To determine the recombinants’ pathogenicity in chicken embryos, 0.2 mL of rH120, rIBYZ, or rH120-S1/YZ virus (diluted to 1:100 in normal saline) was inoculated into the allantoic cavities of five 10-old-day embryonated SPF chicken eggs, respectively. Chick embryo lesions were examined for lesions at 144 h post-inoculation at 37 °C.