Tag: Amphibians

Amphibian populations are declining worldwide and a major cause is a deadly fungus thought to be spread by bullfrogs, but a two-year study shows they can also die from this pathogen, contrary to suggestions that bullfrogs are a tolerant carrier host that just spreads the disease. When researchers raised the frogs from eggs in controlled experimental conditions, they found at least one strain of this pathogen, Batrachochytrium dendrobatidis, also called Bd or a chytrid fungus, can be fatal to year-old juveniles. However, bullfrogs were resistant to one other strain that was tested. The findings, made by researchers at Oregon State University and the University of Pittsburgh, show that bullfrogs are not the sole culprit in the spread of this deadly fungus, and add further complexity to the question of why amphibians are in such serious jeopardy. About 40 percent of all amphibian species are declining or are already extinct, researchers say. Various causes are suspected, including this fungus, habitat destruction, climate change, pollution, invasive species, increased UV-B light exposure, and other forces. “At least so far as the chytrid fungus is involved, bullfrogs may not be the villains they are currently made out to be,” said Stephanie Gervasi, a zoology researcher in the OSU College of Science. “The conventional wisdom is that bullfrogs, as a tolerant host, are what helped spread this fungus all over the world. But we’ve now shown they can die from it just like other amphibians.”

The research suggests that bullfrogs actually are not a very good host for the fungus, which first was identified as a novel disease of amphibians in 1998. So why the fungus has spread so fast, so far, and is causing such mortality rates is still not clear. “One possibility for the fungal increase is climate change, which can also compromise the immune systems of amphibians,” said Andrew Blaustein, a distinguished professor of zoology at OSU and international leader in the study of amphibian declines. “There are a lot of possible ways the fungus can spread. People can even carry it on their shoes.” The average infection load of the chytrid fungus in bullfrogs, regardless of the strain, is considerably lower than that of many other amphibian species, researchers have found. Some bullfrogs can reduce and even get rid of infection in their skin over time. While adult bullfrogs may be carriers of some strains of Bd in some areas, the researchers concluded, different hosts may be as or more important in other locations. International trade of both amphibian and non-amphibian animal species may also drive global pathogen distribution, they said. The findings of this study were published in EcoHealth, a professional journal.

Science Daily
July 9, 2013

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Pathogenic fungi have substantial effects on global biodiversity, and 2 emerging pathogenic species—the chytridiomycete Batrachochytrium dendrobatidis, which causes chytridiomycosis in amphibians, and the ascomycete Geomyces destructans, which causes white-nose syndrome in hibernating bats—are implicated in the widespread decline of their vertebrate hosts. We synthesized current knowledge for chytridiomycosis and white-nose syndrome regarding disease emergence, environmental reservoirs, life history characteristics of the host, and host–pathogen interactions. We found striking similarities between these aspects of chytridiomycosis and white-nose syndrome, and the research that we review and propose should help guide management of future emerging fungal diseases.

Fungi and fungus-like organisms have been recognized historically as prominent plant pathogens that can have detrimental effects on agricultural crops and wild flora. Fisher et al. recently reviewed the increasing role and recognition of pathogenic fungi that affect global biodiversity. Their analyses showed that most (91%) recent extinctions and extirpations caused by fungal disease have affected animals rather than plants. In particular, 2 emerging pathogenic fungi—the chytridiomycete Batrachochytrium dendrobatidis, which causes chytridiomycosis in amphibians, and the ascomycete Geomyces destructans, which causes white-nose syndrome (WNS) in hibernating bats—are implicated in the widespread decline of their vertebrate hosts. In general, increased global biosecurity and monitoring are recommended to prevent and manage emerging fungal diseases, but there are also pressing research needs that can help specifically address these 2 devastating pathogenic fungi. We call attention to parallels between chytridiomycosis and WNS and highlight areas where urgent research is required. Comparison of these diseases also illustrates broader themes and questions that can be used to direct research on future emerging fungal diseases.

Emerging Infectious Diseases
March 19, 2013

Original web page at Emerging Infectious Diseases

Frogs are in trouble. In the 1990s researchers in Spain, Australia and Central America discovered that amphibians in rainforests and mountain lakes were dying in large numbers. The killer, it turned out, was chytridiomycosis, a disease caused by the fungus Batrachochytrium dendrobatidis (Bd), which has since been found around the world. Scientists have rushed to understand the disease, and have attempted different ways to mitigate its spread. But science alone is not sufficient. Mark Auliya, a herpetologist and trade-policy expert at the Helmholtz Centre for Environmental Research in Leipzig, Germany, says that policies have to change on an international level. Auliya is part of the European Union (EU) project Risk Assessment of Chytridiomycosis to European Amphibian Biodiversity (RACE), in which teams of scientists are each looking at different aspects of the disease: genetics, physiological and behavioural effects, and geography. RACE will end in 2013 and Auliya is preparing to make a raft of policy recommendations based on the project. He spoke to Nature about the compelling need for new animal-trade legislation.

