A painkiller used on livestock has wiped out vultures in India, with scientists saying it has killed 500,000 people

New Delhi — Scientists say the rapid adoption of a painkiller by Indian farmers for their livestock in the 1990s led to the accidental deaths of half a million people and massive economic losses — not from harm to livestock, but from the loss of millions of vultures, scavengers that historically devoured animal remains before they rotted and became vectors of disease.

In the early 1990s, the patent on a painkiller called diclofenac was lifted, making the drug cheap and widely available to India’s vast agricultural sector. Farmers use it to treat a wide range of diseases in cattle. But even a small amount of the drug is deadly to vultures. Since its widespread use in India began, the population of domestic vultures has dropped from 50 million to just a few thousand. The impact on humans has been monumental, reflecting the vital role these scavengers play, according to a study published by the American Economic Association.

Vultures have played a crucial role in Indian ecosystems for centuries. According to the authors of the study, “The Social Costs of Keystone Species Collapse: Evidence from Vulture Declines in India,” these large domesticated birds are a “keystone species,” meaning a species that plays an irreplaceable role in an ecosystem.

They are the only scavengers that feed exclusively on carcasses, and they do so extremely efficiently, quickly devouring the remains and leaving little behind that could spread disease. The study authors say that Indian vultures typically ate at least 50 million animal carcasses each year before their population was decimated.

In doing so, they prevented dead livestock from rotting and the deadly bacteria and other pathogens that thrive in carcasses from being transmitted to human populations.

“In a country like India, where beef consumption is banned, most of the cattle end up as carcasses,” Anant Sudarshan, associate professor of economics at the University of Warwick in England and co-author of the study, told CBS News. “Vultures provide an incredible waste disposal service for free. … It takes about 45 minutes for a group of vultures to turn a cow carcass into bones.”

The vultures’ voracious appetite has also helped control populations of competing scavengers, such as wild dogs and rats, which can transmit rabies and a host of other diseases.

In 1994, farmers began giving diclofenac to their cattle and other livestock. The drug caused kidney failure and death to vultures that fed on the carcasses of animals it was given. The population of these birds dropped from 50 million to just 20,000 over the next decade.

Without vultures to do the work, farmers began dumping their dead livestock into local bodies of water, leading to water pollution — and another way for pathogens to reach humans.

Sudarshan and Eyal Frank, a co-author of the study and an environmental economist at the University of Chicago Harris School of Public Policy, examined the impact of the drastic decline in vulture populations on human health by mapping vulture habitats using health data from more than 600 districts in India. Their research shows that 100,000 human deaths each year between 2000 and 2005 could be linked to declining vulture populations, they say.

The study also found economic losses estimated at $69 billion per year, largely due to premature deaths from the collapse of the scavenger population.

These deaths were caused, their research suggests, by the spread of diseases that a thriving vulture population could have mitigated. Stray dog ​​populations, and with them the spread of rabies, also increased during this period, as did the amount of bacteria measured in many local water sources.

“India is now the largest center of rage “Worldwide, the wild dog population has increased dramatically,” Sudarshan told CBS News.

Without a major rebound in vultures, the study authors said the spread of the disease and resulting deaths will only continue in the years to come, as will the associated health care costs.

India banned diclofenac for veterinary use in 2006, but Sudarshan said the ban needed to be enforced much more effectively. He and Eyal called for more conservation funding to boost vulture populations, but warned that even if the Indian government made a major effort, it would take at least a decade for the species to recover to the extent needed because they are “slow breeders.”

As an alternative to the return of the vultures, Sudarshan said India could build a network of incinerators across the country, but the estimated cost of this is around $1 billion per year, and they would use a huge amount of energy and create considerable air pollution, which is already a major problem for India.

“So it makes more sense to go back to the natural way of dealing with the millions of animal carcasses that India produces every year,” he said.

He added that work must begin urgently because “vultures started dying in the 1990s. India has done nothing three decades later.”

The government spends about $3 million a year on Save India’s Native Tigers. Sudarshan said that while vultures may not be a major tourist attraction, a larger question arises regarding “the basis of our conservation policy”.

“Our study shows that the cost of their (vultures) disappearance is about $69 billion a year, which is much higher than the benefits the tiger brings,” he said, adding: “We have to think from a profitability and growth perspective, how should we choose which species to conserve?”

“Understanding the role of vultures in human health underscores the importance of protecting wildlife, and not just the cutest and cuddliest ones,” said co-author Frank. “They all have a role to play in our ecosystems that impacts our lives.”