Established Population of the Gulf Coast Tick, Amblyomma maculatum (Acari: Ixodidae), Infected with Rickettsia parkeri (Rickettsiales: Rickettsiaceae), in Connecticut

The first record of an established population of Amblyomma maculatum (Acari: Ixodidae) in New Jersey, USA

Amblyomma maculatum Koch, the Gulf Coast tick, is expanding northward from its original range in the southeastern United States. In 2013, its most northern collection was in Delaware. Amblyomma maculatum has since been found in Connecticut, Illinois, and New York. It is the vector of the human pathogen Rickettsia parkeri, the causative agent of R. parkeri rickettsiosis. We report the first finding of an established population of A. maculatum in Salem County, NJ, with a R. parkeri infection prevalence rate of 23.8%. Our finding of A. maculatum is consistent with other recent findings in the northeastern United States in that specimens were found in open areas devoid of tree canopy. This discovery demonstrates the importance of tick surveillance in order to identify expanding tick populations and the pathogens they may transmit.

Tick-Borne Co-Infections: Challenges in Molecular and Serologic Diagnoses

Co-infections are a poorly understood aspect of tick-borne diseases. In the United States alone, nineteen different tick-borne pathogens have been identified. The majority of these agents are transmitted by only two tick species, Ixodes scapularis and Amblyomma americanum. Surveillance studies have demonstrated the presence of multiple pathogens in individual ticks suggesting a risk of polymicrobial transmission to humans. However, relatively few studies have explored this relationship and its impact on human disease. One of the key factors for this deficiency are the intrinsic limitations associated with molecular and serologic assays employed for the diagnosis of tick-borne diseases. Limitations in the sensitivity, specificity and most importantly, the capacity for inclusion of multiple agents within a single assay represent the primary challenges for the accurate detection of polymicrobial tick-borne infections. This review will focus on outlining these limitations and discuss potential solutions for the enhanced diagnosis of tick-borne co-infections.

Emerging tickborne viruses vectored by Amblyomma americanum (Ixodida: Ixodidae): Heartland and Bourbon viruses

Heartland (HRTV) and Bourbon (BRBV) viruses are newly identified tick-borne viruses, isolated from serious clinical cases in 2009 and 2014, respectively. Both viruses originated in the lower Midwest United States near the border of Missouri and Kansas, cause similar disease manifestations, and are presumably vectored by the same tick species, Amblyomma americanum Linnaeus (Ixodida: Ixodidae). In this article, we provide a current review of HRTV and BRBV, including the virology, epidemiology, and ecology of the viruses with an emphasis on the tick vector. We touch on current challenges of vector control and surveillance, and we discuss future directions in the study of these emergent pathogens.

A draft of the genome of the Gulf Coast tick, Amblyomma maculatum

The Gulf Coast tick, Amblyomma maculatum, inhabits the Southeastern states of the USA bordering the Gulf of Mexico, Mexico, and other Central and South American countries. More recently, its U.S. range has extended West to Arizona and Northeast to New York state and Connecticut. It is a vector of Rickettsia parkeri and Hepatozoon americanum. This tick species has become a model to study tick/Rickettsia interactions. To increase our knowledge of the basic biology of A. maculatum we report here a draft genome of this tick and an extensive functional classification of its proteome. The DNA from a single male tick was used as a genomic source, and a 10X genomics protocol determined 28,460 scaffolds having equal or more than 10 Kb, totaling 1.98 Gb. The N50 scaffold size was 19,849 Kb. The BRAKER pipeline was used to find the protein-coding gene boundaries on the assembled A. maculatum genome, discovering 237,921 CDS. After trimming and classifying the transposable elements, bacterial contaminants, and truncated genes, a set of 25,702 were annotated and classified as the core gene products. A BUSCO analysis revealed 83.4% complete BUSCOs. A hyperlinked spreadsheet is provided, allowing browsing of the individual gene products and their matches to several databases.

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.

Environmental Drivers of Gulf Coast Tick (Acari: Ixodidae) Range Expansion in the United States

In the United States, the Gulf Coast tick (Amblyomma maculatum Koch) is a species of growing medical and veterinary significance, serving as the primary vector of the pathogenic bacterium, Rickettsia parkeri (Rickettsiales: Rickettsiaceae), in humans and the apicomplexan parasite, Hepatozoon americanum, in canines. Ongoing reports of A. maculatum from locations outside its historically reported distribution in the southeastern United States suggest the possibility of current and continuing range expansion. Using an ecological niche modeling approach, we combined new occurrence records with high-resolution climate and land cover data to investigate environmental drivers of the current distribution of A. maculatum in the United States. We found that environmental suitability for A. maculatum varied regionally and was primarily driven by climatic factors such as annual temperature variation and seasonality of precipitation. We also found that presence of A. maculatum was associated with open habitat with minimal canopy cover. Our model predicts large areas beyond the current distribution of A. maculatum to be environmentally suitable, suggesting the possibility of future northward and westward range expansion. These predictions of environmental suitability may be used to identify areas at potential risk for establishment and to guide future surveillance of A. maculatum in the United States.

