Dynamics and Evolution of Emerging Diseases with Applications to Amphibians

Texas Tech University, Lubbock TX

Investigators

Abstract

The goals of this project are threefold: (1) to contribute to the mathematical theory of the evolution of host-pathogen systems, (2) to apply the theory to amphibian populations, and (3) to conduct an intensive biological investigation of amphibian populations and their associated diseases on the Southern High Plains. Deterministic and stochastic structured epidemic models with host and pathogen genetics will be developed, analyzed, and numerically simulated. Discrete and continuous time structured models are based on difference equations, differential equations, Markov chains, and stochastic differential equations. The mathematical models will be used to study how disease affects persistence, duration, onset of an epidemic, and population size, and how host and pathogen coevolve in response to various control strategies and to different selection pressures. The models will be applied to specific amphibian populations on the Southern High Plains. The proposed research includes a three-year experimental investigation (two years of intensive fieldwork) to determine amphibian abundance, disease prevalence, and immunological characteristics of two common species of amphibians on the Southern High Plains, the tiger salamander and the plains spadefoot toad. The study sites consist of twelve playa lakes on the Southern High Plains. Mathematical and statistical analyses of the data collected from this study address some basic biological questions about the relationships among amphibian abundance, immune response, disease prevalence, life cycle stage (larvae, juvenile, and adult), landuse practices (grassland versus cropland), and climatic conditions. This study provides important information for determining critical factors that are significant in the transmission and persistence of diseases in amphibians. The emergence of infectious diseases in humans and wildlife is a major threat to public health and to the conservation of global biodiversity. Increased population densities, changes in agricultural and livestock practices, dam building, deforestation, encroachment into wildlife habitat, climate change, environmental pollution, and introduction of pathogens into new areas are some of the factors leading to the emergence of infectious diseases. Understanding the dynamics of the pathogens responsible for the emergence of these diseases and the complex and changing relationship between their host and their environment is needed for potential control of these diseases. A variety of human and environmental influences have caused many host-pathogen systems to evolve and to adapt to these changing influences, making control an even more difficult task. Theoretical studies which contribute to our understanding of the evolution of host-pathogen systems are urgently needed. It is the purpose of this investigation to develop, analyze, and simulate mathematical models based on principles from epidemiology, genetics and population dynamics, to apply these models to host-pathogen systems, and to conduct an experimental investigation on a particular host-pathogen system. The host population models developed in the proposed investigation are applied specifically to amphibian populations. The global decline in amphibian populations is thought to be one of the most pressing and enigmatic environmental problems today. Recent evidence indicates that emerging diseases (viral and fungal pathogens) are responsible for mass die-offs of frogs, toads, and salamanders. Indeed, recent outbreaks of diseases in amphibians should be given serious attention as they may signal environmental change on a global scale that may threaten many organisms. A major part of the proposed research involves a two-year field and three-year laboratory investigation. The purpose of the experimental investigation is to assess amphibian abundance, disease prevalence, and immunological characteristics of two common species of amphibians on the Southern High Plains. This study lays the groundwork for future studies on causes of population declines in amphibians. This grant is made under the Joint DMS/NIGMS Initiative to Support Research Grants in the Area of Mathematical Biology. This is a joint competition sponsored by the Division of Mathematical Sciences (DMS) at the National Science Foundation and the National Institute of General Medical Sciences (NIGMS) at the National Institutes of Health.