A lethal virus capable of wiping out amphibian populations has been detected in wild frogs living in Brazil’s highly diverse Atlantic Rainforest biome for the first time, prompting concern over whether the virus has the potential to cause “catastrophic” wipeouts in the region.

"The discovery causes concern, as it's the first time ranavirus has been found in nature here. Epidemics were reported in 2006 and 2009, but they occurred at frog farms, not in the wild,” said study author Joice Ruggeri, of the University of Campinas's Biology Institute (IB-UNICAMP), in a statement. “The virus has been detected in nature elsewhere in the world and is associated with the decline in populations of amphibians, Earth's most endangered group of vertebrates.”

Ranavirus has been linked to the decline or extinction of amphibians in other parts of the world. It causes skin ulcerations, edema, and internal hemorrhage but does not affect humans. Publishing their work in the Journal of Wildlife Diseases, researchers collected wild frogs and tadpoles from two ponds in the southern city of Pass Fundo in November 2017. Of those collected, they found both dead and dying invasive and native species, all of which had been infected by the virus.

"We found many dead tadpoles and fish in these ponds. It was a scene of destruction. We're now analyzing all the data collected, which should provide interesting answers regarding the relations among the different pathogens that are threatening anuran populations in the Atlantic Rainforest," said Ruggeri. One pond had no native amphibians but more than 20 dead American bullfrog tadpoles, an invasive species that can be a carrier of the virus without contracting the disease, with severe skin lesions. The other pond, which had no bullfrog tadpoles, exhibited lower levels of ranavirus.

Native to North America, the American bullfrog has been introduced to more than 40 countries on four continents for farming for human consumption. Brazil is the second largest producer in the world, leading researchers to believe that the virus could have spread from frog farms.

"Frog breeding as a business has ups and downs. Several frog farms have been abandoned since 1990, and many animals escaped into the wild as a result," said study author Luís Felipe de Toledo. However, it’s possible that the virus started in Brazil and may be a different strain than those seen in captive farms.

Two of the bullfrogs also had another fungal infection called Batrachochytrium dendrobatidis (Bd) or amphibian chytrid fungus, which causes chytridiomycosis and has contributed to large biodiversity losses. The fungus disrupts the balance of fluids and electrolytes to ultimately cause heart arrest. In the last 50 years, a global decline has affected at least 501 amphibian species.

"It's one more threat to these animals. The fungus has already been linked to amphibian extinctions here in Brazil. Now that we've found cases of infection by ranavirus, we wonder if it hasn't also caused declines or extinctions," said Toledo.

Both the fungus and virus are highly contagious and transmit through exposure to infected water or contact between frogs and tadpoles.