The Gulf Coast Tick, Amblyomma maculatum (Ixodida: Ixodidae), and Spotted Fever Group Rickettsia in the Highly Urbanized Northeastern United States

We report the multi-year collection of the Gulf Coast tick, Amblyomma maculatum Koch (Acaridae: Ixodida: Ixodidae) in Staten Island, New York City (NYC) as well as their detection in Brooklyn, NYC, and in Atlantic and Cumberland counties in southern New Jersey, USA. The first and most common detections were of adults, however in Freshkills Park on Staten Island larvae were also collected in a following year. The presence of larvae indicates that adults are successfully finding hosts in Staten Island. While it is still unknown how A. americanum reached Staten Island, immatures of this species often parasitize migratory birds, which are now often seen in Freshkills Park. We describe the landscape features of the area in Staten Island where populations were highest and larvae were detected, which could have facilitated the establishment of A. maculatum. Notably, we also report the presence of human pathogens Rickettsia parkeri in 5/10 (50%) of adults tested and R. felis in 1/24 (4.17%) of larvae tested. In addition to established populations in Staten Island we found evidence of A. maculatum in NJ and other NYC boroughs, suggesting current or future establishment is possible. The failure thus far to detect established populations in these areas may be due to inherent difficulties in detecting low density, spatially heterogeneous incipient populations, which could require targeted surveillance efforts for this species. We discuss the consequences to public health of the establishment of A. maculatum and detection of two additional rickettsial pathogens in the densely populated northeastern United States.

Will new ticks invade North America? How to identify future invaders

Invasive tick species and the pathogens they transmit pose increasing threats to human and animal health around the world. Little attention has been paid to the characteristics enabling tick species to invade. Here we analyze examples of tick invasion events in North America to identify factors that facilitated the invasion. Commonalities among invasive ticks are that they thrive in anthropogenically modified habitats, feed on either domestic animals or wildlife occurring in high density, and can survive across a broad range of climatic conditions. Invasive tick species varied widely in life history and reproductive habits, suggesting that invasion occurs when multiple characteristics converge. The combination of potential characteristics leading to invasion, however, improves our ability to predict future invaders and inform surveillance.

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.

Climate change influences on the geographic distributional potential of the spotted fever vectors Amblyomma maculatum and Dermacentor andersoni

Amblyomma maculatum (Gulf Coast tick), and Dermacentor andersoni (Rocky Mountain wood tick) are two North American ticks that transmit spotted fevers associated Rickettsia. Amblyomma maculatum transmits Rickettsia parkeri and Francisella tularensis, while D. andersoni transmits R. rickettsii, Anaplasma marginale, Coltivirus (Colorado tick fever virus), and F. tularensis. Increases in temperature causes mild winters and more extreme dry periods during summers, which will affect tick populations in unknown ways. Here, we used ecological niche modeling (ENM) to assess the potential geographic distributions of these two medically important vector species in North America under current condition and then transfer those models to the future under different future climate scenarios with special interest in highlighting new potential expansion areas. Current model predictions for A. maculatum showed suitable areas across the southern and Midwest United States, and east coast, western and southern Mexico. For D. andersoni, our models showed broad suitable areas across northwestern United States. New potential for range expansions was anticipated for both tick species northward in response to climate change, extending across the Midwest and New England for A. maculatum, and still farther north into Canada for D. andersoni.

Monitoring Trends in Distribution and Seasonality of Medically Important Ticks in North America Using Online Crowdsourced Records from iNaturalist

Simple Summary

An increasing number of cases of tick-borne diseases are being reported across North America and in new areas. This has been linked to the spread of ticks, primarily the blacklegged tick Ixodes scapularis and the lone star tick Amblyomma americanum, into new geographical regions. Tick surveillance systems have played an important role in monitoring the changing distributions of these ticks and have benefitted greatly from including data collected by members of the public through citizen or community science projects. Enlisting the help of community scientists is an economical way to collect large amounts of data over a wide geographical area, and participants can also benefit by receiving information relevant to their tick encounter, for example regarding tick-borne disease symptoms. This study examined tick observations from the online image-based biological recording platform iNaturalist to evaluate its use as an extra tool to collect information on expanding tick distributions. The distribution and seasonality of iNaturalist tick observations were found to accurately represent those of the studied species and identified potential new areas of tick expansion. Free-to-access iNaturalist data is a highly cost-effective method to support existing tick surveillance strategies to aid preparedness and response in emerging areas of tick establishment.

