Vector competence of Amblyomma americanum (Acari: Ixodidae) for Rickettsia rickettsii

Rickettsia rickettsii - the etiologic agent of Rocky Mountain spotted fever (RMSF) - is widely spread across the Americas. In the US, Dermacentor spp. ticks are identified as primary vectors of R. rickettsii and Rhipicephalus sanguineus s.l. has been implicated in transmission of this pathogen in several locations in the Southwest. Conversely, ticks of the genus Amblyomma are recognized vectors of RMSF in Central and South America, but not in the US. A. americanum is one of the most aggressive human-biting ticks in the US, whose geographical range overlaps with that of reported RMSF cases. Despite sporadic findings of R. rickettsii DNA in field-collected A. americanum and circumstantial association of this species with human RMSF cases, its vector competence for R. rickettsii has not been appropriately studied. Therefore, we assessed the ability of A. americanum to acquire and transmit two geographically distant isolates of R. rickettsii. The Di-6 isolate of R. rickettsii used in this study originated in Virginia and the AZ-3 isolate originated in Arizona. Under laboratory conditions, A. americanum demonstrated vector competence for both isolates, although the efficiency of acquisition and transovarial transmission was higher for Di-6 than for AZ-3 isolate. Uninfected larvae acquired the pathogen from systemically infected guinea pigs, as well as while feeding side by side with Rickettsia-infected ticks on non-rickettsiemic hosts. Once acquired, R. rickettsii was successfully maintained through the tick molting process and transmitted to susceptible animals during subsequent feedings. Guinea pigs and dogs infested with infected A. americanum developed fever, scrotal edema and dermatitis or macular rash. R. rickettsii DNA was identified in animal blood, skin, and internal organs. The prevalence of infection within tick cohorts gradually increased due to side-by-side feeding of infected and uninfected individuals from 33 to 49% in freshly molted nymphs to 71-98% in engorged females. Moreover, R. rickettsii was transmitted transovarially by approximately 28% and 14% of females infected with Di-6 and AZ-3 isolates, respectively. Hence, A. americanum is capable of acquiring, maintaining and transmitting R. rickettsii isolates originating from two different geographical regions of the US, at least under laboratory conditions. Its role in ecology and epidemiology of RMSF in the US deserves further investigation.

Maximum Entropy-Based Ecological Niche Model and Bio-Climatic Determinants of Lone Star Tick (Amblyomma americanum) Niche

The potential distribution of Amblyomma americanum ticks in Kansas was modeled using maximum entropy (MaxEnt) approaches based on museum and field-collected species occurrence data. Various bioclimatic variables were used in the model as potentially influential factors affecting the A. americanum niche. Following reduction of dimensionality among predictor variables using principal components analysis, which revealed that the first two principal axes explain over 87% of the variance, the model indicated that suitable conditions for this medically important tick species cover a larger area in Kansas than currently believed. Soil moisture, temperature, and precipitation were highly correlated with the first two principal components and were influential factors in the A. americanum ecological niche. Assuming that the niche estimated in this study covers the occupied distribution, which needs to be further confirmed by systematic surveys, human exposure to this known disease vector may be considerably under-appreciated in the state.

Occurrence and distribution of Ambylomma americanum as determined by passive surveillance in Ontario, Canada (1999-2016)

The lone star tick, Amblyomma americanum, is spreading northward from its historical stronghold in the southeastern United States. As a vector and biting pest, public and veterinary health officials must remain vigilant of the lone star tick's expanding range. We use ticks submitted to Public Health Ontario Laboratory (1999-2016) to describe the spatial and temporal dynamics of A. americanum in Ontario, Canada, as well as submitter demographics. We identified 847 A. americanum submissions during the surveillance period, with 773 (91.3%) non-travel-related and 74 (8.7%) travel-related submissions. Annual A. americanum submissions increased over the surveillance period. Approximately 91% of non-travel-related submissions were adult ticks and 9% were nymphs. The highest submission rates were from individuals living in the Eastern and South West regions of the province. Adult specimens were primarily submitted from May through July and nymphs from March through September. Higher numbers of submissions were from young children (<10 years) and older adults (55-74 years), with equal proportions of male and female submitters. The majority of travel-related submissions were from travellers returning from the southeastern United States (i.e., Florida, North Carolina, South Carolina, Tennessee, Texas). Amblyomma americanum distribution is scattered in Ontario and submissions are likely the consequence of ongoing detection of adventive specimens. Further tick dragging is required to confirm the presence of established lone star tick populations in the province. Given the relatively rapid expansion of blacklegged ticks, Ixodes scapularis, populations in Ontario, we expect climate change to facilitate the range of expansion of A. americanum into the province. We propose an algorithm for identifying A. americanum-risk areas, which will aid public and veterinary health officials when assessing the risks posed by lone star ticks.

