Swabbing a Frog (IMAGE) San Francisco State University Caption San Francisco State University Professor Vance Vredenburg collects a skin swab from a southern mountain yellow-legged frog in California's Sierra Nevada where he and colleagues tracked the spread of the deadly amphibian disease Chytridiomycosis during a 13-year period. New research by Vredenburg, published in PNAS, identifies a dangerous tipping point in infection intensity and suggests that mass frog deaths only tend to occur once infection intensity reaches an average of more than 10,000 fungal spores per skin swab. Chytridiomycosis is caused by an aquatic fungus called Batrachochytrium dendrobatidis. Credit Natalie Reeder Usage Restrictions None License Licensed content Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.