Detection, discrimination and quantitation of 22 bluetongue virus serotypes using real-time RT-PCR with TaqMan MGB probes

Multiplexed serotype-specific real time PCR assays - a valuable tool to support large scale surveillance for bluetongue virus infection

In the last decade, real time PCR has been increasingly adopted for bluetongue diagnosis with both broadly reactive and serotype-specific assays widely used. The use of these assays and nucleic acid sequencing technologies have enhanced bluetongue virus detection, resulting in the identification of a number of new serotypes. As a result, 27 different serotypes are officially recognised and at least 3 more are proposed. Rapid identification of the virus serotype is essential for matching of antigens used in vaccines and to undertake surveillance and epidemiological studies to assist risk management. However, it is not uncommon for multiple serotypes to circulate in a region either concurrently or in successive years. It is therefore necessary to have a large suite of assays available to ensure that the full spectrum of viruses is detected. Nevertheless, covering a large range of virus serotypes is demanding from both a time and resource perspective. To overcome these challenges, real time PCR assays were optimised to match local virus strains and then combined in a panel of quadriplex assays, resulting in 3 assays to detect 12 serotypes directly from blood samples from cattle and sheep. These multiplex assays have been used extensively for bluetongue surveillance in both sentinel animals and opportunistically collected samples. A protocol to adapt these assays to capture variations in local strains of bluetongue virus and to expand the panel is described. Collectively these assays provide powerful tools for surveillance and the rapid identification of bluetongue virus serotypes directly from animal blood samples. This article is protected by copyright. All rights reserved.

BlueTYPE - A low density TaqMan-RT-qPCR array for the identification of all 24 classical Bluetongue virus serotypes

Bluetongue virus is a double-stranded RNA virus with 10 genome segments. VP2 is the primary target for neutralising antibodies and defines the serotype. Today, more than 27 serotypes are known, 24 are defined as "classical", and new serotypes are under investigation. Beside group-specific BTV-genome detection, additional serotype characterisation is important for disease control and epidemiological investigations. Therefore, a low-density RT-qPCR array representing a panel of group- and serotype-specific assays, was combined with an internal control system. For BTV serotype detection, both published and the newly developed in-house PCR systems were combined. The different primer-probe-mixes were placed in advance into a 96-well plate stored at -20 °C until use. At the time of analysis, the only template RNA was added to the prepared primer-probe-mixes and heat denatured at 95 °C for 3 min. After cooling, the master mix was added to each well and the PCR could run for around 90 min. The presented low-density TaqMan-RT-qPCR array enables fast and precise characterisation of the BTV serotype in clinical cases. Furthermore, mixed infections can be easily identified. In addition, the newly developed low-density RT-qPCR-array can easily be adapted to novel BTV strain variants or extended for relevant differential diagnosis.

Development and Evaluation of Real Time RT-PCR Assays for Detection and Typing of Bluetongue Virus

Bluetongue virus is the type species of the genus Orbivirus, family Reoviridae. Bluetongue viruses (BTV) are transmitted between their vertebrate hosts primarily by biting midges (Culicoides spp.) in which they also replicate. Consequently BTV distribution is dependent on the activity, geographic distribution, and seasonal abundance of Culicoides spp. The virus can also be transmitted vertically in vertebrate hosts, and some strains/serotypes can be transmitted horizontally in the absence of insect vectors. The BTV genome is composed of ten linear segments of double-stranded (ds) RNA, numbered in order of decreasing size (Seg-1 to Seg-10). Genome segment 2 (Seg-2) encodes outer-capsid protein VP2, the most variable BTV protein and the primary target for neutralising antibodies. Consequently VP2 (and Seg-2) determine the identity of the twenty seven serotypes and two additional putative BTV serotypes that have been recognised so far. Current BTV vaccines are serotype specific and typing of outbreak strains is required in order to deploy appropriate vaccines. We report development and evaluation of multiple 'TaqMan' fluorescence-probe based quantitative real-time type-specific RT-PCR assays targeting Seg-2 of the 27+1 BTV types. The assays were evaluated using orbivirus isolates from the 'Orbivirus Reference Collection' (ORC) held at The Pirbright Institute. The assays are BTV-type specific and can be used for rapid, sensitive and reliable detection / identification (typing) of BTV RNA from samples of infected blood, tissues, homogenised Culicoides, or tissue culture supernatants. None of the assays amplified cDNAs from closely related but heterologous orbiviruses, or from uninfected host animals or cell cultures.

Emergence of a Novel Bluetongue Virus Serotype, China 2014

One hundred and twenty-six blood samples were collected from healthy sheep and goats in Xinjiang, China, during July 2014. Seventy-three samples (57.93%) were bluetongue virus (BTV) serology-positive, and 39 samples (30.95%) were BTV NS1 gene-positive. BTV strain XJ1407 was isolated from the blood of BTV NS1 gene-positive animals and sequenced. Analysis of its genome sequence suggests that XJ1407 is a novel BTV serotype.

Impaired cellular energy metabolism contributes to bluetongue-virus-induced autophagy

Bluetongue virus (BTV) has been found to trigger autophagy to favor its replication, but the underlying mechanisms have not been clarified. Here, we show that cellular energy metabolism is involved in BTV-induced autophagy. Cellular ATP synthesis was impaired by BTV1 infection, causing metabolic stress, which was responsible for activation of autophagy, since the conversion of LC3 and aggregation of GFP-LC3 (autophagy markers) were suppressed when infection-caused energy depletion was reversed via MP (metabolic substrate) treatment. The reduced virus yields with MP further supported this view. Overall, our findings suggest that BTV1-induced disruption of cellular energy metabolism contributes to autophagy, and this provides new insights into BTV-host interactions.