When inoculated with attenuated S- strain Japanese encephalitis virus vaccine, SPF pigs 1 month old presented no abnormal clinical signs, but retained antibody for a long time and resisted challenge with the high virulent AS-6 field strain. When inoculated with the same vaccine, pregnant SPF sows exhibited no clinical symptoms either. Autopsy on them revealed no abnormal fetuses and no virus was recovered from them.
In a field trial of this vaccine, the frequencies of occurrence of dead fetuses and sows giving birth to abnormal fetuses were lower in sows inoculated once or twice with this vaccine than in those inoculated with no vaccine. In conclusion, this vaccine is safe and well immunogenic for piglets and pregnant sows, and effective for the prevention of stillbirth to be caused by Japanese encephalitis virus in swine.
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