What infectious disease may pose the biggest problem for humans in 2025?

With covid in retreat (thanks to very effective vaccines), the three infectious diseases that most concern public health officials are malaria (a parasite), HIV (a virus) and tuberculosis (a bacteria). Between them they kill around 2 million people a year.

And then there are watch lists of priority pathogens, especially those that have become resistant to the drugs typically used to treat them, such as antibiotics and antivirals.

Scientists must also constantly scan the horizon for the next potential problem. Although this could occur in any form of pathogen, certain groups are more likely than others to cause rapid outbreaks, and that includes influenza viruses.

A flu virus is causing great concern right now and is on the verge of becoming a serious problem in 2025. It is influenza A subtype H5N1, sometimes called ‘bird flu’. This virus is widespread in both wild and domestic birds, such as poultry. Recently, it has also infected dairy cattle in several US states and has been found in horses in Mongolia.

When flu cases start to increase in animals like birds, there is always concern that they could jump to humans. In fact, bird flu has already infected humans with 66 cases in the US this year, mostly in farm workers who come into contact with infected livestock and people who drink raw milk.

Compared to the only two cases in America in the previous two years, this is a pretty big increase. Add to this a 30% mortality rate from human infections, and avian flu is quickly moving up the priority list of public health officials.

Fortunately, H5N1 bird flu does not appear to be transmitted from person to person, greatly reducing its likelihood of causing a pandemic in humans. Flu viruses have to adhere to molecular structures called sialic receptors on the outside of cells in order to enter them and begin replicating.

Influenza viruses that are highly adapted to humans recognize these sialic receptors very well, which makes it easier for them to enter our cells. This contributes to its spread between humans. Avian flu, on the other hand, is highly adapted to the sialic receptors of birds and presents some imbalances when it comes to “binding” to humans. So, in its current form, H5N1 cannot spread easily from person to personyes.

However, a recent study has shown that a single mutation in the flu genome could make H5N1 capable of spreading from human to human, potentially triggering a pandemic.

If this strain of bird flu makes that change and can begin to transmit between humans, governments must act quickly to control the spread. Disease control centers around the world have drawn up pandemic preparedness plans for bird flu and other diseases on the horizon.

For example, the United Kingdom has purchased 5 million doses of the H5 vaccine that can protect against bird flu, in preparation for that risk in 2025.

Even without the potential ability to spread between humans, bird flu is likely to further impact animal health in 2025. This not only has major implications for animal welfare, but also the potential to disrupt food supplies and cause economic effects.

everything is connected

All of this work is framed by the concept of “one health”: considering human, animal and environmental health as interconnected entities, all with the same importance and effect on each other.

By knowing and preventing diseases in our environment and in the animals around us, we can better prepare and combat those that enter humans. Likewise, by monitoring and dismantling infectious diseases in humans, we can also protect the health of our animals and the environment.

However, we must not forget the “slow pandemics” that continue to affect humans, such as malaria, HIV, tuberculosis and other pathogens. Facing them is essential, in addition to scanning the horizon in search of new diseases that may arise.

This article was originally published in The Conversation.