Jakarta, ThedailyID — In March 2024, US veterinarians faced a mystery on dairy farms in Texas and nearby states.
Cows were losing their appetite and producing thick, discolored milk. At the same time, cats on the farms were developing an unknown neurological disease.
For weeks, tests for common cattle diseases came back negative. Eventually, laboratory results identified the culprit as influenza A subtype H5N1, commonly known as bird flu.
The explanation of how bird flu can cross species comes from a TED-Ed YouTube video titled “Everything You Need to Know About Bird Flu,” presented by Benjamin Anderson. The video explains the virus, its ability to evolve and why scientists monitor it closely.
How Bird Flu Gets Its Name
Bird flu belongs to influenza A, one of the four groups of flu viruses. These viruses are classified into subtypes based on two viral proteins.
The first is hemagglutinin, which helps the virus enter host cells. The second is neuraminidase, which helps newly produced viruses leave those cells.
Scientists have identified 18 types of hemagglutinin and 11 types of neuraminidase. Different combinations create different influenza A subtypes.
For example, hemagglutinin 5 combined with neuraminidase 1 creates H5N1.
These proteins also influence which animals a virus can infect. Wild aquatic birds are particularly important because they have receptors for many known versions of these proteins.
As a result, these birds can act as reservoirs for different influenza viruses. They can also spread the viruses through their feces into lakes and ponds.
Why Humans Are Less Vulnerable
Fortunately, humans are not easily infected by most bird flu viruses. Humans have receptors that differ from many of those targeted by avian influenza viruses.
Some bird flu viruses can bind to receptors in human airways. However, the receptors that are more vulnerable to these viruses are deeper in the lungs.
This makes infection less likely and transmission less efficient than with common human flu viruses. Those viruses typically target receptors in the nose and throat.
However, influenza viruses have another way to change.
Two Ways Influenza Viruses Change
The first process is called antigenic drift. Random mutations gradually change molecules on the virus that the immune system recognizes.
The process happens relatively slowly. It is also one reason human flu vaccines need regular updates.
The second process is called antigenic shift. This can occur when two different influenza viruses infect the same host.
The viruses can then exchange entire gene segments. This can create a new virus with different abilities.
For example, a new combination could potentially allow a virus to bind to different receptors. It could also change which species the virus can infect.
Why Scientists Watch H5N1
Birds are vulnerable to many influenza A subtypes. Therefore, they can provide opportunities for viruses to evolve and exchange genetic material.
The H5N1 outbreak on US dairy farms shows how the virus has crossed into mammals. According to the TED-Ed video, H5N1 has been detected in more than 70 mammal species in recent years.
Those species include cats, dairy cows, foxes, seals and bears.
Each infection in a new mammal provides another opportunity for the virus to change. The video explains that these changes could potentially allow the virus to spill over into humans and cause a pandemic.
Still, human bird flu infections remain relatively rare.
The key message is therefore not to panic, but to remain vigilant. Scientists continue to monitor viral evolution, test vaccines and strengthen biosecurity measures.
Source: TED-Ed YouTube, Everything You Need to Know About Bird Flu by Benjamin Anderson
Watch the TED-Ed video on YouTube
