Fig. 7.

ELD50 of WTrIBV and the rN3D/N6D mutant. The virus stocks of WTrIBV and rN3D/N6D of the same titers were 10-fold serially diluted and 0.2 ml diluted virus was injected into the allantoic cavity of 10-day old embryonated SPF eggs and incubated at 37 °C for 5 days. The numbers of live or dead embryos were counted and the 50% embryo lethal dose (ELD50) was calculated using the Reed and Muench method. The bar chart shows the results from two independent experiments with standard deviations.