Federal researchers have found two diseases in the La Crosse area that have been linked to worldwide declines in amphibian populations.
While they did not find any signs of illness, U.S. Fish and Wildlife Service biologists found the parasitic fungus Batrachochytrium dendrobatidis (Bd) and a member of the ranavirus family on frogs collected in La Crosse, Monroe, Trempealeau and Vernon counties, marking the first time the pathogens have been documented in western Wisconsin.
The findings are part of a study conducted at the Midwest Fisheries Center in Onalaska and published last month in the journal Diseases of Aquatic Organisms. Lead researcher Isaac Standish said the goal was to develop a nonlethal test for several recently-discovered diseases that threaten amphibian populations.
“A lot of these tests are lethal. With our test it’s just a simple swab,” Standish said. “It could be used for threatened and endangered species we didn’t want to sacrifice.”
Amphibian populations have been declining, though there was no shortage of hopping frogs as Standish and his team collected samples in the La Crosse River marsh Thursday as part of ongoing research. Standish brushed a cotton-tipped swab over each frog — and one crawfish — before sending them back on their way.
Juvenile green frogs accounted for most of the day’s catch, though they did find one bullfrog and a leopard frog, which they say are increasingly rare.
“The leopard frog populations are lower than what they were decades ago,” said Eric Leis, another biologist who worked on the study. “I grew up on a farm 30 miles away and we saw a lot of leopard frogs and now you just don’t see them. … There’s no good explanation.”
The most serious of the new pathogens, a fungus known as B. Salamandrivorins (Bsal for short), was discovered in 2013 and has been linked to dramatic population declines of the fire salamander in the Netherlands. That led the Fish and Wildlife Service to list 201 salamander species under the Lacey Act, which prohibits trade in illegally obtained wildlife.
While it presents no public health risk, these pathogens can be deadly to amphibians and has even led to the extinction of some species.
“It’s something that we want to keep our eye on,” Standish said. “Amphibians and fish share more pathogens than we thought a few years ago.”
The diseases likely originated in east Asia and have been spread by the pet industry and global trade in general.
Standish said local amphibian populations seem to be coping with the diseases found here but adverse environmental conditions — hot weather, rising water temperatures or chemical contaminants — could decrease their immunity and make them more susceptible.
Researchers say the public can help by not releasing pets into the wild and by reporting anything unusual — such as a mass mortality or sick amphibians — to the Fish and Wildlife Service.
“It might just take somebody going for a walk to see it,” Leis said.