Evaluation of DEET and eight essential oils for repellency against nymphs of the lone star tick, Amblyomma americanum (Acari: Ixodidae)

DEET and Eight commercially available essential oils (oregano, clove, thyme, vetiver, sandalwood, cinnamon, cedarwood, and peppermint) were evaluated for repellency against host-seeking nymphs of the lone star tick, Amblyomma americanum. Concentration-repellency response was established using the vertical paper bioassay technique for each essential oil and compared with that of N,N-diethyl-3-methyl benzamide (DEET), a standard repellent compound present in many commercial repellent formulations. The effective concentration of DEET that repels 50% of ticks (EC50) was estimated at 0.02 mg/cm(2), while EC50s of the essential oils fall between 0.113 and 0.297 mg/cm(2). Based on EC50 estimates, oregano essential oil was the most effective among all essential oils tested, followed by clove, thyme, vetiver, sandalwood, cinnamon, cedarwood, and peppermint oils. None of the tested essential oils demonstrated a level of tick repellency found with DEET. Results from this study illustrated the challenge in search for more effective natural tick repellents.

First hemispheric report of invasive tick species Haemaphysalis punctata, first state report of Haemaphysalis longicornis, and range expansion of native tick species in Rhode Island, USA

BACKGROUND

Invasive arthropod vectors and the range expansions of native vectors can lead to public and veterinary health concerns, as these vectors may introduce novel pathogens or spread endemic pathogens to new locations. Recent tick invasions and range expansion in the USA has been attributed to climate and land use change, an increase in global travel, and importations of exotic animals.

METHODS

A 10-year surveillance study was conducted on Block Island, Rhode Island, from 2010 to 2020 including sampling ticks from small mammal and avian hosts.

RESULTS

We report the discovery and establishment of the red sheep tick (Haemaphysalis punctata) for the first time in the western hemisphere and in the US. This invasive species was first collected in 2010 on Block Island, was collected continuously throughout the study, and was collected from an avian host. We document the first report of the invasive Asian longhorned tick (Haemaphysalis longicornis) in the state of Rhode Island, first observed at our sites in 2018. Finally, we present data on the range expansion and establishment of two native tick species, the lone star tick and the rabbit tick, on Block Island.

CONCLUSION

This study emphasized the importance of long-term surveillance to detect changes in tick host communities, including invasive and expanding native vectors of potential significance to humans and wildlife.

Borrelia burgdorferi DNA absent, multiple Rickettsia spp. DNA present in ticks collected from a teaching forest in North Central Florida

Tick-borne diseases are an emerging public health threat in the United States. In Florida, there has been public attention directed towards the possibility of locally acquired Borrelia burgdorferi sensu stricto, the causative agent of Lyme disease, in association with the lone star tick. The aim of this study was to determine the prevalence of ticks and the pathogens they carry and potentially transmit, such as B. burgdorferi, in a highly utilized teaching and research forest in North Central Florida. Ticks were collected by dragging and flagging methods over a four month period in early 2014, identified, and tested by PCR for multiple pathogens including Anaplasma, Borrelia, Rickettsia, and Ehrlichia species. During the study period the following ticks were collected: 2506 (96.5%) Amblyomma americanum L., 64 (2.5%) Ixodes scapularis Say, 19 (0.7%) Dermacentor variabilis Say, and 5 (0.2%) Ixodes affinis Neuman. Neither Borrelia spp. (0/846) nor Anaplasma spp. (0/69; Ixodes spp. only) were detected by PCR in any of the ticks tested. However, Rickettsia DNA was present in 53.7% (86/160), 62.5% (40/64), 60.0% (3/5) and 31.6% (6/19) of A. americanum, I. scapularis, I. affinis and D. variabilis, respectively. Furthermore, E. chaffeensis and E. ewingii DNA were detected in 1.3% and 4.4% of adult A. americanum specimens tested, respectively. Although receiving an A. americanum bite is likely in wooded areas in North Central Florida due to the abundance of this tick, the risk of contracting a tick-borne pathogen in this specific area during the spring season appears to be low. The potential for pathogen prevalence to be highly variable exists, even within a single geographical site and longitudinal studies are needed to assess how tick-borne pathogen prevalence is changing over time in North Central Florida.