Two or three years ago we had about 200 Bd-infected amphibian species and now we have more than 500. Bd is now distributed in more than 50 countries, on all continents that harbour amphibians. There are almost 7,000 amphibian species, but less than 3% are covered by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES). To control Bd in Europe there has to be a completely new EU-imposed comprehensive disease-control directive, which includes the regulation of all amphibian-trade activities across all entities that house or deal with amphibians. At this stage we cannot focus on specific species — we have to consider them all because potentially every amphibian species can have and spread the disease. There is nothing legislating against Bd in particular. CITES came into effect in the mid 1970s, intended to ensure that species as a whole are not harmed by trade activities. But that didn’t mean by spreading disease. CITES has now officially recognized the spread of diseases through trade activities or through the movement of wildlife. However, it also recognizes that the convention is not the major player in this.

We have hundreds of pet shops across Europe; we have hundreds of exotic-wildlife and reptile fairs; the frog-leg trade is another problem. But we have a lack of enforcement of existing trade regulations, and there are loopholes freely used by the consumers. We need standardized hygiene control. There must be something like an EU veterinary council imposing a single EU-wide hygiene and quarantine strategy to prevent spread of these diseases. We’re not looking at an improved law system, we’re looking at a completely revised law, which encompasses all these issues: trade, conservation of amphibian species and disease control. We also need harder sanctions on wildlife crime, which is still a trivial offence in most countries. What can scientists, such as those involved in RACE, add to the debate? The most striking result accomplished by the scientific community in the past year has been showing very clearly that global trade patterns have contributed to the spread of chytridiomycosis. We know that the global panzootic lineage of Bd has spread through trade activities. We also know that there are species that carry the disease but don’t necessarily die from it, such as the North American bullfrog (Rana catesbeiana), an invasive species that can adapt well to different habitats. There is an upcoming opportunity: the EU’s animal-health strategy is set to be renewed in 2013. Emerging infectious diseases have been put on the agenda, and RACE scientists have a chance to inform how the strategy deals with that. This will probably include wild species, disease control and trade issues. This revised law should ideally impose amphibian-trade regulations among the different stakeholders: the pet industry, biomedical research, zoos and aquaria.

Nature
June 26, 2012

Original web page at Nature

The fungal infection that has killed a record number of amphibians worldwide leads to deadly dehydration in frogs in the wild, according to a new study by University of California, Berkeley and San Francisco State University researchers. High levels of an aquatic fungus called Batrachochytrium dendrobatidis (Bd) disrupt fluid and electrolyte balance in wild frogs, the scientists say, severely depleting the frogs’ sodium and potassium levels and causing cardiac arrest and death. Their findings confirm what researchers have seen in carefully controlled lab experiments with the fungus, but SF State biologist Vance Vredenburg said the data from wild frogs provide a much better idea of how the disease progresses. “The mode of death discovered in the lab seems to be what’s actually happening in the field,” he said, “and it’s that understanding that is key to doing something about it in the future.” The study is published online by peer-reviewed journal PLoS ONE. At the heart of the new study are blood samples drawn from mountain yellow-legged frogs by Vredenburg, who is an assistant professor of biology at SF State, and colleagues in 2004, as the chytrid epidemic swept through the basins of the Sierra Nevada range. “It’s really rare to be able to study physiology in the wild like this, at the exact moment of a disease outbreak,” said UC Berkeley ecologist Jamie Voyles, the lead author of the study. Unfortunately, it is a study that can’t be duplicated, at least not in the Sierra Nevada. Frog populations there have been devastated by chytrid, declining by 95 percent after the fungus was first detected in 2004. “It’s been really sad to walk around the basins and think, ‘Wow, they’re really all gone,'” Vredenburg said. The chytrid fungus attacks an amphibian’s skin, causing it to become up to 40 times thicker in some instances. Since frogs depend on their skin to absorb water and essential electrolytes like sodium from their environment, Voyles and her colleagues knew that chytrid would disrupt fluid balance in the infected amphibians, but were surprised to find that electrolyte levels were much lower than anticipated for the Sierra Nevada sample. “It’s clear that this fungus has a profound effect in the wild,” Voyles said.

“Wildlife diseases can be just as devastating to our health and economy as agricultural and human diseases,” says Sam Scheiner, NSF program officer for EEID. “Bd has been decimating frog and salamander species worldwide, which may fundamentally disrupt natural systems. This study is an important advance in our understanding of the disease, a first step in finding a way to reduce its effects.” Scientists want to learn as much as they can about how chytrid affects wild amphibians, with the hope that these findings will lead to better treatments for the infection. For instance, Voyles said, the new study suggests that individual frogs being treated for the infection might benefit from having electrolyte supplementation in the advanced stages of the disease. Researchers like Vredenburg already are experimenting with different ways of treating individual frogs, such as applying antifungal therapies or inoculating the frogs with “probiotic” bacteria that produce a compound that kills the fungus. “The disease is not very hard to treat in the lab with antifungals. We know we can treat animals there,” Vredenburg said. “But in nature, the disease is still a moving target.”

It is still unclear exactly how chytrid spreads across a region, and which frogs might be susceptible to re-infection after treatment. Earlier this year, Vredenburg and colleagues published a paper showing that a common North American frog might be an important carrier of the infection. Chytrid has killed off more than 200 amphibian species across the globe, but Voyles said the new studies offer “sort of a glimmer of hope that it might be possible to do something to mitigate the loss of frogs in the field.”

