The Looming Threat of Avian Flu: Are We Ready for Another Pandemic?

Think back to 2020. The sudden emergence of a novel virus gripped the world, leading to unprecedented changes in our daily lives due to the global pandemic, COVID-19. Today, another infectious disease is capturing global attention: Avian Influenza, commonly known as bird flu. While it primarily infects birds, the potential for certain strains to cross over to humans and trigger a pandemic is a serious concern globally. Just like the influenza viruses that caused devastating pandemics in the past (Spanish Flu of 1918 and Swine Flu of 2009), avian flu viruses can mutate and evolve. Recent outbreaks in birds and, more worryingly, in mammals such as dairy cattle in the United States are a stark reminder of the ever-present threat of zoonotic diseases. So, the crucial question looms: are we on the brink of another global health crisis originating from the avian world? This post will delve into the complexities of avian flu, explore the current global situation, and discuss what this potential threat means for us.

Avian influenza viruses are broadly categorised based on their ability to cause disease in poultry: Low Pathogenicity Avian Influenza (LPAI) and Highly Pathogenic Avian Influenza (HPAI). LPAI viruses typically cause mild or no illness in birds, while HPAI strains can lead to severe disease and high mortality rates in bird populations, sometimes reaching up to 90-100% within 48 hours for certain strains in chickens.

Of particular concern for humans are the HPAI viruses of the H5 and H7 subtypes, such as H5N1, H7N9, H5N6, and H5N8. These subtypes have been responsible for most human infections with avian influenza.

Transmission of avian influenza from birds to humans usually occurs through direct contact with infected birds, their saliva, mucous, or faeces, or through contaminated environments. The virus can enter the human body through the eyes, nose, or mouth, or by inhaling contaminated droplets or dust. Interestingly, consumption of raw foods, including raw milk from infected animals, also poses a potential transmission risk.

The virulence of avian flu in humans, or how severe the illness becomes, depends on several factors. One key factor is the virus's ability to attach to specific receptors on human cells. Avian influenza viruses prefer to bind to α–2,3–linked sialic acid receptors, which are predominantly found in the lower respiratory tract of humans. This could explain why human avian flu can lead to severe pneumonia. In contrast, human seasonal flu viruses typically bind to α–2,6–linked sialic acid receptors, which are more commonly found in the upper respiratory tract, thus more easily spread to others by coughing and sneezing.

Noteworthy strains like H5N1 have historically shown a high case fatality rate in humans, around 52% based on WHO data from 2003 to 2023, with 878 reported cases and 458 deaths. H7N9, primarily seen in China since 2013, also has a high fatality rate of approximately 40%.

The biggest worry surrounding avian influenza is the virus’s potential to evolve and gain the ability for efficient and lasting human-to-human transmission, which is the distinguishing characteristic of a pandemic. This evolution usually happens through genetic changes to the virus, mainly with mutations and reassortment.

Mutations are changes in the virus's genetic code that can alter its characteristics, such as its ability to bind to different receptors or replicate more effectively in a new host. For example, a single amino acid mutation in a protein of H5N1 has been shown to improve its ability to bind to human-type receptors (α-2,6 linked sialic acids), a crucial step toward human transmissibility. Similarly, other mutations can enhance the virus's ability to replicate efficiently in the cells of mammals. Recent identification of certain mutations in H5N1 viruses from US dairy cattle is very concerning, as they can enhance replication in both bovine and human airway cells. Another mutation has also emerged, further increasing polymerase activity in mammalian cells.

Reassortment is another process where an avian influenza virus can exchange genetic material with a circulating human influenza virus, like seasonal flu, if a person or animal is co-infected with both. This could result in a novel virus of great concern, combining the high virulence of the avian strain with the easy human transmissibility of the seasonal strain. Pigs are often referred to as potential "mixing vessels" because they can be infected by both avian and mammalian influenza viruses. Currently, the risk of sustained human-to-human transmission for circulating avian influenza strains is thankfully considered low by organisations like the CDC and WHO. While limited person-to-person spread has occurred in the past, it hasn't continued. However, the recent detection of mutations in human H5N1 cases and the increasing number of infections in other mammals suggest the virus is adapting and that the risk could easily increase. This includes the novel spread of the virus to US dairy cattle and the spread from humans to domestic cats. 