Abstract

Recent increases in the incidence and geographic range of tick-borne diseases in North America are linked to the range expansion of medically important tick species, including Ixodes scapularis, Amblyomma americanum, and Amblyomma maculatum. Passive tick surveillance programs have been highly successful in collecting information on tick distribution, seasonality, host-biting activity, and pathogen infection prevalence. These have demonstrated the power of citizen or community science participation to collect country-wide, epidemiologically relevant data in a resource-efficient manner. This study examined tick observations from the online image-based biological recording platform iNaturalist to evaluate its use as an effective tool for monitoring the distributions of A. americanum, A. maculatum, I. scapularis, and Dermacentor in the United States and Canada. The distribution and seasonality of iNaturalist tick observations were found to accurately represent those of the studied species. County-level iNaturalist tick occurrence data showed good agreement with other data sources in documented areas of I. scapularis and A. americanum establishment, and highlighted numerous previously unreported counties with iNaturalist observations of these species. This study supports the use of iNaturalist data as a highly cost-effective passive tick surveillance method that can complement existing surveillance strategies to update tick distributions and identify new areas of tick establishment.

Selective Host Attachment by Ixodes scapularis (Acari: Ixodidae): Tick-Lizard Associations in the Southeastern United States

Questing behavior and host associations of immature blacklegged ticks, Ixodes scapularis Say, from the southeastern United States are known to differ from those in the north. To elucidate these relationships we describe host associations of larval and nymphal I. scapularis from 8 lizard species sampled from 5 sites in the southeastern U.S. Larvae and nymphs attached in greater numbers to larger lizards than to smaller lizards, with differential levels of attachment to different lizard species. Blacklegged ticks are generally attached to skinks of the genus Plestiodon in greater numbers per unit lizard weight than to anoles (Anolis) or fence lizards (Sceloporus). The broad-headed skink, Plestiodon laticeps (Schneider), was a particularly important host for immature I. scapularis in our study and in several previous studies of tick-host associations in the southeast. Blacklegged ticks show selective attachment to Plestiodon lizard hosts in the southeast, but whether this results from behavioral host preferences or from ecological factors such as timing or microhabitat distributions of tick questing and host activity remains to be determined.

The Ixodes scapularis Symbiont Rickettsia buchneri Inhibits Growth of Pathogenic Rickettsiaceae in Tick Cells: Implications for Vector Competence

Ixodes scapularis is the primary vector of tick-borne pathogens in North America but notably does not transmit pathogenic Rickettsia species. This tick harbors the transovarially transmitted endosymbiont Rickettsia buchneri, which is widespread in I. scapularis populations, suggesting that it confers a selective advantage for tick survival such as providing essential nutrients. The R. buchneri genome includes genes with similarity to those involved in antibiotic synthesis. There are two gene clusters not found in other Rickettsiaceae, raising the possibility that these may be involved in excluding pathogenic bacteria from the tick. This study explored whether the R. buchneri antibiotic genes might exert antibiotic effects on pathogens associated with I. scapularis. Markedly reduced infectivity and replication of the tick-borne pathogens Anaplasma phagocytophilum, R. monacensis, and R. parkeri were observed in IRE11 tick cells hosting R. buchneri. Using a fluorescent plate reader assay to follow infection dynamics revealed that the presence of R. buchneri in tick cells, even at low infection rates, inhibited the growth of R. parkeri by 86-100% relative to R. buchneri-free cells. In contrast, presence of the low-pathogenic species R. amblyommatis or the endosymbiont R. peacockii only partially reduced the infection and replication of R. parkeri. Addition of host-cell free R. buchneri, cell lysate of R. buchneri-infected IRE11, or supernatant from R. buchneri-infected IRE11 cultures had no effect on R. parkeri infection and replication in IRE11, nor did these treatments show any antibiotic effect against non-obligate intracellular bacteria E. coli and S. aureus. However, lysate from R. buchneri-infected IRE11 challenged with R. parkeri showed some inhibitory effect on R. parkeri infection of treated IRE11, suggesting that challenge by pathogenic rickettsiae may induce the antibiotic effect of R. buchneri. This research suggests a potential role of the endosymbiont in preventing other rickettsiae from colonizing I. scapularis and/or being transmitted transovarially. The confirmation that the observed inhibition is linked to R. buchneri's antibiotic clusters requires further investigation but could have important implications for our understanding of rickettsial competition and vector competence of I. scapularis for rickettsiae.

