COVID appeared suddenly, spread rapidly and killed millions of people worldwide. Since then, I think it’s fair to say that many people have been concerned about the emergence of the next big infectious disease—be it a virus, bacterium, fungus or parasite.
With Covid in retreat (thanks to highly effective vaccines), the three infectious diseases of greatest concern to public health officials are malaria (a parasite), HIV (a virus) and tuberculosis (a bacterium). Between them, they kill about 2 million people each year.
And then there are the watch lists of priority pathogens – especially those that have become resistant to the drugs that are commonly used to treat them, such as antibiotics and antivirals.
Scientists also have to scan the horizon for another potential problem. It can come in any form of pathogen, some groups can cause outbreaks faster than others, and that includes influenza viruses.
An influenza virus is causing great concern now and will emerge as a serious problem in 2025. It is influenza A subtype H5N1, sometimes “Bird flu“. The virus is widely distributed in wild and domestic birds such as poultry. Recently, it is also infecting dairy cattle in several US states and has been found in horses in Mongolia.
When cases of influenza begin to rise in animals such as birds, there is always concern that it could jump to humans. In fact, bird flu can infect humans, with 61 cases reported in the U.S. this year, mostly due to farm workers coming into contact with infected livestock and people. Drinking raw milk.
Compared to just two cases in the US in the previous two years, this is a huge increase. Combining this with a 30% mortality rate from human infection, bird flu is quickly jumping up the priority list of public health officials.
Fortunately, H5N1 bird flu does not appear to be transmitted from person to person, greatly reducing the likelihood of it causing a pandemic in humans. Influenza viruses must attach to molecular structures called sialic receptors on the outside of cells to enter and begin replication.
Flu viruses that are highly adapted to humans recognize these sialic receptors very well, making it easier for them to enter our cells, which contributes to their spread among humans. Bird flu, on the other hand, is highly adapted to bird sialic receptors and has some mismatches in “binding” to humans. So, in its current form, H5N1 cannot easily spread to humans.
When cases of influenza start to rise in animals like birds, there’s always concern that it could jump to humans (Express photo by Tashi Tobgyal)
However, a recent study found that a single mutation in the flu genome could make H5N1 adept at spreading from person to person, triggering a pandemic.
If this strain of bird flu makes that switch and can begin human-to-human transmission, governments must act quickly to control the spread. Centers for Disease Control around the world have developed pandemic preparedness plans for bird flu and other diseases on the horizon.
For example, in preparation for that risk in 2025, the UK has bought 50 million doses of the H5 vaccine that can protect against bird flu.
Even without the potential ability to spread to humans, bird flu is likely to affect animal health even more in 2025. This has the potential to not only have major animal welfare impacts but also disrupt food supplies and have economic impacts.
Everything is connected
This work all falls under the umbrella of “One Health”: viewing human, animal and environmental health as interrelated entities with equal importance and impact on each other.
By understanding and preventing diseases in our environment and the animals around us, we can better prepare for and fight those diseases that enter humans. Likewise, we can protect the health of our animals and the environment by surveying and preventing communicable diseases that can be transmitted to humans.
However, we should not forget about the persistent “slow epidemics” in humans such as malaria, HIV, tuberculosis and other pathogens. Dealing with them is paramount, along with scanning the horizon for any new diseases that may yet emerge.
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