Vultures, drugs and rabies

Over the last few years you may have heard stories about the decline of vultures in India. Population declines of over 95% were observed and some species may go extinct. One reason the press picked up on this around 2004 was the implication for the Indian Zoroastrian Parsi community, who traditionally use vultures to dispose of human corpses in "sky burials".

Eventually it was worked out that the vultures were dying because of a drug, diclofenac, commonly used in livestock. Vultures fed on livestock, ingested the drug, and died.

Now a new study, published in Ecological Economics this week, suggests that this loss of vultures may have led to an additional 50,000 rabies deaths in India. As the vulture numbers declined so the number of feral dogs increased. India has one of the world's highest incidences of rabies. and some of these dogs would have been infected with rabies. Calculations suggest an additional 5.5 million feral dogs between 1992 and 2006 leading to an additional 38.5 million dog bites. In India 123 people die of rabies for every 100,000 dog bites. This suggests at least 47,300 people died of rabies as a result of the vulture die off. Rabies is a very nasty viral disease which has a very high fatality rate. In fact, once symptoms develop, death is practically inevitable. There are only six known cases of a person surviving rabies once symptoms have developed. The best chance of surviving rabies is a prompt post-exposure vaccination that may prevent the virus from progressing to the symptomatic stage.

There is some evidence that vulture numbers may, in some areas of India, be starting to increase after the widespread use of diclofenac was discontinued.