Surveillance of Ticks and Tick-Borne Pathogens in Suburban Natural Habitats of Central Maryland

Mapping the distribution of Lyme disease at a mid-Atlantic site in the United States using electronic health data

Lyme disease is a spatially heterogeneous tick-borne infection, with approximately 85% of US cases concentrated in the mid-Atlantic and northeastern states. Surveillance for Lyme disease and its causative agent, including public health case reporting and entomologic surveillance, is necessary to understand its endemic range, but currently used case detection methods have limitations. To evaluate an alternative approach to Lyme disease surveillance, we have performed a geospatial analysis of Lyme disease cases from the Johns Hopkins Health System in Maryland. We used two sources of cases: a) individuals with both a positive test for Lyme disease and a contemporaneous diagnostic code consistent with a Lyme disease-related syndrome; and b) individuals referred for a Lyme disease evaluation who were adjudicated to have Lyme disease. Controls were individuals from the referral cohort judged not to have Lyme disease. Residential address data were available for all cases and controls. We used a hierarchical Bayesian model with a smoothing function for a coordinate location to evaluate the probability of Lyme disease within 100 km of Johns Hopkins Hospital. We found that the probability of Lyme disease was greatest in the north and west of Baltimore, and the local probability that a subject would have Lyme disease varied by as much as 30-fold. Adjustment for demographic and ecological variables partially attenuated the spatial gradient. Our study supports the suitability of electronic medical record data for the retrospective surveillance of Lyme disease.

Zoonotic implications of white-footed mice habitat selection and territoriality in fragmented landscapes

White-footed mouse (Peromyscus leucopus) populations can thrive in fragmented suburban and urban parks and residential spaces and play a pivotal role in the spread and prevalence of tick-borne diseases. We collected spatial data on 58 individual mice living at the intersection of county park land and residential land in suburban Howard County, MD, U.S.A. We analyzed mouse density, home-range size and overlap, and a Bayesian mixed-effects model to identify the habitats where they were found relative to where they were caught, as well as a resource selection function for general habitat use. We found that as mouse density increased, home-range size decreased. The overlap indices and the resource selection function supported territoriality coupled with site-specific space use in these suburban mouse populations. While mice occurred in open areas, forest edge, and forest, they showed a strong preference for forested areas. Interestingly, mice captured only 30 to 40 m into the forest rarely used the nearby private yards or human structures and this has direct implications for the placement of rodent-targeted tick control treatments. Our study supports the need for zoonotic disease management frameworks that are based on site-specific land cover characteristics as well as specific management objectives.

Human Borrelia miyamotoi Infection in North America

Borrelia miyamotoi is an emerging pathogen that causes a febrile illness and is transmitted by the same hard-bodied (ixodid) ticks that transmit several other pathogens, including Borrelia species that cause Lyme disease. B. miyamotoi was discovered in 1994 in Ixodes persulcatus ticks in Japan. It was first reported in humans in 2011 in Russia. It has subsequently been reported in North America, Europe, and Asia. B. miyamotoi infection is widespread in Ixodes ticks in the northeastern, northern Midwestern, and far western United States and in Canada. In endemic areas, human B. miyamotoi seroprevalence averages from 1 to 3% of the population, compared with 15 to 20% for B. burgdorferi. The most common clinical manifestations of B. miyamotoi infection are fever, fatigue, headache, chills, myalgia, arthralgia, and nausea. Complications include relapsing fever and rarely, meningoencephalitis. Because clinical manifestations are nonspecific, diagnosis requires laboratory confirmation by PCR or blood smear examination. Antibiotics are effective in clearing infection and are the same as those used for Lyme disease, including doxycycline, tetracycline, erythromycin, penicillin, and ceftriaxone. Preventive measures include avoiding areas where B. miyamotoi-infected ticks are found, landscape management, and personal protective strategies such as protective clothing, use of acaricides, and tick checks with rapid removal of embedded ticks.

Newer Surveillance Data Extends our Understanding of the Niche of Rickettsia montanensis (Rickettsiales: Rickettsiaceae) Infection of the American Dog Tick (Acari: Ixodidae) in the United States

Background

Understanding the geographic distribution of Rickettsia montanensis infections in Dermacentor variabilis is important for tick-borne disease management in the United States, as both a tick-borne agent of interest and a potential confounder in surveillance of other rickettsial diseases. Two previous studies modeled niche suitability for D. variabilis with and without R. montanensis , from 2002-2012, indicating that the D. variabilis niche overestimates the infected niche. This study updates these, adding data since 2012.

Methods

Newer surveillance and testing data were used to update Species Distribution Models (SDMs) of D. variabilis , and R. montanensis infected D. variabilis , in the United States. Using random forest (RF) models, found to perform best in previous work, we updated the SDMs and compared them with prior results. Warren's I niche overlap metric was used to compare between predicted suitability for all ticks and 'pathogen positive niche' models across datasets.

