Abstract
Mammalian Orthoreoviruses (MRV) are segmented dsRNA viruses in the family Reoviridae. MRVs infect mammals and cause asymptomatic respiratory, gastro-enteric and, rarely, encephalic infections. MRVs are divided into at least three serotypes: MRV1, MRV2 and MRV3. In Europe, swine MRV (swMRV) was first isolated in Austria in 1998 and subsequently reported more than fifteen years later in Italy. In the present study, we characterized two novel reassortant swMRVs identified in one same Italian farm over two years. The two viruses shared the same genetic backbone but showed evidence of reassortment in the S1, S4, M2 segments and were therefore classified into two serotypes: MRV3 in 2016 and MRV2 in 2018. A genetic relation to pig, bat and human MRVs and other unknown sources was identified. A considerable genetic diversity was observed in the Italian MRV3 and MRV2 compared to other available swMRVs. The S1 protein presented unique amino acid signatures in both swMRVs, with unexpected frequencies for MRV2. The remaining genes formed distinct and novel genetic groups that revealed a geographically related evolution of swMRVs in Italy. This is the first report of the complete molecular characterization of novel reassortant swMRVs in Italy and Europe, which suggests a greater genetic diversity of swMRVs never identified before.
Highlights
Mammalian Orthoreoviruses (MRVs) are double-stranded RNA viruses belonging to the Reoviridae family, Spinareovirinae subfamily, Orthoreovirus genus
The novel MRV3 and MRV2 strains identified in the present study showed a remarkably different genetic constellation from all available swine MRV (swMRV), resulting from reassortant events involving the S1, S4 and M2 genes with the remaining genes that showed a common genetic backbone for both swMRV strains
The absence of data on the MRVs distribution and genetic characteristics in the animal reservoir in Europe jeopardises any conclusion regarding the epidemiology of MRV infections in pigs
Summary
Mammalian Orthoreoviruses (MRVs) are double-stranded RNA viruses belonging to the Reoviridae family, Spinareovirinae subfamily, Orthoreovirus genus. The MRV genome, of about 23,000 base pairs (bp), consists of ten gene segments divided into three Large (L) of about 3,800 bp, three Medium of about 2,200 bp (M), four Small (S) of about 1,100 bp [3]. They have a characteristic protein profile with three lambda (λ), three mu (μ) and four sigma (σ) primary translation products derived from L, M and S genes respectively, as well as additional small gene products that are encoded by polycistronic segments [2].
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