Research Projects
Prairie Restoration Effects on Prevalence of Disease Vectors
Period: March 1, 2020 - Present
Contact: Prairie Fork
Organization: University of Missouri Prairie Fork Trust, Missouri Department of Conservation, National Fish and Wildlife Foundation
Funding Source: PFCA
Objectives: Project Title: Prairie Restoration Effects on Prevalence of Disease Vectors Project Principal Investigator: Samniqueka Halsey
Institution Affiliation: University of Missouri, School of Natural Resources Team Members: 1 graduate student (TBD), 1-2 undergraduate students (TBD)
PROJECT DESCRIPTION
Relationship to the long-term goals of PFCA:
This project addresses the long-term goals of PFCA by seeking to understand how management actions aimed at re-establishing and maintaining the natural prairie and woodland community can affect disease prevalence. This project proposes to collect field data from PFCA to examine both small mammal and invertebrate tick communities for the prevalence of pathogens that are of public health significance in Missouri. Additionally, this project will help train both undergraduate and graduate students in restoration and disease ecology research at PFCA, further promoting innovative research and hands-on learning.
Research priority areas of PFCA
“Restoration and ecology of prairie associated vertebrates and invertebrates”
Our research-specific goals seek to understand how prairie restorations of various ages affect the prevalence of tick-borne diseases. We ultimately hope to design a long-term multi-site ecological study, including PFCA, that surveils and catalogs the vertebrate, invertebrate, and pathogen communities across different landscape types (prairies, oak savannas, and woodlands) across Central Missouri. In particular, by conducting research at PFCA, we will be able to provide insight into the mechanisms through which restoration of prairie habitat can contribute to tick-borne diseases. By using standardized collection methods across sites (e.g., PFCA, Tucker, Tyson), we
hope to use the information gleaned to improve understanding of management strategies (e.g., fire regime) aimed at restoring and maintaining natural biological communities that can influence the prevalence of tick diseases. This data on both vertebrate, invertebrate, and pathogen communities will be used to develop further refine models aimed at reducing tick-borne disease risk in Central Missouri.
Objectives
Our overall research objective at PFCA is to understand how time since restoration and fire regimes influence the presence of small mammals and ticks that are of public health significance. In particular, for several tick species in Missouri, species-specific host-tick information is lacking (e.g., Ixodes scapularis; Halsey et al. 2018). Therefore, we propose to measure how small mammal composition and tick disease vectors change across different landscapes in Central Missouri (e.g., Tucker Prairie, PFCA, Tyson) and determine how these patterns correlate to time since fire and restoration age (time since prairie was first restored).
Justification
Tick-borne pathogens are increasing in the United States (U.S.) with regards to the geographic distribution of many pathogens and their vectors (Lockwood et al. 2018). In particular, there are several tick species and tick vector transmitted pathogens of public health significance in Missouri
Table 1: Tick and pathogens (bacterial and viral) currently found in Missouri
Ticks Pathogens American Dog Tick Rocky Mountain Spotted Fever
Lone Star Tick Lyme Disease
Brown Dog Tick Tularemia
Relapsing Fever Tick Ehrlichiosis
Blacklegged Tick STARI Anaplasmosis Heartland Virus
Bourbon Virus
(Table 1; Hudman & Sargentini 2016). Prairie habitats are of increasing interest with regard to disease reservoirs and transmission pathways (Beckmann et al 2019).
Aside from the many benefits, restorations can result in increased contact between humans and
disease vectors (Miller 2006). Therefore, it is essential that studies involving prairie ecosystem restoration incorporate both small mammal and tick surveillance to identify potential avenues of pathogen transmission.
With tick-borne pathogens expanding their geographic ranges, there is a need for greater proactive surveillance of both tick vectors and their host reservoirs (Eisen et al. 2017). Conducting this research in Central Missouri is of particular interest as this region has most recently been the location where the first reports of transmission of two tick-borne pathogens to humans (i.e., Heartland virus and Bourbon Virus; McMullan et al., 2012, Savage et al. 2017). Also, vector surveillance in the U.S. tends to neither standardized not routine (Eisen et al. 2017), often only occurring ad-hoc after a surge in disease prevalence. Therefore, this presents a unique and exciting opportunity to initiate and design a long-term multi-site ecological study on host-tick-pathogen interactions to determine the effect of restoration age and fire regime on tick-borne disease risk. We aim to address this knowledge gap by determining: the occurrence of small mammals in both remnant and restored prairies, the prevalence of tick species actively questing and feeding on said species, the prevalence of pathogens in both small mammal and tick species and if these patterns vary among restoration and fire regimes.
