bacteria along the periphery of the RLOv inclusions that were morphologically indistinguishable from the WS-RLO. Binding of the WS-RLO-specific in situ hybridization probe to the RLOv inclusions demonstrated sequence similarity between these RLOs. In addition, sequence analysis revealed 98.9-99.4 % similarity between 16S rDNA sequences of the WSRLO and RLOv. Collectively, these data suggest that both of these RLOs infecting California abalone are \"Candidatus Xenohaliotis californiensis,\" and that the novel variant is infected by a putative phage hyperparasite that induced morphological variation of its RLO host.

Anaplasma phagocytophilum , an obligate intracellular bacterial pathogen that lives in a host cell-derived vacuole, causes human and veterinary diseases of global importance. In the pathogen-occupied vacuole, A. phagocytophilum transitions from a replicative, non-infectious morphotype to a non-replicative, infectious morphotype that is released to spread infection. We established that distinct modes of bacterial cell division drive not only A. phagocytophilum replication but also its differentiation to the infectious form and dissemination to naïve cells. How pleomorphism is regulated in most vacuole-adapted bacterial pathogens is poorly understood. Therefore, this study advances fundamental knowledge of vacuole-adapted pleomorphic bacteria pathobiology and could ultimately identify common novel antibiotic targets for treating the diseases they cause.

Background Anaplasma phagocytophilum is a tick-vectored, obligately intracellular bacterium that infects a diversity of vertebrate hosts. In North America, the Ap-ha variant of A. phagocytophilum can cause dangerous infections in humans, whereas symptomatic human infections in Europe are rare. Conversely, the European host-generalist ecotype of A. phagocytophilum frequently causes illness in domestic ruminants while no comparable infections have been recorded from North America. Despite these differences in pathogenicity, the Ap-ha variant is closely aligned phylogenetically with the European host-generalist ecotype. Furthermore, North American populations of A. phagocytophilum are less genetically diverse than those in Europe. Taken together, these observations suggest that the North American Ap-ha variant may represent an introduced population of this bacterium. Methods Data from publicly available whole genomes of A. phagocytophilum were used to compare phylogeographic patterns and the extent of genetic divergence between the North American Ap-ha variant and the European host-generalist ecotype. Results The results confirm that North American Ap-ha samples are phylogenetically nested within the diversity of the European host-generalist ecotype, and that Ap-ha likely radiated within the last 100 years. As expected, the Ap-ha variant also exhibited relatively low genetic diversity levels compared to the European host-generalist ecotype. Finally, North American Ap-ha harbored significantly more derived alleles than the European host-generalist A. phagocytophilum population. Conclusions Collectively, these results support the hypothesis that the Ap-ha variant was recently introduced to North America from Europe and underwent a strong genetic bottleneck during this process (i.e. a ‘founder event’). Adaptation to novel vectors may have also played a role in shaping genetic diversity and divergence patterns in these pathogenic bacteria. These findings have implications for future studies aimed at understanding evolutionary patterns and pathogenicity variation within A. phagocytophilum . Graphical Abstract