Ticks (Acari: Ixodida) on synanthropic small and medium-sized mammals in areas of the northeastern United States infested with the Asian longhorned tick, Haemaphysalis longicornis

The northeastern United States (US) is a hotspot for tick-borne diseases. Adding to an already complex vector landscape, in 2017 large populations of the invasive Haemaphysalis longicornis, the Asian longhorned tick, were detected in New Jersey (NJ) and later found to be widespread from Connecticut to Georgia. In its native range in northeastern Asia, H. longicornis is considered an important vector of deadly pathogens to humans, companion animals, and livestock. To identify the primary hosts of H. longicornis, we surveyed synanthropic small and medium-sized mammals in three different sites in suburban New Brunswick, NJ. Specifically, we collected approximately 9,000 tick specimens belonging to nine species from 11 different species of mammals sampled between May and September 2021. We found that H. longicornis feeds more frequently on rodents than previously thought, and that this invasive tick is likely exposed to important enzootic and zoonotic pathogens. Overall, we obtained detailed information about the seasonal dynamics and feeding patterns of six tick species common in the northeastern US, Haemaphysalis longicornis, Amblyomma americanum, Dermacentor variabilis, Ixodes scapularis, Ixodes texanus and Ixodes cookei. We found that unlike I. scapularis that feeds on mammals of all sizes, H. longicornis feeds on hosts following the general pattern of A. americanum, favoring larger species such as skunks, groundhogs, and raccoons. However, our survey revealed that unlike A. americanum, H. longicornis reaches high densities on Virginia opossum. Overall, the newly invasive H. longicornis was the most numerous tick species, both on multiple host species and in the environment, raising significant questions regarding its role in the epidemiology of tick-borne pathogens, especially those affecting livestock, companion animals and wildlife. In conclusion, our findings provide valuable insights into the tick species composition on mammalian hosts in NJ and the ongoing national expansion of H. longicornis.

Alpha-Gal IgE Prevalence Patterns in the United States: An Investigation of 3,000 Military Recruits

BACKGROUND

IgE to the oligosaccharide galactose-alpha-1,3-galactose (alpha-gal) is an important cause of allergic reactions to mammalian meat. The "alpha-gal syndrome" is strongly associated with a preceding history of tick bites and in the United States is most commonly reported in parts of the southeast, but there has been limited investigation into national alpha-gal sensitization patterns and the relevance of other risk factors.

OBJECTIVE

To systematically investigate alpha-gal IgE prevalence, regional patterns, and risk factors.

METHODS

Alpha-gal IgE was measured by ImmunoCAP in biobanked serum samples collected from 3000 service members who presented for intake to 1 of 10 military bases in the central/eastern United States. Alpha-gal IgE sensitization (cutoff 0.1 international units/mL) was related to home of record at enlistment.

RESULTS

Of the cohort, 2456 (81.9%) subjects were male, median age was 19 years (interquartile range: 18-22 years), and alpha-gal IgE was detected in 179 (6.0%). Home of record spanned all 50 states, with a median of 36 recruits per state (range: 3-261). The highest prevalence rates were in Arkansas (39%), Oklahoma (35%), and Missouri (29%), with several other southeastern states >10%. Granular mapping revealed sensitization patterns that closely mimicked county-level Amblyomma americanum reports and Ehrlichia chaffeensis infections. Sensitization was associated with male sex, rural residence, and White race in univariate and multivariable models.

