First detection of human pathogenic variant of Anaplasma phagocytophilum in field-collected Haemaphysalis longicornis, Pennsylvania, USA

Molecular Detection of Anaplasma phagocytophilum in Small Mammals and Infesting Ticks in Laikipia County, Kenya

Anaplasmosis is a set of disease conditions of various mammals caused by bacteria species of the genus Anaplasma. These are sub-microscopic, Gram-negative, obligate intracellular pathogens that infect both vertebrate and invertebrate hosts. Significant species that infect domestic and wildlife animals include Anaplasma marginale, Anaplasma ovis, Anaplasma mesaeterum, Anaplasma platys, and Anaplasma phagocytophilum. Although A. phagocytophilum has a widespread distribution, there are only a few epidemiological reports from sub-Saharan Africa. This study focused on molecular detection and characterization of A. phagocytophilum in small mammals and their infesting ticks in Laikipia County, Kenya. A total of 385 blood and 84 tick archival samples from small mammals (155 females and 230 males) were analyzed. The blood samples were subjected to a nested PCR-HRM melt analysis using species-specific primers to amplify the 16S ribosomal RNA genes. The ticks were also subjected to nested PCR-HRM involving 16S rRNA gene primers. Anaplasma phagocytophilum DNA was detected in 19 out of 385 samples using species-specific 16S rRNA gene primers giving a prevalence of 4.9% for A. phagocytophilum. Analysis of the tick's samples using 16S rRNA gene species-specific primers also detected A. phagocytophilum in 3 samples from Haemaphysalis leachi ticks (3/84) equivalent to prevalence of 3.6%. Sequencing of 16S rRNA PCR products confirmed A. phagocytophilum in small mammals and ticks' samples. Phylogenetic analysis of the haplotype from this study demonstrated a close ancestral link with strains from Canis lupus familiaris, Alces alces, Apodemus agrarius, and ticks (Haemaphysalis longicornis) reported in Europe, China, and Africa. Comparison was also made with a known pathogenic A. phagocytophilum variant HA and a nonpathogenic variant 1 that were clustered into a distinctive clade different form haplotypes detected in this study. All the haplotype sequences for A. phagocytophilum from this study were submitted and registered in GenBank under the accession numbers OQ308965-OQ308976. Our study shows that small mammals and their associated ticks harbor A. phagocytophilum. The vector competence for H. leachi in A. phagocytophilum transmission should further be investigated.

Antibody-blocking of a tick transporter impairs Anaplasma phagocytophilum colonization in Haemaphysalis longicornis ticks

The invasive Asian longhorned tick Haemaphysalis longicornis that vectors and transmits several animal pathogens is significantly expanding in the United States. Recent studies report that these ticks also harbor human pathogens including Borrelia burgdorferi sensu lato, Babesia microti, and Anaplasma phagocytophilum. Therefore, studies that address the interactions of these ticks with human pathogens are important. In this study, we report the characterization of H. longicornis organic anion-transporting polypeptides (OATPs) in interactions of these ticks with A. phagocytophilum. Using OATP-signature sequence, we identified six OATPs in the H. longicornis genome. Bioinformatic analysis revealed that H. longicornis OATPs are closer to other tick orthologs rather than to mammalian counterparts. Quantitative real-time PCR analysis revealed that OATPs are highly expressed in immature stages when compared to mature stages of these ticks. In addition, we noted that the presence of A. phagocytophilum upregulates a specific OATP in these ticks. We also noted that exogenous treatment of H. longicornis with xanthurenic acid, a tryptophan metabolite, influenced OATP expression in these ticks. Immunoblotting analysis revealed that antibody generated against Ixodes scapularis OATP cross-reacted with H. longicornis OATP. Furthermore, treatment of H. longicornis with OATP antibody impaired colonization of A. phagocytophilum in these ticks. These results not only provide evidence that the OATP-tryptophan pathway is important for A. phagocytophilum survival in H. longicornis ticks but also indicate OATP as a promising candidate for the development of a universal anti-tick vaccine to target this bacterium and perhaps other rickettsial pathogens of medical importance.

Virome diversity shaped by genetic evolution and ecological landscape of Haemaphysalis longicornis

BACKGROUND

Haemaphysalis longicornis is drawing attentions for its geographic invasion, extending population, and emerging disease threat. However, there are still substantial gaps in our knowledge of viral composition in relation to genetic diversity of H. longicornis and ecological factors, which are important for us to understand interactions between virus and vector, as well as between vector and ecological elements.

