Veterinary use of the drug diclofenac—used in the treatment of livestock—has been linked to the collapse of vulture populations throughout South Asia. Vultures are keystone species that perform a vital ecosystem service by disposing of carrion and their decline has had dramatic ecological and socio-economic consequences.
In the early 1990s, the Gyps vultures of India and South Asia were among the most abundant large raptors in the world. However, within a decade the populations of three species, White-rumped Vulture Gyps bengalensis, Indian Vulture G. indicus, and Slender-billed Vulture G. tenuirostris, had declined so precipitously that all three are considered Critically Endangered (BirdLife International 2008). The most recent surveys in India show that the country’s Indian and Slender-billed Vulture populations declined by almost 97 percent between 1992 and 2007. White-rumped Vultures fared even worse, dropping by 99.9 percent, to just one thousandth of their 1992 population (Prakash et al. 2007).
Extensive research has identified the cause of the decline to be diclofenac, a non-steroidal anti-inflammatory drug (NSAID) used to treat livestock (Oaks et al. 2004, Shultz et al. 2004). Vultures feeding on the carcasses of animals recently treated with the drug suffer renal failure and die. Modelling has demonstrated that even very low rates of diclofenac contamination—between 1:130 and 1:760—are sufficient to account for the population crash (Green et al. 2004).
Vultures provide a crucial ecosystem service through the disposal of livestock carcasses and their loss has had huge socio-economic impacts across the Indian Subcontinent. Without vultures, hundreds of thousands of animal carcasses have gone uneaten—left to rot in the sun, these pose a serious risk to human health. Livestock carcasses provide a breeding ground for numerous infectious diseases, including anthrax, and encourage the proliferation of pest species such as rats.
Most worryingly, the loss of vultures has resulted in an explosion in the number of feral dogs—the bites of which are the most common cause of human rabies in the region. A recent study in India estimates that, concurrent with the vulture die-off, there has been an increase in the feral dog population of at least 5.5 million (Markandya et al. 2008). It is calculated that this has resulted in over 38.5 million additional dog bites and more than 47,300 extra deaths from rabies. The researchers believe that the increased number of rabies victims may have cost the Indian economy $34 billion.
In 2006, the governments of India, Pakistan and Nepal finally introduced a ban on the manufacture of diclofenac and pharmaceutical firms are now encouraged to promote an alternative drug, meloxicam, which is proven to be safe for vultures (Birdlife International 2006, Swan et al. 2006). The manufacturing ban has had some success in reducing the drug’s prevalence—for example the use of diclofenac has dropped by 90 percent in parts of Nepal (Birdlife International 2008). Unfortunately, there is still no ban on the sale or use of the drug and the overall trend across South Asia remains one of continuing vulture declines.
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BirdLife International (2008) Vultures are under threat from the veterinary drug diclofenac. Presented as part of the BirdLife State of the world's birds website. Available from: http://www.birdlife.org/datazone/sowb/casestudy/156. Checked: 22/05/2013