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Abstract
SUMMARY
Four temperature-sensitive(ts) mutants of the A7 strain of Semliki Forest virus (SFV) have been isolated. All mutants were defective in RNA synthesis at the restrictive temperature (39 °C) compared to the permissive temperature (30 °C). Since the body temperature of mice fluctuates between 37 °C and 39 °C, multiplication was also examined at 37 °C; only the multiplication of ts4 was restricted. After intraperitoneal infection of 8-day pregnant mice, the wild-type induced rapid abortion.Ts4 and ts26 had no effect on embryonic development. Litters born to ts4-infected mothers developed no postnatal immunity whereas 50 % of litters from ts26-infected mothers were immune. Unlike the wild-type, tsl4 induced the same or higher virus titres in placental tissue in most mice than in foet al tissue. Ts22 and ts14 induced a range of development defects, including developmental arrest, mummification, abortion and postnatal death. Most surviving offspring were immune. Although ts4 induced no viraemia, tsl4, ts22 and ts26 induced a lower titre but longer lasting viraemia than the wild-type. It is concluded that infections of pregnant mice with tsl4 and ts22 in particular are good models for analysis of the mechanism of virus-induced developmental defects.
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