January 29, 2004
A Drug Used for Cattle Is Said to Be Killing Vultures
mysterious and precipitous plunge in the number of vultures in South Asia, which has pushed three species to the brink of extinction, is probably a result of inadvertent poisoning by a drug used widely in livestock to relieve fever and lameness, scientists reported yesterday.
Studies in Pakistan showed that the drug, diclofenac, an anti-inflammatory commonly prescribed for arthritis and pain in people, caused acute kidney failure in vultures when they ate the carcasses of animals that had recently been treated with it. The findings, which followed a two-year investigation by an international team of 13 scientists, were published online by the journal Nature.
Dr. J. Lindsay Oaks, an assistant professor of veterinary medicine at Washington State University who was the primary author of the report, said the devastation of vulture populations was the first clear case of major ecological damage caused by a pharmaceutical product.
There has been growing concern among scientists and environmentalists about the "vast amount of drugs that end up in the environment one way or another," he said, but no effect of this magnitude.
A study in 2002 by the United States Geological Survey found traces of many different pharmaceuticals and "personal care products" — including steroids, insect repellents and many others — in the American water supply. The effect of these traces is unknown, but the concern is about the unexpected. One laboratory study suggested, for example, that antidepressants like Prozac could trigger spawning in some shellfish.
The vulture finding in South Asia comes as a surprise: while environmental toxins had been suspected in the deaths, a pharmaceutical drug had not. Scientists in India and England suggested that disease was the cause of vulture deaths in India, but they found no infectious agent. The scientists who did the research in Pakistan said the situation in India was likely to be the same as that in Pakistan. But they said they did not have conclusive evidence.
Dr. Oaks said the investigation, which began in 2000, was prompted by reports of a 95 percent drop in the number of Asian white-backed vultures (Gyps bengalensis), Indian vultures (Gyps indicus) and slender-billed vultures (Gyps tenuirostris). All three are listed as critically endangered by the World Conservation Union, the international environmental agency based in Switzerland.
Thomas E. Lovejoy, president of the H. John Heinz III Center for Science, Economics and the Environment, who has long been a leader in environmental policy, said he thought the paper made a "watertight" case for diclofenac as the culprit in the vulture decline.
"I think what it actually says is that we really need to look systematically at the use of pharmaceuticals for veterinary purposes," Dr. Lovejoy said. He added, "It does raise a question of whether we should be looking more closely at the trace chemicals from human use."
In the United States diclofenac, which is in the same class of nonsteroidal anti-inflammatory drugs as ibuprofen, is not used in veterinary medicine, although it is often prescribed for people. In Asia the drug is widely given to cattle because it is cheap and because losing livestock to lameness or fever can be devastating to small farmers with only a few animals.
The rapid decline in vulture populations was first reported in the late 1990's by Dr. Vibhu Prakash of the Bombay Natural History Society. Vulture populations had been shrinking gradually from loss of habitat and disease throughout Asia, but what happened in India and Pakistan was different. The decline was quick and severe and posed a problem in a part of the world that relied heavily on the ubiquitous vultures for the efficient disposal of dead livestock.
The decline also threatened the traditions of the Parsis, a sect of Zoroastrians who have traditionally exposed their dead to the elements rather than burying or cremating them. In Bombay they had to stop putting their dead on the stone Towers of Silence because the birds that once quickly consumed them were vanishing.
The plight of the vultures attracted worldwide attention, prompting the Peregrine Society, a bird conservation group based in Boise, Idaho, to begin an investigation with the Ornithological Society of Pakistan.
Dr. Oaks, who is a diagnostician, said the investigation of the cause of vulture deaths followed a painstaking course. Examination of dead vultures provided the first clues. Eighty-five percent showed evidence of acute kidney failure. The scientists then tested the vulture tissue for traces of obvious causes of kidney failure: heavy metals, pesticides and other chemicals. They found none of the substances they were looking for.
The next step was to survey veterinarians and the sellers of veterinary drugs to find which medications were regularly used in livestock, since domestic animals formed a major portion of the vultures' diet.
Because an overdose of diclofenac can cause kidney damage in humans, the drug seemed to be a likely cause of death in the vultures. Further tests established that there were residues of diclofenac in dead vultures. The researchers then conducted experiments that showed that the amount of diclofenac a vulture might ingest from a carcass could kill it within days.
Unlike DDT, which devastated populations of birds of prey, diclofenac does not accumulate in the tissues of livestock or birds. But for the vultures, it is poison.
The drug, the researchers conclude, "may also be responsible for vulture declines in the rest of the Indian subcontinent wherever diclofenac is used for the treatment of livestock." The Peregrine Fund, the researchers and other organizations said theyintend to push for a ban on the drug in veterinary use in India, Nepal and Pakistan.