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Lyme disease is the most commonly reported vector-borne disease in the United States, and the number of cases reported each year continues to rise. The complex nature of the relationships between the pathogen (Borrelia burgdorferi sensu stricto), the tick vector (Ixodes scapularis Say), multiple vertebrate hosts, and numerous environmental factors creates challenges for understanding and predicting tick population and pathogen transmission dynamics. LYMESIM is a mechanistic model developed in the late 1990s to simulate the life-history of I. scapularis and transmission dynamics of B. burgdorferi s.s. Here we present LYMESIM 2.0, a modernized version of LYMESIM, that includes several modifications to enhance the biological realism of the model and to generate outcomes that are more readily measured under field conditions. The model is tested for three geographically distinct locations in New York, Minnesota, and Virginia. Model-simulated timing and densities of questing nymphs, infected nymphs, and abundances of nymphs feeding on hosts are consistent with field observations and reports for these locations. Sensitivity analysis highlighted the importance of temperature in host finding for the density of nymphs, the importance of transmission from small mammals to ticks on the density of infected nymphs, and temperature-related tick survival for both density of nymphs and infected nymphs. A key challenge for accurate modeling of these metrics is the need for regionally representative inputs for host populations and their fluctuations. LYMESIM 2.0 is a useful public health tool that downstream can be used to evaluate tick control interventions and can be adapted for other ticks and pathogens.

During September–December 2018, 25 live ticks were collected on-post at Fort Leavenworth, Kansas, in a home with a history of bat occupancy. Nine ticks were sent to the Army Public Health Center Tick-Borne Disease Laboratory and were identified as Carios kelleyi (Cooley and Kohls, 1941), a species that seldom bites humans but that may search for other sources of blood meals, including humans, when bats are removed from human dwellings. The ticks were tested for numerous agents of human disease. Rickettsia lusitaniae was identified by multilocus sequence typing to be present in two ticks, marking the first detection of this Rickettsia agent in the United States and in this species of tick. Two other Rickettsia spp. were also detected, including an endosymbiont previously associated with C. kelleyi and a possible novel Rickettsia species. The potential roles of C. kelleyi and bats in peridomestic Rickettsia transmission cycles warrant further investigation.

Adult females and males of Ixodes affinis and Ixodes scapularis are illustrated by focus stacking image photography, and morphological character states are described that reliably differentiate the two species. In conjunction with other environmental cues, such as the questing phenology of adults, these characteristics will enable the rapid identification of adults of either sex along the southern Coastal Plain of the United States, where these species are sympatric.

Lyme and other tick-borne diseases are increasing in the eastern United States and there is a lack of research on integrated strategies to control tick vectors. Here we present results of a study on tick-borne pathogens detected from tick vectors and rodent reservoirs from an ongoing 5-yr tick suppression study in the Lyme disease-endemic state of Maryland, where human-biting tick species, including Ixodes scapularis Say (Acari: Ixodidae) (the primary vector of Lyme disease spirochetes), are abundant. During the 2017 tick season, we collected 207 questing ticks and 602 ticks recovered from 327 mice (Peromyscus spp. (Rodentia: Cricetidae)), together with blood and ear tissue from the mice, at seven suburban parks in Howard County. Ticks were selectively tested for the presence of the causative agents of Lyme disease (Borrelia burgdorferi sensu lato [s.l.]), anaplasmosis (Anaplasma phagocytophilum), babesiosis (Babesia microti), ehrlichiosis (Ehrlichia ewingii, Ehrlichia chaffeensis, and ‘Panola Mountain’ Ehrlichia) and spotted fever group rickettsiosis (Rickettsia spp.). Peromyscus ear tissue and blood samples were tested for Bo. burgdorferi sensu stricto (s.s), A. phagocytophilum, Ba. microti, and Borrelia miyamotoi. We found 13.6% (15/110) of questing I. scapularis nymphs to be Bo. burgdorferi s.l. positive and 1.8% (2/110) were A. phagocytophilum positive among all sites. Borrelia burgdorferi s.s. was found in 71.1% (54/76) of I. scapularis nymphs removed from mice and 58.8% (194/330) of captured mice. Results from study on tick abundance and pathogen infection status in questing ticks, rodent reservoirs, and ticks feeding on Peromyscus spp. will aid efficacy evaluation of the integrated tick management measures being implemented.

