The United States Department of Agriculture recently reported that a pig on a small farm in Oregon tested positive for bird flu.
As the bird flu outbreak has evolved, cases of the A/H5N1 strain have been identified across various animals, including different bird species, wild animals, and dairy cattle.
Fortunately, there hasn’t been sustained human-to-human transmission so far. However, the virus detection in a pig raises new concerns about the virus’s spread.
How Did We Get Here?
Currently, the most concerning type of bird flu in circulation is the A/H5N1 clade 2.3.4.4b strain of influenza A.
Since 2020, this strain has infected a wide variety of birds, wild animals, and livestock that had never been affected by bird flu before.
While Europe remains a hotspot, attention is also focused on the U.S., where dairy cattle were first infected in 2024, affecting over 400 herds in at least 14 states. Bird flu’s impact on farming is vast, leading to culling of infected poultry flocks and contamination risks in dairy products. Fortunately, pasteurization should make milk safe to consume.
Farmers have faced heavy losses due to the H5N1 strain, which also poses a risk of mutating to cause a human pandemic.
Bird and human respiratory systems have different receptors that flu viruses bind to, similar to a lock (receptors) and key (virus). Bird flu viruses adapt to birds and spread easily among them, but they struggle to infect humans.
To date, human cases have mainly been found among individuals with close contact with infected animals, primarily farm workers in the U.S.
The concern is that the virus might evolve to infect humans more easily. A key step would be a shift allowing the virus to attach to receptors in the human respiratory tract—effectively mutating its “key” to fit the human “lock.”
A recent study of an A/H5N1 sample from an infected human revealed worrisome mutations that could make the virus more transmissible among humans.
Why Are Pigs a Concern?
A human pandemic strain can develop through close contact between humans and infected animals, creating conditions for genetic mixing between bird and human flu viruses.
Pigs are particularly susceptible to this genetic mixing since their respiratory systems can host both bird and human flu viruses.
This means pigs can contract bird flu and human flu at the same time, allowing genetic exchange between the viruses, which may enable them to mutate to spread more easily among humans.
Interestingly, pigs were less susceptible to A/H5N1 in the past, but recent mutations have made them more vulnerable.
In the Oregon case, A/H5N1 was detected in a pig on a non-commercial farm following a poultry outbreak on the same farm. This strain originated from wild birds rather than the strain common in U.S. dairy cattle.
Infecting a pig acts as a warning. If the virus spreads to commercial pig farms, the risk of a pandemic increases, especially as the U.S. heads into flu season.
How Can We Reduce the Risk?
Early surveillance is crucial in detecting potential pandemic strains. This includes robust testing and reporting in both birds and animals, alongside financial support for farmers to encourage timely reporting.
Enhancing global flu surveillance is essential, as unusual pneumonia spikes and severe respiratory illnesses could signal a potential pandemic. The EPIWATCH system, for instance, searches for early warnings, which can accelerate vaccine development.
If clusters of human cases appear and Influenza A is detected, further testing (or subtyping) is needed to determine whether it’s a seasonal flu strain, an avian strain, or a new pandemic strain.
Early identification is key to containing a pandemic. Delays in identifying an emerging strain could allow the virus to spread globally.
Australia’s first A/H5N1 human case was reported in a child who contracted the virus while traveling in India. After initial tests detected Influenza A, further subtyping was delayed.
This type of delay can be risky if a human-adapted strain of A/H5N1 is mistaken for seasonal flu. Currently, only around 5% of positive Influenza A tests are further subtyped in Australia and other countries.
Given the current situation, governments should consider subtyping Influenza A cases more frequently. Emerging rapid tests that differentiate between seasonal and H5 flu should also be included in pandemic preparedness plans.
An Increased Risk
The U.S. Centers for Disease Control and Prevention states that the current risk of H5N1 to the general public remains low.
However, with H5N1 now infecting pigs and showing troubling mutations that suggest adaptation to humans, the risk is increasing. With the virus so widespread among animals and birds, the probability of a pandemic is higher than ever.
The silver lining is that we are better prepared for an influenza pandemic than other types. Once the genome of a pandemic strain is identified, vaccines can be updated to target it.
Partially matched vaccines already exist, and some countries, like Finland, are vaccinating high-risk farm workers.
No comments:
Post a Comment