First Human H5N5 Bird Flu Case Reported in US: Understanding Transmission, Symptoms, and Prevention

Humans can contract H5N5 bird flu through unprotected close contact with infected birds or contaminated environments.

Health officials reported last week that a US man has become the first human case of H5N5 strain of avian influenza. The patient, described as an older adult with underlying health conditions, was hospitalized in early November exhibiting symptoms consistent with bird flu, according to confirmation from the Washington State Department of Health.

Laboratory testing initially identified the virus as influenza A H5, with further analysis confirming it as the H5N5 subtype—a strain previously documented only in birds and animals, never before in humans.

The individual maintained a mixed backyard poultry flock that had been exposed to wild birds. Health officials believe either the domestic birds or wild birds were the most likely source of infection, though investigations continue to determine the exact exposure pathway.

Avian influenza, commonly known as "bird flu," is caused by Influenza A viruses that primarily affect birds, according to the Centers for Disease Control and Prevention (CDC). These viruses naturally circulate among wild aquatic birds, which serve as natural reservoirs.

Influenza A viruses are categorized based on their surface proteins: hemagglutinin (H) and neuraminidase (N). Multiple subtypes exist, including various H5 viruses such as H5N1, H5N5, and H5N8.

These strains are classified as either low pathogenic avian influenza (LPAI), causing mild illness in birds, or highly pathogenic avian influenza (HPAI), which can rapidly cause high mortality in bird populations.

The H5N5 virus raises concern because Influenza A (H5) viruses demonstrate genetic diversity and can reassort, potentially creating new variants, according to the World Organisation for Animal Health. While current risk remains low, these viruses' "pandemic potential" necessitates vigilant monitoring, particularly in animal populations where they circulate.

In birds, the virus transmits through respiratory secretions and feces. Human infection typically occurs through close, unprotected contact with infected birds or contaminated environments such as poultry farms or live bird markets.

Transmission can happen via droplets, dust, or by touching contaminated surfaces and subsequently touching one's eyes, nose, or mouth, according to the World Health Organization.

Human symptoms range from asymptomatic or mild to severe. Common manifestations include fever, cough, sore throat, shortness of breath, fatigue, muscle aches, and occasionally gastrointestinal problems like vomiting or diarrhea.

Some patients develop conjunctivitis, as reported by Johns Hopkins Medicine. Severe cases may progress to pneumonia, acute respiratory distress syndrome, or death, according to the Pan American Health Organization.

Prevention measures include avoiding close contact with sick or dead birds, using appropriate protective equipment (masks, gloves) when handling poultry or cleaning bird enclosures, and avoiding consumption of raw or undercooked poultry products, meat, eggs, and raw milk from infected animals.

Public health agencies recommend ongoing surveillance and rapid identification of new human infections to monitor the situation.