| 摘要 |
<p>The cold-adapted (ca) temperature-sensitive (ts) vaccine is prepared by serially passaging a suitably selected virus (e.g. Arkansas-type DPI strain) through a culture medium at a suboptimal replication temperature which is less than about 35.degree.C, e.g. 28.degree.C, and harvesting the live, cold-adapted mutant for formulation into dosage units of, for example, about 10 3 to about 10 5 EID50 /bird. The ca ts mutant is much less able to replicate at 40-42.degree.C (internal avian body temperatures) than at the temperature of the bird's upper respiratory tract, which is below 40.degree.C. The vaccine can be administered by any of the usual techniques, including the spray technique. Vaccines of this invention appear to be very effective (immunogenic), but are also safe (non-pathogenic).</p> |
