Fresh infective allantoic fluid with a HA titre >1/16 (>24 or >log2 4 when
expressed as the reciprocal) is diluted 1/10 in sterile isotonic saline.
0.1 ml of the diluted virus is injected intravenously into each of ten 6-week-old
SAN susceptible chickens; if possible, SPF chickens should be used.
Birds are examined at 24-hour intervals for 10 days. At each observation, each
bird is scored 0 if normal, 1 if sick, 2 if severely sick, 3 if dead. (The judgement
of sick and severely sick birds is a subjective clinical assessment. Normally,
‘sick’ birds would show one of the following signs and ‘severely sick’ more than
one of the following signs: respiratory involvement, depression, diarrhoea,
cyanosis of the exposed skin or wattles, oedema of the face and/or head,
nervous signs. Dead individuals must be scored as 3 at each of the remaining
daily observations after death4.)
The IVPI is the mean score per bird per observation over the 10-day period. An
index of 3.00 means that all birds died within 24 hours, and an index of 0.00
means that no bird showed any clinical sign during the 10-day observation
period.