Evidence for the long-distance transport of ticks and tick-borne pathogens by human travellers to Texas, USA

BACKGROUND

The incidence of tick-borne diseases in the USA has surged in recent years, with >50 000 cases reported from an estimated half-million cases annually. While domestic vectors are well characterized, the role of human travel in transporting exotic ticks and pathogens remains poorly understood.

METHODS

We analysed 4808 submissions of ticks removed from individuals to the Tick-Borne Disease Research Laboratory in Texas, USA, from 2004 to 2024. Tick species were identified phenotypically or through DNA-based sequencing, and pathogens (Borrelia spp., Rickettsia spp., Ehrlichia spp., Anaplasma phagocytophilum and Babesia microti) were detected using molecular assays. Submitter travel histories were cross-referenced with known tick geographic ranges to identify long-distance transport.

RESULTS

We documented cases of intercontinental, international and domestic interstate transport of ticks by human travellers. Four Ixodes ricinus ticks-originating from Europe-were transported to Texas; one tick carried Borrelia afzelii, a Lyme disease pathogen not endemic to North America. Central and South American Amblyomma species were repeatedly imported, raising concerns for pathogen transmission and tick establishment. Domestic travellers also carried Ixodes scapularis ticks infected with Borrelia burgdorferi sensu stricto, Babesia microti and A. phagocytophilum from Lyme-endemic regions of the USA to Texas, along with non-native species Ixodes pacificus, Dermacentor andersoni and Dermacentor occidentalis from endemic areas in the western United States.

CONCLUSIONS

Long-distance transport of ticks by travellers represents an underrecognized pathway for the global spread of ticks and tick-borne pathogens. Clinicians should consider travel history in tick-borne illness diagnostics. Enhanced surveillance, public education and travel screening are critical to mitigating these risks.

A simple improved method for extracting DNA from ethanol-preserved hard ticks and its applications

Hard tick exoskeletons, composed primarily of chitin, pose a significant challenge for researchers attempting to extract genetic material. This study presents a simple modified, alternative method for extracting DNA from ethanol-preserved hard ticks. The extracted DNA was further used for PCR amplification of phylogenetic markers for population genetics studies. The study also improvises the DNA extraction methods from commercial kits. We have used four DNA extraction methods: Modified Simple Alkaline Lysis, and other commercial kit-based methods (Kit X, Kit Y & Kit Z). The modified method for DNA extraction yielded comparable results in terms of concentration, and purity from all the life stages (adult, nymph, and larvae). The extracted DNA from each method was quantified and subjected to PCR amplification of molecular markers, ITS-1 and ITS-2. The nucleotide sequences from both markers were characterized for the first time and used for phylogenetic analysis of Amblyomma integrum, which is a potential vector for Kyasanur Forest Disease Virus (KFDV), causing monkey fever disease in India. These results demonstrate a cost-effective approach for isolating genomic DNA suitable for PCR amplification and subsequent nucleotide sequencing. Importantly, this simple method offers an option for population genetics study in resource-limited settings, facilitating field research with minimal equipment requirements. Additionally, the study showed tick homogenization can significantly improve DNA yield from commercial kits.

Exotic ticks removed from German travelers

We report the finding of five nymphs and three adult ticks attached to German tourists while traveling the American continents. All eight specimens were morphologically identified and confirmed genetically using the 16S rRNA gene and screened for Rickettsia spp. infections. Five tick species were identified: one Amblyomma mixtum nymph from Ecuador, one Amblyomma varium nymph from Colombia, three Amblyomma coelebs nymphs from Costa Rica, one Amblyomma americanum male from the USA, one Dermacentor andersoni female and one D. andersoni male from Canada. Tick-borne microorganisms screening using the pan-Rickettsia-PCR resulted in two positive and six negative ticks. The A. mixtum nymph was positive for Rickettsia amblyommatis, while the D. andersoni female was positive for Rickettsia peacockii.

