Undergraduate Research in Biology: Ticks

Chair: Dr. Holly Gaff, Department of Biological Science

Preliminary Analysis of an Agent-Based Model for a Tick-Borne Disease

Ticks have a unique life history including a distinct set of life stages and a single blood meal per life stage. This makes tick-host interactions more complex from a mathematical perspective. In addition, any model of these interactions must involve a significant degree of stochasticity on the individual tick level. In an attempt to quantify these relationships, I have developed an individual-based model of the interactions between ticks and their hosts as well as the transmission of tick-borne disease between the two populations. The results from this model are compared with those from previously published differential equation based population models. The findings show that the agent-based model produces significantly lower prevalence of disease in both the ticks and their hosts than what is predicted by a similar differential equation model

Spatial heterogeneity in ecological models : two case studies

Two models are developed to explore the dynamics associated with spatial heterogeneity. The first model is the expansion of a single cell, fish population model to a landscape of interacting cells. The second model is a tick-borne disease model using a set of differential equations applied to a series of spatial patches. The spatially-explicit landscape fish population model (ALFISH) is a part of the Across Trophic Level System Simulation (ATLSS) project for the freshwater wetlands of the Everglades and Big Cypress Swamp. ALFISH was applied as part of the ATLSS project to Everglades restoration, one of the largest ecological restoration projects in the world. ALFISH has been improved to include new field information as that information became available. The only variable input into ALFISH is the hydrology. Up to 35% of variation in fish populations observed in field data corresponds to the variations predicted by ALFISH. The differential equations underlying the tick-borne disease model designed for the lone star tick (Amblyomma americanum) are analytically evaluated for one patch. The results show that under given criteria for the parameters, the system would be locally stable. For further study, the system is then solved numerically. Patches are identified as either grass or wooded and connected by migration. The disease is endemic in both patches unless some type of control is applied. If a control is applied, the disease is reduced to extremely low levels. If two patches, one grass and one wooded, are linked by migration, applying the control to the wooded patch is effective for controlling the disease while applying it in the grass patch is not. A final simulation using a twelve patch system is run to create results to compare with field data. The results show that the model produced qualitatively similar results to the field data which give reductions of 60% in tick density in the areas with control applied

Review: Application of Tick Control Technologies for Blacklegged, Lone Star, and American Dog Ticks

Tick population control technologies have been studied for several decades but no method is successful in all situations. The success of each technology depends on tick species identity and abundance, host species identity and abundance, phenology of both ticks and hosts, geographic region, and a multitude of other factors. Here we review current technologies, presenting an overview of each and its effect on three common tick species in the eastern United States: blacklegged ticks (Ixodes scapularis (Say; Ixodida: Ixodidae)), lone star ticks (Amblyomma americanum (Linnaeus; Ixodida: Ixodidae)), and American dog ticks (Dermacentor variabilis (Say; Ixodida: Ixodidae)). Moreover, we assess the relative success among methods within the same season, as well as over successive years, in reducing tick populations by life stage. For each tick species and life stage, we present published findings, and in the absence of published studies, we hypothesize the most likely outcome based on tick life history. Integrated tick management over a specific time scale, using a variety of tick control technologies, will have the greatest effect on reducing tick abundance

Understanding the Natural History of Juvenile \u3ci\u3eAmblyomma maculatum\u3c/i\u3e in Southeastern Virginia

Amblyomma maculatum, the Gulf Coast tick, is a species of increasing public health concern. Adult A. maculatum is a known vector of several pathogens including Rickettsia parkeri, the causative agent of Rickettsia parkeri rickettsiosis. Amblyomma maculatum has expanded northward from its historic range along the Gulf Coast, with populations reportedly establishing in southeastern Virginia in 2010. Recently established populations of A. maculatum tend to have higher R. parkeri infection prevalence compared to longer established populations. This pattern holds for all populations found so far in southeastern Virginia, with a prevalence of R. parkeri in about 60% of A. maculatum compared to a prevalence of around 10-40% in these ticks in most regions of the United States. While the predominant hosts of all life stages of A. maculatum in Virginia are unknown, preliminary work has found native rodent species acting as hosts to immature A. maculatum, with two species likely playing a role in the enzootic cycle of R. parkeri.https://digitalcommons.odu.edu/gradposters2022_sciences/1002/thumbnail.jp

Modelling the Effects of Habitat and Hosts on Tick Invasions

Many tick species are invading new areas because of anthropogenic changes in the landscape, shifting climatic variables and increasing populations of suitable host species and tick habitat. However, the relative influences of habitat and hosts in tick dispersal and tick population establishment remain in question. A spatially explicit agent-based model was developed to explore the spatio-temporal dynamics of a generic tick population in the years immediately following the introduction of ticks into a novel environment. The general model was then adapted to investigate a case study of two recent tick species invasions into the Mid-Atlantic United States. The recent simultaneous range expansions of two ixodid tick species, Ixodes affinis and Amblyomma maculatum, provided an opportunity to determine if invasion patterns observed in the field could be replicated in silico on a small scale. The models presented here indicated that for generalist parasites, habitat connectivity is a better indicator than host mobility for spatial and genetic patterns of parasite range expansion. In addition, our results demonstrate the utility of including genetic variables into agent-based models: gene flow functions as a proxy for measuring dispersal, and models can be validated using results from the field

Tick-Bourne Pathogens of Potential Zoonotic Importance in the Southern African Region

The aim of this communication is to provide preliminary information on the tick-borne pathogens of potential zoonotic importance present in southern Africa, mainly focusing on their geographical distribution and host range, and to identify research gaps. The following tick-borne zoonoses have been reported to occur in southern Africa based mainly on case reports: Crimean–Congo haemorrhagic fever caused by Crimean–Congo haemorrhagic fever virus; ehrlichiosis caused by Ehrlichia ruminantium, Ehrlichia canis and Anaplasma phagocytophilum; babesiosis caused by Babesia microti; relapsing fever caused by Borrelia duttonii and rickettsioses caused by Rickettsia africae, Rickettsia aeschlimannii and Rickettsia conorii. The epidemiological factors influencing their occurrence are briefly reviewed