Veterinarians warned to take heed
Posted April 1, 2004
A veterinary drug, diclofenac, is killing vultures in Pakistan and other parts of the Indian subcontinent where it is used widely in livestock as an anti-inflammatory drug, according to a recent study in Nature. Three species of vultures are in danger of becoming extinct, and their demise could have public health consequences. The drug may become available in the United States, and wildlife veterinarians want practitioners to take heed of the situation abroad.
"By all accounts, diclofenac is a great veterinary drug for livestock," said Dr. J. Lindsay Oaks, an assistant professor in the Department of Veterinary Microbiology and Pathology at Washington State University and lead author of the study. "It seems to be effective, very safe, very cheap ... it just has this unexpected environmental consequence."
Investigating a dwindling species
Since the early 1990s, populations of three species of vultures—oriental white-backed (Gyps bengalensis), slender-billed (Gyps tenuirostris), and long-billed (Gyps indicus)—have plummeted in India, Pakistan, and Nepal. The three species are now listed as critically endangered by BirdLife International, a global alliance of conservation organizations.
Because of the declining vulture populations, the number of rotting carcasses that litter the landscape has increased dramatically.
To manage the crisis, the Peregrine Fund, an Idaho-based organization working to conserve birds of prey, initiated the Asian Vulture Crisis Project with the Ornithological Society of Pakistan. Researchers originally suspected an infectious disease was at work, and they started examining dead birds.
Necropsies revealed that the vultures had visceral gout, a sign of kidney failure, which researchers thought must be caused by exposure to a toxin. Investigators turned their focus to the vultures' primary food source, livestock carcasses, and started to explore whether a veterinary drug could be the toxin.
Dead livestock are typically left out for scavengers to remove on the Indian subcontinent, and in the past, vultures have cleaned things up quickly. The dead animals are not likely to be eaten in Pakistan for religious reasons, and, in India, because many are vegetarian. In those countries, there is also a scarcity of fuel to incinerate the carcasses.
Researchers surveyed 74 veterinarians and veterinary pharmaceutical retailers in Pakistan to identify drugs that are known to be toxic to kidneys and absorbed orally. The only drug that met the criteria was diclofenac, which is used in mammals as an analgesic and antipyretic, in addition to being an anti-inflammatory drug. Testing for diclofenac residues in tissues from affected vultures and experiments with live birds verified the drug was the toxic agent.
Dr. Oaks says that the three vulture species are declining at a rate of about 30 percent each year; if this continues, the birds will become extinct in two to five years. The problem poses risks for animal health as well as public health. Without vultures to dispose of carcasses, wild dogs and other scavengers will move in to feed off animal remains, spreading various diseases.
"In India, there has been an explosion in the population of feral dogs that carry rabies. So, in India, there is concern that it could lead to problems with rabies," Dr. Oaks said. "There are theoretical concerns as well as practical concerns of having rotting carcasses (in the open). It's not very aesthetic."
So far, no evidence indicates the vulture decline has affected the incidence of disease.
In February, veterinarians, scientists, politicians, and others with a stake in the matter met in Nepal to discuss possible measures to control the problem. Those included controlling the drug's use and encouraging other ways of disposing of livestock.
"We are just getting started," Dr. Oaks said. "(It's going to take) a big education campaign, targeted all the way from the top down-ministry of health, agriculture, and environment ... all the way down to the villagers, targeting all the different stakeholders."
In the interim, vultures are being brought into captivity for later release and\or captive breeding restoration efforts further down the road.
While animal carcasses are not usually left out in the open in the United States, American veterinarians should be aware of the situation abroad. In the United States, IDEXX Laboratories is attempting to obtain approval from the Food and Drug Administration for its diclofenac product for treating equine lameness.
If diclofenac is approved in the United States, the possibility of accidentally poisoning scavenging birds exists. In the past, the veterinary drug sodium pentobarbital (used in some euthanasia solutions) has been implicated in accidental poisonings, when raptors and other wildlife have gained access to carcasses contaminated with the drug (see JAVMA, Jan. 15, 2002).
"If diclofenac was present in a carcass, it could be ingested in the same manner (as sodium pentobarbital)," said Kathryn Converse, PhD, a wildlife disease specialist at the U.S. Geological Survey's National Wildlife Health Center in Madison, Wisc.
Accidental poisonings of wild scavenging birds can be avoided by not leaving carcasses of dead animals in fields, shallow graves, or uncovered landfills. "Disposal can include incineration or burial," Dr. Converse said. "Carcasses taken to landfills must be reported to landfill authorities in advance, to ensure they are completely covered before scavenging (can) occur."
As long as safe disposal practices are followed, says Dr. Converse, drugs such as sodium pentobarbital and diclofenac should "cause minimal problems for wildlife."