Deformities of chick embryos in experimental Akabane virus infection.

A material containing 10(3.0) approximately 10(5.0) TCID50 of Akabane virus was inoculated into 6-day-old chick embryos by the yolk sac route. Death of embryos did not increase in the course of embryonic development till 18 days of age, as compared with control groups. Later than 18 days of age, however, the numbers of dead and peeping but unhatched embryos increased, making the hatching rate significantly low. Deformities, such as arthrogryposis and hydranencephaly, appeared in almost all the dead and unhatched embryos. They were severe in dead embryos, considerably severe in peeping unhatched embryos, and comparatively mild, though highly frequent, in affected hatched chicks. Many of the hatched chicks manifested ataxia, abnormal gait, astasia, or tremor of body or legs separately or together. Virus growth was demonstrated in chick embryos inoculated at 7 days of age. The virus titer was the highest (10(3.25 approximately 10(3.75) TCID50/O.1g) in head, trunk, and muscle, and the second highest (10(2.0) approximately 10(2.5) in brain, heart, and other visceral organs. It was the highest (10(4.0) approximately 10(4.5)) in muscle and a mixture of cerebellum and brain stem in embryos inoculated at 8 days of age.