Transplacental transmission of the Italian Bluetongue virus serotype 2 in sheep

In order to study the capability of a Bluetongue virus serotype 2 (BTV-2) field isolate to cross the placental barrier, 2 groups of 5 pregnant ewes were infected with a field BTV-2 Italian strain (Group A) or with the same strain passaged once in Culicoides cells (Kc) (Group B). Following infection, EDTA-blood and serum samples were collected weekly and tested for the presence of BTV RNA/infectious virus and anti-BTV-2 antibodies, respectively. At lambing, precolostral EDTA-blood and serum samples were collected from lambs and tested as before. The lambs were then sampled as scheduled for the dams. All sheep seroconverted on day 12 post-infection (pi) and remained seropositive throughout the sampling period (day 68 pi). BTV was isolated from day 7 pi to day 14 pi in animals of Group A and from day 5 pi to day 12 pi in animals of Group B. None of the 14 lambs born had pre-colostral antibodies. Three lambs born from two ewes of Group B were viraemic at birth and in one lamb infectious virus was isolated from blood up to 11 days of age.This study proved for the first time that a single passage of BTV-2 field strain in Kc cells is able to give to BTV the ability to cross the placenta barrier and infect foetal tissues.