Expected benefits and outcomes
This project will help advance the mission of PFCA by contributing to the understanding of how the ecology of restored prairies can influence disease transmission. As restoration efforts in the Midwest increase to combat historical degradation from human land use (Samson and Knopf 1994), there is a need to understand whether these management actions may have unintended consequences of increased pathogen transmission to humans. Combined with the recent changes in the geographic distribution of both tick vectors and pathogens, conducting research at PFCA
and, more broadly, Central Missouri, may allow us to observe tick and pathogen invasion and establishment over the long-term. As PFCA is an outdoor laboratory that advances science and engages students in active learning, our research will not only provide information about the current state of tick-borne pathogens at PFCA, but also inform current management actions that may reduce disease risk. Additionally, to contribute to the educational value of PFCA, PI Halsey and her graduate and undergraduate students will enthusiastically attend educational events to talk about the importance of our work, provide demonstrations of our field collecting methods, and instruct the young scholars about the importance of performing tick checks after leaving grassy and wooded areas.
Background and rationale
Prairie restorations can inadvertently increase the prevalence of tickborne diseases by providing habitat for small mammals hosts that are
highly competent reservoirs for pathogens (e.g. rodents, Beckman et al. 2019, Card et al. 2019). Despite this, few studies of wildlife hosts for ticks and tick-borne pathogens have been performed in prairie ecosystems throughout the Midwest
(Halsey et al. 2018, Figure 1)
With the geographic distribution of many pathogens and their vector(s) expanding
Figure 1: Map of eastern United States where studies involving animal captures for research on Ixodes scapularis and Borrelia burgdorferi that took place from 1970 to 2017. The number of studies in each state is indicated in parentheses. Published in Halsey et al. 2018
and the regular detection of novel pathogens (Mansfield et al. 2017); finding cost-effective, practical approaches to reducing tick-borne disease risk is more important than ever (Lockwood
et al. 2018, Gleim et al. 2019). One solution may be prescribed fire, a common management practice in prairie and grassland systems to enhance wildlife habitat and improve the overall health of an ecosystem (Hoch et al 1972, Gleim et al. 2019). Previous research has shown that fire may be a useful tool to control both ticks and tick-borne diseases (Gleim et al. 2014, MacDonald et al. 2018) as it alters leaflitter cover, temperature, and humidity regimes, consequently affecting the abundance and diversity of vertebrate tick-hosts (e.g., Davidson et al. 1994, Elliot et al. 1999, Allan 2009). A critical gap that has significant consequences for understanding the spread of both ticks and tick-borne pathogens is understanding how fire can mediate the expected increases in disease risk that come from prairie restorations in a human- dominated landscape (Beckmann et al. 2019). Results from this project will lay the foundation for future research with applications for both restoration and human health.
Preliminary Results:
Lead PI Halsey has performed research on disease ecology over the last five years. As a computational ecologist, she brings her expertise in the ecology of tick-borne diseases, in particular, Lyme disease. She has conducted a 50 year, a nationwide meta-analysis on host-tick interactions for the most significant tick vector, Ixodes scapularis (see Halsey et al. 2018). From this, she has a great understanding of which field collections methods are most efficient in obtaining data, the timing of data collection, and the most salient information needed to inform her models. PI Halsey has used her models to experimental alter the abundance of small mammals to determine the mechanisms of biodiversity on disease risk. However, this was tailored to the Northeast U.S. for which there is substantially more data (Halsey and Miller 2018, Halsey in press). The proposed PFCA project builds on her previous work by providing the opportunity to tailor her developed models to local sites in Missouri, something her previous
work was not been able to address due to lack of data collection in this region. She is excited for the opportunity to be able to ground-truth her models with local data as well as collect data that has been previously not collected.
