Human impacts on the prevalence of the amphibian infectious diseases, Batrachochytrium dendrobatidis and ranavirus, in Oklahoma, USA

Batrachochytrium dendrobatidis (Bd) and ranavirus (RV) are pathogens contributing to the global decline of amphibian populations. Both pathogens can be spread through direct contact between amphibians, through water carrying the infection, the accidental movement of disease particles between waterbodies by cattle, boats, or aquatic recreational equipment, or the intentional movement of infected amphibians used as fishing bait. Amphibians can also experience indirect human-caused effects due to environmental pollutants, including increased stress levels and reduced immunity. We conducted a meta-analysis regarding the effects of human impact on Bd and RV pathogen prevalence and infection loads in Oklahoma amphibians, based on field research conducted 2015–2017. Research sites were identified as having minimal, moderate, or high human impact with regard to the degree of land usage for aquatic recreation, grazing, and oil/natural gas. Samples were screened for both Bd (gene ITS1) and RV (gene MCP) via published qPCR methodologies; results are reported for both prevalence and infection load (calculated based on qPCR output of mean gene copies multiplied by the dilution factor and extraction volume). We found an average prevalence of 47% for Bd and 19.2% for RV infection in amphibians (sample sites pooled), with a trend of increasing prevalence for Bd and RV with increasing human interaction. For both pathogens, specimens collected from “moderate” sites had the highest infection loads. We advise land managers overseeing the public use of Oklahoma lands to share educational material regarding amphibian infectious disease, to prevent future spread.