Scientists have unraveled the dynamics of a deadly disease that is wiping out amphibian populations across the globe. New findings, published today in the Proceedings of the National Academy of Sciences, suggest that infection intensity -- the severity of the disease among individuals -- determines whether frog populations will survive or succumb to an amphibian fungal disease called Chytridiomycosis. The research identifies a dangerous tipping point in infection intensity, beyond which Chytrid causes mass mortalities and extinctions, and finds that continual re-infection causes the disease to reach this threshold.
"We found that mass frog die-offs only occur when the severity of the Chytrid infection reaches a critical threshold among the individual frogs," said Vance Vredenburg, assistant professor of biology at San Francisco State University. "Now that we know this limit, which is a specific number of fungal spores per frog, conservation efforts may be able to save susceptible frog species by preventing the disease from reaching this point."
In the first of two separate studies, Vredenburg and colleagues tracked the invasion and spread of Chytrid among frogs in California's Sierra Nevada Mountains during a 13-year period, focusing on two species of the mountain yellow-legged frog (Rana muscosa and Rana sierrae). The study found that Chytrid is particularly destructive when it invades a previously unexposed population, similar to the smallpox epidemics that devastated human populations in the 17th and 18th centuries.
"When Chytrid hits nave host populations, it grows so quickly that the usual checks and balances, which prevent a pathogen from causing extinction, don't have a chance to kick in," Vredenburg said. "We are living in a time when the global movement of people and goods is likely spreading this disease to areas where it wasn't present before, interrupting
|Contact: Elaine Bible|
San Francisco State University