RESULTS

We conducted the meta-transcriptomic sequencing of 136 pools of H. longicornis and identified 508 RNA viruses of 48 viral species, 22 of which have never been reported. Phylogenetic analysis of mitochondrion sequences divided the ticks into two genetic clades, each of which was geographically clustered and significantly associated with ecological factors, including altitude, precipitation, and normalized difference vegetation index. The two clades showed significant difference in virome diversity and shared about one fifth number of viral species that might have evolved to "generalists." Notably, Bandavirus dabieense, the pathogen of severe fever with thrombocytopenia syndrome was only detected in ticks of clade 1, and half number of clade 2-specific viruses were aquatic-animal-associated.

CONCLUSIONS

These findings highlight that the virome diversity is shaped by internal genetic evolution and external ecological landscape of H. longicornis and provide the new foundation for promoting the studies on virus-vector-ecology interaction and eventually for evaluating the risk of H. longicornis for transmitting the viruses to humans and animals. Video Abstract.

Detection of multiple tick-borne pathogens in Ixodes scapularis from Hunterdon County, NJ, USA

Several human pathogens vectored by the blacklegged tick (Ixodes scapularis Say; Acari: Ixodidae) are endemic in the state of New Jersey. Disease incidence data suggest that these conditions occur disproportionately in the northwestern portion of the state, including in the county of Hunterdon. We conducted active surveillance at three forested sites in Hunterdon County during 2020 and 2021, collecting 662 nymphal and adult I. scapularis. Ticks were tested for five pathogens by qPCR/qRT-PCR: Anaplasma phagocytophilum, Babesia microti, Borrelia burgdorferi, Borrelia miyamotoi, and Powassan virus (POWV) lineage 2. Over 2 years, 25.4% of nymphs and 58.4% of adults were found infected with at least one pathogen, with 10.6% of all ticks infected with more than one pathogen. We report substantial spatial and temporal variability of A. phagocytophilum and B. burgdorferi, with high relative abundance of the human-infective A. phagocytophilum variant Ap-ha. Notably, POWV was detected for the first time in Hunterdon, a county where human cases have not been reported. Based on comparisons with active surveillance initiatives in nearby counties, further investigation of non-entomological factors potentially influencing rates of tick-borne illness in Hunterdon is recommended.

Host-pathogen associations revealed by genotyping of European strains of Anaplasma phagocytophilum to describe natural endemic cycles

BACKGROUND

The zoonotic intracellular alpha-proteobacterium Anaplasma phagocytophilum is a tick-transmitted pathogen. The associations between vertebrate reservoirs and vectors are described as wide-ranging, and it was previously shown that the pathogenicity of A. phagocytophilum differs depending on the combination of pathogen variant and infected host species. This leads to the question of whether there are variations in particular gene loci associated with different virulence. Therefore, this study aims at clarifying existing host-variant combinations and detecting possible reservoir hosts. To understand these interactions, a complex toolset for molecular epidemiology, phylogeny and network theory was applied.

METHODS

Sequences of up to four gene loci (msp4, msp2, groEL and 16S rRNA) were evaluated for different isolates from variable host species, including, for example, dogs, cattle and deer. Variant typing was conducted for each gene locus individually, and combinations of different gene loci were analysed to gain more detailed information about the genetic plasticity of A. phagocytophilum. Results were displayed as minimum spanning nets and correlation nets.

RESULTS

The highest diversity of variants for all gene loci was observed in roe deer. In cattle, a reduced number of variants for 16S rRNA [only 16S-20(W) and 16S-22(Y)] but multiple variants of msp4 and groEL were found. For dogs, two msp4 variants [m4-20 and m4-2(B/C)] were found to be linked to different variants of the other three gene loci, creating two main combinations of gene loci variants. Cattle are placed centrally in the minimum spanning net analyses, indicating a crucial role in the transmission cycles by possibly bridging the vector-wildlife cycle to infections of humans and domestic animals. The minimum spanning nets confirmed previously described epidemiological cycles of the bacterium in Europe, showing separation of variants originating from wildlife animals only and a set of variants shared by wild and domestic animals.

CONCLUSIONS

In this comprehensive study of 1280 sequences, we found a high number of gene variants only occurring in specific hosts. Additionally, different hosts show unique but also shared variant combinations. The use of our four gene loci expand the knowledge of host-pathogen interactions and may be a starting point to predict future spread and infection risks of A. phagocytophilum in Europe.

