Molecular Characterization Of Novel Orthoreoviruses Isolated In Malaysia

Abstract

Isolation of Kampar virus (KamV) and Melaka virus (MelV) from patients with acute respiratory syndrome suggest new pathogenic viruses emerging. KamV and MelV had been shown to be new members closely related to the Pulau virus (PulV) and Nelson Bay virus (NBV). PulV and NBV are mammalian fusogenic orthoreovirus which are isolated from fruit bats, Pteropus hypomelanus (Malaysia) and Pteropus poliocephalus (Australia), respectively. All four viruses are Orthoreovirus from the Reoviridae family, which contains a ten-segmented double-stranded RNA genome within an icosahedral, non-enveloped, double layer protein capsid. So far, only the S-class segments and corresponding -proteins of these mammalian fusogenic orthoreoviruses have been sequenced and analyzed. Single primer amplification technique was utilized to characterize the L- and M- class segments of KamV, PulV and MelV at the sequence level. The complete nucleotide sequence of the L- and M- class gene segments and their respective deduced amino acid sequences of KamV, MelV and PulV were studied in detail. L1, L2 and L3 segments (3896, 3832, 3954 base pairs, respectively) encode C, B and A proteins (1286, 1259, 1291 amino acids, respectively). M1, M2 and M3 segments (2295, 2028, 1896 base pairs, respectively) encode A, B and NS proteins (730, 675, 631 amino acids, respectively). Conserved motifs of avian reoviruses and mammalian reoviruses were found in KamV, PulV, MelV, indicating similar protein functionality. Phylogenic tree analysis showed possible segment reassortment in S- class segments among KamV, MelV and PulV. The M2 segments of the three viruses, which encode viral outer capsid protein, produce phylogenetic trees of different topology from M1 and M3 segments. This may be due to high selective mutation pressure acting on the M2 segment in order for the viruses to adapt to a different host. Similar topology of phylogenetic tree was observed in the L- class segments, indicating that no reassortment had occurred. Based on S- segments and - proteins of the three mammalian fusogenic orthoreoviruses, it can be concluded that a new genetic lineage of Nelson Bay Orthoreovirus species is co-circulating in the population. KamV, PulV and MelV are novel orthoreoviruses that diverged away from NBV. Expression of C proteins of these three fusogenic mammalian orthoreoviruses show cross reactivity with each other, but not with NBV.