Comparison of the pathogenicity for pregnant sheep of Rift Valley fever virus and a live attenuated vaccine.

A live attenuated mutant of Rift Valley fever virus, MV P12, was previously shown to be non-pathogenic in young lambs, but capable of producing protective immunity. The studies reported here show that the abortion in sheep caused by an infection with virulent virus is the result of necrosis of the maternal villi and cotyledons arising from an acute inflammation of the maternal caruncles. Pregnant ewes infected with the attenuated mutant virus MV P12 showed none of these lesions in the placenta and gave birth to healthy lambs. Colostrum from ewes infected with MV P12 virus was able to induce protective immunity in the offspring. These data along with previously published results suggest that the mutant virus MV P12 is an excellent candidate for use as a live attenuated veterinary vaccine.

Recoverability of Rift Valley fever and sandfly fever Sicilian viruses from infected Phlebotomus papatasi (Diptera: Psychodidae) trapped in various oils.

We studied the effects of various oils used to trap sand flies on the recovery of virus from infected adult Phlebotomus papatasi. Both Rift Valley fever and sandfly fever Sicilian viruses were readily recovered from virus-inoculated specimens held at 26 degrees C on mineral, olive or castor oil-soaked sheets for up to 12 h. However, after 50 h on oil-soaked paper, significantly greater titers were recovered from sand flies trapped with mineral oil than from sand flies trapped with either of the other oils. This indicates that sand flies trapped on oil-soaked paper would be suitable for virus isolation attempts and that mineral oil had the least effect on virus recovery.