Established Populations of Rickettsia parkeri-Infected Amblyomma maculatum Ticks in New York City, New York, USA

Objectives: We sought to determine the habitat associations and pathogen status of Amblyomma maculatum ticks in New York City (NYC), New York, USA, a newly expanded portion of their range. Methods: We collected 88 ticks from two NYC parks on Staten Island, one of the five boroughs of NYC, and compared our findings with similar habitat in Brooklyn, New York during the same time period (April 30-September 1). We tested 76 for pathogens. Results: We found adult and immature ticks in native and invasive grasses at Freshkills and Brookfield parks on Staten Island. No A. maculatum ticks were found in Brooklyn. 52.6% of ticks tested were infected with Rickettsia parkeri-the etiological agent of R. parkeri rickettsiosis. Conclusions: This high rate of R. parkeri in a dense urban center is of concern to the medical community, who should be aware of this species' presence and the symptoms of R. parkeri rickettsiosis.

First Record of Established Populations of the Invasive Pathogen Vector and Ectoparasite Haemaphysalis longicornis (Acari: Ixodidae) in Connecticut, United States

A number of invasive tick species capable of transmitting pathogens have been accidentally introduced into the U.S. in recent years. The invasion and further range expansion of these exotic ticks have been greatly facilitated by frequent global travel and trade as well as increases in legal and illegal importation of animals. We describe the discovery of the first established populations of Haemaphysalis longicornis Neumann and the first fully engorged human parasitizing specimen documented through passive tick surveillance in Fairfield County, Connecticut, U.S. We also report several individual specimens of this invasive arthropod and vector of multiple pathogens of medical and veterinary importance collected through active tick surveillance from three counties (Fairfield, New Haven, and New London). Considering the potential for invasive ticks to transmit numerous native and emerging pathogens, the implementation of comprehensive surveillance programs will aid in prompt interception of these ticks and reduce the risk of infection in humans and wildlife.

Phylogenetic Differentiation of Rickettsia parkeri Reveals Broad Dispersal and Distinct Clustering within North American Strains

The tick-borne pathogen Rickettsia parkeri causes a mild rickettsiosis, with cases reported from several countries to its known distribution in the Americas. Molecular analyses have identified a clear distinction between strains of R. parkeri sensu stricto (s. s.) and R. parkeri sensu lato (s. l.) as well as separation between North American and South American R. parkeri s. s. strains. To expand on this previous work, we developed a multilocus sequence typing analysis with two aims: first, to investigate the genetic diversity within strains of North American R. parkeri s. s., and second, to further the understanding of the genetic relationships between R. parkeri s. s. and R. parkeri s. l. Sixty-four R. parkeri isolates and 12 R. parkeri-positive tick lysates were analyzed using a novel typing scheme consisting of four coding regions and two intergenic regions. A concatenated Bayesian phylogeny that identified eight clades was constructed: three represent the R. parkeri s. l. strains, and five represent the R. parkeri s. s. strains. The clades appear to be generally phylogeographically organized and associated with specific tick vectors. However, while one of the four R. parkeri s. s. North American clades appears to be limited to the southwestern United States, the other North American clades exhibit broad dispersal, most notably seen in the largest group, which includes representative samples extending from northern Mexico to Delaware. This work highlights the increasingly recognized geographic range of R. parkeri in the Americas and suggests a potential public health risk for these areas.

IMPORTANCE Since 1937, when Rickettsia parkeri was originally identified in Amblyomma maculatum group ticks, the recognized range and associated vectors for this pathogen have expanded significantly. In recent years, R. parkeri has been identified in 12 tick species from seven countries in the Americas. Herein, we provide evidence that the greatest genetic diversity within R. parkeri exists in North America, where one R. parkeri sensu lato and four R. parkeri sensu stricto genotypes are present. While one distinct R. parkeri sensu stricto genotype exists only in the southwestern United States, three genotypes are broadly distributed in the eastern United States, with the largest of these found across the known range of R. parkeri in North America. In contrast, the South American R. parkeri sensu stricto samples represent a single genotype and are completely clonal at the loci analyzed, irrespective of their country of origin.