The effects of two strains of influenza virus on cardiac development in the chick embryo.

To investigate the teratogenic effects of influenza virus on cardiac development two strains of influenza virus (Ty/Calif/5142/66 and Ty/Calif/64/M. Meleagrium) were injected into the yolk sac of fertile white Leghorn eggs during stage 23. Eggs injected with normal saline served as controls. The number of live embryos was significantly reduced in eggs injected with the 5142 strain, whereas the Meleagrium strain did not affect the number of live embryos in a significant manner. Serial sections of the live embryo hearts, extracted during stage 35, showed no cardiac anomalies in control groups. However, cardiac malformations were increased significantly in the embryos infected with the influenza viruses. A comparison of the two viral strains showed that the 5142 strain produced significantly more abnormal hearts than the Meleagrium strain. We conclude that (1) influenza infection during critical stages of embryonic development can lead to the cardiac anomalies, and (2) the virulence of a viral strain has a significant bearing on its teratogenic potential, at least in chick embryo hearts.