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Worries as avian flu virus breaches species barriers
H5N1 virus has killed tigers, leopards, and house cats, and severely affected a Canadian girl, raising concerns about its ability to jump species.
In the span of a month, H5N1 has killed three tigers and a leopard in India, 11 house cats in California, and forced a teenage girl in Canada onto life support.
The virus, which is better known as the avian influenza virus and is mostly prevalent in birds, spreading through dairy farms across America for much of 2024, appears to be breaching species barriers with increasing ease.
Although the overall number of human infections related to H5N1 has been low, the steady drip of human and animal detections is not a good sign, experts say. The virus has shown an unprecedented ability to jump between species, suggesting a pathogen testing the boundaries of its potential reach.
“If there’s anything to worry about, it should be avian influenza that is seeing a jump from birds to animals to humans,” said Anurag Agrawal, dean of BioSciences and Health Research at Ashoka University’s Trivedi School of Biosciences. “However, it may not be equal to the Covid-19 situation as things stand now. Even if there is human-to-human transmission, it is likely so low grade that it won’t be picked up and shouldn’t worry public. It is high-transmission that one should worry about, which we haven’t seen so far.”
The big cats at Nagpur’s Gorewada facility displayed severe symptoms including limping, diarrhoea, vomiting, and fever before their deaths between December 20 and 23. The infection was confirmed on January 3, prompting heightened biosecurity measures across Maharashtra’s wildlife facilities.
These deaths coincided with troubling developments in the West. In California, 11 house cats have died since December after consuming contaminated raw milk and pet food. The virus continued its march through American dairy farms, with two more herds in California testing positive on New Year’s Day, bringing the total to 915 affected herds across 16 states.
At the same time, experts reported in the New England Journal of Medicine the case of 13-year-old girl in British Columbia, Canada --- chronicling a rare human case with severe outcome. The infection began as conjunctivitis and fever but progressed to respiratory failure, requiring intubation and extracorporeal membrane oxygenation. Though she recovered after treatment with multiple antivirals, her case revealed the virus had acquired mutations potentially associated with enhanced virulence and human adaptation.
“The mutations evident in the Canadian case highlight the urgent need for vigilant surveillance of emerging mutations and assessment of the threat of human-to-human transmission,” said an accompanying editorial in NEJM, pointing to critical weaknesses in current monitoring efforts: genomic sequencing data from animals often lacks crucial metadata about where and when samples were collected, limiting scientists’ ability to track the virus’s spread and evolution.
In the Indian case, too, officials are unsure of where the tigers and the leopards that died caught the H5N1 virus. The tigers, aged between three and four years, had been brought to the rescue centre from Chandrapur district following human-wildlife conflict incidents. The leopard had been at the centre since March 2023 after its rescue from Buldhana district.
The NEJM editorial points out that since late 2021, the virus has carved a path from Europe to North America, and then to South America, where it devastated bird populations and marine mammals. Its latest jump to dairy cattle represents a new expansion of its host range.
Among humans, the US has reported 66 confirmed and seven probable cases of H5N1 infection in people in 2024, caused by either the avian strain (D1.1) or the bovine strain (B3.13). Data from other countries was not immediately available.
“We need a robust tracking and surveillance mechanism in place to pick up cases but public at large need not panic at this stage,” Agrawal emphasised, speaking on the Indian context.
A scientist at the National Institute of Virology (NIV), Pune, too said requisite measures are in place. “It may be worrisome but all measures and surveillance is in place. In fact, it is due to the active surveillance that we have put in place that we were able to detect cases quickly,” said Dr Pragya Yadav, senior scientist, ICMR-NIV, who specialises in high-risk pathogens.
