Portuguese 
Recurring outbreaks of ranavirus have been recorded over three consecutive seasons in a reserve in the Atlantic Forest. Researchers found hundreds of dead tadpoles, extremely high viral loads, and an 82.6% reduction in the reproduction of the monkey frog.
A small pond surrounded by preserved Atlantic Forest in Santa Catarina has become the site of a phenomenon that has attracted the attention of both Brazilian and foreign researchers. Between 2024 and 2026, hundreds of tadpoles began appearing dead in the water, many exhibiting hemorrhaging, swelling, and visible injuries, while others lost the ability to dive and died shortly thereafter.
The investigation revealed that the cause was associated with recurring outbreaks of ranavirus, a disease caused by viruses that can affect amphibians, fish, and reptiles. The impact has been particularly severe on the Phyllomedusa distincta, known as the monkey frog or leaf frog, an endemic species in Brazil and associated with the Atlantic Forest.
Hundreds of dead tadpoles over three consecutive years
The case was documented at the Rã-Bugio Private Natural Heritage Reserve in Guaramirim, Santa Catarina, an area of approximately 4.75 hectares dedicated to the protection of the Atlantic Forest. The location has been monitored for decades by researchers and conservationists, allowing for the recent situation to be compared with earlier periods.
-
One Hour of Downtime Can Cost US$125,000: Industrial Lubrication as a Crucial Strategy to Mitigate Risks in Critical Operations
-
PRF Helicopter Lands in One of Porto Alegre’s Busiest Avenues, Shuts Down Intersection, Surprises Passersby, and Mobilizes Over 100 People in Simulated Rescue That Transferred Airplane “Victims” to Hospitals
-
In 1960, Japan’s Future Emperor Received Just 18 Bluegills as a Gift, Leading to an Invasive Crisis in the Country’s Largest Lake Decades Later
-
6 kg Female Puma Cub Found Malnourished Near Gas Station in Paraná, Undergoes Examinations and Heads for Rehabilitation Before Returning to the Wild After Night Rescue
According to a study published in the scientific journal Biodiversity and Conservation, 324 dead tadpoles were collected between 2024 and 2026. Of this total, 315 belonged to the species Phyllomedusa distincta, and nine were of the species Boana bischoffi, popularly known as the pajama frog.
Laboratory tests showed that 287 of the 324 animals, equivalent to 88.6%, were infected with ranavirus. Among the Phyllomedusa distincta specimens, 279 tested positive, indicating an extremely high presence of the pathogen during the mortality episodes.
The first major outbreak began in January 2024 and lasted until April. New episodes were observed from November 2024 to January 2025 and again from November 2025 to March 2026, forming a sequence of outbreaks that had not previously been recorded in such detail in the region.
Animals exhibited hemorrhaging and could die within minutes
During the most critical periods, researchers observed that some populations of tadpoles experienced near-total mortality. After the first dead animals appeared, the number of carcasses quickly increased in the pond.
Infected tadpoles showed signs such as intense red coloration, bleeding, edema, swollen abdomens, skin lesions, and even bleeding from the eyes. Some of the animals observed still alive could no longer dive normally, remained close to the surface, and died within approximately 30 minutes or less.
Analyses performed on the livers of infected animals found extensive areas of necrosis and destruction of tissue structure, reinforcing that the virus was not only present in the organisms but was causing active and severe disease.
Researchers also identified extraordinarily high viral loads. In some specimens of Phyllomedusa distincta, up to 9.81 billion viral copies per microliter were detected in the analyzed samples.
Monkey Frog Reproduction Plummeted by 83%
The impact was not limited to the death of the tadpoles. Long-term monitoring revealed an approximate 82.6% decline, rounded to 83%, in the production of egg masses by the monkey frog during the period affected by the outbreaks.
Before the epidemics, the estimated egg deposition rate was approximately 5.74 times higher. To reach this conclusion, researchers compared historical records prior to the outbreaks with recent data collected after the onset of mass deaths.
The Rã-Bugio Sanctuary has been monitoring the reproduction of the species since 1999. Females lay their eggs on leaves located above the water and fold the vegetation around the egg mass. After hatching, the tadpoles fall directly into the pond, where they complete part of their development.
The recorded drop does not mean that 83% of adult animals have disappeared. The figure specifically refers to a reduction in reproductive performance, but researchers warn that the decrease in the generation of new individuals could lead to a severe population decline if the phenomenon continues.
Low Humidity May Favor Outbreaks
Researchers found a strong association between mortality episodes and periods of lower humidity. With an average of about 65% humidity in the two preceding weeks, the estimated probability of deaths reached 97.7%, while it dropped to around 7% with humidity close to 90%.
The hypothesis is that drier weather induces stress in amphibians and reduces the water volume in the pond, concentrating the tadpoles and facilitating the transmission of the virus. Nevertheless, the study did not find evidence that long-term climate changes alone explain the decline in reproduction.
Virus origin still unknown
Genetic analyses indicated that the agent belongs to the group Ranavirus rana1, closely related to Frog Virus 3, but its origin has not yet been determined. It may have been present in the region for years or been introduced more recently.
Another pond located just 450 meters from the affected site did not show similar mortality, suggesting that outbreaks can occur in a highly localized manner.
This case stands out for providing molecular, histological, and population evidence that recurrent outbreaks of ranavirus can cause mass mortality and reduce reproduction in wild amphibians. Monitoring will continue to assess the virus’s distribution and potential impacts on other populations in the Atlantic Forest.
