Abstract
In 2011, Bluetongue virus serotype 14 (BTV-14) was detected in Russia during routine surveillance, and was subsequently found in a number of European countries. The strain had high sequence similarity to a BTV-14 vaccine strain. We aimed to determine the risk of this BTV-14 strain causing disease in a UK sheep breed. Four Poll Dorset sheep were infected with a Polish isolate of BTV-14 and infection kinetics were monitored over 28 days. BTV RNA was detected in EDTA blood by 4 days post-infection (dpi) and remained detectable at 28 days post-infection (dpi). Peak viraemia occurred at 6 and 7 dpi with Ct values ranging between 24.6 and 27.3 in all infected animals. BTV antibodies were detected by 10 dpi using a commercial ELISA and neutralising antibodies were detected from 10 dpi. BTV was isolated between 6 and 12 dpi. All infected sheep developed mild clinical signs such as reddening of conjunctiva and mucosal membranes, with one sheep demonstrating more overt clinical signs. Two uninoculated control animals remained clinically healthy and did not have detectable BTV RNA or antibodies. The overall mild clinical symptoms caused by this BTV-14 in this highly susceptible sheep breed were in accordance with the asymptomatic infections observed in the affected countries.
Highlights
Bluetongue virus (BTV) of the genus Orbivirus, family Reoviridae, is transmitted between vertebrate hosts by biting midges (Culicoides spp.) [1] and causes the economically important disease known as “bluetongue”
BTV segment-2 encodes the most variable BTV protein (VP2) which is the primary determinant of serotype [2,3] of which 24 classical serotypes exist (BTV-1 to BTV-24) while more recently, several atypical serotypes (BTV-25 to BTV-27 and onwards) have been discovered [4,5,6]
We aimed to determine the infection kinetics of this Bluetongue virus serotype 14 (BTV-14) strain in Poll Dorset sheep to determine the risk to a UK sheep breed and enhance our understanding of BTV pathogenesis for specific strains
Summary
Bluetongue virus (BTV) of the genus Orbivirus, family Reoviridae, is transmitted between vertebrate hosts by biting midges (Culicoides spp.) [1] and causes the economically important disease known as “bluetongue”. BTV is a serologically and genetically diverse virus with a genome comprising 10 double-stranded RNA segments that encode several structural and nonstructural proteins. Bluetongue occurs primarily in sheep ( European breeds) and in species of deer and cattle. Multivalent modified live vaccines have been available for many years [10], only inactivated vaccines are approved for use within the EU [11] due to the risk of vaccine transmission and the potential for clinical disease in highly susceptible sheep breeds [12,13,14]. Despite the development of novel vaccine candidates which can be modified for a number of BTV serotypes and are transmissible [15], their commercial uptake has been minimal far
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