EVIDENCE OF PROTOZOAN AND BACTERIAL INFECTION AND CO-INFECTION AND PARTIAL BLOOD FEEDING IN THE INVASIVE TICK HAEMAPHYSALIS LONGICORNIS IN PENNSYLVANIA

The Asian longhorned tick, Haemaphysalis longicornis, an invasive tick species in the United States, has been found actively host-seeking while infected with several human pathogens. Recent work has recovered large numbers of partially engorged, host-seeking H. longicornis, which together with infection findings raises the question of whether such ticks can reattach to a host and transmit pathogens while taking additional bloodmeals. Here we conducted molecular blood meal analysis in tandem with pathogen screening of partially engorged, host-seeking H. longicornis to identify feeding sources and more inclusively characterize acarological risk. Active, statewide surveillance in Pennsylvania from 2020 to 2021 resulted in the recovery of 22/1,425 (1.5%) partially engorged, host-seeking nymphal and 5/163 (3.1%) female H. longicornis. Pathogen testing of engorged nymphs detected 2 specimens positive for Borrelia burgdorferi sensu lato, 2 for Babesia microti, and 1 co-infected with Bo. burgdorferi s.l. and Ba. microti. No female specimens tested positive for pathogens. Conventional PCR blood meal analysis of H. longicornis nymphs detected avian and mammalian hosts in 3 and 18 specimens, respectively. Mammalian blood was detected in all H. longicornis female specimens. Only 2 H. longicornis nymphs produced viable sequencing results and were determined to have fed on black-crowned night heron, Nycticorax nycticorax. These data are the first to molecularly confirm H. longicornis partial blood meals from vertebrate hosts and Ba. microti infection and co-infection with Bo. burgdorferi s.l. in host-seeking specimens in the United States, and the data help characterize important determinants indirectly affecting vectorial capacity. Repeated blood meals within a life stage by pathogen-infected ticks suggest that an understanding of the vector potential of invasive H. longicornis populations may be incomplete without data on their natural host-seeking behaviors and blood-feeding patterns in nature.

Equine Granulocytic Anaplasmosis

Equine granulocytic anaplasmosis is a clinically significant and common disease of equids that has a broader prevalence than was once thought. The most common clinical signs include high fever and edema, with mild to mderate thrombocytopenia and lymphopenia typically noted on complete blood count. Subclinical cases are reported and many are self-limiting. Rare clinical presentations include neurologic disease, vasculitis, dysphagia, rhabdomyolysis, or bicavitary effusion. Most cases resolve rapidly with appropriate antimicrobial intervention.

Rapid invasion and expansion of the Asian longhorned tick (Haemaphysalis longicornis) into a new area on Long Island, New York, USA

Since its discovery in the United States in 2017, the Asian longhorned tick (Haemaphysalis longicornis) has been detected in most eastern states between Rhode Island and Georgia. Long Island, east of New York City, a recognized high-risk area for tick-borne diseases, is geographically close to New Jersey and New York sites where H. longicornis was originally found. However, extensive tick surveys conducted in 2018 did not identify H. longicornis on Long Island. In stark contrast, our 2022 tick survey suggests that H. longicornis has rapidly invaded and expanded in multiple surveying sites on Long Island (12 out of 17 sites). Overall, the relative abundance of H. longicornis was similar to that of lone star ticks, Amblyomma americanum, a previously recognized tick species abundantly present on Long Island. Interestingly, our survey suggests that H. longicornis has expanded within the Appalachian forest ecological zone of Long Island's north shore compared to the Pine Barrens located on the south shore of Long Island. The rapid invasion and expansion of H. longicornis into an insular environment are different from the historical invasion and expansion of two native tick species, Ixodes scapularis (blacklegged tick or deer tick) and A. americanum, in Long Island. The implications of H. longicornis transmitting or introducing tick-borne pathogens of public health importance remain unknown.

Microhabitat modeling of the invasive Asian longhorned tick (Haemaphysalis longicornis) in New Jersey, USA

The Asian longhorned tick (Haemaphysalis longicornis) is a vector of multiple arboviral and bacterial pathogens in its native East Asia and expanded distribution in Australasia. This species has both bisexual and parthenogenetic populations that can reach high population densities under favorable conditions. Established populations of parthenogenetic H. longicornis were detected in the eastern United States in 2017 and the possible range of this species at the continental level (North America) based on climatic conditions has been modeled. However, little is known about factors influencing the distribution of H. longicornis at geographic scales relevant to local surveillance and control. To examine the importance of local physiogeographic conditions such as geology, soil characteristics, and land cover on the distribution of H. longicornis we employed ecological niche modeling using three machine learning algorithms - Maxent, Random Forest (RF), and Generalized Boosting Method (GBM) to estimate probability of finding H. longicornis in a particular location in New Jersey (USA), based on environmental predictors. The presence of H. longicornis in New Jersey was positively associated with Piedmont physiogeographic province and two soil types - Alfisols and Inceptisols. Soil hydraulic conductivity was the most important predictor explaining H. longicornis habitat suitability, with more permeable sandy soils with higher hydraulic conductivity being less suitable than clay or loam soils. The models were projected over the state of New Jersey creating a probabilistic map of H. longicornis habitat suitability at a high spatial resolution of 90×90 meters. The model's sensitivity was 87% for locations sampled in 2017-2019 adding to the growing evidence of the importance of soil characteristics to the survival of ticks. For the 2020-2022 dataset the model fit was 57%, suggestive of spillover to less optimal habitats or, alternatively, heterogeneity in soil characteristics at the edges of broad physiographic zones. Further modeling should incorporate abundance and life-stage information as well as detailed characterization of the soil at collection sites. Once critical parameters that drive the survival and abundance of H. longicornis are identified they can be used to guide surveillance and control strategies for this invasive species.

