Epidemiology of vector-borne diseases
Vector-borne diseases present problems in epidemiology and ecology because systems are inherently multi-trophic, often modulated by community biodiversity, and typically dynamic and variable across space and time. We evaluate model systems of vector-borne disease in people, domestic animals, and wildlife in order to understand ecological characteristics and to provide tools for disease management. Special interests include granulocytic anaplasmosis, Lyme disease, and plague. Recent projects include assessing tick-borne disease ecology among the many chipmunk species present in California and detecting community determinants that affect the persistence and emergence of anaplasmosis in various ecosystems.
Evolution of antigens in Anaplasma phagocytophilum
As a tick-transmitted, obligate intra-cellular parasite, Anaplasma phagocytophilum experiences a set of evolutionary forces including drift particularly at the low population sizes that occur early after tick inoculation, high rates of mutation (recombination), and strong selection as the host develops immunity. We study the host and bacterial evolution in animal models, including rodent reservoir species, to understand how this pathogen utilizes a large array of functional pseudogenes to evade immunity and persist in nature.
Simulation and analytical modeling of infectious disease persistence and emergence in nature.
Leptospirosis is a "forgotten" disease. Cases occur frequently in dogs, causing kidney and sometimes liver failure and death. Humans also experience leptospirosis often associated with water-oriented sporting events and exposure to domestic animals and wildlife, especially rats. Yet we lack diagnostic capability to define various strains of Leptospira interrogans that could cycle in nature and we don't understand most aspects of L. interrogans ecology. We know that raccoons and rats may harbor the bacterium but we don't know where infection is most prevalent, which specific reservoirs maintain which enzootic cycles, and how best to test for infection and bacterial shedding in dogs and wildlife. Our research currently focuses on the epidemiology of leptospirosis in dogs, small mammals, and mesocarnivores in California.
The amphibian pathogens Batrochochytrium dendrobatidis and Ranavirus occur in a large number of aquatic ecosystems causing problems ranging from species extinction to widespread mortality to inapparent infection in some resistant species. In California, amphibian infections cause broad deciines in populations of high alpine frog species but also occur in salamanders and the "resistant" bullfrog. Our research examines the ecology of amphibian infectious disease in several locations and particularly aims to understand how multiple interacting host species can contribute to persistence of the pathogens in nature and how this contributes to disease risk in vulnerable species.
Disease and forest change
Serious anthropogenic habitat change can alter the probability of disease emergence. In the literature, changes often are attributed to global warming but deforestation, reforestation, and fire also can catastrophically alter natural communities and change disease risk. Our work focuses on anthropogenic forest change and its impact on diseases transmitted by ticks including Ixodes ricinus group hard ticks such as Lyme disease and anaplasmosis.
Conservation ecology and disease
We are involved in a variety of projects aimed at discovering the risk infectious agents pose to vulnerable wildlife species. These include a survey of infections in western pond turtles, assessment of disease risk due to climate change and overlap with sympatric small mammals in pikas, assessment of hydrologic and other habitat stresses and disease risk in Amargosa voles, and study of emergence of mange in bobcats.