METHODS
Experimental design
Our experiment design includes three study sites: 1) PFCA, 2) Tucker Prairie, and 3) Tyson Research Center. For each site, we will use a two-stage stratified sampling design where the primary sampling units based on fire regime interval (i.e., time since fire) and restoration age (e.g., time since restoration) and landcover type (e.g., prairie vs. woodland). It is important to note that not all primary sampling units will exist at all sites (e.g., Tucker Prairie is a remnant prairie; therefore, it will not have a restoration age sampling unit). Within each primary unit, we will use ArcGIS v10 to randomly select locations for five parallel 100-m2 transects >500 m apart, to maximize the potential diversity captured across the landscape.
Procedures proposed to accomplish the objectives
Tick collection from small mammals: From May to September 2020, we will use Sherman and
Tomahawk traps to capture individuals from the overall small mammal host community. Traps will be set along sampling transects at 15 m intervals. We will conduct trapping on two consecutive days each week between 6-8 pm and check traps the next morning between 6-8 am. This will maximize the likelihood of catching both diurnal and nocturnal species and reduce small mammal death. All captured animals will be identified to species and sex, marked with an ear tag if unmarked, weighed, searched thoroughly for ticks, and obtain a blood and tissue sample before being released at the point of capture. All ticks will be placed into vials filled with 70% ethanol to be counted, sorting, and identification at a later date. Blood and tissue samples
will be stored according to approved Institutional Animal Care and Use Committee (IACUC) Protocols.
Tick collection from the environment: Weekly from May to September 2020, we will sample
questing ticks using a combination of drag-sampling and carbon dioxide trapping along sampling transects to maximize the diversity of tick species found as different tick species engage in different questing behaviors (Carroll and Schmidtmann 1992, Falco and Fish 1992). All ticks will be placed in vials of 70% ethanol for further sorting and identification in the laboratory using a dissecting microscope and referencing standard taxonomic keys (e.g., Keirans and Durden 1998).
Analytical procedures
From the resulting data, we will be able to estimate the effect of restoration age, fire regime, or ecosystem type on the occurrence of both on- and off-host ticks and tick-borne pathogens. To do this, for each small tick species, we will calculate the average prevalence (number of tick-infested hosts/ total number of hosts captured) and intensity (mean number of ticks per individual host infested) for each small mammal species. We will also calculate small mammal species richness, biodiversity (e.g., Simpson D) and estimate density for each sampling unit. Because we are tagging small mammal species we will be able to more accurately estimate population size as well are determine the level of animal movement between sampling units.
We will use a model selection approach using our fixed effects as candidate models. We will then utilize generalized linear regressions models to account for our stratified sampling design. Our dependent variables will be pathogen prevalence, tick prevalence, and intensity for each mammal species. Our fixed effects will be restoration age, time since last fire, ecosystem. We will perform this analysis for each tick and pathogen species.
Support from the PFCA for this project will provide essential preliminary data to help support future grants associated with understanding the ecology of tick-borne diseases in Missouri. PI Halsey is currently seeking funding from the Northeast Climate Adaptation Science Center Midwest division to further expand her data collection to additional conservation sites in Missouri to further broaden the spatial scale of this project. In collaboration with colleagues at Washington University and Tyson Research Center, she also intends to submit grant proposals to NIH, NSF, and private foundations (e.g., Keck Foundation) for future funding to initiate a long-term surveillance and sampling as well as pathogen testing. As the number of reported cases of notifiable tick-borne diseases has steadily increased, geographic distributions of many tick vectors and tick-borne diseases have expanded, and new tick-borne disease agents have been recognized, NIH just recently released a Strategic Plan for Tick-Borne Disease Research in Fall 2019 which showcases the importance and necessity of this proposed research to large grant agencies.
Schedule and duration:
Field data collection at PFCA will occur over the course of 5 months (May – September) for two consecutive days each week to encompasses the full seasonality of larval and juvenile tick phenology for several tick species. Sorting and identification of ticks will occur throughout the summer and continue through the winter. Preliminary research results on small mammal and tick surveillance will be available by December 2020, with final results completed by Spring 2021. Results from pathogen testing are dependent on additional funding sources but will likely be completed by Spring 2021; else, samples will be stored until funding becomes available. Information Transfer:
We anticipate completing at least one publication in a peer reviewed journal from our findings. Additionally, our graduate student will present this work at the local annual Midwest Ecology and Evolution Conference in the spring of 2021. We are also willing to present on our work for PFCA- sponsored outreach events.
No previous PFCA funding has been received by PI Halsey.
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