Nav: Home

Amphibians infected by ranavirus found in Atlantic rain forest

June 28, 2019

Researchers have found bullfrog tadpoles with clear signs of infection by ranavirus in Brazil. The specimens were collected from two ponds in the city of Passo Fundo, South of the country (state of Rio Grande do Sul), in November 2017. Ranavirus causes skin ulcerations, edema and internal hemorrhage. It does not affect humans but can be lethal to amphibians and fish.

This is the first infection of wild amphibians detected in Brazil. "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. 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," said Joice Ruggeri, a researcher at the University of Campinas's Biology Institute (IB-UNICAMP) and first author of the article published in the Journal of Wildlife Diseases.

The discovery resulted from Ruggeri's postdoctoral research, supported by São Paulo Research Foundation - FAPESP.

The aim of the project was to investigate the dynamics of ranavirus in different species of anurans (frogs and toads), its interaction with other pathogens, and possible imbalances or threats to populations of these animals in the Atlantic Rainforest biome.

Ruggeri collected specimens of wild anurans in areas from Rio de Janeiro state in Southeast Brazil to Rio Grande do Sul in the South, including ponds in Passo Fundo.

"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," Ruggeri told.

The discovery also raises questions about the relations between invasive and native species. According to the article, the researchers found dead and dying adults and tadpoles of both native species and the American bullfrog (Lithobates catesbeianus), an invasive species. All had been infected by the virus.

L. catesbeianus can be infected with ranavirus without contracting any disease, thereby acting as a vector for its dissemination. This reinforces the hypothesis, as yet unconfirmed, that native species are being infected by the invasive species.

The weight of invasive species

L. catesbeianus is native to North America and has been introduced to over 40 countries on four continents. It is one of the main species farmed for human consumption. Brazil is the second-ranking producer. Most farms are located in areas of Atlantic Rainforest between Rio de Janeiro and Rio Grande do Sul, rationalizing the researchers' choice of these areas for data collection.

"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 Luís Felipe de Toledo, a professor at IB-UNICAMP and one of the authors of the article.

The researchers believe the virus may have spread through the Atlantic Rainforest biome from frog farms, but there are other hypotheses. "We know many of these frogs escaped from captivity and may have taken the virus into the natural environment, but we're not yet sure whether they have any link to the virus detected in species native to Brazil," Ruggeri said.

Dual threat

The discoveries do not stop there. Two of the bullfrogs studied had been coinfected by ranavirus and by the fungus Batrachochytrium dendrobatidis, also known as Bd or amphibian chytrid fungus, which causes chytridiomycosis and is responsible for the greatest biodiversity loss due to a single pathogen ever recorded.

In an article published in Science in March 2019, researchers from 16 countries, Toledo among them, reported that the fungus has caused a decline in the populations of at least 501 species of amphibians in the past 50 years.

"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," Toledo said.

Both fungi and viruses are transmitted via exposure to infected water or direct contact between frogs or tadpoles, making dispersal of these microorganisms highly effective. While the fungus disrupts the balance of fluids and electrolytes, ultimately causing a heart arrest, the virus can cause cell death in multiple organs.

"When an amphibian is infected by both pathogens, it becomes even more vulnerable. However, our understanding of the consequences of this coinfection is still insufficient," Ruggeri said.

Having analyzed the data collected, the researchers will now investigate the ranavirus strains found in South Brazil. "The virus's lineage could be Brazilian. We also plan to determine whether the viruses identified in the wild and at frog farms are from the same lineage. The discovery points to several lines of research," Toledo said.

High mortality

Low levels of ranavirus were detected in native tadpoles living in one of the ponds, which contained no bullfrog tadpoles.

More than 20 dead bullfrog tadpoles were found in the other pond, and no native anuran species were found. All the animals found had severe skin lesions and were infected by ranavirus. Only two tadpoles were found alive, and these had low levels of infection.

The fungus was detected in seven out of 19 dead tadpoles, including samples of native and invasive species collected from both ponds. However, the researchers ruled out chytridiomycosis as the cause of death because the fungal load was low.

Although bullfrogs are generally tolerant of ranavirus, high viral loads were found in their blood, and they displayed clear clinical signs of disease.
About São Paulo Research Foundation (FAPESP)

The São Paulo Research Foundation (FAPESP) is a public institution with the mission of supporting scientific research in all fields of knowledge by awarding scholarships, fellowships and grants to investigators linked with higher education and research institutions in the State of São Paulo, Brazil. FAPESP is aware that the very best research can only be done by working with the best researchers internationally. Therefore, it has established partnerships with funding agencies, higher education, private companies, and research organizations in other countries known for the quality of their research and has been encouraging scientists funded by its grants to further develop their international collaboration. You can learn more about FAPESP at and visit FAPESP news agency at to keep updated with the latest scientific breakthroughs FAPESP helps achieve through its many programs, awards and research centers. You may also subscribe to FAPESP news agency at

The article "First case of wild amphibians infected with ranavirus in Brazil" (doi: 10.1038/s41467-019-08909-4) by Joice Ruggeri, Luisa P. Ribeiro, Mariana R. Pontes, Carlos Toffolo, Marcelo Candido, Mateus M. Carriero, Noeli Zanella, Ricardo L. M. Sousa and Luís Felipe Toledo can be read at

Fundação de Amparo à Pesquisa do Estado de São Paulo

Related Invasive Species Articles:

'Trojan fish': Invasive rabbitfish spread invasive species
For some time, unicellular benthic organisms from the Indo-Pacific have been spreading in the Mediterranean.
New York schools help Cornell monitor local waterways for invasive species
With 7,600 lakes and 70,000 miles of creeks and rivers to monitor, Cornell researchers struggled to stay ahead of round goby and other invasive species -- until they tapped into New York's network of teachers looking to bring science alive for their students.
Documenting the risk of invasive species worldwide
In the first global analysis of environmental risk from invasive alien species, researchers say one sixth of the world's lands are 'highly vulnerable' to invasion, including 'substantial areas in developing countries and biodiversity hotspots.' The study by biogeographer Bethany Bradley at the University of Massachusetts Amherst and Regan Early at the University of Exeter, UK, with others, appears in the current issue of Nature Communications.
Invasive species could cause billions in damages to agriculture
Invasive insects and pathogens could be a multi-billion- dollar threat to global agriculture and developing countries may be the biggest target, according to a team of international researchers.
Entomological Society of America releases statement on the dangers of invasive species
The Entomological Society of America has issued a statement about the dangers of invasive species and the potential threats they pose to US national interests by undermining food security, trade agreements, forest health, ecosystem services, environmental quality, and public health and recreation.
More Invasive Species News and Invasive Species Current Events

Best Science Podcasts 2019

We have hand picked the best science podcasts for 2019. Sit back and enjoy new science podcasts updated daily from your favorite science news services and scientists.
Now Playing: TED Radio Hour

Teaching For Better Humans
More than test scores or good grades — what do kids need to prepare them for the future? This hour, guest host Manoush Zomorodi and TED speakers explore how to help children grow into better humans, in and out of the classroom. Guests include educators Olympia Della Flora and Liz Kleinrock, psychologist Thomas Curran, and writer Jacqueline Woodson.
Now Playing: Science for the People

#535 Superior
Apologies for the delay getting this week's episode out! A technical glitch slowed us down, but all is once again well. This week, we look at the often troubling intertwining of science and race: its long history, its ability to persist even during periods of disrepute, and the current forms it takes as it resurfaces, leveraging the internet and nationalism to buoy itself. We speak with Angela Saini, independent journalist and author of the new book "Superior: The Return of Race Science", about where race science went and how it's coming back.