Bird flu cases are rising in the Northern Hemisphere, and testing is likely to continue as farmers and public health officials are determined to stop its spread this winter.
The current circulating “clade” of H5N1, which is carried primarily by birds, is highly pathogenic, meaning it can cause severe avian influenza (or bird flu).
Although H5N1 was first detected in the mid-1990s, outbreaks have occurred annually since 2020.
H5N1 is now present on every continent, including Antarctica, and remains a concern for health officials, disease scientists and wildlife experts.
In Germany, half a million chickens, ducks, geese and turkeys, as well as thousands of livestock, have been culled on major farms to prevent the disease from spreading further.
Denmark and the Netherlands have taken similar action to remove thousands of infected birds, and nearby countries such as Belgium and France have been forced to take protective action to prevent farm stock from being exposed.
Why are bird flu cases increasing now?
It’s fall in the Northern Hemisphere, so migratory bird populations are beginning their annual journey to warmer climates in the Southern Hemisphere.
As flocks stop to rest during their long journeys, they come into contact with other local, wild and farm birds.
But as bird migration began earlier this year, more species – such as migratory storks – have become infected with the H5N1 disease. This has increased the chances of poultry becoming infected, especially when sick birds die nearby.
“Previously, bird flu was thought to occur only in winter, but now cases occur all year round, at least in wild birds,” said Ursula Hoefle, a veterinary scientist at the University of Castilla-La Mancha in Spain.
The danger of wild and domestic animals being in close contact with each other has been shown most recently in Germany. Infected storks have died during their journey south near the capital Berlin in the east of the country and Stuttgart, a city in the southwest. To prevent transmission, farms have been forced to mass cull and dispose of half a million poultry birds.
The Friedrich Loeffler Institute (FLI), Germany’s federal agency responsible for animal health research, expects more infections and transmissions in November.
Farms in the Netherlands have also killed thousands of birds, while France and Belgium have raised their alert level to “high”, with chickens now being kept indoors. Cases have also been found in the UK and Slovakia.
H5N1: a zoonotic disease that spreads from animals to humans
Influenza viruses, including those that cause bird flu, often infect more than their host species. They are constantly circulating in animal populations, including humans, horses, pigs, bats, and birds.
When it comes to H5N1, it is very easy for carrier birds to spread the infection to others. Typically, this occurs through direct contact with a carrier, inhalation of viral particles in the air, or contact with contaminated surfaces. H5N1 particles can be “shed” in the bird’s saliva, body fluids and feces.
Such transmission routes make it possible for poultry to become infected by wild birds. Other farm animals and humans can contract the virus through close contact with an infected bird. Agricultural workers are being reminded to wear protective clothing to avoid infection.
“In addition to the protective suit, this also includes disposable gloves, safety goggles, and an FFP3 respirator,” said Tim Harder, viral diagnostics laboratory manager at FLI.
Some people – mainly agricultural workers – have been infected with H5N1 in recent years; Most have survived, and none have transmitted the infection to others.
This is important. A bigger fear is that this strain of bird flu could eventually undergo enough genetic modifications to spread. between People, potentially leading to another COVID-style pandemic.
“The more times this virus has an opportunity to infect a human, to infect an animal, the more likely it is — if there’s a change in the genetics that makes it easier — for it to be transmitted human-to-human,” said Meghan Davis, an environmental health researcher at the Johns Hopkins Bloomberg School of Public Health.
Epidemic Question: Can Bird Flu Spread Between Humans?
There remains a small, but real, risk that the H5N1 virus could evolve and spread from human to human.
Currently, it is known that only close and repeated contact with infected animals increases a person’s risk of contracting the disease.
“H5N1 virus […] Those that predominate in Europe and the US are estimated by the ECDC [European Centre for Disease Prevention and Control] To be less zoonotic,” Harder said.
There is also danger in infected animals like cows and pigs. Authorities have warned against the consumption of raw food, especially raw milk and related products, as they may contain influenza virus particles.
In 2024, the state of California took precautionary measures against the consumption of raw milk products that have not been pasteurized to remove pathogens.
Food production is likely to be affected as the outbreak increases
“It is always devastating to see a resurgence of highly pathogenic avian influenza, particularly in poultry,” said Kristen Coleman, an airborne infectious disease researcher at the University of Maryland, US.
Farmers in areas affected by mass killing may report shortages of eggs and meat products, resulting in higher prices for consumers.
“It’s definitely having an impact on our food supply,” Coleman said. He said American consumers will feel the pinch around Thanksgiving in November if turkey supplies are short.
But Coleman said culling birds often is the best way to deal with bird flu outbreaks. This can prevent the disease from spreading to other farms, wild bird populations and other mammals.
In 2023, an outbreak of H5N1 in Argentina spread to and destroyed more than 24,000 seals on the Pacific and Atlantic coasts of South America.
Edited by: Zulfikar Abbani