Avian Influenza

Excerpt

Because infection with avian influenza can be particularly deadly in comparison to other viruses, providers may not be aware of the extra caution required when evaluating possible cases of infection. This article will impress on providers the severity of the disease and the need for high suspicion in specific scenarios as well as the need for early escalation of care. Avian influenza is an umbrella term describing the disease caused by various strains of influenza A virus known to infect birds that occasionally cause outbreaks of viral illness in humans. Numerous well-known outbreaks of avian influenza include an outbreak of the H5N1 strain in Hong Kong in 1997 and H7N9 in Eastern and Southern China in 2013. Although adapted to birds, and often causing only mild illness, avian influenza viruses can be extremely dangerous with successful transmission to humans with a high percentage of confirmed cases requiring hospitalization and frequently intensive care unit (ICU) care.

Influenza A viruses are part of the Orthomyxoviridae family. Other viruses in this group include influenza B and C viruses, thogotovirus, and isavirus. While influenza B and C have been found in other species, only influenza A has been found to infect birds. The exact mechanism of bird-to-bird transmission is not currently well known. The virus is released in large quantities from infected birds in feces and the respiratory tract. In birds, avian influenza strains are characteristically highly pathogenic avian influenza (HPAI) and low pathogenicity avian influenza (LPAI). In birds, LPAI strains are more common and usually cause limited disease. In humans, both HPAI and LPAI strains can cause deadly avian influenza outbreaks, although HPAI strains do so more frequently.

The influenza A virus splits into subtypes based on the antigen present on two of the virus’s surface glycoproteins, haemagglutinin (with 16 known possible antigens), and neuraminidase (with nine known possible antigens). The virus then gets described using the antigen combination, such as H5N1. The haemagglutinin glycoprotein gets produced as a precursor in this virus; this is important because the proteins required to process and activate this protein in LPAI strains of the virus are found only in specific parts of the body such as gastrointestinal and respiratory tracts, while those required for HPAI strains are generally ubiquitous in the host.

Avian influenza viruses (AIVs) occur in most bird species, both wild and domestic. Generally, domestic birds are responsible for human disease outbreaks as they have more human contact. Some diseases spread, though, may be implicated in migratory birds that could carry disease to different locations where subsequent infection of domestic birds leads to human transmission. Avian influenza is transmitted to humans most commonly from direct contact with live birds or contact with raw poultry in factories and restaurants.