Clear and Present Danger
After the infamous diclofenac debacle that caused the most plunging decline of vultures in the history of South Asia, another brand-new threat rears its ugly head. This feature investigates how common antimicrobial treatments meted to livestock affect and jeopardize surviving populations of this impressive species.
The end of the last millennium saw a severe collapse in the population of two raptor species, the White-backed Vulture (Gyps bengalensis) and the Indian Vulture (Gyps indicus), from the landscape of the Indian subcontinent. What we have left now is a mere fraction of the once widespread populations. Labelled as Critically Endangered, these species are, nevertheless, still struggling for their existence.
This is one of the most comprehensive ecological disasters to happen in the recent past, both in terms of scale and speed. The culprit was new – wrapped in the innocuous acceptance of a medicinal molecule, diclofenac, a painkiller, which could be in your medicine box even today. Diclofenac, a potent analgesic and anti-inflammatory drug was being used for both animals and humans, back in the ‘90s. It made its way to the vultures through the carcasses of livestock treated with diclofenac. The residue of the drug, once consumed by the vultures along with the flesh of livestock caused failure of kidneys, which subsequently resulted in their deaths. Unfortunately, as these vultures were once abundant, an immediate decline was not observed until it was too late. It was only in 2004 that the cause of the decline was understood by a collaborative international group of scientists. Subsequently, the drug was forbidden for veterinary usage, but just the ban alone proved to be ineffective due to the lack of enforcement by regulatory agencies. This was probably the first episode of an ecological toxicity on such massive scale by a pharmaceutical molecule. Unfortunately, this is where my story begins.
Fall of the mighty
Back in 2011, I had started working on population dynamics of wintering Egyptian Vultures (Neophronpercnopterus) at a large carcass-dumping site in the Thar Desert. Over the course of two years, I visited the dump quite frequently. I remember this one day when I saw 20 vultures of three different species: Cinereous (Aegypiusmonachus), Griffon (Gyps fulvus) and Himalayan Vultures (Gyps himalayensis), scattered in a moribund state in and around the dump. Prompt veterinary action saved all but four. The story continued, as I kept finding a few dead vultures almost every time I visited the dumping site. What was killing these birds?
The outcomes of my studies based on the vultures I observed from the site were published in two international journals – results of hundreds of mentally and physically exhaustive work hours. But these findings only made be more uneasy. Almost all the bacteria extracted from the ailing and deceased vultures were resistant to the common antibiotics that we used. Such bacteria are known as Multiple Antimicrobial Resistant(MAR) bacteria. Additionally, these were potentially pathogenic species, such as Klebsiellapneumoniaand Pseudomonas aeruginosa, which could infect humans as well. Both bacteria are infamous for harbouring antimicrobial resistance, and P. aeruginosahas the notorious reputation of infecting humans admitted in a hospital, a phenomenon known as nosocomial infection.
Resistance to anti microbials is common in bacteria affecting humans as well as animals. One of the most significant reasons for developing such resistance is repeated exposure to anti microbials during the course of treatment of a disease. Bacteria, although single-celled, are very dynamic entities at a molecular level. They have special mechanisms to survive adverse conditions unlike most other species. The DNA of a bacterium changes a few sequences of its nucleotides and starts producing enzymes that ultimately either destroy or impair antimicrobial molecules. This bacterial resistance to anti microbials is a cause of worldwide concern now, because we have almost exhausted the potency of different anti microbials to fight against life-threatening bacteria. In simpler words, anti microbials will not work against bacterial infections and even a seemingly simple disease could become life-threatening!
The antimicrobial conundrum
What perplexed me during my case study was determining where these vultures were getting the antimicrobial-resistant bacteria in the wild. The obvious answer would be through carcasses of domestic animals which were treated with anti microbials prior to their deaths. There are few other mechanisms which can transfer non-resistant bacteria, but consumption of food having antimicrobial residues could probably the only mechanism for the development of resistance in the bacteria, which the vultures naturally consume. Along with increasing the resistance of bacteria, another harmful effect of ingestion of antibiotics is that it suppresses the immune system of the body. Anti microbials are also commonly used, just like painkillers, in veterinary treatments. So if diclofenac can make it through the carcasses, why can’t antimicrobial drugs?
