STUDIES ON A FIELD ISOLATE OF INFECTIOUS BURSAL DISEASE VIRUS

An isolate of infectious bursal disease (IBD) virus, obtained in the f ace of outbreak of IBD in poultry at Namakkal area of Tamil Nadu (desi gnated N93), was 25 times serially passaged, in chicken embryos by ino culation through chorio-allantoic membrane (CAM). The titre (embryo le thal dos-ELD(50)) was assessed at different passage levels. The titre stabilized at 10(6.5)/0.1ml of harvest at 20th passage level. Growth c urve studies at 20th passage level with an input of 10(4)ELD/0.01ml sh owed a maximum titre of virus in the harvest (10(65)/0.1ml) at 63rd ho ur post-inoculation, The embryonic suspension had a maximum titre of v irus (10(65)/0.1 ml) followed by CAM (10(455)/0.1 ml) and amnio-allant oic fluid (AAF) (10(355)/0.1ml). Freezing and thawing of embryo suspen sion thrice followed by chloroform treatment (20% v/v for 10 min) libe rated maximum concentration of virus from the embryonic suspension, th an 3 cycles of freezing and thawing alone.