Isolation and preliminary characterization of @entity3597 mutants with altered pathogenicity for XXXX embryos.

@entity3598 @entity19 @entity71030 @entity245 @entity71031 @entity1167 @entity3597 @entity204
Four temperature-sensitive (ts) mutants of the A7 strain of @entity3597 ( @entity3598 ) have been isolated. All mutants were defective in RNA synthesis at the restrictive temperature (39 degrees C) compared to the permissive temperature (30 degrees C). Since the body temperature of @entity19 fluctuates between 37 degrees C and 39 degrees C, multiplication was also examined at 37 degrees C; only the multiplication of @entity71030 was restricted. After intraperitoneal infection of 8-day pregnant @entity19 , the wild-type induced rapid abortion. @entity71030 and ts26 had no effect on embryonic development. Litters born to @entity71030 -infected mothers developed no postnatal immunity whereas 50% of litters from ts26-infected mothers were immune. Unlike the wild-type, @entity71031 induced the same or higher virus titres in placental tissue in most @entity19 than in foetal tissue. Ts22 and @entity71031 induced a range of development defects, including @entity1167 , mummification, @entity204 . Most surviving offspring were immune. Although @entity71030 induced no viraemia, @entity71031 , ts22 and ts26 induced a lower titre but longer lasting viraemia than the wild-type. It is concluded that infections of pregnant @entity19 with @entity71031 and ts22 in particular are good models for analysis of the mechanism of virus-induced @entity245 .