CONCLUSIONS

In this systematic survey, the prevalence of alpha-gal IgE among incoming military personnel was 6.0%. There were significant regional differences, with an overall pattern consistent with the known range of the lone star tick (A. americanum) and highest frequency in an area including Arkansas, Oklahoma, and Missouri.

Effective control of the motile stages of Amblyomma americanum and reduced Ehrlichia spp. prevalence in adults via permethrin treatment of white-tailed deer in coastal Connecticut, USA

The lone star tick, Amblyomma americanum, is a common human-biting species whose range has been largely restricted to the southeastern United States, until recent detections of established populations on Long Island, New York and throughout coastal southern New England. We evaluated the effectiveness of topical treatment of 10 % permethrin delivered via 4-poster devices to white-tailed deer, Odocoileus virginianus, in the management of a newly discovered A. americanum population in Norwalk, Connecticut. Using a high-density deployment of one 4-poster device/12.7 ha, we were successful in significantly reducing densities of host-seeking adults (93 % reduction), nymphs (92 %), and larvae (96 %) from 2018 to 2020. We also documented a significant reduction (87 %) in parasitizing adults and nymphs on white-tailed deer from 2018 to 2019. The prevalence of Ehrlichia chaffeensis and Ehrlichia ewingii combined in host-seeking adults declined significantly from 47 % at the time the A. americanum population was discovered in 2017 to 7% in 2020. However, the prevalence in nymphs remained static (∼9%) throughout the study period. These data demonstrate that, when properly deployed in a density-dependent manner in terms of deer abundance, 4-poster devices can effectively manage parasitizing and host-seeking A. americanum populations and reduce the prevalence of two ehrlichial species of public health importance.

Evaluation of oral fluralaner (Bravecto®) for efficacy against nymphs of Amblyomma americanum and Rhipicephalus sanguineus (sensu lato)

BACKGROUND

Amblyomma americanum and Rhipicephalus sanguineus (sensu lato) nymphs commonly feed on and transmit pathogens to dogs (Canis familiaris). Control of immature and adult tick life stages is necessary to fully protect animals. We evaluated efficacy of oral fluralaner (Bravecto®) against induced infestations with A. americanum and R. sanguineus (s.l.) nymphs on dogs in two experiments.

METHODS

In each experiment, 10 dogs were administered oral fluralaner chewable tablets one time on Day 0 at a targeted minimum dose of 25 mg/kg body weight and 10 dogs remained non-treated controls. Dogs were infested with two groups of 50 A. americanum nymphs and two groups of 50 R. sanguineus (s.l.) nymphs on Days -1, 6, 28, 56 and 84. At 48 h and 72 h post-infestation, nymphs were collected from dogs, assessed as live or dead, and enumerated into categories defining attachment and engorgement status. Fluralaner efficacy was determined in separate analyses against all live nymphs and against live-fed nymphs, i.e. live nymphs that were attached to dogs at the time of collection and/or were engorged. Fluralaner was considered effective when mean numbers of live ticks were reduced in fluralaner-treated dogs by ≥ 90%.

RESULTS

Fluralaner efficacy against all live and live-fed A. americanum nymphs in the first experiment was > 94% on all collection days. Efficacy against all live R. sanguineus (s.l.) nymphs in the first experiment was  > 96% on all collection days  excluding the 48 h counts for infestations on Days 28 (83.7%), 56 (82.9%) and 84 (86.7%); efficacy against live-fed R. sanguineus (s.l.) nymphs was > 95% on all 48 h/72 h count days. Fluralaner efficacy against all live A. americanum nymphs in the second experiment was > 93% on all collection days for 8 weeks excluding the 48 h count for infestation on Day 56 (87.8%); efficacy against live-fed A. americanum nymphs was > 91% on all count days for 8 weeks. Efficacy against all live R. sanguineus (s.l.) nymphs in the  second experiment was > 91% on all 72 h collection days  except for infestations on Days 28 (76.8%) and 56 (86.3%); efficacy against live-fed R. sanguineus (s.l.) nymphs was 100% on all 72 h count days.

CONCLUSIONS

A single administration of oral fluralaner to dogs is effective against A. americanum and R. sanguineus (s.l.) nymphs for up to 12 weeks.

