EXPERIMENTAL-INFECTION WITH AVIAN INFECTIOUS-BRONCHITIS VIRUS (KAGOSHIMA-34 STRAIN) IN CHICKS AT DIFFERENT AGES

Chicks at 2, 4 or 6 weeks of age were experimentally infected individu ally with a nephrosis/nephritis-causing avian infectious bronchitis vi rus (IBV) strain Kagoshima-34. The susceptibility of chicks in each gr oup to the infection was compared, based on the clinical signs, excret ion of virus in the faeces and antibody titres in the serum. The resul ts showed that although all chicks appeared to be susceptible to IBV i nfection, the most severe clinical response was observed following inf ection at 2-week-old. Likewise, whilst the virus was also recovered fr om the faeces of all the chicks infected, the duration of viral excret ion was longest in the 2-week-old chicks. A high antibody titre was de tected at 4 weeks post infection (PI) and was maintained for at least another 16 weeks in the 4- and 6-week-old chicks. In contrast, a low a ntibody titre was detected only between 8 to 12 weeks PI in the 2-week -old chicks. Thereafter, no antibody was detected despite the presence of clinical signs.