Amphibian Disease Program

Dr. Matthew Gray leads the Amphibian Disease Program in the Center for Wildlife Health at the University of Tennessee.  This program focuses on the influences of anthropogenic land use on pathogen transmission and prevalence in amphibians.  It is hypothesized that environmental stressors, such as cattle grazing in wetlands, may increase pathogen prevalence in resident amphibians by negatively affecting their immune system.  Cattle may cause stress in amphibians, particularly tadpoles, by decreasing water quality.  Studies have shown reduced numbers of white blood cells in tadpoles exposed to low water quality.  Current research in the Amphibian Disease Program is examining the influences of cattle access in temperate wetlands on pathogen prevalence in amphibians.  Pathogens of concern include frog virus 3, the bacterium Aeromonas hydrophila and the trematode Ribeiroia spp.  These pathogens have been linked to amphibian die-offs and malformations in North America. 

The second focus of the Amphibian Disease Program is examining whether amphibians can serve as hosts for zoonotic pathogens of concern to cattle and humans, such as Cryptosporidium parvum, Salmonella spp., E. coli O157:H7, Camplyobacter spp., Mycobacterium avium paratuberculosis and Listeria monocytogenes.  Cattle infected with these pathogens may defecate in water sources, such as farm-pond wetlands, and facilitate transmission to herd members when individuals drink contaminated water.  Moreover, wild vertebrates may serve as ‘spill-over’ hosts (sensu Science 287:443-449) of cattle-derived pathogens, and result in a permanent reservoir for reinfection.  For example, tadpoles may ingest pathogens shed by cattle and become infected.  Tadpoles with sublethal infections could release pathogens in their feces and facilitate cattle reinfection.  In addition, tadpoles metamorphose, thus potentially could transport pathogens overland to naïve amphibian populations and neighboring cattle herds.  Ultimately, these pathogens could be transmitted to humans and result in foodborne illness, particularly if beef products are undercooked.  Research is planned in the Amphibian Disease Program to investigate infection and shedding rates of zoonotic pathogens for larval amphibians.

From left to right:  Frog virus 3 isolated from tadpoles in Tennessee (left), Salmonella culture plate (middle), and cross-section of a trematode (Clinostomum attenuatum) metecercaria encysted in a barred tiger salamander from Texas (right).  Photos courtesy of Dr. Debra Miller. 

The Amphibian Disease Program works very closely with the University of Georgia Veterinary Diagnostic and Investigational Laboratory in Tifton, Georgia.  Collaborators include Drs. Debra Miller, Sandy Baldwin and Sreekumari Rajeev.  For more information on current research projects or questions about amphibian diseases, please contact Drs. Matt Gray (865-974-2740) or Debra Miller (229-386-3340).

Read about the University of Tennessee's Wetlands Program.

Read about our E. coli O157:H7 mesocosm study.

Undergraduate Course: WFS493/560 Amphibian Ecology and Conservation