Vultures in India and Pakistan play a vital environmental role by quickly removing dead livestock, inactivating pathogens, and probably controlling the spread of livestock disease. Vultures are also essential to the “sky burials” practiced by Zoroastrian sects. So the sudden and precipitous decline in vulture population caused great consternation throughout the subcontinent.

Over the past decade, the population of the Oriental white-backed vulture has declined by more than 95 percent. Other vulture species have experienced similar catastrophic declines. When Washington State University veterinary diagnostician Lindsay Oaks arrived in Pakistan in 2000 to investigate the mysterious deaths, he selected for study three colonies of perhaps 1,000 breeding pairs each. As of this year, says Oaks, two of those colonies are completely extinct. The other one has declined by 65-70 percent.

Oaks and colleagues from the Peregrine Fund and other agencies initially suspected a viral disease. But once they had eliminated viral and other microbial causes and known toxins, they turned their attention to veterinary pharmaceuticals. They hypothesized that veterinary drugs administered to livestock before they died might be the cause of the observed renal disease in the scavengers.

Following an exhaustive investigation, Oaks narrowed the suspects to diclofenac, a nonsteroidal anti-inflammatory drug widely used in India and Pakistan to treat lameness and fever in cattle-conditions humans treat with ibuprofen, which belongs to the same class of anti-inflammatories.

Diclofenac is sold in the United States as a human pharmaceutical under the name Voltaren, says WSU pharmaceutical scientist Neal Davies, an expert on it and similar pharmaceuticals. “It’s very effective and comparatively safe.”

It is also easily made and “cheap as chips,” says Davies.

Oaks and his coinvestigators found that the drug is ubiquitous in Pakistan and India. “Everybody uses it routinely,” he says.

Once Oaks and his team focused on diclofenac, they confirmed their suspicion through repeated analyses of tissues from the dead birds and by feeding diclofenac-treated carcasses to captive, non-releasable vultures. The effort involved not only international conservation groups, but also a group of graduate students from a Bahauddin Zakariya University, who gathered much of the data. Oaks and his colleagues published their findings in the 12 February 2004 issue of Nature.

Although their findings are conclusive, the reason for vultures’ sensitivity to the drug remains a mystery. Crows and kites feed on the same carcasses, for example, with no apparent effect.

Other birds may be resistant to the drug, says Oaks. Or it could be that because they are primary scavengers, vultures get the choice bits, the liver and kidney where the drug concentrates. However, says Oaks, “We do know that the vultures will die eating muscle alone.”

Understanding the reason, says Davies, would require a pharmacokinetic examination. Pharmacokinetics, which is Davies’s field, is the effect of the body on the drug, rather than the pharmaceutical effect on the body.

“Animals have preferential toxicity,” he says. For example, Tylenol, though widely used by humans, will kill a dog. Although diclofenac’s effects have been widely studied in mammals, Davies knows of no such work in birds.

The vulture case is particularly notable in that it is the first fully to show that a pharmaceutical is responsible for a serious environmental problem. Scientists have long worried about the effect of pharmaceuticals and other personal-care products in the environment. A 2002 study by the U.S. Geological Survey found traces of many such products in the American water supply. Other work, says Oaks, has shown that Prozac affects the development of frogs and that a commonly used veterinary wormer kills dung beetles.

Davies observes that the distinction between pharmaceuticals and other synthetic chemicals is primarily semantic. After all, he says, pesticides are really a pharmaceutical for bugs. The actual effect of pesticides in the environment, such as DDT on the bald eagle, has long been known. “History is just repeating itself,” he says.

Frank Loge, Civil and Environmental Engineering, points out that effects of endocrine disruptors have been documented in fish. Loge studies the health effects of engineered natural systems, such as recycled drinking water. A good thing to point out, he says, is that many drugs in the environment do not exhibit an acute health end point, such as the death of the vultures. Many of the drugs exhibit a chronic effect. Such low-level chronic exposure to drugs in the environment is very difficult to detect. A striking example is exposure is to PBDE, or polybrominated diphenyl ether, used as a flame retardant.

The compound is significant, because it is used in almost all plastic combustible devices, such as computers. Researchers have found it just about everywhere they’ve looked, including Antarctic seals and human breast milk. The compound has been documented to suppress the immune system of animals.

Regardless of such distinctions, says Oaks, the concern that pharmaceuticals released into the environment can have dire effects is no longer just theoretical.

Without dramatic intervention, Oaks and others fear that the remaining vultures may be in their last breeding season. He attended a meeting in Katmandu earlier this year to develop a strategy that involves controlling the drug, education, and capturing birds to hold for safekeeping until the environment is safe for them again.