Bird flu in humans, pets and cattle: Why virologists fear an H5N1 pandemic

As H5N1 bird flu spreads across species in the US, global experts warn that ongoing mutations, cross-species infections, and rising human cases could push the virus closer to sustained transmission

There’s a new health threat grabbing attention across the globe—H5N1, better known as bird flu. And it’s not just affecting birds anymore. Since early 2024, the virus has spread to dairy cattle and even caused infections in people in the United States (US), with confirmed infections in over 995 dairy cattle herds, more than 168 million birds, 1,650+ flocks, and at least 70 humans. The epizootic is now present in all 50 states, with human cases reported in 13 states and Canada. 

Why does this matter? Because when a virus jumps from animals to humans and begins mutating, it could be the early sign of a much bigger problem.

 

Cross-species transmission of H5N1 raises pandemic concerns

The H5N1 avian influenza outbreak has expanded across the US, infecting not only poultry but also dairy cattle and domestic cats. Human cases, including one fatality, have occurred in individuals with no known animal contact, raising fears of viral adaptation that could enable sustained human-to-human transmission.

 

According to the US Centers for Disease Control and Prevention (CDC), sporadic HPAI A(H5N1) virus infections in mammals have also been reported in Asia, North America, South America, and Europe. 

What is H5N1 and why experts are alarmed

H5N1 is a subtype of the influenza A virus, classified as highly pathogenic avian influenza (HPAI). The “H” and “N” denote two surface proteins—haemagglutinin and neuraminidase. While several subtypes exist (such as H1N1 and H3N2), H5N1 is considered among the most dangerous due to its capacity to cause severe illness in both birds and humans.

 

First identified in 1996, H5N1 has led to over 889 confirmed human infections globally, with a mortality rate exceeding 50 per cent. Although human-to-human transmission remains limited, the high fatality rate poses a major public health risk.

 

Now present in birds, mammals, and humans, H5N1 represents a growing zoonotic threat. The Global Virus Network (GVN)—an organisation representing virologists from over 40 countries—has warned that ongoing mutations and sporadic human infections heighten the risk of a potential pandemic.

 

A new report published in The Lancet Regional Health — Americas by GVN, titled Enhancing the response to avian influenza in the US and globally, calls for urgent measures to address the growing threat. “The virus continues to circulate in wild birds, backyard flocks, and hunted migratory species, further amplifying the risk to humans and domestic animals,” the report notes.

How the H5N1 virus spreads

In birds, H5N1 is transmitted through saliva, nasal discharge, and faeces. Domestic poultry—chickens and turkeys in particular—are especially vulnerable. Migratory birds can spread the virus across continents, making containment difficult.

 

Humans typically become infected through direct or close contact with infected birds or droppings, often in live bird markets, farms, or while handling raw poultry. Although human-to-human transmission has not been sustained, experts caution that mutations could change that, making pandemic preparedness vital. 

Symptoms of H5N1 infection in humans

Human symptoms of H5N1 infection can resemble seasonal flu—fever, cough, and sore throat—but may escalate into serious conditions such as pneumonia and acute respiratory distress syndrome (ARDS). Some patients also experience diarrhoea, encephalitis, and multi-organ failure.

 

The Lancet report warns that the co-circulation of H5N1 with swine or seasonal human influenza viruses—especially during winter in the Northern Hemisphere—could result in reassortant strains capable of efficient human transmission.

 

CDC currently classifies H5N1 as a “moderate pandemic risk” among influenza A viruses.

Virus spreads to all 50 US states: Animals and humans affected

Between 2024 and April 2025, H5N1 has been found in over 168 million birds, 1,650 poultry flocks, and more than 995 dairy herds across the US. At least 70 human infections—primarily among farmworkers—have been confirmed in 13 US states and Canada. One individual died following exposure to infected wild birds. Domestic cats have also contracted the virus, typically from raw meat or milk.

Can domestic pets transmit H5N1 to humans?

According to The Lancet, domestic and wild cats may serve as vectors for H5N1 transmission. Cats can contract the virus from consuming infected birds or contaminated food. Once infected, they can shed the virus via respiratory droplets, saliva, and faeces.

 

Given that the fatality rate of H5N1 in cats may reach 90 per cent, researchers are urging continued surveillance and public education to reduce zoonotic spillover risks involving household pets. 

How is H5N1 treated?

There is no definitive cure for bird flu, but early treatment can reduce the severity of illness. Care typically involves antiviral medications, supportive therapies, and isolation.

 

Antiviral medications

 

Doctors may prescribe Oseltamivir (Tamiflu) or Zanamivir (Relenza) to slow virus replication. These work best when taken within 48 hours of symptom onset.

 

Supportive care for severe symptoms

 

Severe cases may require:

• Oxygen therapy 
• IV fluids 
• Antipyretics like paracetamol 
• Hospitalisation or ventilator support in ARDS or pneumonia cases

 

At-home care for mild infections:

• Rest and hydration 
• Fever-reducing medications 
• Isolation to prevent potential spread

Pandemic risk: What experts are saying

Although sustained human transmission has not occurred, experts warn that mutations, mammal-to-mammal transmission (e.g. in sea lions and mink), and reassortment with seasonal flu strains increase the pandemic threat. CDC’s Influenza Risk Assessment Tool ranks H5N1 as having moderate future pandemic potential. 

What researchers recommend

• Increase surveillance of livestock and environmental samples (milk, wastewater) 
• Enhance global genomic data sharing 
• Mandate PPE and biosecurity on farms 
• Distribute self-diagnosis kits for farmworkers 
• Fund outbreak response teams, especially in high-risk zones 
• Focus research on predictive genetic markers in viral evolution 
• Fast-track vaccine and treatment development for humans and animals 
• Conduct real-time clinical studies on emerging strains 

Impact on economy and food supply

The poultry sector has been severely hit, with millions of birds culled. Egg prices have soared, and concerns persist over milk contamination from infected cattle. While pasteurisation neutralises H5N1, raw milk remains risky. The dairy industry faces a long-term challenge of regaining consumer trust.

 

What happens next: Global preparedness

GVN and The Lancet recommend:

• Seasonal flu vaccination and PPE for agriculture workers 
• Government-backed genomic surveillance and data transparency 
• Rapid rollout of diagnostics and vaccines 
• Public awareness campaigns 
• Cross-border collaboration to coordinate global response 

Bird flu prevention: How to stay safe from H5N1 in India

India has no public H5N1 vaccine, so prevention is key:

 

Avoid bird contact

• Stay away from live bird markets, sick birds, and poultry farms 
• Use gloves and masks if working with birds

 

Maintain hygiene

• Wash hands thoroughly after contact with poultry 
• Clean surfaces after preparing raw meat 
• Avoid touching your face during food handling 

Cook poultry safely

• Cook chicken to at least 75°C 
• Avoid raw or undercooked eggs 
• Buy only from certified sources 

Stay informed and alert

 

Monitor updates from health authorities 

Report bird deaths promptly 

Seek medical care if flu symptoms follow bird exposure

 

Avoid high-risk travel zones 

• Postpone visits to outbreak areas 
• If unavoidable, mask up and keep distance from birds 

According to the CDC, the spread of H5N1 beyond birds to mammals and humans signals a troubling shift in the virus’s trajectory, underscoring the urgent need for global vigilance. While sustained human-to-human transmission hasn’t occurred yet, the increasing number of infections, expanding host range, and signs of viral adaptation highlight the real possibility of a future pandemic. As the world watches closely, preparedness, not panic, must be the guiding principle in mitigating the impact of this growing zoonotic menace.  For more health updates and wellness insights, follow #HealthWithBS