Fatal attraction: lone star ticks (Amblyomma americanum) exhibit preference for human female breath over male breath

Ticks use a variety of chemical cues to locate hosts, the main cue being carbon dioxide, which is exhaled by hosts. This study sought to experimentally determine whether ticks exhibit preference among human hosts based on host sex, as the chemical components of human male and female breath have been shown to differ. We focused on the lone star tick, Amblyomma americanum, due to its importance as a disease vector in the United States and its active host-seeking behavior. To test the hypothesis that ticks exhibit preference based upon host sex, we conducted a binary choice behavioral bioassay. Male and female human volunteers (n = 20 pairs) breathed into opposite sides of a secured polycarbonate tube containing 10 adult A. americanum and the proportion of ticks that exhibited a host preference was recorded. We found that under controlled conditions, human females attract a significantly larger proportion of ticks than males. Possible mechanisms to explain these results include that (1) female breath contains components that ticks find attractive, and/or (2) male breath contains a repellent chemical component.

A case of morphological anomalies in Amblyomma americanum (Acari: Ixodidae) collected from nature

We describe a case of morphological anomalies in Amblyomma americanum, a medically important species associated with several human diseases and medical conditions. Based on morphological characters using dichotomous morphological keys, high-resolution light microscopy, and scanning electron microscopy imaging, the tick was identified as Am. americanum nymph exhibiting various morphological anomalies including ectromely associate with asymmetry, olygomely (lack) of the fourth left leg, and schizomely (bifurcation of palpus) on the right side. We believe this is the first report of the presence of several spontaneous anomalies in one Am. americanum specimen. Morphological identity of the specimen was corroborated by DNA sequencing of the mitochondrial 16S region. We discuss recent reports of morphological anomalies in ixodid ticks and emphasize the significance of additional studies of teratology in medically important tick species and its potential implications.

Comparative speed of kill provided by lotilaner (Credelio™), sarolaner (Simparica Trio™), and afoxolaner (NexGard™) to control Amblyomma americanum infestations on dogs

BACKGROUND

Canine acaricides with rapid onset and sustained activity can reduce pathogen transmission risk and enhance pet owner experience. This randomized, complete block design, investigator-masked study compared the speed of kill of Amblyomma americanum provided by three monthly-use isoxazoline-containing products.

METHODS

Eight randomized beagles per group were treated (day 0), per label, with sarolaner (combined with moxidectin and pyrantel, Simparica Trio™), afoxolaner (NexGard™), or lotilaner (Credelio™), or remained untreated. Infestations with 50 adult A. americanum were conducted on days - 7, - 2, 21, and 28, and tick counts were performed on day - 5 (for blocking), and at 4, 8, 12, 24, 48, and 72 h following treatment and subsequent infestations. Efficacy calculations were based on geometric mean live tick counts. A linear mixed model was used for between-group comparisons.

RESULTS

On day 0, only lotilaner significantly reduced an A. americanum infestation by 12 h (43.3%; P = 0.002). Efficacy of lotilaner and afoxolaner at 24 h post-treatment was 95.3% and 97.6%, respectively, both significantly different from sarolaner (74%) (P = 0.002, P < 0.001, respectively). On day 21, at 12 h postinfestation, lotilaner efficacy (59.6%) was significantly different from sarolaner (0.0%) (P < 0.001) and afoxolaner (6.3%) (P < 0.001). At 24 h, lotilaner efficacy (97.4%) was significantly different (P < 0.001) from sarolaner and afoxolaner (13.6% and 14.9%, respectively). On day 28, at 12 h postinfestation, lotilaner efficacy (47.8%) was significantly different from sarolaner (17.1%) (P = 0.020) and afoxolaner (9.0%) (P = 0.006). At 24 h, lotilaner efficacy (92.3%) was significantly different from sarolaner 4.9% (P < 0.001) and afoxolaner (0.0%) (P < 0.001). Speed of kill for sarolaner and afoxolaner, but not lotilaner, significantly declined over the study period. Following reinfestation on day 28, neither sarolaner nor afoxolaner reached 90% efficacy by 48 h. By 72 h, sarolaner efficacy was 97.4% and afoxolaner efficacy was 86.3%. Only lotilaner achieved ≥ 90% efficacy by 24 h post-treatment and 24 h postinfestation on days 21 and 28. Time to ≥ 90% efficacy following new infestations consistently occurred 24-48 h earlier for lotilaner compared with sarolaner or afoxolaner.