Results

Warren's I indicated <2% change in predicted niche, and there was no change in order of importance of environmental predictors, for D. variabilis or R. montanensis positive niche. The updated D. variabilis niche model overpredicted suitability compared to the updated R. montanensis positive niche in key peripheral parts of the range, but slightly underpredicted through the northern and midwestern parts of the range. This reinforces previous findings of a more constrained pathogen-positive niche than predicted by D. variabilis records alone.

Conclusions

The consistency of predicted niche suitability for D. variabilis in the United States, with the addition of nearly a decade of new data, corroborates this is a species with generalist habitat requirements. Yet a slight shift in updated niche distribution, even of low suitability, included more southern areas, pointing to a need for continued and extended monitoring and surveillance. This further underscores the importance of revisiting vector and vector-borne disease distribution maps.

Patterns of white-tailed deer movements in suburban Maryland: implications for zoonotic disease mitigation

Understanding the ecology of the often dense white-tailed deer populations in urban and suburban landscapes is important for mitigating a variety of conflicts that arise with dense human populations, such as issues surrounding zoonotic disease mitigation. We collared white-tailed deer in highly suburban areas of Howard County, Maryland with high-resolution GPS collars. Then, we created autocorrelated kernel density home ranges for broader land use analyses and concurrently used general additive models to characterize fine-scale hourly measures of speed, activity, and proximity to residential buildings. Suburban deer home ranges encompassed approximately 35% direct residential land, and an average of 71 and 129 residential properties were found within female and male core ranges, respectively. Sex, time of day, and day of year all influenced fine-scale speeds, activity levels, and proximity to residential property buildings. Deer moved into residential areas nightly, especially in winter, and exhibited bouts of increased speed and activity shortly after sunrise and sunset, with distinctive seasonal changes. We discuss how variation in home ranges and movements may influence population management success and explore year-round periods of increased risk of deer transporting ticks to residential areas. These findings focus our broad understanding of deer movements in suburban and urban landscapes to improve deer population management and to mitigate the spread of ticks into residential areas.

Relevance of Spatial and Temporal Trends in Nymphal Tick Density and Infection Prevalence for Public Health and Surveillance Practice in Long-Term Endemic Areas: A Case Study in Monmouth County, NJ

Tick-borne diseases are a growing public health problem in the United States, and the US northeast has reported consistently high case rates for decades. Monmouth County, New Jersey, was one of the earliest jurisdictions to report Lyme disease cases in 1979 and reports several hundred cases per year nearly 40 yr later. In the time since, however, tick-borne health risks have expanded far beyond Lyme disease to include a variety of other bacterial pathogens and viruses, and additional vectors, necessitating a continually evolving approach to tick surveillance. In 2017, Monmouth County initiated an active surveillance program targeting sites across three ecological regions for collection of Ixodes scapularis Say (Acari: Ixodidae) and Amblyomma americanum L. (Acari: Ixodidae) as well as testing via qPCR for associated bacterial pathogens. During the first five years of this program (2017-2021), we report high levels of spatiotemporal variability in nymphal density and infection prevalence in both species, limiting the granularity with which human risk can be predicted from acarological data. Nonetheless, broader patterns emerged, including an ongoing trend of A. americanum dominance, risks posed by Borrelia miyamotoi, and the frequency of coinfected ticks. We present some of the first county-level, systematic surveillance of nymphal A. americanum density and infection prevalence in the northeastern US. We also documented a temporary decline in Borrelia burgdorferi that could relate to unmeasured trends in reservoir host populations. We discuss the implications of our findings for tick-borne disease ecology, public health communication, and tick surveillance strategies in endemic areas.

Multi-scale analysis of habitat fragmentation on small-mammal abundance and tick-borne pathogen infection prevalence in Essex County, MA

Habitat fragmentation and heterogeneity transform otherwise contiguous tracks of forest into smaller patches in the northeastern U.S. and likely impact abundances, movement patterns, and disease transmission pathways for small-mammal communities at multiple scales. We sought to determine the structure of a small-mammal community in terms of mammal abundance and infection prevalence of Borrelia burgdorferi sensu stricto (s.s.), Anaplasma phagocytophilum, and Babesia microti within a fragmented landscape in Essex County, Massachusetts, USA. We studied communities at multiple spatial scales, including vegetation, edge type, and landscape (including 200-m, 500-m, and 1000-m radii) scales. A total of 16 study sites were chosen to represent four edge types: interior forest, pasture edge, natural edge, and residential edge. At each site, we trapped small mammals and conducted vegetation surveys and GIS analysis. Upon capture, a tissue sample was collected to analyze for presence of pathogens. Northern short-tailed shrew (Blarina brevicauda) abundance did not differ based on edge type, whereas abundance of the white-footed mouse (Peromyscus leucopus) was greatest at pasture edges, although the relationship was relatively weak. White-footed mouse abundance was negatively associated with amount of forested area within a 500-m radius, whereas northern short-tailed shrew abundance demonstrated a positive relationship with fragmentation indices at the 200-m radius. White-footed mice captured at interior-forest habitat were more likely be infected with B. burgdorferi (s.s.) than individuals from edge habitat. Greater prevalence of B. burgdorferi infection of white-footed mice in forest interiors compared to edge habitats counters previous studies. Reasons for this and implications are discussed.