The ixodid tick species Ixodes affinis is expanding its range northward, changing the tick community population dynamics in the Mid-Atlantic United States. We present five years of surveillance on newly established populations of I. affinis throughout southeastern Virginia and discuss the habitat and host associations of I. affinis in this northernmost extent of its range. We found that I. affinis populations tend to persist once they are established, and populations tend to increase as ecological succession progresses, provided a vegetated understory persists. Populations of I. affinis were never found in the smallest habitat fragments or in xeric dune habitats, and the highest densities of I. affinis were found in mixed pine-hardwood forests with an herbaceous understory. We also document several new mammalian hosts for I. affinis, including house mice (Mus musculus) and coyotes (Canis latrans) and discuss how these hosts may facilitate the continued dispersal of I. affinis and the maintenance of these newly established populations.

Small mammals are often parasitized by the immature stages of hard-bodied ticks (family Ixodidae) and may serve as reservoir hosts of tick-borne pathogens. Amblyomma maculatum, the Gulf Coast tick, is the primary vector of Rickettsia parkeri, the causative agent of R. parkeri rickettsiosis. This hard-bodied tick species is expanding its historical range from the Gulf Coast of the U.S. up the Mid-Atlantic coast. In Mid-Atlantic states, such as Virginia, R. parkeri prevalence is higher in these ticks than those found in its historical range. This high prevalence may be explained in part by small mammal populations. In this study, small mammals were trapped and checked for the presence of immature A. maculatum. The ticks as well as tissue samples from these mammals were tested for the presence of R. parkeri. This study found six rodent species acting as hosts to immature A. maculatum and three species that may play a role in the enzootic cycle of R. parkeri in Virginia.

In the early 1980s, Ixodes spp. ticks were implicated as the key North American vectors of Borrelia burgdorferi (Johnson, Schmid, Hyde, Steigerwalt and Brenner) (Spirocheatales: Spirochaetaceae), the etiological agent of Lyme disease. Concurrently, other human-biting tick species were investigated as potential B. burgdorferi vectors. Rashes thought to be erythema migrans were observed in patients bitten by Amblyomma americanum (L.) (Acari: Ixodidae) ticks, and spirochetes were visualized in a small percentage of A. americanum using fluorescent antibody staining methods, sparking interest in this species as a candidate vector of B. burgdorferi. Using molecular methods, the spirochetes were subsequently described as Borrelia lonestari sp. nov. (Spirocheatales: Spirochaetaceae), a transovarially transmitted relapsing fever Borrelia of uncertain clinical significance. In total, 54 surveys from more than 35 research groups, involving more than 52,000 ticks, have revealed a low prevalence of B. lonestari, and scarce B. burgdorferi, in A. americanum. In Lyme disease-endemic areas, A. americanum commonly feeds on B. burgdorferi-infected hosts; the extremely low prevalence of B. burgdorferi in this tick results from a saliva barrier to acquiring infection from infected hosts. At least nine transmission experiments involving B. burgdorferi in A. americanum have failed to demonstrate vector competency. Advancements in molecular analysis strongly suggest that initial reports of B. burgdorferi in A. americanum across many states were misidentified B. lonestari, or DNA contamination, yet the early reports continue to be cited without regard to the later clarifying studies. In this article, the surveillance and vector competency studies of B. burgdorferi in A. americanum are reviewed, and we conclude that A. americanum is not a vector of B. burgdorferi.

Ticks are the most significant vectors of infectious diseases in the United States, inspiring many researchers to study aspects of their biology, ecology, and their effects on public health. However, regional differences in tick abundance and pathogen infection prevalence result in the inability to assume results from one area are relevant in another. Current local information on tick ranges, infection rates, and human cases is needed to assess tick-borne disease risk in any given region. The Mid-Atlantic Tick Summit III brought together over 100 area experts and researchers to share regional updates on ticks and their associated pathogens. We report some meeting highlights here. Regional meetings foster cross-disciplinary collaborations that benefit the community, and open novel lines of inquiry so that tick-bite risk can be reduced and tick-borne diseases can be treated effectively.

The Gulf Coast tick Amblyomma maculatum Koch is increasingly relevant to medical and veterinary communities as human infection rates of Rickettsia parkeri rise, the risk of introduction of Ehrlichia ruminantium increases, and the range of this tick expands into the densely populated Mid-Atlantic region of the United States. We report on the results of five years of field surveillance to better describe the ecology of A. maculatum in newly established populations in southeastern Virginia. We document habitat preferences, host preferences, and the phenology of the adult human-biting life stage. We discuss key ecological factors needed for A. maculatum establishment and the influence of the successional process and anthropogenic activities on the persistence of A. maculatum populations in Virginia.