CONCLUSIONS

Credelio (lotilaner) has a more rapid onset of acaricidal activity against A. americanum than Simparica Trio (sarolaner-moxidectin-pyrantel) and NexGard (afoxolaner). Only lotilaner's speed of tick kill is sustained throughout the dosing period.

Is dragging a drag or is trapping a trap? A comparison of two methods for collecting Amblyomma americanum ticks in sites near the species range boundary

The incidence of tick-borne diseases in the United States has more than doubled since the early 2000s. Research on ticks is a priority to mitigate the spread of tick-borne diseases. Thus, it is important to understand how to efficiently collect large numbers of ticks for studies of genetics, behavior, physiology, vector competence, tick repellants, and acaricides. In this study, we compared the efficiency of two methods-dragging and CO2-baited trapping-for collecting lone star ticks (Amblyomma americanum) across two distinct regions of its expanding range. We performed simultaneous dragging and trapping collections at six sites, three in Oklahoma and three in New York and New Jersey, USA. Our results demonstrate that dragging was more efficient than trapping for collecting lone star tick nymphs. However, dragging and trapping were similar in efficiency for collecting adult males and females. There were no regional differences in trapping or dragging efficiency. Additionally, we discuss material and labor costs of each method to inform researchers who need to rapidly collect as many ticks as possible with the most efficient and cost-effective method.

Comparison of the initial and residual speed of Amblyomma americanum kill on dogs treated with a single dose of Bravecto® Chew (25 mg/kg fluralaner) or Simparica TRIO® (1.2 mg/kg sarolaner, 24 µg/kg moxidectin, 5 mg/kg pyrantel)

BACKGROUND

To manage tick infestations and reduce tick-borne pathogen transmission risk to dogs, compliant administration of a fast-acting ectoparasiticide is necessary. Isoxazoline-containing ectoparasiticide products provide systemic whole-body coverage; however, differences in tick kill have been observed between products and these differences may be more pronounced when controlling common dose-limiting tick species such as Amblyomma americanum.

METHODS

Dogs were ranked by tick carrying capacity, randomly allocated to one of three treatment groups, and administered Bravecto® Chews (minimum 25 mg/kg fluralaner), Simparica TRIO® (minimum 1.2 mg/kg sarolaner, 24 µg/kg moxidectin, 5 mg/kg pyrantel), or no treatment. Dogs were infested with approximately 50 unfed adult (25 female, 25 male) A. americanum on days -2, 21, 28, and 35. Live tick counts were performed at 8, 12, 24, 48, and 72 h post-treatment (day 0) and post-infestation on days 21, 28, and 35. At each tick count timepoint, product efficacy was determined by comparing geometric mean live tick counts for each product-treated group to the untreated group and a linear mixed model was used for between-group comparisons.

RESULTS

Compared with untreated dogs, significant control of existing A. americanum infestations began by 8 h post-treatment (81.6%) and reached 98.0% control by 12-h for Bravecto®-treated dogs. In comparison, significant control for Simparica TRIO®-treated dogs began by 24 h post-treatment (97.7%). When reinfested on day 21, A. americanum infestations were controlled more quickly for Bravecto® compared with Simparica TRIO®-treated dogs at 12 h (efficacy 95.3% versus 25.5%, P < 0.001) and 24 h (efficacy 99.7% versus 70.9%, P < 0.001) post-infestation. Similarly, when reinfested on day 28, faster A. americanum control occurred for Bravecto® compared with Simparica TRIO®-treated dogs at 12 h (efficacy 87.9% versus 18.3%, P < 0.001) and at 24 h (99.2% versus 59.3%, P < 0.001) post-infestation. Finally, when reinfested on day 35, time to ≥ 90% efficacy was achieved by 48 h for Bravecto®-treated dogs compared with 72 h post-infestation for Simparica TRIO®-treated dogs. Both products performed within label indications and no treatment-related adverse reactions occurred during the study.

