Induction of cystic oviducts and protection against early challenge with infectious bronchitis virus serotype D388 (genotype QX) by maternally derived antibodies and by early vaccination

Since the end of 2003, strains of the D388 serotype (QX genotype) of infectious bronchitis virus (IBV) have caused considerable damage to the Dutch poultry industry. In order to better understand the pathogenesis of infection caused by this infectious bronchitis variant and to be able to support the poultry industry with substantiated advice to prevent or decrease the damage caused by the D388 strain, several vaccination and challenge experiments were performed in young specific pathogen free layers, young layers with maternally derived antibodies against the D388 strain and young commercial broiler breeders. The experiments confirmed the field observations that the D388 strain of the QX genotype is a very pathogenic strain that is able to cause cystic oviducts in a high percentage of birds, mortality due to nephritis and respiratory distress with complete tracheal ciliostasis and airsacculitis. Vaccination programmes using different combinations of heterologous live vaccines at day 0 or at days 0 and 14 induced a reasonable to high level of protection in the trachea, kidney, oviduct and air sacs against challenge with the D388 strain at 28 days of age. However, for very early protection, maternally-derived D388-neutralizing antibodies were shown to be very important. Titres of 9 to 10 log(2) maternally-derived D388 virus-neutralizing antibodies, which provided partial protection against tracheal damage and a high protection against replication of D388 in the kidney after challenge at 6 or 10 days of age, could be achieved using a broad heterologous live priming and subsequent boosting using inactivated IBV vaccines containing two or three heterologous IBV antigens.