American bullfrogs are resistant to the lethal amphibian disease known as chytrid, and since they are commonly traded overseas, they are becoming the Typhoid Marys of the amphibian world. (Photography: Kenneth H. Thomas / Photo Researchers, Inc.)
A recent study in the Proceedings of the National Academy of Science reported that global trade in amphibians is one of the big culprits in spreading a fungal disease known as chytrid, responsible for the stunning die-off of amphibians across the world.
Half of all amphibians are in decline, while a third are threatened with extinction, because of the pathogen, which carries the formal name Batrachochytrium dendrobatidis. It infects the amphibians’ skin cells — through which most amphibians take in water and salts, including those of sodium and potassium — and thickens the skin, reducing its ability to absorb water and salts.
The recent study indicates that not only has the trade spread the disease, it may have created it.
Rhys Farrer of the Imperial College London and his team found that different strains of the chytrid fungus were identified in different parts of the globe. Through sequencing of the fungal genome, they found that the extremely lethal form of the fungus was created when two distinct strains came together to create a potent killer.
A likely explanation is that the global trade during the last century brought two strains together, experts say. “Chytrid is one of the most devastating wildlife diseases with the largest host range of any, and responsible for dozens of species’ extinctions and many more extirpations of local populations,” Dr. Farrer said.
The finding highlights the dangers of the worldwide movement of wildlife, including the huge global trade in pets. According to EcoHealth Alliance, a New York nonprofit that researches and works to prevent disease caused by wildlife, 120 million animals – fish, birds and reptiles – are shipped around the globe annually, legally and illegally.
A baby sugar glider in a Minnesota home. (Photography: Associated Press)
American bullfrogs, which are carriers of the chytrid pathogen but resistant to it, are also widely available for sale; another study, done in 2009, looked at records from the ports of San Francisco, Los Angeles and New York from 2000 through 2005 and found “Importation of live amphibians into these ports totaled almost 28 million individuals over this six-year period.”
The illegal wildlife trade, valued at as much as $20 billion a year, is second only to the drug trade in terms of its worth, according to EcoHealth. Some 13 million animals are taken illegally from ecosystems for the pet trade. Many of those species come from “hot spots” in tropical regions where the risk of diseases’ emergence from the wild are high.
Even legal wildlife importation poses a disease risk, not only to other wildlife but to people as well. Diseases in other mammals pose the biggest threat to humans of all wildlife ailments, said Dr. Peter Daszak, president of EcoHealth. “Phylogenetically they are closer to us, which means we are more likely to share viruses we carry.” he said. “That means if we get infected there’s a higher change of that virus being transmitted human to human.”
One species that he is particularly worried might pass a disease into the human sphere is the sugar glider from Indonesia.
“They are extremely cute, really good looking little animals, very cheap and very trendy,” Dr. Daszak said. The trouble is, he said, they are coming in straight from the forest, in an emerging disease hotspot.
Plucking animals out of the wild can also cause declines in populations and lead to extinctions.
Earlier this year the EcoHealth Alliance started a program called PetWatch that seeks to educate consumers to the dangers of exotic diseases on imported pets, from parrots to turtles to monkeys. They also include factors like invasive threats, the sustainability of wild populations and animal welfare issues.
The best bet for a disease-free animal is one that is bred in captivity and so is unlikely to harbor a disease from the wild. Among the best choices, according to Pet Watch, are the bearded dragon and cockatiels, while the worst include the African grey parrot and the squirrel monkey.
Author: Jim Robbins
Source: The New York Times