[Animals] A terrifying fungal disease infects frogs in Africa.

[#Steeven.™]

Deadly spores lurk in the water, infecting the skin of creatures they touch. Spreading on contact and then invading the body, this fungal disease causes ulcers and scaling, so that severe skin sloughs off in sheets.

Joints in the leg begin to lock up, and soon after symptoms appear, the disorder can lead to cardiac arrest and death.

The deadliest disease to affect vertebrates in recorded history, chytridiomycosis has wreaked havoc on amphibians for decades, including frogs, toads and salamanders.
The disease is not known to infect humans, but scientists caution that these outbreaks are crucial to understanding how fungal pathogens spread and learning to understand a mass extinction event affecting our amphibian friends.

The disease has already decimated amphibian po[CENSORED]tions in the Americas, Australia and parts of Europe, and the latest research has shown it may now be making its way across Africa. The disease may be killing animals in hordes without scientists realizing it, warned Dr. Vance Vredenburg, a professor of biology at San Francisco State University and a research associate at the Museum of Vertebrate Zoology at the University of California, Berkeley. .

"There could be hundreds of species (in Africa) that could be endangered by this pathogen," said Vredenburg, co-author of a new study published March 15 in Frontiers in Conservation Science that reveals the pervasiveness of chytridiomycosis in Africa for the first time. .

To amphibians, the disease is making the Black Death that ravaged Europe in the Middle Ages "seem like a drop in the ocean," Vredenburg said.

 

Why does it matter
Chytridiomycosis is caused by a pathogen called Batrachochytrium dendrobatidis, or Bd for short. The disease was one of the main contributors to the threat of extinction facing amphibian species around the world. About 41% of amphibians are currently endangered, according to the International Union for Conservation of Nature's Red List of Threatened Species.

Understanding Bd and how it spreads has been a major focus of Vredenburg's career. He began studying the pathogen in the late 1990s, tracking Bd around the world and observing its deadly impact. He recalled visiting the Sierra Nevada between 2004 and 2008, where he witnessed a particularly brutal outbreak and "watched thousands of frogs die in front of my eyes from this disease."

"Scientists didn't believe that one fungal pathogen could (affect) hundreds of species. But, in fact, the nightmare story is true," said Dr. Vance Vredenburg, a professor of biology at San Francisco State University.

"Honestly, before it happened, I didn't believe it," he said. Vredenburg said he has "changed the way scientists look at disease and their ability to really control wildlife po[CENSORED]tions."

In places where scientists have taken a closer look at the devastating impact of Bd, the "disease has caused the decline or complete extinction of more than 200 species of frogs and other amphibians," according to the Wildlife Health Laboratory of the Cornell University.

Scientists previously thought that amphibians in Africa were relatively spared from the scourge of Bd. But Vredenburg set out to see if the pathogen was present in museum specimens of amphibians from Africa and enlisted colleagues abroad to collect live samples in nature. He also analyzed previous studies of the continent. In total, more than 16,900 animals were analysed.

Signs of Bd in Africa were low, below 5%, from the 1930s to the late 1990s, the study found. Then the cases exploded.

Infection rates rose to more than 17% and again to nearly 22% in the 2010s. The most serious outbreaks appeared to be in places where scientists had the most data, including in countries like Burundi, where rates of infection exceeded 73%.

Those rates are worrisome, Vredenburg added, because they could indicate that amphibian po[CENSORED]tions are going extinct en masse.

"Unless you're really looking, you might not notice they're gone until they're gone," she said. “We really should understand why it is such a big problem in these vertebrates. They have been around for 400 million years.”

The million dollar question for scientists is why there is such a sudden and dramatic threat to their existence, Vredenburg said.

 

The hidden threat of the disease that affects frogs
It's hard to pin down how amphibian po[CENSORED]tions are coping with the disease. Most frogs and their ilk are nocturnal, so humans don't always come into contact with them when they get sick. The pathogen is also fast, killing those infected soon after symptoms begin. And amphibian carcasses decompose rapidly, Vredenburg added, erasing evidence of mass die-off before scientists can discover the carcasses.

However, Bd does not always trigger a deadly outbreak, a positive but puzzling fact that the researchers considered in the new study. The pathogen can be found in some frog po[CENSORED]tions that manage to survive, much like humans adapt to pandemics.

The amphibians the study authors sampled in Africa, Vredenburg noted, didn't always show physical symptoms of the disease, even though they tested positive for Bd. Those po[CENSORED]tions could still end up dead, or they may have a natural defense against the disease. And that is part of the reason why Vredenburg urges to continue the study of the presence of the disease in the continent.

The scientists were also able to treat and immunize frogs in captivity, Vredenburg added, although it would be virtually impossible to attempt to do so in the wild. Frogs, of course, cannot coordinate the global distribution of vaccines as humans can in times of pandemic.

 

Spread and impact of the disease
There are certain steps that scientists said humans should take to mitigate the spread of Bd. Vredenburg noted that the fungus can spread through the exotic animal trade if an amphibian is captured in one location and then returned to the wild. somewhere else. Stopping that type of trading can help thwart the spread of Bd.

Once the Bd appears in a certain place, it spreads on contact. Frogs can contract chytridiomycosis from the pathogen by swimming in infested water, where the fungus lives, or by brushing against another infected animal.

Amphibian po[CENSORED]tions are already at risk from habitat loss, said biologist Dr. JJ Apodaca, executive director of the US nonprofit Amphibian and Reptile Conservancy, who was not involved in the new study. Apodaca said the study offered a valuable new perspective on how such a devastating pathogen has spread.

The disease is "the last straw" when it comes to amphibian conservation, he said. “When animals are stressed by habitat loss, all of those things come together, and then disease comes along and ends it.”

Apodaca is focusing on po[CENSORED]tions of frogs and other amphibians in the United States, but knowing how Bd is spreading in Africa helps to understand the origins of the pathogen and the causes of the outbreaks.

“My greatest wish would be for people to simply understand that these problems exist,” added Apodaca. Threats like Bd “will get a big flash on the bread news event and then the next day it's the next problem. …But in the meantime, our wildlife, our native amphibians and reptiles are being hit.”

 

https://cnnespanol.cnn.com/2023/03/25/una-aterradora-enfermedad-fungica-esta-infectando-a-las-ranas-en-africa-te-contamos-por-que-es-importante-trax/