Hundreds of Egyptian vultures, an endangered scavenger, flock to India in October where they spend the winter voraciously feasting on the plentiful supply of livestock carcasses at a communal dump site in Rajasthan. But a team of researchers have found that this diet has fuelled a rapid change in the Escherichia coli (E coli) community in the migrant vultures. The birds also showed varying levels of resistance to certain antibiotics – likely mirroring those found in the carcasses – during their sojourn.

Although antibiotic resistance in wild animals has been widely documented, this is the first study from wild birds in India “where wildlife, domestic animals and humans come into contact regularly”, said KS Gopi Sundar, an ecologist at Mysuru’s Nature Conservation Foundation, and senior author of the study.

“That they can apparently pick up resistance to new drugs relatively quickly, is a matter of concern,” he said. “With the spectre of bacterial diseases looming, it may well be a good idea for the veterinary departments in India to implement better monitoring protocols at such dump sites,” he added.

A group of Egyptian vultures at Jorbeer carcass dump site in Bikaner, Rajasthan. (Photo credit: Pradeep Sharma)
A group of Egyptian vultures at Jorbeer carcass dump site in Bikaner, Rajasthan. (Photo credit: Pradeep Sharma)

Barry McMahon, a lecturer in wildlife conservation and zoonotic epidemiology at the University College Dublin in Ireland, said that “the results are not that surprising given the feeding ecology of vultures”. He explains that vultures are “excellent sentinels” indicating the spread of human-mediated antibiotic resistance and because the Egyptian vulture “moves long distances within a short period of time” this could be of potential public health significance.

The E coli strains in the intestines and faeces of animals reflect their diet, environment and the degree of exposure to human-dominated environments. Egyptian vultures spend six months in India, arriving in October and flying back to their breeding grounds in Europe during March of the following year.

‘Melting pot’ of antibiotic resistance

The team observed a group of vultures, among almost 2,000, congregating at Jorbeer, a site in Bikaner, Rajasthan. A large numbers of carcasses of antibiotic-treated farm animals – mostly cattle, including those from dairies – are dumped at this site.

“Carcasses are of animals that die of accidents, have died of old age and diseased animals – most of the carcasses are likely to be from the last category,” said Pradeep Sharma, a veterinarian at Rajasthan University of Veterinary and Animal Sciences, Bikaner, and lead author of the study.

Egyptian vultures feasting on livestock carcasses at Jorbeer in Bikaner, Rajasthan. (Photo credit: Pradeep Sharma)
Egyptian vultures feasting on livestock carcasses at Jorbeer in Bikaner, Rajasthan. (Photo credit: Pradeep Sharma)

Faecal samples were collected four times covering the entire wintering season: in February 2011, a month before the vultures headed back; in October of the same year, when they had just arrived for the winter; a month later in November; and in March 2012, prior to their departure. The E coli strains from the samples were examined as well as their resistance to 13 commonly used antimicrobials in both veterinary and human medicine.

The samples showed high levels of E coli (90%) with high resistance to multiple antibiotics (71%). While the overall percentage of resistance to all of the drugs remained constant over the wintering period, there were patterns that emerged with spikes in resistance to certain drugs.

The vultures were resistant to both cefepime and cephotaxime in February 2011, likely due to a heavy dose of the drugs injected into the carcasses during the wintering period of October 2010 to February 2011. In contrast, when they arrived again several months later in October 2011, they were sensitive to both of the drugs. But towards the end of the 2011-2012 wintering period, the bacteria again picked up resistance to cephotaxime.

These antibiotic-resistant E coli “don’t pose an imminent threat” to the vultures “but indicate exposure of veterinary antibiotic residuals to the vultures”, said Sharma. He warned that “prolonged exposure of these drugs could be detrimental”.

Notably, the E coli “strains changed very rapidly in the migratory vultures”, said Sharma. After only a month, the strain diversity was “nearly entirely replaced”. “Such a rapid change was not known before in a wild species,” he added. Dining on the carcass dump, which acted “as a ‘melting pot’ of antimicrobial resistance”, likely brought about these changes in the E coli community in the birds.

“Vultures have evolved very strong gastric juices to help them combat potential disease-causing stuff in their foods,” explained Gopi Sundar. “This is additionally why we were pretty surprised to see the E coli communities change over the winter in this species.”

From wild animals to other species

What is concerning is that these vultures can potentially transport and spread these resistant E coli strains. Although humans do not consume vultures, “bacteria like E coli can be spread via the droppings and even sometimes by contact of humans to things like moulted feathers”, Gopi Sundar pointed out.

He added that “there is of course the risk of livestock and other domestic animals getting infected, which are then potential vectors for humans who either eat them or use them for protein, like milk from cows”.

“Certainly, resistance can spread from humans, insects, animals and the article brings in the role of migratory birds as well,” said Sumanth Gandra, an infectious diseases researcher at New Delhi’s Centre for Disease Dynamics, Economics & Policy. “The bottom line is that we need to have proper sanitation, access to clean water and good hygiene to decrease the chance of the spread of resistant bacteria and genes at least among humans.”

The “usage of antibiotics is indiscriminate and injudicious throughout India”, said Sharma. “Strict regulatory measures and selective usage of antibiotics” as well as “a system of tracking of these drugs from manufacturing to end-user consumption use can greatly help”, he asserted.

As the “life cycle of these vultures involves migration”, said Sharma, they “can disseminate multiple antimicrobial-resistant bacteria to distant geographical locations.” As a result, “any planning for this aspect of wildlife health needs to necessarily have a multi-country or international effort”, advised Gopi Sundar.

Sharma stressed the importance of a “One Health” approach “to comprehensively understand and address” the “emergence of antimicrobial resistance”. “One Health” is a “holistic approach” recognising that “humans, livestock and wild bird species require to be addressed together”, he elaborated.

Unfortunately, little is done “primarily due to a lack of information from most developing countries”, said Gopi Sundar. Unlike other studies that are snapshots of a single point in time, “this study underscores the importance” of covering “the entire wintering season of migratory birds”.

In order to understand the various ways bacteria can acquire resistance besides being exposed to antibiotics, more studies like this one covering “multiple wintering and breeding sites of the Egyptian vulture” are required, said Sharma. He also suggested “broad-scale monitoring of veterinary residuals in carcasses to assess the extent of exposure and subsequent policy planning to safeguard the vultures”.

This article first appeared on Mongabay.