For Preliminary Examination:  Influenza, H5N1

 

For Mains Examination: GS III - Science & Technology

 

 

Avian influenza, commonly known as bird flu, is a viral infection primarily affecting birds.A global outbreak of H5N1, a highly pathogenic avian influenza virus, has been spreading across the world since late 2020, driven by a new emerging lineage of the virus—2.3.4.4b

 

 

H5N1

 

Influenza

 

 

• Avian influenza, or bird flu, is a viral infection that primarily affects bird species. Since late 2020, a global outbreak of the highly pathogenic H5N1 avian influenza virus has been unfolding, fueled by the emergence of a new lineage, 2.3.4.4b. H5N1 has long been a public health concern due to its severe impact on humans and its ability to infect various hosts, including poultry, wild birds, and mammals.
• Although it has predominantly affected the poultry industry since its discovery in the late 1990s, sporadic human infections have raised alarms about its potential to spark a pandemic.
• Recent cases in British Columbia, Canada, and California, USA, have heightened fears about the virus’s adaptability and the possibility of mutations enabling human-to-human transmission.
• In November 2024, a teenager from Fraser Health, British Columbia, was diagnosed with H5N1, marking Canada’s first domestically acquired human case. The patient initially presented with conjunctivitis, fever, and cough, which rapidly progressed to acute respiratory distress syndrome, necessitating intensive care.
• Genomic analysis revealed the virus belonged to the 2.3.4.4b clade, genotype D1.1, similar to strains found in wild birds in the Fraser Valley, but unrelated to poultry farm outbreaks in the region.
• This genotype differs from those infecting dairy workers in the U.S. and a child in California. Despite extensive testing of household contacts, pets, nearby animals, and environmental samples, health officials could not pinpoint the source of the teenager's infection.
• British Columbia’s health officer, Bonnie Henry, suggested the virus might have evolved after infecting the patient. This hypothesis stems from the unusual progression of symptoms, starting with conjunctivitis and advancing to severe respiratory distress. Serial samples from the patient are being analyzed to identify any mutations that may have arisen during the infection.

Genomic Analysis

• Although no additional cases have been reported, genomic sequencing identified mutations in the virus that suggest enhanced adaptation to human hosts, including improved cell-receptor binding and deeper lung penetration.
• One notable mutation, PB2-E627K, is associated with faster replication in human cells and more severe illness and likely emerged during the infection.
• These findings raise concerns about the virus’s potential to cause more severe respiratory disease in humans, although there is no evidence of transmission to others from the Canadian teenager.
• Meanwhile, the U.S. Centers for Disease Control and Prevention (CDC) confirmed the first human case of H5N1 in a child from Alameda County, California. The child, who experienced mild respiratory symptoms, is recovering after antiviral treatment.
• Tests on family members found no evidence of human-to-human transmission. While over 50 cases of human H5N1 infections were reported in the U.S. in 2024, this case marks the second infection in a North American child.
• These cases are particularly concerning because their transmission routes differ significantly from earlier North American cases in 2024, which primarily involved individuals with direct contact with infected birds, such as farm workers.
• The CDC has noted that human infections without clear exposure to infected animals are rare, making these recent cases critical for understanding the virus’s evolving nature. Researchers remain vigilant for mutations that could enable easier human-to-human transmission, which would pose a significant public health threat.

Implications for Public Health

These developments underscore the urgent need to understand and address the evolving epidemi