Highly Pathogenic Avian Influenza (HPAI)

OIE Definition of HPAI
(2003)

HPAI is an OIE List A disease. Avian influenza is classified as HPAI if it conforms to these criteria:

1. Any influenza virus that is lethal for six, seven or eight of eight 4–8-week-old susceptible chickens within 10 days following intravenous inoculation with 0.2 ml of a 1/10 dilution of a bacteria-free, infective allantoicfluid.
   
2. The following additional test is required if the isolate kills from one to five chickens but is not of the H5 or H7subtype:
   • growth of the virus in cell culture1 with cytopathic effect or plaque formation in the absence oftrypsin. If no growth is observed, the isolate is not considered to be a HPAI isolate.
     
3. For all H5 and H7 viruses of low pathogenicity and for other influenza viruses, if growth is observed in cellculture without trypsin, the amino acid sequence of the connecting peptide of the haemagglutinin must bedetermined. If the sequence is similar to that observed for other HPAI isolates, the isolate being tested willbe considered to be highly pathogenic.

EU Defintion of HPAI
(June 2003)

The defintition of HPAI as stated in EU Directive 92/40/EEC, uses the intravenous pathogenicity index (IVPI) as a measure of virulence:

"an infection of poultry caused by an influenza A virus that has an intravenous pathogenicity index in 6-week old chickens >1.2 or any infection with influenza A viruses of H5 or H7 subtype for which nucleotide sequencing has demonstrated the presence of multiple basic amino acids at the cleavage site of the haemagglutinin."