Health

Bird flu pandemic threat as high as in 1997; focus on wild bird migration routes, say experts

Experts urge investment in developing newer generation vaccines based on mRNA technology 

 
By Taran Deol
Published: Friday 03 March 2023
Currently, we are in the midst of the worst outbreak of this virus, which has led to the culling of nearly 100 million poultry across the world. Representative photo: iStock.
Currently, we are in the midst of the worst outbreak of this virus, which has led to the culling of nearly 100 million poultry across the world. Representative photo: iStock. Currently, we are in the midst of the worst outbreak of this virus, which has led to the culling of nearly 100 million poultry across the world. Representative photo: iStock.

The H5N1 virus, more commonly known as bird flu, is once again making headlines after an 11-year-old girl died of the infection in Cambodia.

Currently, we are in the midst of the worst outbreak of this virus, which has led to the culling of nearly 100 million poultry across the world. The human infection case from Asia and another recent one from China, preceded by instances of the virus being found in new mammalian species like minks, has many worried that it won’t be long before humans become prey to this disease. 


Also read: What is spillover? Bird flu outbreak underscores need for early detection to prevent the next big pandemic


While the pandemic threat from H5N1 is high, it has not particularly increased since 1997, when the first human cases were reported from Hong Kong — 18 infections and six deaths.

Since then, more than 800 human cases of the bird flu virus have been recorded, with half of them succumbing to the disease.

Richard Webby, director of the World Health Organization Collaborating Centre for Studies on the Ecology of Influenza in Animals and Birds, told Down To Earth.

It is very difficult to assign a quantitative risk to these viruses. We have some idea of what changes this virus has to make to become more human-adapted, but we don’t have a good feel for how easily the viruses can make these changes.

This is mainly due to how widespread it is in wild birds. The more birds infected, the more chances humans will be exposed to the virus, either by exposure to wild birds or to other infected populations, Webby added.

Historically, H5N1 has been infecting humans who come into close contact with sick or dead poultry infected with the disease. But so far, there are no identified strains which cause sustained human-to-human transmission, Krutika Kuppalli, chair of the Global Health Committee, Infectious Diseases Society of America, explained.


Also read: We should only worry about bird flu making us sick when we see human-to-human transmission


“What we need to do is continue surveillance and look for signs of spillover events into humans as well as look for changes which could indicate there is sustained human to human transmission,” she said.

What is concerning about this current outbreak is the increasing number of mammals the virus is infecting. More than 100 reports of mammalian infections with H5N1 were recorded in 2022-2023, including in bears, foxes, skunks, possums, racoons, and seals, according to the United States department of agriculture.

“I think the increase in mammal infections now is simply due to more viruses being in wild birds which is leading to more sick or dead birds being eaten by scavenging mammals,” Webby said. 

Some mutations have been seen in the infected mammals, but the key changes that would substantially increase pandemic risk have not yet been seen.

While mammal-to-mammal transmission has been recorded in some instances — seals, sea lions, and mink — it is rare. It remains difficult to gauge what path H5N1 may take and the possibilities of what it can do to the human population. Webby guessed this virus would become endemic in wider regions of Africa, the Americas and Europe.

The World Organization for Animal Health (WOAH) illustrated three key factors that affect the transmission and spread of H5N1: Globalisation and international trade, live bird markets and wild birds and migratory routes.

Wild aquatic birds including waterbirds such as ducks, geese, swans, gulls and terns and shorebirds, such as storks, plovers and sandpipers — are the host reservoirs of the bird flu virus where it is endemic. Occurring naturally in these species, the H5N1 virus finds its way into domesticated poultry and other bird and animal species, either directly or indirectly.

“When birds have little or no symptoms of the virus, it allows them to spread the viruses between neighbouring countries or over long distances, along their migratory pathways. Wild birds also play a major role in avian influenza viruses evolution and maintenance during low seasons,” the WOAH noted.


Also read: Centre confirms bird flu in Jharkhand government farm after hundreds of chickens died last week


What needs to be studied better and is an active field of research currently underway is how changing temperatures are impacting the routes migratory birds take.

“Anything that changes the paths infected birds take impacts spread (of the virus),” Webby said.

A 2014 paper on climate change and the shift in H5N1 risk in migratory birds published in ScienceDirect concluded that “by the end of 2030, Europe may be at higher risk for H5N1 outbreaks in January and February.”

Northern Africa and southern and western Asia will likely be at a higher risk for H5N1 outbreaks from April to June, the research added.

“Our findings suggest a potential shift in H5N1 risk from Southeast Asia to the western part of the world due to climate change,” said the researchers.

They found minimum daily temperature in the winter (−15 to −11°C, 15 to 17°C) and maximum daily temperature in the summer (12-15°C, 30-35°C) impacted wild bird migratory routes while air pressure and humidity levels governed the size of the outbreak.

“Changes in migratory pathways, breeding behaviour, wintering and stopover sites may lead to the emergence of new enzootic areas and constitute major threats to the poultry industry in regions overlapping with migratory flyways,” the paper noted in conclusion.

While the influenza virus has been isolated from more than 100 different birds, Anseriformes (ducks, swans and geese) and Charadriiformes (gulls, terns and shorebirds) remain its key hosts.

Studies so far have largely focused on the former, ignoring the role gull and goose species play in expanding the virus’ geographic footprint.

IN PHOTOS: Bird flu spreads to mammalian species

A May 2022 paper published in PLOS Pathogens aimed to fill this lacuna. It found “gulls were responsible for moving HPAI H5 more rapidly than any other host, a finding that may reflect their long-distance, pelagic movements and their immuno-naïve status against this subtype.”

The transmission route of H5N1 is complex and such findings only strengthen the urgent need for surveillance. Both Webby and Kuppalli argue we can always do better on this front. 

Bird flu outbreaks have a multitude of debilitating consequences; in the form of economic loss for farmers who experience high mortality rates in their poultry, job losses in the poultry industry and restrictions in the international trade of live birds, which can impact national economies and travel limitations which could impact tourism.

Culling healthy poultry remains the mainstay mitigation step in the event of an avian influenza outbreak.

“A vaccine has already been developed for H5N1 so if needed the production could be increased. That being said, if we had a situation where the virus mutated and was causing human to human transmission it is unclear how well this current vaccine would work,” Kuppalli said.

We need to invest in developing newer generation vaccines based on mRNA technology used to create the vaccines for COVID-19 as well as additional therapeutics and diagnostic tests.

 “As we have seen with COVID-19, it is a package of medical countermeasures that are important when it comes to managing a respiratory virus,” she added.

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