Infectious bursal disease viral infections. II. The relationship of age, complement levels, virus-neutralizing antibody, clotting, and lesions.

Experimental infection with infectious bursal disease virus (IBDV) reduced the complement (C) titer in 8-week-old chickens on days 3, 5, and 7 postinfection. Since the C titer was much lower in normal 2-week-old chickens than in normal 8-week-old chickens it could not be determined whether there was a reduction in titer during the infection process. Virus-neutralizing antibody rose rapidly following infection in both 2- and 8-week-old chickens. Hyper-immune serum given during infection in an attempt to produce immune complexes did not increase disease severity in either 2- or 6-week-old susceptible chickens.