What is Influenza?
Influenza is a negative-sense, single-stranded RNA virus belonging to the family Orthomyxoviridae. These viruses are spherical or pleomorphic in shape, with sizes ranging from 80–120 nm in diameter. There are four types of influenza viruses: A, B, C, and D. However, Influenza A and B viruses are responsible for seasonal flu epidemics in humans.
Influenza A Virus: Subtypes and Host Adaptation
Influenza A viruses are classified based on two surface proteins:
- Hemagglutinin (H) – 18 known subtypes (H1–H18)
- Neuraminidase (N) – 11 known subtypes (N1–N11)
Of these, 16 hemagglutinin subtypes have been found in waterfowl and seabirds, while H17N10 and H18N11 are detected only in bats. The ability of influenza viruses to infect different species depends on their interaction with host sialic acid (SA) receptors:
- Avian and equine influenza viruses bind to α-2,3-SA receptors
- Human influenza viruses prefer α-2,6-SA receptors
- Swine influenza viruses bind to both, making pigs potential “mixing vessels” for viral reassortment between birds and humans
How Influenza Viruses Evolve: Antigenic Drift and Shift
Influenza viruses undergo constant genetic changes, making them challenging to control:
- Antigenic Drift: Gradual point mutations during viral replication, leading to seasonal flu variations and annual vaccine updates.
- Antigenic Shift: A sudden emergence of a new HA or HA-NA combination, creating highly distinct strains that can cause pandemics.
There have been four pandemics of Influenza A viruses in history, each caused by major antigenic shifts.
Avian Influenza (Bird Flu) and Its Growing Threat
HPAI vs. LPAI: The Two Forms of Bird Flu
Avian influenza viruses are classified into:
- Low Pathogenic Avian Influenza (LPAI) – Causes mild illness in birds.
- Highly Pathogenic Avian Influenza (HPAI) – Leads to severe systemic illness with high mortality rates in birds.
Strains of H5 and H7 are known to cause HPAI, with H5N1 being particularly concerning due to its ability to infect humans.
H5N1: A Growing Concern for Human Health
Since its emergence in 1997, H5N1 has been circulating in poultry across Asia and Africa, leading to human infections and deaths. Since 2003, over 890 cases of human infection have been reported across 23 countries.
In 2024, the HPAI A(H5N1) virus (clade 2.3.4.4b) was detected in dairy cattle for the first time, leading to a multi-state outbreak and contamination of raw milk. Exposure to infected poultry or cattle has caused a range of human symptoms, from mild respiratory illness to fatal pneumonia. Other avian influenza strains, including H7N9 and H9N2, have also been found in humans.
The Role of Environmental Changes in Influenza Transmission
Climate Change and Avian Migration
Climate change, deforestation, and biodiversity loss have increased human-animal interactions, leading to a higher risk of zoonotic infections like avian flu. Climate change has altered:
- Migration patterns of birds
- Breeding sites and stopover points
- Timing and duration of migration
These factors have intensified the spread of influenza viruses between wild and domestic birds.
Urbanization and Farm Location Risks
Urban expansion and land use changes are contributing to increased influenza transmission. Farms located near water bodies with high densities of waterfowl are at greater risk of virus introduction than those in drier regions.
Additional biosecurity challenges include:
- Poor waste management (e.g., leaving poultry feed outside)
- Lack of protective equipment
- Inadequate disinfection measures
- Housing multiple poultry species together, increasing cross-species transmission
How Ventilation and Biosecurity Can Reduce Virus Spread
The Role of Ventilation in Virus Control
Proper airflow and ventilation in farms, marketplaces, and live poultry farms can significantly impact the spread of avian influenza. Studies show that:
- Higher wind speeds aid ventilation, reducing H5N1 outbreaks.
- High humidity levels cause airborne virus particles to fall faster, limiting their spread.
- Dry air conditions allow viruses to remain suspended for longer, increasing infection risks.
Engineering Controls for Better Biosecurity
Improving Heating, Ventilation, and Air Conditioning (HVAC) systems can reduce influenza transmission. Effective strategies include:
- Filtered air supply to poultry farms
- Exhausting filtered air back into the environment
- Regular HVAC maintenance to remove dust, feathers, and contaminants
- Installing additional disinfection systems, such as:
- Germicidal UV devices
- Electrostatic filters
- Biocides
Additionally, proper waste treatment and disposal prevent water contamination and further virus spread.
The Importance of Independently Testing Air Purification Systems
Why Independent Testing is Crucial
With numerous HVAC filters, air cleaners, and disinfection devices available in the market, independent testing is essential to validate their effectiveness. Many manufacturers make bold claims, but only scientific verification can ensure they meet public health standards.
Key Factors in Testing
Independent testing evaluates:
- Filtration efficiency – How well the system removes viral particles.
- Airflow resistance – Ensuring optimal airflow without disrupting ventilation.
- Pathogen inactivation – Effectiveness in neutralizing viruses.
Regulatory Standards for Air Quality
Tested and certified air purification systems must comply with:
- ASHRAE (American Society of Heating, Refrigerating, and Air-Conditioning Engineers) standards
- Asthma and Allergy Friendly® certifications
- Other industry regulations
Improving Public Health with Verified Air Systems
By installing independently tested HVAC filters and air disinfection devices, businesses, farms, and healthcare facilities can ensure:
- Better indoor air quality
- Reduced airborne virus transmission
- A safer environment for both humans and animals
Conclusion: A Call for Sustainable Virus Control
The rising threat of avian influenza demands proactive measures to mitigate its spread. Strengthening biosecurity in farms, improving ventilation systems, and adopting eco-friendly farming practices are essential. Additionally,independent testing of air purification technologies ensures greater efficiency and reliability in protecting public health.
By addressing climate-driven disease transmission and implementing sustainable solutions, we can reduceoutbreaks and create a healthier future for both humans and animals.
Are you a manufacturer looking to certify your air cleaning technology?
Contact the Airmid Healthgroup team today to learn more about the independent testing process and how it can enhance your product’s credibility in the market.
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Key Words
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