US Confirms World’s First Human Case of H5N5 Bird Flu: Here’s What We Know So Far

The United States has reported the world’s first-ever human case of H5N5 bird flu, health officials confirmed last week. The infected individual—an older adult with underlying health issues—was hospitalised in early November after developing symptoms consistent with avian influenza, according to the Washington State Department of Health.

Initial testing identified the virus as influenza A (H5), and further genomic analysis confirmed it as the H5N5 subtype, a strain previously found only in birds and animals and never before recorded in humans.

Likely Source of Infection

Officials said the patient keeps a mixed backyard flock of domestic poultry that had been in contact with wild birds. Either the domestic birds or wild species are considered the most probable source of exposure. Investigations are ongoing to determine the exact route of transmission.

What Is Avian Influenza?

Avian influenza—or “bird flu”—is caused by influenza A viruses, which naturally circulate among wild aquatic birds. These birds often act as reservoirs, spreading the virus to domestic poultry and sometimes to other animal species.

Influenza A viruses are classified by two surface proteins:

• Hemagglutinin (H)
• Neuraminidase (N)

Examples of H5 viruses include H5N1, H5N5, H5N8, and more.

Some variants cause mild illness in birds (LPAI), while others are highly pathogenic (HPAI), leading to rapid die-offs in poultry.

Why H5N5 Matters

Experts say H5 viruses are genetically unstable and prone to reassortment, meaning they can mix genetic material and produce new strains. This evolutionary flexibility is why health organisations monitor these viruses closely for potential pandemic risk, even though the current threat remains low.

How Bird Flu Spreads

In birds, transmission occurs through:

• Respiratory secretions
• Feces
• Contaminated surfaces

Humans typically become infected through close, unprotected contact with infected birds, poultry farms, or contaminated environments. Droplets, dust particles, or touching contaminated surfaces and then touching the face can spread the virus.

Symptoms in Humans

Human symptoms can vary widely, from no symptoms to severe illness. Common signs include:

• Fever
• Cough & sore throat
• Shortness of breath
• Fatigue & muscle pain
• Vomiting or diarrhea
• Eye infections (conjunctivitis)

Severe cases may progress to pneumonia, respiratory failure, or death, according to global health agencies.

How to Stay Safe

Health organisations recommend:

• Avoiding contact with sick or dead birds
• Using masks and gloves around poultry
• Avoiding raw or undercooked meat, eggs, or milk
• Continuing strong surveillance and rapid reporting of new cases

Authorities emphasize that while this single case is concerning, there is no evidence of human-to-human transmission at this time.