Transplacental transmission of field and rescued strains of BTV-2 and BTV-8 in experimentally infected sheep

Abstract

Transplacental transmission of bluetongue virus has been shown previously for the North European strain of serotype 8 (BTV-8) and for tissue culture or chicken egg-adapted vaccine strains but not for field strains of other serotypes. In this study, pregnant ewes (6 per group) were inoculated with either field or rescued strains of BTV-2 and BTV-8 in order to determine the ability of these viruses to cross the placental barrier. The field BTV-2 and BTV-8 strains was passaged once in Culicoides KC cells and once in mammalian cells. All virus inoculated sheep became infected and seroconverted against the different BTV strains used in this study. BTV RNA was detectable in the blood of all but two ewes for over 28 days but infectious virus could only be detected in the blood for a much shorter period. Interestingly, transplacental transmission of BTV-2 (both field and rescued strains) was demonstrated at high efficiency (6 out of 13 lambs born to BTV-2 infected ewes) while only 1 lamb of 12 born to BTV-8 infected ewes showed evidence of in utero infection. In addition, evidence for horizontal transmission of BTV-2 between ewes was observed. As expected, the parental BTV-2 and BTV-8 viruses and the viruses rescued by reverse genetics showed very similar properties to each other. This study showed, for the first time, that transplacental transmission of BTV-2, which had been minimally passaged in cell culture, can occur; hence such transmission might be more frequent than previously thought.

Virological, immunological and pathological findings of transplacentally transmitted bluetongue virus serotype 1 in IFNAR1-blocked mice during early and mid gestation

“…These results were concorded with earlier findings in non-pregnant ewes and goats infected with BTV-8 13,16 . Pregnant ewes were inoculated with either field or rescued strains of BTV-2 and BTV-8 resulted in seroconvertion by 6 dpi and antibody levels reached the diagnostic threshold level by 10 dpi and antibodies levels were maintained up to 28 dpi 46 . The significantly increased antibody levels were well correlated with antigenic stimulation resulted in proliferation of CD4 + and CD8 + T lymphocytes in spleen and PBMCs, and germinal centers formation with proliferation of B cell areas in lymph nodes and spleen of dams was noticed led to high humoral immune response.…”

Assessment of listing and categorisation of animal diseases within the framework of the Animal Health Law (Regulation (EU) No 2016/429): bluetongue

“…Oral BTV infection of both ruminant livestock and wild or zoo carnivores has been described, including infection of calves via the feeding of infective colostrum (Alexander et al., ; Mayo et al., ) and experimentally via cultured viruses or urine from an experimentally infected sheep. At least some BT strains (including members of serotypes 1, 2 and 8) can be transmitted directly between ruminants in close contact (van der Sluijs et al., ; Rasmussen et al., ; van der Sluijs et al., ). The mechanisms of contact transmission are still uncertain.…”

Bluetongue Virus in wild ruminants in Europe: Concerns and facts, with a brief reference to bluetongue in cervids in Greece during the 2014 outbreak

“…Additionally, during the parturition period, a direct contamination or digestion of contaminated placental or foetal tissue may lead to infection and disease of individual animals (De Clercq et al, 2008;Menzies et al, 2008). Finally, transmission of the virus to pregnant females may lead to transplacental infections, resulting in foetal deaths, stillbirths or births of neonates that would die in their early life (Osburn, 1994;Mayo et al, 2010;Rasmussen et al, 2013;van der Sluijs et al, 2013).…”