A neuraminidase in duck embryo rabies vaccine.

While studying variations amony immunizing potentials of rabies vaccines, we were led to consider the possibility that the antigen in the vaccine derived from duck embryos may have been degraded by enzymes arising from host tissues. Such an enzyme, a neuraminidase, was found in duck embryo rabies vaccine through the application of a periodate-linked thiobarbituric acid assay. This acitvity could not be found in two other rabies vaccines derived from tissue cultures. We have thus concluded that there is a strong possibility that a modified antigen is present in duck embryo vaccine. In addition, the injection of this vaccine will introduce a neuraminidase which may produce localized effects in the tissues of the recipient.