Life cycle of the taiga tick Ixodes persulcatus (Acari: Ixodidae) in the North-West of Russia

Endogenous Viral Elements in Ixodid Tick Genomes

The documentation of endogenous viral elements (EVEs; virus-derived genetic material integrated into the genome of a nonviral host) has offered insights into how arthropods respond to viral infection via RNA interference pathways. Small non-coding RNAs derived from EVE loci serve to direct RNAi pathways in limiting replication and infection from cognate viruses, thus benefiting the host's fitness and, potentially, vectorial capacity. Here we use informatic approaches to analyze nine available genome sequences of hard ticks (Acari: Ixodidae; Rhipicephalus sanguineus, R. microplus, R. annulatus, Ixodes ricinus, I. persulcatus, I. scapularis, Hyalomma asiaticum, Haemaphysalis longicornis, and Dermacentor silvarum) to identify endogenous viral elements and to illustrate the shared ancestry of all elements identified. Our results highlight a broad diversity of viral taxa as having given rise to 1234 identified EVEs in ticks, with Mononegavirales (specifically Rhabdoviridae) well-represented in this subset of hard ticks. Further investigation revealed extensive adintovirus integrations in several Ixodes species, the prevalence of Bunyavirales EVEs (notably not observed in mosquitoes), and the presence of several elements similar to known emerging human and veterinary pathogens. These results will inform subsequent work on current and past associations with tick species with regard to the viruses from which their "viral fossils" are derived and may serve as a reference for quality control of various tick-omics data that may suffer from misidentification of EVEs as viral genetic material.

Geographical distribution of Ixodes persulcatus and associated pathogens: Analysis of integrated data from a China field survey and global published data

The increasing incidence and range expansion of tick-borne diseases have caused global threats to human and animal health under the background of climate and socioeconomic changes. As an efficient vector in transmission of tick-borne diseases, a growing burden caused by Ixodes persulcatus and associated pathogens could not be underestimated. This study summarized the distribution, hosts, and pathogens of I. persulcatus, and predicted the suitable habitats of this tick species worldwide. An integrated database involving a field survey, reference book, literature review, and related website was constructed. Location records of I. persulcatus and associated pathogens were incorporated into distribution maps using ArcGIS software. Positive rates for I. persulcatus-associated agents were estimated by meta-analysis. The global distribution of the tick species was predicted using Maxent model. I. persulcatus was distributed in 14 countries across the Eurasian continent, involving Russia, China, Japan, and several Baltic Sea states, which ranged between 21°N to 66°N. The tick species fed on 46 species of hosts, and 51 tick-borne agents could be harbored by I. persulcatus. The predictive model showed that I. persulcatus could be predominantly distributed in northern Europe, western Russia, and northern China. Our study fully clarified the potential public health risks posed by I. persulcatus and I. persulcatus-borne pathogens. Surveillance and control measures of tick-borne diseases should be enhanced to promote the health of humans, animals, and ecosystems.

Jingmenviruses: Ubiquitous, understudied, segmented flavi-like viruses

Jingmenviruses are a group of viruses identified recently, in 2014, and currently classified by the International Committee on Taxonomy of Viruses as unclassified Flaviviridae. These viruses closely related to flaviviruses are unique due to the segmented nature of their genome. The prototype jingmenvirus, Jingmen tick virus (JMTV), was discovered in Rhipicephalus microplus ticks collected from China in 2010. Jingmenviruses genomes are composed of four to five segments, encoding for up to seven structural proteins and two non-structural proteins, both of which display strong similarities with flaviviral non-structural proteins (NS2B/NS3 and NS5). Jingmenviruses are currently separated into two phylogenetic clades. One clade includes tick- and vertebrate-associated jingmenviruses, which have been detected in ticks and mosquitoes, as well as in humans, cattle, monkeys, bats, rodents, sheep, and tortoises. In addition to these molecular and serological detections, over a hundred human patients tested positive for jingmenviruses after developing febrile illness and flu-like symptoms in China and Serbia. The second phylogenetic clade includes insect-associated jingmenvirus sequences, which have been detected in a wide range of insect species, as well as in crustaceans, plants, and fungi. In addition to being found in various types of hosts, jingmenviruses are endemic, as they have been detected in a wide range of environments, all over the world. Taken together, all of these elements show that jingmenviruses correspond exactly to the definition of emerging viruses at risk of causing a pandemic, since they are already endemic, have a close association with arthropods, are found in animals in close contact with humans, and have caused sporadic cases of febrile illness in multiple patients. Despite these arguments, the vast majority of published data is from metagenomics studies and many aspects of jingmenvirus replication remain to be elucidated, such as their tropism, cycle of transmission, structure, and mechanisms of replication and restriction or epidemiology. It is therefore crucial to prioritize jingmenvirus research in the years to come, to be prepared for their emergence as human or veterinary pathogens.

