Frog once imported for pregnancy testing brought deadly amphibian disease to US

African frogs, originally imported for early 20th century pregnancy tests, carried a deadly amphibian disease to the US, according to new findings. African Clawed Frogs have long been suspected of spreading a harmful fungus called Batrachochytrium dendrobatidis. The earliest known case of the fungus was found in these frogs in their native South Africa. Now scientists have found the first evidence of the disease among introduced feral populations in the US.



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MercuryNews.com

Frogs imported to California likely transmitted deadly fungal disease
By Lisa M. Krieger lkrieger@mercurynews.com San Jose Mercury News

Bay Area scientists believe they have discovered the Typhoid Mary of the frog world: a flat, feral creature that carried a deadly fungus from Africa to California's ponds and puddles through global trading.

Genetic analysis revealed that eight of 206 African clawed frogs -- caught wild or preserved in jars at the California Academy of Sciences -- carried the fungal plague called chytridiomycosis, which leaves them unharmed but kills native frogs in catastrophic numbers.

An infection was detected in a frog captured in Africa in 1934, supporting the theory that the fungus thrived there before spreading worldwide. Another infected frog, still alive, was recently trapped in Golden Gate Park's Lily Pond.

"It confirms our suspicions that this is one means of spread of the fungus into the environment, through frogs that were not native," said Sherril Green, professor and chairwoman of comparative medicine at Stanford University, who collaborated on the study with San Francisco State biologist Vance Vredenburg.

The African clawed frog resembles roadkill, but it has served an important role in medicine and research. It was first brought to the United States for use as a pregnancy test in the early 20th century, when it was routinely injected with the urine of female patients. The frogs were useful because they ovulate when injected with human urine, produce eggs all year long, and were easily imported from Africa in large numbers.

Although the practice is now discontinued, the African frogs likely were released into the environment by hospital workers, Green said. It was a well-intended gesture -- with deadly consequences.

"Today, these frog populations are often found in or near urban areas," said Vredenburg, associate professor of biology at San Francisco State. "It's amazing that more than a half-century after being brought to California, these frogs are still here, and they still carry this highly infectious disease."

The African frog may not be the only culprit. A University of Michigan study also has implicated bullfrogs, farmed as a food source in South America and shipped to America.
While the urban world and wild frogs have been at odds for a long time, the fungus is particularly tough on the thin-skinned creatures.

Called Batrachochytrium dendrobatidis, or "Bd," it kills frogs by clogging their pores, deranging their blood chemistry and causing their tiny brains to swell.
The infection has led to the recent decline or extinction of 200 frog species worldwide, from the Sierra yellow-legged frog to the exotic jewel-colored creatures that decorate calendars, postage stamps and National Geographic magazine covers.

Some species seem resistant, such as the Bay Area's common Pacific tree frog.
But scientists have not figured out a way to transfer such resiliency to vulnerable frogs. Vaccines, a routine type of human protection, are impractical.

To determine the African frogs' role in the spread of the disease, Stanford and San Francisco State scientists and students spent hours in the basement of the California Academy of Sciences, sorting through thousands of specimen jars filled with old frogs floating in ethanol since 1871. Swabbing DNA from the skin between the toes and around the claws, they found that of 178 frogs, five (2.8 ercent) were positive for the fungus, confirming that the fungus was present among indigenous populations in Kenya and Uganda before they were exported worldwide.

They also embarked on frog-hunting expeditions. Traps -- baited with supermarket chicken -- caught 28 African clawed frogs, of which three (13 percent) tested positive. One lived in Golden Gate Park.

"It was a bit of forensic detective work," Green said. The paper is published in Thursday's issue of the journal PLOS ONE.

The timing of the epidemic's spread fits with their theory, Green said. "It takes decades to see the effect of what an invading species does," she said. "We are beginning to see now what happened long ago."

Because the frogs are widely dispersed across the globe, Green and Vredenburg said containing the epidemic is a major challenge. The well-established fungus also can spread through water, wind and feathers of birds, Green said.
The frogs' use, sale and transport are now highly regulated in California, but the damage has been done, they said. (A pygmy version, a favorite of aquarium enthusiasts, is less hardy, so it's not considered a threat.)

"Now we need to be cautious about other introduced species," Vredenburg said. "There could be other animals out there that are carrying diseases that we don't even know about yet."
Contact Lisa M. Krieger at 650-492-4098.

Original article here.

