The combined influence of age of embryo and temperature and duration of incubation on the replication and yield of avian infectious bronchitis (IB) virus in the developing chick embryo.
Two experiments were undertaken to investigate the combined influence of the age of embryo at infection and the temperature and duration of incubation on the replication and yield of the Beaudette strain of IB virus lin allantoic fluid and the chorio allantoic membrane. In general a higher titre of virus was found in the allantoic fluid and chorioallantoic membrane of living embryos than of dead ones and with continued incubation of dead embryos the titre of virus fell still further. For embryos of the same age at infection peak titres were similar for those incubated at 32 degrees C and 37 degrees C but were greater than for the corresponding embryos at 42 degrees C. The range of titres for embryos of all ages associated with duration of incubation was narrower for those incubated at 32 degrees C than at 37 degrees C and 42 degrees C and a longer survival period was observed for embryos incubated at 32 degrees C. Peak titres of virus for all age groups were observed after 24 h at 32 degrees C and after 12 h at 37 degrees C and 42 degrees C and then declined. The highest titre for virus in allantoic fluid, in both experiments, was in the 10 d old embryos at 32 degrees C harvested after 24 h. For the chorioallantoic membrane the highest titre in the first experiment was in 12 d old embryos at 32 degrees C, harvested after 24 h, while in the second it was also in 12 d old embryos but at 37 degrees C and harvested after 12 h. The lowest titre of all was in 10 d old embryos incubated at 42 degrees C. It is considered that the maximum total yield of virus from the allantoic fluid and chorio allantoic membrane of the same embryo will be in those infected at 10 - 12 d of age incubated at 32 degrees C to 37 degrees C.