Ixodes affinis Neumann (Acari: Ixodidae) is a hard-bodied tick species distributed throughout much of the southeastern United States. Although I. affinis does not parasitize humans, it is a competent vector of Borrelia burgdorferi sensu stricto, the causative-agent of Lyme disease, and thus contributes to the enzootic maintenance of this pathogen. This study presents evidence of I. affinis parasitizing five new host passerine species. During 2012-2014, 1,888 birds were captured and examined for ticks, and 18 immature I. affinis were collected from 12 birds-six Carolina Wrens (Thyrothorus ludovicianus); two Brown Thrashers (Toxostoma rufum); and one American Robin (Turdus migratorius), Eastern Towhee (Pipilo erythrophthalmus), Northern Cardinal (Cardinalis cardinalis), and White-throated Sparrow (Zonotrichia albicollis). Of 15 larvae and 3 nymphs collected, one nymph tested positive for B. burgdorferi DNA. I. affinis was found co-feeding on birds with immature Amblyomma americanum (L.), Ixodes brunneus Koch, Ixodes dentatus Marx, Ixodes scapularis Say, and Haemaphysalis leporispalustris Packard. The results of this research provide a better understanding of I. affinis hosts and identify avian taxa that may play a role in the maintenance and dispersal of this tick species.

Background Since 1997, human-biting ticks submitted to the Department of Defense Human Tick Test Kit Program (HTTKP) of the US Army Public Health Command have been tested for pathogens by PCR. We noted differences in the phenology and infection prevalence among Ixodes scapularis ticks submitted from military installations in different geographic regions. The aim of this study was to characterize these observed differences, comparing the phenology and pathogen infection rates of I. scapularis submitted from soldiers at two sites in the upper Midwest (Camp Ripley, MN, and Ft. McCoy, WI) and one site in the northeastern US (Ft. Indiantown Gap, PA). Methods From 1997 through 2012, the HTTKP received 1,981 I. scapularis from the three installations and tested them for Anaplasma phagocytophilum, Babesia microti, Borrelia burgdorferi and the Ehrlichiamuris-like (EML) agent using PCR; pathogen presence was confirmed via sequencing or amplification of a second gene target. Pathogen and co-infection prevalence, tick engorgement status, and phenology were compared among installations. Results Greater rates of A. phagocytophilum and Ba. microti infections were detected in ticks submitted from installations in Minnesota than in Wisconsin or Pennsylvania, and the EML agent was only detected in ticks from Minnesota and Wisconsin. Midwestern ticks were also more likely to be co-infected than those from Pennsylvania. Both adult and nymphal ticks showed evidence of feeding on people, although nymphs were more often submitted engorged. Adult I. scapularis were received more frequently in June from Minnesota than from either of the other sites. Minnesota adult and nymphal peaks overlapped in June, and submissions of adults exceeded nymphs in that month. Conclusions There were clear differences in I. scapularis phenology, pathogen prevalence and rates of co-infection among the three military installations. Seasonal and temperature differences between the three sites and length of time a population had been established in each region may contribute to the observed differences. The synchrony of adults and nymphs observed in the upper Midwest has implications for pathogen infection prevalence. The EML agent was only detected in Minnesota and Wisconsin, supporting the previous assertion that this pathogen is currently limited to the upper Midwest.

The incidence of tick-borne rickettsial disease in the southeastern United States has been rising steadily through the past decade, and the range expansions of tick species and tick-borne infectious agents, new and old, has resulted in an unprecedented mix of vectors and pathogens. The results of an ongoing 4-year surveillance project describe the relative abundance of questing tick populations in southeastern Virginia. Since 2009, more than 66,000 questing ticks of 7 species have been collected from vegetation in a variety of habitats, with Amblyomma americanum constituting over 95% of ticks collected. Other species represented included Ixodes scapularis, Dermacentor variabilis, Amblyomma maculatum, Ixodes affinis, Haemaphysalis leporispalustris, and Ixodes brunneus. We found that 26.9–54.9% of A. americanum ticks tested were positive for Rickettsia amblyommii, a non-pathogenic symbiont of this tick species. We also found no evidence of R. rickettsii in D. variabilis ticks, although they did show low infection rates of R. montanensis (1.5–2.0%). Rickettsia parkeri and Candidatus R. andeanae were found in 41.8–55.7% and 0–1.5% A. maculatum ticks, respectively. The rate of R. parkeri in A. maculatum ticks is among the highest in the literature and has increased in the 2 years since R. parkeri and A. maculatum were first reported in southeastern Virginia. We conclude that tick populations in southeastern Virginia have recently undergone dramatic changes in species and abundance and that these populations support a variety of rickettsial agents with the potential for increased risk to human health.