EXPERIMENTAL-INFECTION OF PREGNANT CATTLE WITH BLUETONGUE VIRUS SEROTYPE-11 BETWEEN POSTBREEDING DAYS 21 AND 48

Four bluetongue virus (BTV)-seronegative heifers and 2 BTV-seropositiv e heifers were inoculated with the virulent strain UC-8 of BTV-11 betw een postbreeding days (PBD) 21 and 30. The heifers were observed for 1 0-18 days after inoculation for clinical signs, and pregnancy was moni tored by ultrasound examination of the uterus and by plasma progestero ne levels. Blood samples were collected daily after inoculation and pr ocessed for virus isolation and titration. Heifers were euthanized bet ween PBD 31 and PBD 48, and tissues were collected for virologic and p athologic examination. All but 1 heifer inoculated on PBD 21 remained pregnant after BTV inoculation. A cystic corpus luteum was found in th e ovary of the nonpregnant heifer, but BTV was not isolated from the r eproductive tract of this heifer. Three of the inoculated heifers that remained pregnant showed mild multifocal areas of perivascular lympho cytic infiltration in the ovary. BTV was reisolated from spleen and pr escapular and peribronchial lymph nodes 10 days after inoculation from 3 of the 4 BTV-seronegative heifers. BTV was also reisolated from the uterus of 1 of the heifers that remained pregnant, but microscopic le sions were not found in this organ.