Rhipicephalus Capensis (Acari: Ixodidae), A geographically restricted South African tick, returning with a human traveler to the United States

Accelerated frequency of recreational travel, globalization of business, and legal and illegal plant and animal trades have contributed to enduring introductions of exotic ticks into the United States. We herein report a new incursion of a female Rhipicephalus capensis on a human traveler returning to Connecticut from South Africa. Natural distribution of R. capensis is restricted to the Western Cape Province and southwestern portion of the Northern Cape Province of South Africa, an area called the Fynbos Biome, and adults of this species primarily parasitize large, wild ungulate hosts. Only one previous international introduction of this tick is documented on imported South African plant material into the United States in 1985. The specimen described here was identified initially by morphological means and subsequently, a partial DNA sequence for the mitochondrial ribosomal RNA gene was generated in a PCR assay, which showed 94.86% identity to an R. capensis sequence in GenBank. We also provide information on several other previously unreported or under-reported incursions by South African ticks into the United States in association with imported Fynbos floricultural materials and speckled Cape tortoises, Chersobius signatus. Documentation of these additional exotic tick species incursions highlights ongoing challenges of the international movement of humans, animals, and other goods carrying ticks of human and veterinary importance.

Biosecurity and post-arrival pathways in New Zealand: relating alien organism detections to tourism indicators

Between-country tourism is established as a facilitator of the spread of invasive alien species; however, little attention has been paid to the question of whether tourism contributes to the arrival and subsequent dispersal of exotic organisms within national borders. To assess the strength of evidence that tourism is a driver for the accidental introducing and dispersal of exotic organisms, we sourced three national databases covering the years 2011 to 2017, namely international and domestic hotel guest nights and national population counts, along with records of exotic organism detections collected by the Ministry for Primary Industries, New Zealand’s government agency that oversees biosecurity. We fitted statistical models to assess the strength of the relationship between monthly exotic organism interception rate, guest nights and population, the latter as a baseline. The analysis showed that levels of incursion detection were significantly related to tourism records reflecting the travel of both international and domestic tourists, even when population was taken into account. There was also a significant positive statistical correlation between the levels of detection of exotic organisms and human population. The core take-home message is that a key indicator of within-country human population movement, namely the number of nights duration spent in specific accommodation, is statistically significantly correlated to the contemporaneous detection of exotic pests. We were unable to distinguish between the effects of international as opposed to domestic tourists. We conclude that this study provides evidence of impact of within-country movement upon the internal spread of exotic species, although important caveats need to be considered.

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.

The Contribution of Wildlife Hosts to the Rise of Ticks and Tick-Borne Diseases in North America

Wildlife vertebrate hosts are integral to enzootic cycles of tick-borne pathogens, and in some cases have played key roles in the recent rise of ticks and tick-borne diseases in North America. In this forum article, we highlight roles that wildlife hosts play in the maintenance and transmission of zoonotic, companion animal, livestock, and wildlife tick-borne pathogens. We begin by illustrating how wildlife contribute directly and indirectly to the increase and geographic expansion of ticks and their associated pathogens. Wildlife provide blood meals for tick growth and reproduction; serve as pathogen reservoirs; and can disperse ticks and pathogens-either through natural movement (e.g., avian migration) or through human-facilitated movement (e.g., wildlife translocations and trade). We then discuss opportunities to manage tick-borne disease through actions directed at wildlife hosts. To conclude, we highlight key gaps in our understanding of the ecology of tick-host interactions, emphasizing that wildlife host communities are themselves a very dynamic component of tick-pathogen-host systems and therefore complicate management of tick-borne diseases, and should be taken into account when considering host-targeted approaches. Effective management of wildlife to reduce tick-borne disease risk further requires consideration of the 'human dimensions' of wildlife management. This includes understanding the public's diverse views and values about wildlife and wildlife impacts-including the perceived role of wildlife in fostering tick-borne diseases. Public health agencies should capitalize on the expertise of wildlife agencies when developing strategies to reduce tick-borne disease risks.