Now, why is this more dangerous than diclofenac to the vultures? Almost all species of vultures in India are Vulnerable, Endangered or Critically Endangered now. These powerful birds have been widely known to be resistant to diseases because of their feeding behavior,but this may no longer be the case. Just to put things in perspective, we might have a situation where we have vultures carrying pathogenic, MAR bacteria, with reduced capacity to fight infections, and they may be feeding on food material that is most likely to have loads of pathogenic bacteria!
The vultures that were found in time, as reported earlier, were given fluids and anti microbials, and most responded well. The necropsy of the dead vultures didn’t reveal much, but indicated some infection in the lungs. It was a stroke of luck that the given anti microbials worked against this infection in most of the birds. The frightening thing is that this might be happening on a much larger scale than one would like to believe, and there are probably such instances going unreported elsewhere. But on a logical note, it would be too early to conclude if the vultures are threatened by an exposure to veterinary antimicrobial residue.
More studies need to be undertaken on the levels of residual anti microbials in carcasses. It takes enormous time to validate the results in the form of scientific publications. In the meanwhile, it will be helpful to keep a record of the livestock animals thrown at dumping sites, and to know if the animal had received any treatment prior to its death. This work is usually done by municipal agencies or contractors, so no new outfit has to be employed separately for this. Also ‘vulture restaurants’ are regularly screened for presence of diclofenac. It wouldn’t be too much of a task if the levels of antimicrobial drugs were also examined simultaneously. Finally, an outreach program has to be worked out to convince people to either bury or incinerate livestock carcasses which contain any type of veterinary drug. Learning from the diclofenac debacle, we must not ignore any potential threat; any lapse from our end can send two of the most majestic vultures in our country into the list of the extinct.
Flunixin – one more enemy
– Dr. Pramod Patil
A recent finding by a group of scientists from Spain, published in October in Society for Conservation Biology, pointed towards another serious killer drug. A carcass of a wild Griffon Vulture (Gyps fulvus), found in a game reserve in Andalucia (Spain), was examined forensically and found to have severe visceral gout – a finding consistent with Gyps vultures from Asia that have been poisoned with diclofenac. Liver and kidney samples from this Griffon Vulture were found to contain elevated levels of flunixin. More importantly, the samples tested negative for pesticides and diclofenac. Flunixin, also known as meglumine, is a potent non-steroidal anti-inflammatory drug (NSAID), analgesic and anti pyretic, used in the form of injection in cattle, horses and other animals. It is a potent inhibitor of the enzyme cyclo oxygenase.
This is the first reported instance of mortality in the wild resulting from environmental exposure to a NSAID, other than diclofenac. Interestingly, a recent survey of zoos and rehabilitation centers from around the world suggested that a wide range of scavenging birds may be susceptible to an equally wide range of NSAIDs. In this survey, flunixin was shown to have caused mortality in 7 out of 24 therapeutically treated birds belonging to a variety of species. As suggested by the author of this article, this might be just the tip of the iceberg. Since we do not have any idea about the current market use and percentage of residual occurrence of this drug in carcasses in India, there is immense need to undertake short scale surveys and studies to get some idea on this (questionably) silent killer.
Misuse and consequences
By Dr. Vibhu Prakash & Dr. Asad R. Rahmani, BNHS
The article brings the problem of blatant misuse of antibiotics in treating humans and animals to the fore. The finding of the presence of Multiple Antimicrobial Resistant (MAR) bacteria in the vultures is quite worrying but not entirely unexpected. Vultures feed on dead animals and through the meat they could ingest administered drugs as well as bacteria and other pathogens carried by them. So the guts of vultures could have plenty of transient bacteria which remain for a while and are passed out of the body without causing any disease. The bacteria Klebsiellla pneumonia and Pseudomonas aeruginosahave also been reported as transient fauna in vultures by other studies. The digestive tract of vultures is very acidic and very few bacteria can survive in it. Fortunately, most of the birds treated with anti-microbial drugs mentioned in the article survived, which indicate that all pathogen bacteria were not drug resistant. After diclofenac was found to be killing vultures, the conservation actions initiated have made an impact, and now the population appears to be stabilizing and not showing any downward trends. The finding of MRS in vultures is unlikely to be the cause of crash in vulture populations but their presence in the environment should ring alarm bells.
Illustrations – Dr Pramod Patil