Jane J. Lee
National Geographic
Published May 15, 2013
Apocalyptic, catastrophic, devastating: All words used to describe chytrid fungus infections that are wiping out amphibians around the world, including hundreds of frog and salamander species.
“It did a really huge number on an entire genus of frogs in Central America,” said Marm Kilpatrick, a disease ecologist at the University of California, Santa Cruz (UCSC). The fungus probably caused several species of this harlequin frog (Atelopus) to go extinct, he added. (Related:“Endangered Frogs Get Helping Hand.”)
Chytrid is also largely responsible for endangering California’s mountain yellow-legged frog (Rana muscosa).
"It's the single biggest threat to vertebrate diversity in the world," Kilpatrick said. (Related: "30 Amphibian Species Wiped Out in Panama Forest.")
The fungus, which seems to attack only amphibians, causes a thickening of the infected amphibian’s skin, preventing the animal from breathing properly and interfering with its electrolyte balance. The infection can eventually lead to cardiac arrest, although some frog species are better able to cope with it than others.
A new study delving into how this fungus spreads has now linked chytrid outbreaks in California—one of the more recent areas experiencing huge amphibian die-offs—to the spread of the African clawed frog (Xenopus laevis).
And the study’s implications could extend far beyond California, providing scientists with a potential road map showing how a devastating infection continues to spread around the world.
Until now, direct evidence of the chytrid fungus in African clawed frogs in regions of the world that have seen big amphibian die-offs has been missing, write the authors of the new study.
"I was surprised that nobody did this study before us, actually," said Vance Vredenburg, a conservation biologist at San Francisco State University and lead author of the new study, published May 15 in the journal PLoS ONE.
That could be because labs like his have been in crisis mode, scrambling to find a way to combat the fungus and save as many amphibians as possible, rather than trying to parse chytrid’s origins.
A Questionable Path
Chytrid's origins and how it spread have long been a big unanswered question for researchers, said Kilpatrick, who was not involved in the study.
Researchers in South Africa first proposed in 2004 that the African clawed frog was responsible for the spread of chytrid fungus around the world, said Vredenburg.
That earlier study suggested that the spread of chytrid was aided by the pet trade in African clawed frogs and by the animal’s widespread use as a research animal. Until the 1970s, the frog was also used in many hospitals as an indicator of human pregnancy; injecting the urine of a pregnant woman into the frog caused it to lay eggs.
Individual frogs that escaped or were released into the wild by hospital workers or pet owners may have carried the chytrid fungus, introducing the pathogen to new habitats around the world.
New Techniques
But a new technique developed by Vredenburg in 2011 allowed researchers to quickly evaluate whether amphibians, preserved as museum specimens, had the chytrid fungus or not.
Scientists could quickly swab the skin of an amphibian, analyze any DNA they picked up, and determine whether the chytrid fungus had infected the animal.
In what Vredenburg called the “old-school” way of testing for the fungus, analysis of a single tadpole required students in his lab to examine 200 skin samples under a microscope.
The new technique enabled Vredenburg’s research team to test 201 preserved frogs in the genus that includes the African clawed frog, collected from Africa and California between 1871 and 2010. The specimens, housed at the California Academy of Sciences in San Francisco, were all caught in the wild.
The researchers confirmed that wild specimens of the African clawed frog did indeed carry the chytrid fungus, yielding direct evidence of infection in this species outside of Africa.
That confirmation, combined with correlations between recorded instances of African clawed frogs around California and outbreaks of chytrid fungal infections, brings researchers one step closer to figuring out how this deadly infection became a global scourge.
Blame Game
But the blame for chyrid’s spread might not fall squarely on the African clawed frog, Kilpatrick cautioned.
The American bullfrog (Rana catesbeiana) is a popular source of frog legs served in restaurants around the world. And their movements can also be correlated to the spread of the chytrid fungus.
"The trade or movement of those two species has been responsible for the spread of [chytrid]," Kilpatrick said.
This pathogen could also have been present around the world in a nonlethal form, said Anna Savage, an evolutionary geneticist with the Smithsonian Conservation Biology Institute, who was not involved in the study.
Perhaps something in the environment changed, so that amphibians were no longer able to withstand the chytrid fungus, explained Savage, a former National Geographic grantee.
We’re still trying to compile basic information on this pathogen and how hosts, such as frogs, respond to it, she said. “So just knowing where it came from and how it spread, that’s really important information in terms of management strategies in dealing with this.”
Vredenburg is currently working on building a living library of beneficial bacteria that could help amphibians around the world combat chytrid infections. (Related: "Amphibian Bacteria Fights Off Deadly Fungus, Study Says.")
His team is working to isolate bacteria native to amphibian populations that help some species resist chytrid. They're hoping to culture those beneficial bacteria and dose any infected populations, giving their systems a boost to help fight off the fungus.