Science Daily
May 15, 2012

Original web page at Science Daily

There is no point sending healthy animals out into the world if they’re just going to catch a deadly disease. Pacific tree frogs that can survive a normally lethal fungus infection are spreading it to species that cannot. Such “reservoir” species could threaten frogs released from captive breeding programmes. Between 2003 and 2010, the deadly chytrid fungus slashed the populations of two frog species in the Sierra Nevada, while populations of a third species – the Pacific tree frog (Pseudacris regilla) – held steady. That isn’t because the Pacific tree frogs avoided infection: two-thirds of the Sierra Nevada population carry the fungus, Vance Vredenburg of San Francisco State University has now found. That suggests they can tolerate infection and so could spread the pathogen to new areas. Conservationists are breeding threatened amphibians in captivity in the hope of eventually re-establishing them in the wild. But reintroductions will fail if there is a reservoir species nearby, Vredenburg warns. The solution may be to breed from frog populations already decimated by the chytrid fungus, says Matthew Fisher of Imperial College London. There is evidence that some frogs are evolving tolerance, and survivors from an affected population are more likely to have the vital genes. These frogs could be cross-bred with susceptible individuals, accelerating the spread of tolerance – although Fisher admits the approach will be expensive. Journal reference: PLoS One.

New Scientist
April 3, 2012

Original web page at New Scientist

Smithsonian scientists have confirmed that chytridiomycosis, a rapidly spreading amphibian disease, has reached a site near Panama’s Darien region. This was the last area in the entire mountainous neotropics to be free of the disease. This is troubling news for the Panama Amphibian Rescue and Conservation Project, a consortium of nine U.S. and Panamanian institutions that aims to rescue 20 species of frogs in imminent danger of extinction. Chytridiomycosis has been linked to dramatic population declines or even extinctions of amphibian species worldwide. Within five months of arriving at El Cope in western Panama, chytridiomychosis extirpated 50 percent of the frog species and 80 percent of individuals. “We would like to save all of the species in the Darien, but there isn’t time to do that now,” said Brian Gratwicke, biologist at the Smithsonian Conservation Biology Institute and international coordinator for the Panama Amphibian Rescue and Conservation Project. “Our project is one of a few to take an active stance against the probable extinction of these species. We have already succeeded in breeding three species in captivity. Time may be running out, but we are looking for more resources to take advantage of the time that remains.”

The Darien National Park is a World Heritage site and represents one of Central America’s largest remaining wilderness areas. In 2007, Doug Woodhams, a research associate at the Smithsonian Tropical Research Institute, tested 49 frogs at a site bordering the Darien. At that time, none tested positive for the disease. In January 2010, however, Woodhams found that 2 percent of the 93 frogs he tested were infected. “Finding chytridiomycosis on frogs at a site bordering the Darien happened much sooner than anyone predicted,” Woodhams said. “The unrelenting and extremely fast-paced spread of this fungus is alarming.” The Panama Amphibian Rescue and Conservation Project has already established captive assurance colonies in Panama of two priority species endemic to the Darien — the Pirre harlequin frog (Atelopus glyphus) and the Toad Mountain harlequin frog (A. certus). In addition, the Smithsonian’s National Zoo maintains an active breeding program for the Panamanian golden frog, which is Panama’s national animal. The Panamanian golden frog is critically endangered, according to the International Union for Conservation of Nature, and researchers have not seen them in the wild since 2008.

“We would like to be moving faster to build capacity,” Gratwicke said. “One of our major hurdles is fundraising to build a facility to house these frogs. Until we jump that hurdle, we’re limited in our capacity to take in additional species.” Nearly one-third of the world’s amphibian species are at risk of extinction. While the global amphibian crisis is the result of habitat loss, climate change and pollution, chytridiomycosis is at least partly responsible for the disappearances of 94 of the 120 frog species thought to have gone extinct since 1980. “These animals that we are breeding in captivity will buy us some time as we find a way to control this disease in the wild and mitigate the threat directly,” said Woodhams, who was the lead author of a whitepaper Mitigating Amphibian Disease: strategies to maintain wild populations and control chytridiomycosis. This paper, published in Frontiers in Zoology, systematically reviews disease-control tools from other fields and examines how they might be deployed to fight chytrid in the wild. One particularly exciting lead in the effort to find a cure is that anti-chytrid bacteria living on frog skin may have probiotics properties that protect their amphibian host from chytrid by secreting anti-fungal chemicals. Woodhams recently discovered that some Panamanian species with anti-chytrid skin bacteria transmit beneficial skin chemicals and bacteria to their offspring. The paper, Social Immunity in Amphibians: Evidence for Vertical Transmission of Innate Defenses, was published in Biotropica in May. “We are all working around the clock to find a cure,” Gratwicke said. “Woodhams’ discovery that defenses can indeed be transferred from parent to offspring gives us hope that if we are successful at developing a cure in the lab, we may find a way to use it to save wild amphibians.”

Science Daily
June 28, 2011

Original web page at Science Daily