A discrete tick population dynamics model with continuous and seasonal birth breeding

In this paper, we formulate a discrete two-stage model with two types of birth mechanisms, continuous and seasonal. We divide tick population into two subgroups, i.e. immature and mature. We also consider diapause as an important adaptive process for ticks in respond to climate change in both stages. We derive a formula for the inherent net reproductive numbers and explore their stability analysis. When breeding is continuous, there exists a unique globally asymptotically stable positive fixed point provided that the inherent net reproductive number is larger than one; the extinction fixed point is globally asymptotically stable if the inherent net reproductive number is less than one. When breeding is seasonal with 2-periodic birth function, there exists a unique globally asymptotically stable periodic solution provided that the inherent net reproductive number is larger than one, while the population goes to extinction if this value is less than one. For the cases with multi-periodic birth function, we use numerical simulation to compare their complex behaviors.

Characterization of Microbial Communities in Ixodes persulcatus (Ixodida: Ixodidae), a Veterinary and Medical Important Tick Species in Northeastern China

The importance of ticks in veterinary and medical science has received much attention. The dominant tick species in northeastern China, Ixodes persulcatus tick can transmit various pathogens to humans and animals and there are some studies on the microbiome composition of this tick. Our study characterized the bacterial communities in I. persulcatus by 16S amplicon pyrosequencing and described the differences of microorganisms in male and female tick and assessed the variation of microorganisms in the development stages in northeastern China. We mainly found the following bacteria genera: Pseudomonas (Pseudomonadales: Pseudomonadaceae), Citrobacter (Enterobacteriales: Enterobacteriaceae), and Rickettsia (Rickettsiales: Rickettsiaceae). Rickettsia is common and harmful pathogen transmitted by ticks. Meanwhile, we found there were differences between male and female tick of microbiomes, and the diversity of microbiome increased from engorged female ticks to eggs, but decreased when the eggs were molting into larvae. Our data showed that male ticks exhibited greater microbial diversity than female I. persulcatus tick and larvae presented with a different bacterial community compared to engorged female tick and hatched eggs. These findings may be useful for further understanding the interaction between I. persulcatus and microbiome biology.

Long-term dynamics of Ixodes persulcatus (Acari: Ixodidae) abundance in the north-west of its range (Karelia, Russia)

The article presents the results of long-term observations of variations in the abundance of Ixodes persulcatus, carried out since 1982, in the middle taiga subzone of Karelia. Adult questing ticks were collected from vegetation following standard flagging procedures. The time series was evaluated by singular spectrum analysis. Correlation coefficients were calculated for the observed tick abundances and meteorological data (mean daily air temperature and precipitation) for the current year and preceding years. Analysis of the time series revealed the trend and harmonic components with periods of 8, 2.5 and 4 years. Around 83% of the total variance is explained by the first principal component, which governs the general vector of change-a gradual reduction in I. persulcatus abundance from 2003 to 2017. Correlations between tick abundance and climatic indices were observed in all years and were associated with both temperature and precipitation. The greatest number of significant coefficients was obtained for correlations between tick abundance and weather conditions in the preceding season. An equation was suggested where tick abundance is described by a linear function with four variables: mean air temperature in April and July, total precipitation in February, and annual number of days with temperatures above 5 °С. Thus, the observed long-term dynamics are characterized by the following key patterns: a sharp population rise early in the 2000s, some recent decline (stabilization) of the abundance, the presence of quasi-periodic cycles, and a close correlation between tick abundance and climatic variables.

Differential diagnosis of Ixodes ricinus and Ixodes persulcatus: nymphs and larvae

We developed a method for differential diagnosis of nymphs and larvae of sheep (Ixodes ricinus (L.)) and taiga (I. persulcatus Sch.) ticks (Parasitiformes: Ixodidae) which allows to identify live material in the field.

[Influence of meteorological factors on the activity of the adult taiga tick (Ixodes persulcatus Sch., Ixodinae) in St. Petersburg and its environs]

The article deals with influence of meteorolical factors on the activity of the taiga tick Ixodes persulvatus Sch. in St. Petersburg and its environs. The results of correlation analysis of meteorological data (21 index) and data ticks collected in 1980-2012 allowed determining linear dependence between 11 meteorological indices an average amount of ticks. Factor analysis reduced dimentionality down to 3 indices: sum of temperatures higher than +5.0 °C, sum of precipitation higher than 5 mm per year, and Selyaninov hydrothermal coefficient. It was demonstrated that, at the background of the general tendency for the decrease of the average number of active ticks in the studied territories, correlation between the amount of ticks and meteorological indices can significantly vary as in the correlation density, so in the character and in dependence of microclimatic features of the collecting site. When variability of the mean abundance of ticks during years of investigation is low, the methods of collecting can significantly affect the results of the statistical analysis. This fact must be taken in consideration during prognosis of both dates of the beginning of epidemiological season and its intensity.