Original article here.

Amphibian Bacteria Fights Off Deadly Fungus, Study Says
Scott Norris
for National Geographic News
May 29, 2007
Bacteria that occur naturally on the skin of some salamanders can slow the progression of a deadly fungal disease responsible for mass die-offs of amphibians worldwide, a new study has found.
Because some amphibians do not carry the bacteria in sufficient amounts to battle the fungus, called chytrid, scientists took red-backed salamanders susceptible to the disease and bathed them in two separate types of bacteria.
Red-backed salamanders treated with laboratory-grown strains of the bacteria species Pedobacter cryoconitis, which had been isolated from disease-resistant individuals, were better able to fight off infection by the lethal fungus known as chytrid.
The finding strengthens the hope that biologists may be able to use the protective bacteria to inoculate some dwindling amphibian populations threatened by chytrid.
The chytrid epidemic has been particularly severe in portions of Central and South America and Australia.
The disease is ranked among the top perils facing amphibians—along with habitat destruction and climate change.
(See related: "Frog Extinctions Linked to Global Warming" [January 12, 2006].)
Reid Harris, of James Madison University in Harrisonburg, Virginia, delivered the new results last week at the annual meeting of the American Society for Microbiology in Toronto, Canada.
Harris's team had previously reported that eight different types of bacteria found in the skin secretions of two salamander species inhibited the growth of chytrid fungus in laboratory petri dishes.
The new work confirms that at least one bacteria species protects live amphibians, when administered at greater concentrations than may be present naturally.
Bacterial Armor
Many amphibian populations may naturally possess some anti-chytrid bacteria, Harris said, but not enough to keep the disease at bay.
In a separate study in California, his team showed that northern populations of the mountain yellow-legged frog are able to persist despite chytrid infection, while southern populations drop to near-extinction levels when the disease arrives.
In the frog populations that co-exist with chytrid, there are more animals with at least one species of anti-chytrid bacteria living on their skin, Harris said.
The ability to isolate, grow, and apply the beneficial bacteria may make it possible to bolster the defenses of amphibians living in areas where the arrival of the disease is expected.
One option is capturing amphibians at ponds and bathing them with anti-fungal bacteria, Harris said.
"The concept would be to build a 'fire line' to stop the epidemic spread of the pathogen," he said.
Karen Lips, of Southern Illinois University, in Carbondale, has been studying the effects of chytrid disease on frog populations in Central America.
The work by Harris's team is an "important discovery," Lips said, "because it provides additional evidence that some species of amphibians have defenses that can successfully defeat the disease.
"Just as we have used microbes to break down chemical contaminants and fight agricultural pests," she said, "we might be able to figure out how to use this microbe to protect frogs from chytrid in captivity, and perhaps in the wild."
Bacteria on Board
Other research has shown that some frogs produce chemical compounds that are effective defenses against chytrid. But this ability seems rare.
Work by Harris and others has also shown that communities of beneficial bacteria living in a frog's skin secretions assist in fighting off many types of fungal infection.
Bacterial defenses may be particularly vital for amphibians that care for their eggs, Harris said.
In such species, parent frogs and salamanders coat the developing embryos in mucus that is rich in antibiotic compounds produced by resident bacteria.
Harris's team was studying how bacteria help protect amphibian eggs from a different fungal disease when they came across the anti-chytrid strains.
The researchers are now working to isolate additional and perhaps more effective varieties of protective bacteria, focusing on amphibian species that have survived in regions where others perished from chytrid.
But Harris also added a note of caution, saying that the fungal diseases explosive spread may have been triggered by outside factors.
(See related: "Frog, Lizard Extinctions Caused by Climate, Not Fungus, Study Suggests" [April 17, 2007].)
Amphibians may have become more susceptible to the disease because their protective bacteria may have been damaged by global warming or pesticide contamination, Harris said.
If so, Harris added, "applications of beneficial skin bacteria may not be a long-term solution until underlying factors are addressed."

Original artilce here.