Morphometrics of Amblyomma mixtum in the State of Veracruz, Mexico

The tick Amblyomma mixtum is an ectoparasite of veterinary and public health importance because of its role as a vector of zoonotic pathogens. However, little is known about A. mixtum intraspecific variability and if morphological differentiation exists between populations across its geographic range. This study aimed to determine by electron microscopy the morphological variability of A. mixtum populations in the state of Veracruz, which has a large livestock population among states in Mexico. Forty male and 40 female A. mixtum collected from the 10 natural regions of Veracruz state were analyzed microscopically to accomplish main component analysis for each sex. Clusters were calculated with the out-tree method and a dendrogram produced to group the specimens according to their morphometric characteristics. Using 10 main components, 77% of the morphological variation of the ticks was explained. This is a reflection of scarce intraspecific variation between females. The dendogram for females grouped six clusters of specimens with similar characteristics. Morphometric variability in males was described using eight main components. Limited intraspecific variation was also observed between males. In males, the dendogram yielded six groups with similar morphometric characteristics. Morphometric analyses confirmed that the only species from the Amblyomma cajennense complex that are parasites to livestock in Veracruz state is A. mixtum. The eryxenous nature of A. mixtum combined with the frequent movement of livestock hosts may contribute to the apparent homogeneous phenotype of this tick species in Mexico.

Detection of Dermacentor andersoni (Acari: Ixodidae) in Brazil on a Human Traveler Returning from the United States

Only one previous record of an exotic tick on a Brazilian traveler has been reported. Here, we report the detection of Dermacentor andersoni (Stiles) in Brazil while attached to a human traveler returning from the United States. This report is the fifth record of D. andersoni as an exotic tick, and the second record of an exotic tick on a South American traveler.

Surveys for ticks on wildlife hosts and in the environment at Asian longhorned tick (Haemaphysalis longicornis)-positive sites in Virginia and New Jersey, 2018

Haemaphysalis longicornis, the Asian longhorned tick (ALT), is native to eastern Asia, but it has become invasive in several countries, including Australia, New Zealand and recently in the eastern United States (US). To identify wild mammal and avian host species in the US, we conducted active wildlife surveillance in two states with known ALT infestations (Virginia and New Jersey). In addition, we conducted environmental surveys in both states. These surveillance efforts resulted in detection of 51 ALT-infested individuals from seven wildlife species, including raccoon (Procyon lotor), Virginia opossum (Didelphis virginiana), red fox (Vulpes vulpes), woodchuck (Marmota monax), eastern cottontail (Sylvilagus floridanus), striped skunk (Mephitis mephitis) and white-tailed deer (Odocoileus virginianus). We found ALT in the environment in both states and also collected three native tick species (Amblyomma americanum, Dermacentor variablis and Ixodes scapularis) that are vectors of pathogens of public health and veterinary importance. This study provides important specific information on the wildlife host range of ALT in the US.

First glimpse into the origin and spread of the Asian longhorned tick, Haemaphysalis longicornis, in the United States

Established populations of Asian longhorned ticks (ALT), Haemaphysalis longicornis, were first identified in the United States (US) in 2017 by sequencing the mitochondrial cytochrome c oxidase subunit I (cox1) 'barcoding' locus followed by morphological confirmation. Subsequent investigations detected ALT infestations in 12, mostly eastern, US states. To gain information on the origin and spread of US ALT, we (1) sequenced cox1 from ALT populations across 9 US states and (2) obtained cox1 sequences from potential source populations [China, Japan and Republic of Korea (ROK) as well as Australia, New Zealand and the Kingdom of Tonga (KOT)] both by sequencing and by downloading publicly available sequences in NCBI GenBank. Additionally, we conducted epidemiological investigations of properties near its initial detection locale in Hunterdon County, NJ, as well as a broader risk analysis for importation of ectoparasites into the area. In eastern Asian populations (China/Japan/ROK), we detected 35 cox1 haplotypes that neatly clustered into two clades with known bisexual versus parthenogenetic phenotypes. In Australia/New Zealand/KOT, we detected 10 cox1 haplotypes all falling within the parthenogenetic cluster. In the United States, we detected three differentially distributed cox1 haplotypes from the parthenogenetic cluster, supporting phenotypic evidence that US ALT are parthenogenetic. While none of the source populations examined had all three US cox1 haplotypes, a phylogeographic network analysis supports a northeast Asian source for the US populations. Within the United States, epidemiological investigations indicate ALT can be moved long distances by human transport of animals, such as horses and dogs, with smaller scale movements on wildlife. These results have relevant implications for efforts aimed at minimizing the spread of ALT in the United States and preventing additional exotic tick introductions.