Evidence of reduced viremia, pathogenicity and vector competence in a re-emerging European strain of bluetongue virus serotype 8 in sheep

Flannery, J.; Sanz-Bernardo, B.; Ashby, M.; Brown, H.; Carpenter, S.; Cooke, L.; Corla, A.; Frost, L.; Gubbins, S.; Hicks, H.; Qureshi, M.; Rajko-Nenow, P.; Sanders, C.; Tully, M.; Breard, E.; Sailleau, C.; Zientara, S.; Darpel, K.; Batten, C.

doi:10.1101/469460

bioRxiv · 10.1101/469460

Evidence of reduced viremia, pathogenicity and vector competence in a re-emerging European strain of bluetongue virus serotype 8 in sheep

Flannery, J.·Sanz-Bernardo, B.·Ashby, M.·Brown, H.·Carpenter, S.·Cooke, L.·Corla, A.·Frost, L.·Gubbins, S.·Hicks, H.·Qureshi, M.·Rajko-Nenow, P.·Sanders, C.·Tully, M.·Breard, E.·Sailleau, C.·Zientara, S.·Darpel, K.·Batten, C.

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Abstract

The outbreak of bluetongue virus (BTV) serotype 8 (BTV-8) during 2006-2009 in Europe was the most costly epidemic of the virus in recorded history. In 2015, a BTV-8 strain re-emerged in France which has continued to circulate since then. To examine anecdotal reports of reduced pathogenicity and transmission efficiency, we investigated the infection kinetics of a 2007 UK BTV-8 strain alongside the re-emerging BTV-8 strain isolated from France in 2017. Two groups of eight BTV-naive British mule sheep were inoculated with 5.75 log10TCID50 ml-1 of either BTV-8 strain. BTV RNA was detected by 2 dpi in both groups with peak viremia occurring between 5-9 dpi. A significantly greater amount of BTV RNA was detected in sheep infected with the 2007 strain (6.0-8.8 log10 genome copies mL-1) than the re-emerging BTV-8 strain (2.9-7.9 log10 genome copies mL-1). All infected sheep developed BTV-specific antibodies by 9 dpi. BTV was isolated from 2 dpi to 12 dpi for 2007 BTV-8-inoculated sheep and from 5 to 10 dpi for sheep inoculated with the remerging BTV-8. In Culicoides sonorensis feeding on the sheep over the period 7-12 dpi, vector competence was significantly higher for the 2007 strain than the re-emerging strain. Both the proportion of animals showing moderate (as opposed to mild or no) clinical disease (6/8 vs 1/8) and the overall clinical scores (median 5.25 vs 3) were significantly higher in sheep infected with the 2007 strain, compared to those infected with the re-emerging strain. However, one sheep infected with the re-emerging strain was euthanized at 16 dpi having developed severe lameness. This highlights the potential of the re-emerging BTV-8 to still cause illness in naive ruminants with concurrent costs to the livestock industry.\n\nSummaryThe re-emerging Bluetongue virus serotype 8 still presents a threat to naive ruminants in Europe despite reduced virulence

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Flannery, J., Sanz-Bernardo, B., Ashby, M., Brown, H., Carpenter, S., Cooke, L., Corla, A., Frost, L., Gubbins, S., Hicks, H., Qureshi, M., Rajko-Nenow, P., Sanders, C., Tully, M., Breard, E., Sailleau, C., Zientara, S., Darpel, K., Batten, C.. 2018-11-19. Evidence of reduced viremia, pathogenicity and vector competence in a re-emerging European strain of bluetongue virus serotype 8 in sheep. https://doi.org/10.1101/469460

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