White-Tailed Deer Spatial Distribution in Relation to '4-Poster' Tick Control Devices in Suburbia

Deer are keystone hosts for adult ticks and have enabled the spread of tick distributions. The ‘4-Poster’ deer bait station was developed by the United States Department of Agriculture to control ticks feeding on free-ranging deer. Although effective in certain scenarios, ‘4-Poster’ deer treatment stations require the use of bait to attract deer to one location, which may cause increased deer disease transmission rates and habitat damage. To better understand and manage the impact of baited ‘4-Poster’ stations on deer movements, we captured and GPS-monitored 35 deer as part of an integrated pest management project. Fifteen ‘4-Poster’ stations were deployed among three suburban county parks to control ticks. To quantify the effects of ‘4-Poster’ stations, we calculated deer movement metrics before and after feeders were filled with whole kernel corn, and we gathered information on visitation rates to feeders. Overall, 83.3% of collared deer visited a feeder and revisited approximately every 5 days. After feeders were refilled, collared deer were ~5% closer to feeders and conspecifics than before filling. Males used a higher percentage of available feeders and visited them more throughout the deployment periods. Although these nuanced alterations in behavior may not be strong enough to increase local deer abundance, in light of infectious diseases affecting deer populations and effective ‘4-Poster’ densities, the core range shifts and clustering after refilling bait may be a cause for concern. As such, trade-offs between conflicting management goals should be carefully considered when deploying ‘4-Poster’ stations.

Borrelia burgdorferi (Spirochaetales: Spirochaetaceae) Infection Prevalence and Host Associations of Ticks Found on Peromyscus spp. in Maryland

Lyme disease, caused by Borrelia burgdorferi sensu stricto and most commonly transmitted by Ixodes scapularis Say (Ixodida: Ixodidae), is the most common tick-borne disease in Maryland. Because B. burgdorferi s.s. is maintained in enzootic cycles among wild mice (Peromyscus spp) and Ixodes spp ticks, differing patterns of parasitism of ticks on mice could impact the infection prevalence with B. burgdorferi. We determined the infection prevalence of Peromyscus spp as well as questing and partially engorged nymphal ticks collected at six sites on private land in five counties in Maryland from May to August 2020. Questing nymph infection prevalence (NIP) was 14%. We trapped 1258 mice and collected 554 ticks and 413 ear tissue samples. The prevalence of infested Peromyscus spp varied based on host age and sex, with older and male mice more likely to be infested. We detected a significant difference amongst the proportion of attached Ixodes and the location of trapping. Similarly, the prevalence of B. burgdorferi infected Peromyscus spp mice varied between locations (average mouse infection prevalence was 40%), with the highest prevalence in locations where Ixodes were the most commonly found ticks. The B. burgdorferi infection prevalence in partially engorged I. scapularis nymphs retrieved from Peromyscus spp was ~36% which lends further support to the host infection prevalence. Local differences in distribution of infected vectors and reservoirs are important factors to consider when planning interventions to reduce Lyme disease risk.

Spatial Heterogeneity of Sympatric Tick Species and Tick-Borne Pathogens Emphasizes the Need for Surveillance for Effective Tick Control

Three tick species that can transmit pathogen causing disease are commonly found parasitizing people and animals in the mid-Atlantic United States: the blacklegged tick (Ixodes scapularis Say), the American dog tick (Dermacentor variabilis [Say]), and the lone star tick (Amblyomma americanum [L.]) (Acari: Ixodidae). The potential risk of pathogen transmission from tick bites acquired at schools in tick-endemic areas is a concern, as school-aged children are a high-risk group for tick-borne disease. Integrated pest management (IPM) is often required in school districts, and continued tick range expansion and population growth will likely necessitate IPM strategies to manage ticks on school grounds. However, an often-overlooked step of tick management is monitoring and assessment of local tick species assemblages to inform the selection of control methodologies. The purpose of this study was to evaluate tick species presence, abundance, and distribution and the prevalence of tick-borne pathogens in both questing ticks and those removed from rodent hosts on six school properties in Maryland. Overall, there was extensive heterogeneity in tick species dominance, abundance, and evenness across the field sites. A. americanum and I. scapularis were found on all sites in all years. Overall, A. americanum was the dominant tick species. D. variabilis was collected in limited numbers. Several pathogens were found in both questing ticks and those removed from rodent hosts, although prevalence of infection was not consistent between years. Borrelia burgdorferi, Ehrlichia chaffeensis, Ehrlichia ewingii, and Ehrlichia "Panola Mountain" were identified in questing ticks, and B. burgdorferi and Borrelia miyamotoi were detected in trapped Peromyscus spp. mice. B. burgdorferi was the dominant pathogen detected. The impact of tick diversity on IPM of ticks is discussed.