ADVERTISEMENT

From Living Room to Lily Pad: Is the Fatal Amphibian Chytrid Fungus Spread via Pet Frogs?

Is your store-bought frog carrying a deadly secret?


My pet frog Gunther is clamped inside a latex-covered fist. His skinny leg sticks out the side and flails helplessly. Another gloved hand moves in and slips a cotton swab over his leg and between his toes; Gunther does not appear to be enjoying this. He wriggles free and splashes into a tub of water, but the ordeal isn't over yet, and the hands grab him again. Despite several more escape attempts, including a few desperate hops across the lab table, they eventually manage to swab Gunther's belly, backside and both legs.

"The gloves are not to protect him from me or me from him, but to protect the frogs from each other," explains biocultural anthropologist Eben Kirksey of the City University of New York Graduate Center. He has just finished testing my frog for chytrid fungus—a skin disease that is wreaking havoc in frog and salamander populations around the world. "This frog species is sort of like the Typhoid Mary of amphibians," Kirksey says. "It is the likely culprit for bringing the disease around the world initially. What's not known is whether it's still spreading the disease."

That's why Gunther and roughly 50 other African clawed frogs (Xenopus laevis) are taking part in Kirksey's experiment; he wants to find out whether frogs from local pet stores are carrying the fungus. If they are, they may still be introducing the disease into wild populations. On July 14 around a dozen New Yorkers brought their pet frogs in for testing at the Proteus Gowanus gallery in Brooklyn to help out with the study.

"A lot of people are wondering whether the pet trade is exacerbating the spread of [the fungus]," says Lisa Schloegel, a wildlife disease ecologist with EcoHealth Alliance. "It's definitely something that should be investigated."

Chytridiomycosis has devastated at least 200 amphibian species globally. It is caused by a microscopic fungus named Batrachochytrium dendrobatidis (Bd). Infection triggers lethargy, weight loss, sloughing of the skin and, often, death. "Bd may be responsible for the greatest disease-caused loss of biodiversity in recorded history," biologists Kellie Whittaker and Vance Vredenburg wrote on the Web site AmphibiaWeb.

Reid Harris, an ecologist at James Madison University, said that although the precise origins of Bd are uncertain, ample evidence indicates that the disease is native to Africa. The earliest known case (pdf) of chytridiomycosis was documented in an X. laevis individual that had been collected in South Africa in 1938.  Beginning in the 1930s large numbers of the species were shipped from Africa to labs in England, the U.S. and Australia, where they became essential in pregnancy tests and laboratory research (pdf). Scientists believe that the fungus traveled with the frogs as they were shipped around the world.

In the wild, 5 to 10 percent of X. laevis harbor Bd on their skin without exhibiting symptoms of disease. (North American bullfrogs are also tolerant of the fungus, suggesting that they may have helped to spread it, too.) Once these carriers bring the fungus to previously unexposed species the disease spreads like wildfire. More than 50 percent of amphibian species become locally extinct within six months of Bd's arrival in an area. Even for species that survive, 80 percent of individuals die. The disease has been detected in nearly every state in the U.S., including in several threatened and endangered species, and on every continent except Antarctica.

Still widely used in genetics and developmental biology research, X. laevis remain popular pets. "This is one of the very cheap pets you might give a five-year-old," Kirksey says. "But people at the pet stores usually don't tell you, 'Hey, this frog's going to live 15 years, and it'll be as big as your hand when it's fully grown.' So a lot of them get thrown in the toilet or let go into streams."

According to Kirksey's research, some frog wholesalers breed and store the animals on a mass scale. "We're talking about hundreds of thousands, if not millions of frogs living on top of each other," he says. And if one frog has a chytrid infection, he says, it’'s likely that all of its tank-mates have it, too.

Evidence does suggest that pet store frogs may be infected. In a study of imported bullfrogs sold live in U.S. food markets, 62 percent tested positive for Bd. Another study found that more than a quarter of amphibians in Japanese pet stores (pdf) may be carrying the fungus. Kirksey says that if chytrid is common in New York City pet stores, he intends to find out which frog wholesalers are moving the fungus around.

"There's no legislation on selling frogs with Bd at this point in time," Schloegel says, and pet wholesalers are not required to test for Bd. Mike Khadavi, a former director of the Amphibian Steward Network who has been collaborating with Kirksey on the project, expects that some pet suppliers may not want to test their frogs because they won't want to spend the money to quarantine and treat the frogs.

The U.S. Fish and Wildlife Service is considering legislation to prevent the importation of Bd. The act would classify amphibians infected with chytrid as "injurious wildlife" and would require traders to certify that their amphibians are chytrid-free before they could import the animals into the country or transport them across state lines.

"The pet industry is actually very aware of the problem, and they're doing a lot to minimize the threat," Schloegel says. In 2007 the Pet Industry Joint Advisory Council launched their "Bd-Free" campaign, which aimed to educate pet industry personnel and consumers about the dangers of the fungus.

Still, not all pet traders are aware that there's a problem. When Kirksey, Khadavi and I visited a locally owned pet shop in Brooklyn, the owner said he didn't know anything about the fungus, but he didn't object to having his frogs tested. "Basically we have these little Q-tips," Kirksey explained, "and we can run it on the frog and test it, and if the frog does have the disease, then there's a way to cure them of it"—namely, with inexpensive antifungal baths.

"If the frogs were tested on a regular basis to make sure they are disease-free, I think that would solve the problem," Schloegel says. "There needs to be a little more oversight in monitoring the disease."

Harris says it is particularly important to prevent the spread of Bd in light of recent research, which suggests that the deadly fungus arose when two non-virulent strains of fungus mated. By limiting the movement of the fungus, the pet industry may be able to prevent a similar such unholy union from occurring again in future, he says.

Gunther's skin swab was sent to a testing lab in San Diego. It could take up to two weeks for the results to come back. In the meantime it occurs to me that I'm flushing chytrid spores down the drain and into the local environment every time I change Gunther's water. If my frog does carry the fungus, he'll have to spend about 10 days in an antifungal bath—a moderately unpleasant treatment which will cure him of the infection, but which is not available to his millions of wild relatives.

Rights & Permissions
Share this Article:

Comments

You must sign in or register as a ScientificAmerican.com member to submit a comment.
Scientific American Special Universe

Get the latest Special Collector's edition

Secrets of the Universe: Past, Present, Future

Order Now >

X

Email this Article

X