How a common painkiller may have led to thousands of deaths in India

 In a study titled ‘The Social Costs of Keystone Species Collapse: Evidence From The Decline of Vultures in India’, researchers Eyal Frank and Anant Sudarshan indicate how the use of veterinary drug Diclofenac to relieve pain in animals has likely affected the population of vultures in the Asian country.

Vultures were once common in India, with a population that might have reached over fifty million. However, their numbers have dropped by more than 95% in recent years.

This decline started when farmers began using diclofenac, a painkiller originally introduced by the pharmaceutical company Ciba-Geigy (now Novartis) in 1973 for humans.

In the 1990s, after the drug's patent expired and cheaper generic versions became available, farmers started using it to treat livestock.

This is reflected in the drop in vulture populations because of the effect of the drug on these birds. When vultures feast on the carcasses of animals treated with diclofenac, they suffer kidney failure and die within weeks.

The more vultures died, the more their population decreased because it took a vulture about a year to produce an egg and another five years for a vulture to reach sexual maturity.

How do vultures dying cause human deaths?

As vultures disappeared their role of eating carcasses was lost. According to Frank and Sudarshan, it takes a flock of vultures (a committee) to clean up the carcass of a 385kg cow to bones within 40 minutes. These scavenger birds have the capacity to ingest meat which contains harmful bacteria.

This leaves no animal waste to create and spread diseases either through scavengers like dogs and rats or through water bodies.

With their absence, there are more rotting carcasses in the open. This also gives more room for rats and feral dogs to feast on these carcasses which are dumped mostly in the outskirts of towns within India when they are not incinerated or buried.

The dogs and rats through feeding then carry diseases like rabies in the process.  

"Carcass dumps in India tend to be on the outskirts of towns. We find that elevated mortality is largest in these populated areas”

Beyond rabies, the uncollected carcasses pose other health risks. Without vultures, harmful bacteria like anthrax can spread more easily to other animals and contaminate water sources.

"We also find evidence of worse water quality in districts affected by the disappearance of vultures after their collapse," the research pointed out.

Death rate figures

Frank and Sudarshan closely examined death rates before and after the decline of vulture populations in India. They found that areas with large vulture populations experienced a noticeable increase in death rates after the birds began to disappear.

Initially, from 1988 to 1993, areas that were unsuitable for vultures, such as cooler and drier regions, had slightly higher death rates, with an extra 1.2 deaths per 1,000 people. The researchers believe this was due to the problem of rotting carcasses, which led to disease in places where vultures were scarce.

However, when vulture numbers plummeted in 1996, the trend reversed. Areas that had previously benefited from large vulture populations started seeing a higher death rate, with 0.65 additional deaths per 1,000 people. By 2005, the gap had widened to 1.4 extra deaths per 1,000 people in these areas.

Now with the spread of rabies through dogs and rats who have access to carcasses, there have been increased rates of rabies in India. In 2023, there were 3 million dog bite cases in India, leading to 4.7 million rabies vaccinations, yet 286 people still died. The study suggests that the loss of vultures directly contributed to this alarming increase in deaths.