Infectious bursal disease viral infections. I. Complement and virus-neutralizing antibody response following infection of susceptible chickens.

Complement (C) titers were decreased at 3 days postinfection, and virus-neutralizing (VN) antibody was detectable at 3 or 4 days postinfection in chickens with infectious bursal disease virus (IBDV). Clotting times were prolonged in all groups tested during the acute phase of the disease. Mortality appeared to be associated with the severity of decrease in C titer. The results suggest that the mortality and many of the clinical signs seen with infectious bursal disease are associated with: 1) a depletion in circulating levels of hemolytic C from the formation of immune complexes at sites of viral replication; and/or 2) a depletion in some clotting factor which results in hemorrhage.