Vector competence is strongly affected by a small deletion or point mutations in bluetongue virus

Abstract

Background: Transmission of vector-borne virus by insects is a complex mechanism consisting of many different processes; viremia in the host, uptake, infection and dissemination in the vector, and delivery of virus during bloodfeeding leading to infection of the susceptible host. Bluetongue virus (BTV) is the prototype vector-borne orbivirus (family Reoviridae). BTV serotypes 1-24 (typical BTVs) are transmitted by competent biting Culicoides midges and replicate in mammalian (BSR) and midge (KC) cells. Previously, we showed that genome segment 10 (S10) encoding NS3/NS3a protein is required for virus propagation in midges. BTV serotypes 25-27 (atypical BTVs) do not replicate in KC cells. Several distinct BTV26 genome segments cause this so-called 'differential virus replication' in vitro. Methods: Virus strains were generated using reverse genetics and their growth was examined in vitro. The midge feeding model has been developed to study infection, replication and disseminations of virus in vivo. A laboratory colony of C. sonorensis, a known competent BTV vector, was fed or injected with BTV variants and propagation in the midge was examined using PCR testing. Crossing of the midgut infection barrier was examined by separate testing of midge heads and bodies. Results: A 100 nl blood meal containing ±10 5.3 TCID 50 /ml of BTV11 which corresponds to ±20 TCID 50 infected 50% of fully engorged midges, and is named one Midge Alimentary Infective Dose (MAID 50). BTV11 with a small in-frame deletion in S10 infected blood-fed midge midguts but virus release from the midgut into the haemolymph was blocked. BTV11 with S1[VP1] of BTV26 could be adapted to virus growth in KC cells, and contained mutations subdivided into 'corrections' of the chimeric genome constellation and mutations associated with adaptation to KC cells. In particular one amino acid mutation in outer shell protein VP2 overcomes differential virus replication in vitro and in vivo. Conclusion: Small changes in NS3/NS3a or in the outer shell protein VP2 strongly affect virus propagation in midges and thus vector competence. Therefore, spread of disease by competent Culicoides midges can strongly differ for very closely related viruses.

Letea Virus: Comparative Genomics and Phylogenetic Analysis of a Novel Reassortant Orbivirus Discovered in Grass Snakes (Natrix natrix)

“…Reoviridae is a very successful family of segmented dsRNA viruses, having wide host ranges across various econiches. The family's repertoire of evolutionary strategies also includes deletion [82,83], gene duplication and concatemerisation [9,84,85]. These strategies were also observed previously in aquareoviruses [86], rotaviruses [87], phytoreoviruses [88] and even in a cross-family heterologous recombinant virus containing reovirus genomic components [89].…”

Heterologous Combination of ChAdOx1 and MVA Vectors Expressing Protein NS1 as Vaccination Strategy to Induce Durable and Cross-Protective CD8+ T Cell Immunity to Bluetongue Virus

“…This reduction of viremia not only prevents the development of clinical signs in the immunized animals but may also reduce viral acquisition by Culicoides bites. Experimental infections of Culicoides sonorensis with BTV-11 and BTV-1 infected blood showed that the efficiency of infection of midges was dose-dependent and the 50% Midge Alimentary Infective Dose (MAID50) was estimated to a blood meal titer around 2 × 10 5 TCID50/mL [ 62 , 63 ]. In the case of BTV-4M, a virus titer between 10 5 and 10 6 TCID50 is enough to ensure BTV infection rates of 100% for C. imicola and ~83% for C. obsoletus / scoticus [ 64 ].…”

A protective bivalent vaccine against Rift Valley fever and bluetongue

“…Although the viremia was not abrogated in the immunized sheep, the titers of virus found in two out of three sheep were 10 3 PFU/ml or lower. Experimental infections of Culicoides sonorensis with BTV-11 and BTV-1 infected blood showed that the efficiency of infection of midges was dose-dependent and the 50% Midge Alimentary Infective Dose (MAID 50 ) was roughly calculated to a blood meal titer of ±2 × 10 5 and ±10 6 Median Tissue Culture Infectious Dose (TCID 50 )/ml for BTV-11 and BTV-1, respectively 43 , 44 . According to these experimental infections, the level of virus detected in the blood of the MVA-GnGc-NS1-vaccinated sheep was 200 times lower than the minimal dose required for the insect vector infection, not being sufficient to infect midges and then avoiding the transmission of the virus.…”