Question
Avian influenza
Answer
Avian influenza (“bird flu”) refers to infection with influenza A virus subtypes that are primarily adapted to and circulate among birds (their natural reservoir), but which can, in certain circumstances, cross the species barrier to infect humans, causing severe and often fatal disease.
Important subtypes with human infection potential: H5N1 — the most extensively documented avian influenza subtype causing severe human infection, first identified in Hong Kong in 1997, associated with high case-fatality rates; H7N9 — emerged in China, also capable of causing severe human disease; other subtypes (H5N6, H9N2, H10N8) have caused sporadic human cases.
Transmission: primarily through direct contact with infected poultry (live bird markets, poultry farming) or contaminated environments (poultry faeces, contaminated surfaces) — human-to-human transmission is rare and generally inefficient with most avian strains, which is why sustained pandemic spread has not yet occurred with these subtypes, despite their severity in the individuals infected; however, this remains a major pandemic preparedness concern, since a strain acquiring efficient human-to-human transmissibility (via mutation or reassortment with a human-adapted strain) could trigger a severe pandemic given the general lack of pre-existing population immunity to these novel HA subtypes.
Clinical features: presents with a severe respiratory illness — high fever, cough, and rapidly progressive pneumonia, frequently complicated by Acute Respiratory Distress Syndrome (ARDS), multiorgan failure, and a notably high case-fatality rate (historically exceeding 50% for H5N1 in confirmed cases) compared to typical seasonal influenza.
Laboratory diagnosis: RT-PCR is the standard diagnostic method, with specific primers/probes for the relevant subtype (H5, H7, etc.); testing requires appropriate biosafety precautions given the severity of the illness and pandemic-potential concern; viral culture is generally restricted to specialized reference laboratories.
Prevention and management: surveillance and control of avian influenza outbreaks in poultry (culling of infected flocks); protective measures for individuals with occupational poultry exposure; neuraminidase inhibitors (oseltamivir) are used for treatment; no widely available vaccine for general population use exists, though pandemic-preparedness vaccine stockpiles against specific concerning strains have been developed in some countries.