Avian Influenza | Bird Flu

Definition of Avian Influenza

Avian influenza, which is caused by influenza A viruses, can affect a variety of domestic and wild bird species. Infection can range from asymptomatic to severe, depending on the virulence of the virus and the susceptibility of the avian host. Avian influenza in domestic chickens and turkeys is classified according to disease severity, with two recognized forms: highly pathogenic avian influenza (HPAI), also known as fowl plague, and low-pathogenic avian influenza (LPAI). Avian influenza viruses that cause HPAI are highly virulent and mortality rates in infected flocks often approach 100%. While LPAI viruses are generally of lower virulence, LPAI in flocks should be controlled because LPAI viruses can serve as progenitors to HPAI viruses.

Notifiable avian influenza is defined by the World Organization for Animal Health (OIE) as "an infection of poultry caused by any influenza A virus of the H5 or H7 subtypes or by any avian influenza virus with an intravenous pathogenicity index (IVPI) greater than 1.2 (or as an alternative at least 75% mortality)" (see References: OIE 2004). The OIE further classifies avian influenza as HPAI or LPAI according to the following criteria:

HPAI viruses have an IVPI in 6-week-old chickens greater than 1.2 or, as an alternative, cause at least 75% mortality in 4-to 8-week-old chickens infected intravenously. H5 and H7 viruses which do not have an IVPI of greater than 1.2 or cause less than 75% mortality in an intravenous

lethality test should be sequenced to determine whether multiple basic amino acids are present at the cleavage site of the haemagglutinin molecule (HA0); if the amino acid motif is similar to that observed for other HPAI isolates, the isolate being tested should be considered as HPAI.
LPAI are all influenza A viruses of H5 and H7 subtype that are not HPAI viruses.

According to the OIE International Animal Health Code, countries that identify HPAI should report the occurrence to OIE within 24 hours.

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1. Definition of Avian Influenza?

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5. Key Outbreaks of HPAI in Domestic Avian Populations?

6. Current Status of H5N1 in Asia?

7. HPAI As a Biological Weapon?

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