CONCLUSIONS

Amblyomma americanum infestations are controlled more quickly immediately upon treatment and at 21, 28, and 35 days post-treatment for Bravecto® compared with Simparica TRIO®-treated dogs.

Early onset of pre-lethal effects of lotilaner (Credelio®) on Amblyomma americanum ticks on experimentally infested dogs

Background

The speed with which acaricides paralyze and kill ticks is relevant to impeding pathogen transmission. The objective of this study was to assess early-onset lotilaner effects on the motility and weights of Amblyomma americanum ticks collected from treated dogs.

Methods

Twelve healthy dogs were randomized between two groups to receive either lotilaner (Credelio^®) on Day 0 or to be sham treated. On Day 7, 25 male and 25 female A. americanum were placed under bandages, two on each flank of each dog. After 30 or 45 min, all unattached ticks were removed and T = 0 was set. At T = 2, 4, 8 and 24 h post attachment, 5 attached ticks removed from each bandage on each dog were weighed, assessed by blinded observers for righting ability and movement recorded.

Results

After the infestation period significantly fewer treated than control dogs had 20 ticks attached (50.0% versus 91.7%, P = 0.0015). At 24 h post attachment, mean weights of ticks from treated dogs (males 1.69 mg; females 2.72) were significantly less than ticks from controls (males 2.66 mg; females 4.67) (P_male = 0.0002; P_female < 0.0001). Mean tick weights from the treated group were significantly lower at 24 h than at earlier time points (P_male < 0.0307; P_female = 0.0021). At 4 and 8 h, significantly fewer ticks from treated (14.3%, 0.0%, respectively) than from control dogs could right (73.3%, 70.0%) (P_4h < 0.0001; P_8h = 0.0024) (at 24 h, all ticks from treated dogs were dead), and distance moved was significantly less at all time points (P_2h = 0.0413; P_4h, P_8h < 0.0001). Mean and maximum velocity of ticks from treated dogs were significantly lower, relative to controls, at 4 and 8 h (P ≤ 0.0001). Within the treated group, collected ticks had significantly lower mean and maximum velocities at 4 and 8 h compared to 2 h (P_mean < 0.0042; P_max < 0.0194).

Conclusion

The observed changes indicate that lotilaner may disrupt tick attachment. In ticks that attached, a progressive impairment of neuromuscular processes began within 2 h. Those irreversible changes could substantially reduce the risk of pathogen transmission from tick to host.

Modeling of historical and current distributions of lone star tick, Amblyomma americanum (Acari: Ixodidae), is consistent with ancestral range recovery

The lone star tick, Amblyomma americanum L., is a three-host hard tick notorious for aggressive feeding behavior. In the early to mid-20th century, this species' range was mostly limited to the southern USA. Since the 1950s, A. americanum has been detected in many new localities in the western, northcentral, and northeastern regions of the country. To examine the influence of climate on this apparent expansion, we used historical (1748-1950) lone star locations from the literature and museum records to model areas suitable for this species based on past environmental conditions in the late 1800s - early 1900s. We then projected this model forward using present (2011-2020) climatic conditions and compared the two for evidence of climate-associated distributional shifts. A maximum entropy distribution or Maxent model was generated by using a priori selected climatic variables including temperature, precipitation, and vapor pressure deficit. Temperature and vapor pressure deficit were selected as the most important factors in creating a sensitive and specific model (success rate = 82.6 ± 6.1%) that had a good fit to the existing data and was significantly better than a random model [partial ROC (receiver operating characteristic) to AUC (area under the ROC curve) ratio = 1.97 ± 0.07, P < 0.001]. The present projected model was tested with an independent dataset of curated museum records (1952-2020) and found to be 95.6% accurate. Comparison of past and present models revealed > 98% A. americanum niche overlap. The model suggests that some areas along the western fringe are becoming less suitable for A. americanum, whereas areas in some Great Lakes and coastal northeastern regions are becoming more suitable, results that are compatible with possible effects of climate change. However, these changes are minor, and overall climate in North America does not appear to have changed in ways significant to A. americanum's distribution. These findings are consistent with an alternative hypothesis that recent changes in A. americanum's distribution are a result of this species re-occupying its historical range, driven predominantly by factors other than climate, such as shifts in land use and population densities of major hosts.