Transplacental transmission of Bluetongue virus serotype 8 in ewes in early and mid gestation.

The ability of Bluetongue virus serotype 8 (BTV-8) originating from the 2006 European outbreak to cross the ovine placenta during early and mid gestation was investigated in two separate experiments. In the first experiment, 16 ewes were infected with BTV-8 at 70-75 days gestation. The foetuses were collected at 18-19 days after infection (dpi). BTV-8 could be isolated from at least two organs of 19 out of 40 lambs and from 11 out of 16 infected ewes. In the second experiment, 20 BTV-8 infected ewes in early gestation (day 40-45) were euthanized at 10 days (10 ewes) or 30 days (10 ewes) after infection. The presence of BTV could be demonstrated in two foetuses from two ewes at 10 dpi and in 4 foetuses from four ewes at 30 dpi. The main pathological findings in the foetuses in mid gestation were meningo-encephalitis and vacuolation of the cerebrum. In the foetuses early at gestation, haemorrhages in various foetal tissues and necrosis and haemorrhages in the placentomes were found. These experiments demonstrate for the first time the presence of infectious BTV in lamb foetuses at different stages of gestation, combined with a difference in transmission rate depending on the gestation stage. The high transmission rate found at mid term gestation (69%) makes our model very suitable for further research into the mechanisms of transplacental transmission and for research into the reduction of this route of transmission through vaccination.