The world is currently experiencing widespread avian influenza outbreaks in wild birds, poultry, and various other animals, with a significant surge in H5N1 infections since 2022. This sustained and wide circulation globally increases the chances of the virus spilling over into humans and other mammals and also provides more opportunities for genetic changes. Consequently, there have been reported human cases of avian influenza. In the United States alone, over 70 cases of H5N1 infection have been seen since 2022. A notable portion of these recent cases has been linked to exposure to sick dairy cows, marking a new transmission route and an international concern. While most of these infections have presented with mild symptoms like conjunctivitis and mild respiratory issues, it is possible that severe illness or death could occur. For example, the first reported US death from H5N1 occurred recently, in January 2025, in Louisiana. Canada also reported a severe human H5N1 case in British Columbia in November 2024. China continues to report human cases of various subtypes, but importantly, there has been no observed human-to-human transmission to date.

Several concerning trends are emerging, though. There has been an increase in avian influenza infections reported in various mammals, including dairy cattle, domestic cats, and marine mammals, in addition to domestic poultry. Furthermore, genetic analysis of H5N1 viruses from human cases has revealed worrying mutations suggesting there is adaptation towards human hosts. For instance, there is a mutation identified in the H5N1 virus currently circulating in US dairy cows, which could increase its ability to bind to human cell receptors – a critical step for potential human-to-human transmission. These trends highlight the dynamic nature of the avian influenza virus and the urgent need for heightened surveillance and to be prepared, especially if human-to-human infection occurs.

A bird flu outbreak with pandemic potential could have profound and severe impacts, particularly on vulnerable populations like those in aged care facilities or the elderly in general. Older adults are especially susceptible to influenza viruses due to age-related changes in their immune systems, or immunosenescence. As we age, our immune systems become less effective at recognising and fighting off new infections, and our response to vaccines may also be weaker. Moreover, older adults are more likely to have underlying chronic health conditions such as heart disease, lung disease, and diabetes, which will significantly increase their risk of developing severe complications from influenza. During seasonal influenza epidemics, older adults bear the heaviest burden of severe disease, accounting for a disproportionately high number of hospitalisations and deaths.

If we consider a potential bird flu pandemic, the aged care sectors in Australia and New Zealand face significant challenges. Aged care facilities house a large number of individuals with advanced age and complex health needs, residing in a communal environment.

To strengthen preparedness and response in the face of a potential bird flu pandemic, several key measures are critical, particularly within aged care settings in Australia and New Zealand. Vaccinations for both residents and staff against seasonal influenza are of primary concern, as they can reduce the overall facility burden of respiratory illness and potentially offer some cross-protection from a new virus. Strict infection prevention and control measures, including meticulous hand hygiene, proper use of personal protective equipment (PPE), and thorough environmental cleaning, are essential. Timely administration of antiviral medications like oseltamivir can be significant, especially when started early in the course of illness. Clear guidelines and protocols for managing outbreaks, including early detection, isolation of cases, and visitor restrictions, when necessary, must be in place and regularly included in training. Clear and consistent communication with residents, families, and public health authorities is also vital during an outbreak.

Beyond aged care, there are actionable steps we can all take:

Ongoing surveillance of avian influenza in both animal and human populations is critical to detect any changes in the virus that could increase its pandemic potential. International collaboration and the sharing of information are also essential for global preparedness.

In conclusion, the threat of avian influenza as a potential pandemic remains a significant concern due to its zoonotic nature and the demonstrated severity of certain strains like H5N1 and H7N9 in humans. The ongoing evolution of avian influenza viruses, particularly the potential for mutations enabling human-to-human transmission, is the primary factor health experts are closely monitoring. While current global outbreaks primarily affect animals, human infections are sporadic with no sustained human spread. However, the increasing number of spillover events in other mammals underscores the changing nature of this threat. Given the vulnerability of populations like the elderly in aged care settings, preparedness and vigilance are vital. As this evolving landscape continues, what role do you think proactive measures and global collaboration play in safeguarding against a potential avian influenza pandemic?

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