A seldom-studied parasite fatal to frogs is more widespread than previously thought and growing deadlier as the world warms, a new University of Central Florida study found. The deadly disease it causes worsens with the heavier rains of climate change and in concert with an Ebola-like virus that also kills frogs.
The parasite, Amphibian Perkinsea, infected a third of frogs that UCF researchers sampled, according to their recently published in the Journal of Animal Ecology. Florida gopher frogs, which live in threatened gopher tortoise burrows, had the highest prevalence and intensity of the disease. That's concerning, the UCF researchers say, because the gopher frog is declining in most of its range.
“We have this pathogen that we basically know nothing about, and this is the first real stab at trying to understand where it's showing up and why,” said Matthew Atkinson, a lecturer in UCF’s biology department and lead author of the study, coauthored by Anna Savage, an associate professor in the same department.
The study is the latest in a litany of research showing climate change forging more opportunities for pathogens at the same time pollution and other environmental stress taxes wildlife immune systems. In 2017, researchers at the U.S. Geological Survey found that severe Perkinsea infections caused 21 mass amphibian mortalities in 10 states spanning from Florida to Alaska, all involving tadpoles. Up to 95% of the tadpoles died during those die-offs. USGS examined 247 frog die-offs in 43 states from 1999 through 2015.
UCF's study used genetic sequencing to determine the presence and intensity of the parasite and co-infection with also deadly Ranavirus — known as "the Ebola of frogs" — across 1,234 frogs sampled in Central Florida from 2017 to 2019. Ranavirus prevalence was 17% overall. The parasite may be worsening susceptibility to the virus, not the other way around, the researchers said. There is no evidence either frog pathogen infects humans.
One of UCF's major field sites was Forever Florida in Osceola County.
Why should we care?
Frogs play a vital role in food webs. Like canaries in a coal mine, they are considered an indicator species. Because of their sensitivity to pollution and other environmental changes, frogs and other amphibians can be early warning signs of ecosystem disruption.
The researchers sampled frogs from 20 wetlands across Central Florida. Sampling data included average pH, presence of standing water, number of frog species, and fish and crayfish prevalence. For DNA, only a small tissue sample from the frogs' toe or tail was removed. The innovative method enabled researchers to quantify pathogen presence and intensity without euthanasia.
What is Perkinsea?
Perkinsea is part of a unique group of organisms called protists that don’t fit easily into the categories of plant, animal or fungi. When Perkinsea spores enter a frog, they wind up in its liver and other organs and "eat the tissue from the inside out, leading to death," the UCF researchers said.
“And we can't do anything for protecting species unless we know what's actually happening in the first place," Atkinson said. "So that's been a big focus with us.”
As climate change warms northern regions, more areas could experience conditions favorable to Perkinsea infections in frogs, the researchers said.
While more frogs are infected and dying from the parasite than previously thought, increasing winter temperatures in the state might actually decrease infections, based on UCF's finding that lower monthly temperatures were associated with higher prevalence of the parasitic disease. But increased temperatures in other parts of North America may mimic the winter temperatures seen in Florida that are most favorable to the parasite, increasing parasitic infections in other regions.
But "only time and more research will show if Perkinsea disease will actually increase under climate change," Savage added.
Heavy rain, such as during Hurricane Irma in 2017, also was linked to the parasitic disease as was the presence of Ranavirus. And climate change predictions include more heavy rain events.
How big a risk are these diseases to frogs?
It's unclear how many frogs the two pathogens are killing.
"Perkinsea research is in its infancy and the core studies on host susceptibility, or what’s going on with Ranavirus co-infection, have not yet been done," Savage wrote in an email. "We have unpublished datasets and planned experiments, but even for Ranavirus that has been studied for decades, it’s still unclear among thousands of potential host species exactly how susceptible each one is, or what exactly determines whether and how quickly they die."
Unknowns aside, the UCF researchers say their findings can help conservation efforts.
“While this is only a starting point for managing and protecting species, it tells us where and when to focus, so that in the future we could do things like avoid releasing head-started frogs (those raised in captivity) of threatened and managed species into the wild at times of year when they are more likely to suffer from disease,” Savage said in a release.
“Gopher frogs are the most threatened and most susceptible species we know of to date, so those are the species that could benefit the most,” she added.
How People Can Protect Frogs?
We can help frogs by not spreading animals and pathogens around, Savage said.
“If you like to boat, fish or hike, be aware that all of the major frog diseases can survive on your nets, shoes and boots for days," she said, "and you could be spreading spores from one location to the next if you don’t decontaminate your gear in between sites."
Preventing spread is easy, she added.
"All it takes is rinsing things in a weak solution of household bleach or leaving items out to dry in the sun for at least a few days before traveling somewhere new," Savage said.
Part of the solution may be political, the researchers said. They suggest writing local representatives to let them know that conserving natural areas and preventing more development of state lands is the main way to prevent species declines.
“Diseases are a major problem, but losing habitat and connectivity among frog populations is an even bigger problem that, when combined with disease, can cause us to lose populations entirely,” Savage said.
This article originally appeared on Florida Today: Parasite that lingers with 'frog Ebola' killing more frogs than thought