Science

Cattle drug poses deadly new threat to Asia’s vultures

Two decades after a now-banned drug nearly wiped out vultures in several Asian countries, conservationists have identified another pharmaceutical threat to these ecologically vital scavengers. Two recent studies indicate vultures can die from eating the carcasses of cattle that were given nimesulide, an anti-inflammatory drug that is increasingly popular in Asia as a veterinary treatment. “It’s quite worrying news,” says Vibhu Prakash, deputy director of the Bombay Natural History Society (BNHS).

Environmental groups hope the new evidence will help persuade governments to ban the use of nimesulide in cattle. They are embracing a report last month that an anti-inflammatory drug already used in cattle, tolfenamic acid, is safe for vultures, only the second such alternative identified.

In the early 1990s, tens of millions of vultures lived in India alone. The large scavengers quickly stripped the carcasses of the country’s many cows and other animals that died in the open, helping prevent the spread of disease. Then the population of vultures crashed, especially numbers of the common white-rumped vulture (Gyps bengalensis). They were suffering kidney failure after ingesting diclofenac, a drug commonly given to cattle to treat pain, fever, and inflammation.

India banned the veterinary use of diclofenac in 2006, and neighboring nations followed. Vulture numbers stabilized, but the damage was done: Populations had dropped by up to 99%. Cattle carcasses accumulated and sustained a booming population of feral dogs, increasing the need to vaccinate people against rabies.

The bans did not eliminate the threat of anti-inflammatory drugs, and in India the vulture population has not rebounded. It is still legal for pharmacies to sell diclofenac for human use, and covert studies of retail pharmacies have revealed the drug is being diverted to treat cattle. One reason is the speed with which it works. Diclofenac is called a “cup of tea” drug because sick cows improve by the time the veterinarian finishes a drink with the owner.

Other drugs still legally sold cause problems, too. Aceclofenac, for example, breaks down in cattle into diclofenac. Ketoprofen is also toxic to vultures, causing Bangladesh in February to completely ban its use in order to protect “vulture safe zones.” Widely available and fast-acting nimesulide, meanwhile, has been growing in popularity. Researchers first raised concerns about the drug in 2016, after they discovered it in the tissues of several dead vultures.

The case against nimesulide is now strengthening. In June, researchers led by ecotoxicologist Subramanian Muralidharan of the Sálim Ali Centre for Ornithology and Natural History reported in Environmental Science and Pollution Research that four dead white-rumped vultures found in India’s Gujarat state had nimesulide throughout their tissues, but not other drugs or pesticides. The birds also had renal failure and gout. “That’s a red flag,” says Julia Ponder, a veterinarian at the University of Minnesota, Twin Cities.

Toby Galligan, formerly with the Royal Society for the Protection of Birds (RSPB), and colleagues clinched the case with an experiment. After injecting the drug into cattle in South Africa, they slaughtered the animals and calculated a realistic exposure for a vulture feeding on a carcass. Then they gave a solution of nimesulide to two Cape vultures (G. coprotheres). Both died within 30 hours, and necropsies revealed gout and signs of renal failure, the team reports in a preprint posted last week on bioRxiv. Two vultures given water as a control remained healthy. (All the birds came from a wildlife sanctuary and were unfit to return to the wild.) The work is an “important, well-conducted study,” says ecotoxicologist Barnett Rattner of the U.S. Geological Survey.

To co-author John Mallord of RSPB, the evidence is compelling that nimesulide should now be banned for use in cattle. Other anti-inflammatory and pain relief medications are available, they note. Meloxicam, for example, is safe for vultures. So is tolfenamic acid, according to a study by Chandra Mohan of the Indian Veterinary Research Institute including colleagues from BNHS. The findings were reported in a bioRxiv preprint posted last month. “Having more than one drug is a real breakthrough,” says Jemima Parry-Jones, director of the International Centre for Birds of Prey. “It means that vets have more choice to offer their clients.”

So far, the pace of regulatory reform has been frustratingly slow, says Rhys Green, a conservation biologist at the University of Cambridge who heads Saving Asia’s Vultures from Extinction (SAVE), an alliance of conservation groups. “The weight of evidence required by governments to achieve these bans is immense,” notes biologist Campbell Murn of the Hawk Conservancy Trust.

Yet Green has hope for more immediate efforts to encourage sales of drugs that don’t harm the birds. Two companies are marketing meloxicam as “vulture safe” in Bangladesh, he says. And SAVE’s members in India are reaching out to cattle sanctuaries and state agencies that supply villages with drugs for their cattle to encourage them to buy safer drugs, which cost about the same. Countries in South Asia and elsewhere have also agreed to create recovery plans for vulture species as part of the global Convention on the Conservation of Migratory Species of Wild Animals, which last year passed a resolution that existing and proposed veterinary anti-inflammatory drugs should be tested for vulture safety. Despite the drug threats to vultures, says Roger Safford of BirdLife International. “There’s a lot to be optimistic about.”

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