HOW DANGEROUS IS BIRD FLU?
When influenza cases start increasing in animals such as birds, there is always a worry that it could jump to humans. Indeed, bird flu can infect humans with 61 cases in the US this year already, mostly resulting from farm workers coming into contact with infected cattle and people drinking raw milk.
Compared with only two cases in the Americas in the previous two years, this is quite a large increase. Coupling this with a 30 per cent mortality rate from human infections, bird flu is quickly jumping up the list of public health officials’ priorities.
Luckily, H5N1 bird flu doesn’t seem to transmit from person to person, which greatly reduces its likelihood of causing a pandemic in humans. Influenza viruses have to attach to molecular structures called sialic receptors on the outside of cells in order to get inside and start replicating.
Flu viruses that are highly adapted to humans recognise these sialic receptors very well, making it easy for them to get inside our cells, which contributes to their spread between humans.
Bird flu, on the other hand, is highly adapted to bird sialic receptors and has some mismatches when “binding” (attaching) to human ones. So, in its current form, H5N1 can’t easily spread in humans.
However, a recent study showed that a single mutation in the flu genome could make H5N1 adept at spreading from human to human, which could jump-start a pandemic.
If this strain of bird flu makes that switch and can start transmitting between humans, governments must act quickly to control the spread. Centres for disease control around the world have drawn up pandemic preparedness plans for bird flu and other diseases that are on the horizon.
For example, the UK has bought 5 million doses of 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 affect animal health even more in 2025. This not only has large animal welfare implications but also the potential to disrupt food supply and have economic effects as well.