The wild life of ticks: Using passive surveillance to determine the distribution and wildlife host range of ticks and the exotic Haemaphysalis longicornis, 2010-2021

Background

We conducted a large-scale, passive regional survey of ticks associated with wildlife of the eastern United States. Our primary goals were to better assess the current geographical distribution of exotic Haemaphysalis longicornis and to identify potential wild mammalian and avian host species. However, this large-scale survey also provided valuable information regarding the distribution and host associations for many other important tick species that utilize wildlife as hosts.

Methods

Ticks were opportunistically collected by cooperating state and federal wildlife agencies. All ticks were placed in the supplied vials and host information was recorded, including host species, age, sex, examination date, location (at least county and state), and estimated tick burden. All ticks were identified to species using morphology, and suspect H. longicornis were confirmed through molecular techniques.

Results

In total, 1940 hosts were examined from across 369 counties from 23 states in the eastern USA. From these submissions, 20,626 ticks were collected and identified belonging to 11 different species. Our passive surveillance efforts detected exotic H. longicornis from nine host species from eight states. Notably, some of the earliest detections of H. longicornis in the USA were collected from wildlife through this passive surveillance network. In addition, numerous new county reports were generated for Amblyomma americanum, Amblyomma maculatum, Dermacentor albipictus, Dermacentor variabilis, and Ixodes scapularis.

Conclusions

This study provided data on ticks collected from animals from 23 different states in the eastern USA between 2010 and 2021, with the primary goal of better characterizing the distribution and host associations of the exotic tick H. longicornis; however, new distribution data on tick species of veterinary or medical importance were also obtained. Collectively, our passive surveillance has detected numerous new county reports for H. longicornis as well as I. scapularis. Our study utilizing passive wildlife surveillance for ticks across the eastern USA is an effective method for surveying a diversity of wildlife host species, allowing us to better collect data on current tick distributions relevant to human and animal health.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13071-022-05425-1.

Range Expansion of Native and Invasive Ticks, a Looming Public Health Threat

Native and invasive tick species pose a serious public health concern in the United States. Range expansion of several medically important tick species has resulted in an increasing number of communities at risk for exposure to ticks and tickborne pathogens.

Pathogen Spillover to an Invasive Tick Species: First Detection of Bourbon Virus in Haemaphysalis longicornis in the United States

Haemaphysalis longicornis (Neumann, 1901) (Acari: Ixodidae), the Asian longhorned tick, is an invasive tick species present in the USA since at least 2017 and has been detected in one-third of Virginia counties. While this species is associated with the transmission of multiple pathogens in its native geographical range of eastern Asia, little is known about its ability to acquire and transmit pathogens in the USA, specifically those that are transmissible to humans, although from an animal health perspective, it has already been shown to vector Theileria orientalis Ikeda strains. Emerging tick-borne viruses such as Bourbon virus (genus: Thogotovirus) are of concern, as these newly discovered pathogenic agents have caused fatal clinical cases, and little is known about their distribution or enzootic maintenance. This study examined H. longicornis collected within Virginia (from ten counties) for Bourbon and Heartland viruses using PCR methods. All ticks tested negative for Heartland virus via qRT-PCR (S segment target). Bourbon-virus-positive samples were confirmed on two different gene targets and with Sanger sequencing of the PB2 (segment 1) gene. Bourbon virus RNA was detected in one nymphal stage H. longicornis from Patrick County, one nymph from Staunton City, and one larval pool and one adult female tick from Wythe County, Virginia. An additional 100 Amblyomma americanum (Linnaeus 1758; lone star tick) collected at the same Patrick County site revealed one positive nymphal pool, suggesting that Bourbon virus may have spilled over from the native vector, potentially by co-feeding on a shared Bourbon-virus-infected vertebrate host. Blood tested from local harvested deer revealed a 11.1% antibody seroprevalence against Bourbon virus, exposure which further corroborates that this tick-borne virus is circulating in the southwest Virginia region. Through these results, it can be concluded that H. longicornis can carry Bourbon virus and that pathogen spillover may occur from native to invasive tick species.