Open Access Research

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

Lasse Dam Rasmussen1, Giovanni Savini2, Alessio Lorusso2, Anna Bellacicco2, Massimo Palmarini34, Marco Caporale234, Thomas Bruun Rasmussen1, Graham J Belsham1 and Anette Bøtner1*

Author Affiliations

1 National Veterinary Institute, Technical University of Denmark, 4771 Kalvehave, Lindholm, Denmark

2 Istituto Zooprofilattico Sperimentale dell’Abruzzo e Molise “G. Caporale”, G. Caporale, via Campo Boario, Teramo 64100, Italy

3 MRC Centre for Virus Research, Institute of Infection, Immunity and Inflammation, University of Glasgow, 464 Bearsden Road, Glasgow G61 1QH, Scotland, UK

4 College of Medical, Veterinary and Life Sciences, University of Glasgow, 464 Bearsden Road, Glasgow G61 1QH, Scotland, UK

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Veterinary Research 2013, 44:75  doi:10.1186/1297-9716-44-75

Published: 5 September 2013

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.