Exploration of Complex Interactions Between Multiple Pathogens and Environmental Stress, Using Amphibians as Model Hosts

EPA Grant Number: FP916402
Title: Exploration of Complex Interactions Between Multiple Pathogens and Environmental Stress, Using Amphibians as Model Hosts
Investigators: Romansic, John M.
Institution: Oregon State University
EPA Project Officer: Lee, Sonja
Project Period: January 1, 2004 through December 31, 2004
Project Amount: $109,037
RFA: STAR Graduate Fellowships (2004) RFA Text |  Recipients Lists
Research Category: Fellowship - Zoology , Academic Fellowships , Biology/Life Sciences


Infectious diseases occur in complex environments that include multiple pathogens and changing environmental conditions. Environmental stressors are known to affect disease susceptibility of hosts. The ways that multiple pathogens combine to affect hosts, however, are not well understood. I will use amphibians as model hosts to test experimentally hypotheses about how multiple pathogens interact and how environmental stress influences multiple-pathogen interactions. The hypotheses are that: (1) two pathogens can interact synergistically; (2) a synergism between two pathogens can occur even when exposure to the different pathogens occurs at separate stages in the life cycle of the host; and (3) synergisms between multiple pathogens vary in magnitude along a gradient of an environmental stressor. The objective of my research project is to help develop general principles about the ways that multiple pathogens interact to build better strategies for controlling infectious diseases.


Experiments will be performed in outdoor mesocosms (artificial ponds) to approximate conditions in natural amphibian ponds. Each experiment will be conducted on three different frog species, Bufo boreas (western toad), Hyla regilla (Pacific treefrog), and Rana aurora (red-legged frog). Each frog species will be tested separately. I will use a three-pathogen system consisting of the fungus Batrachochytrium dendrobatidis, the yeast Cryptococcus humicolus (equals Candida humicola), and the water mold Saprolegnia. The first set of experiments will test whether B. dendrobatidis and C. humicolus interact synergistically to affect survival, infection status, growth, and development of frog tadpoles. The second set of experiments will test whether exposure to Saprolegnia at the embryo life history stage results in a carry-over effect of increased susceptibility to B. dendrobatidis and C. humicolus at the tadpole life history stage. The last set of experiments will test how the separate and combined effects of multiple pathogens on embryos and tadpoles vary over a gradient of an environmental stressor. This set of experiments will use three different two-pathogen combinations (B. dendrobatidis-C. humicolus, Saprolegnia-B. dendrobatidis, and Saprolegnia-C. humicolus). I will use nitrate as an environmental stressor because it is an anthropogenic pollutant present in aquatic ecosystems on a global scale and because it has a variety of sublethal effects on a wide range of organisms, including amphibians.

Supplemental Keywords:

fellowship, pathogens, hosts, environmental stress, amphibians, synergism, multiple pathogen, interaction, infectious disease,, RFA, Health, Scientific Discipline, PHYSICAL ASPECTS, ENVIRONMENTAL MANAGEMENT, Ecosystem Protection/Environmental Exposure & Risk, Environmental Chemistry, Health Risk Assessment, amphibians, Risk Assessments, Monitoring/Modeling, Biochemistry, Physical Processes, Ecological Risk Assessment, Risk Assessment, environmental monitoring, biomarkers, exposure, animal model, population decline, amphibian decline, developmental stability, human exposure, ecosystem health, environmental stress, multiple pathogens, causal mechanisms, amphibian bioindicator, exposure assessment, human health risk, biomarker

Relevant Websites:

2004 STAR Graduate Fellowship Conference Poster (PDF, 1p., 121KB, about PDF)

Progress and Final Reports:

  • Final