The True Host/s of Picobirnaviruses

Abstract

Picobirnaviruses (PBVs) are bisegmented double-stranded RNA viruses that have been detected in a wide variety of animal species including invertebrates and in environmental samples. Since PBVs are ubiquitous in feces/gut contents of humans and other animals with or without diarrhea, they were considered as opportunistic enteric pathogens of mammals and avian species. However, the virus remains to be propagated in animal cell cultures, or in gnotobiotic animals. Recently, the classically defined prokaryotic motif, the ribosomal binding site sequence, has been identified upstream of putative open reading frame/s in PBV and PBV-like sequences from humans, various animals, and environmental samples, suggesting that PBVs might be prokaryotic viruses. On the other hand, based on the detection of some novel PBV-like RNA-dependent RNA polymerase sequences that use the alternative mitochondrial genetic code (that of mold or invertebrates) for translation, and principal component analysis of codon usage bias for these sequences, it has been proposed that PBVs might be fungal viruses with a lifestyle reminiscent of mitoviruses. These contradicting observations warrant further studies to ascertain the true host/s of PBVs, which still remains controversial. In this minireview, we have focused on the various findings that have raised a debate on the true host/s of PBVs.

Understanding the Genetic Diversity of Picobirnavirus: A Classification Update Based on Phylogenetic and Pairwise Sequence Comparison Approaches

“…There has been an attempt to further classify species by virtue of the infected host (e.g., human picobirnavirus, rabbit picobirnavirus, etc. ), but given the ability to readily jump from one species to the next, this is clearly inaccurate [ 11 , 12 ]. Likewise, PBV strains derived from various animals are widely distributed throughout the phylogenetic tree, again demonstrating the lack of a continuous spectrum of viruses linked to a particular host [ 3 , 4 ].…”

Molecular Epidemiology and Characterization of Picobirnavirus in Wild Deer and Cattle from Australia: Evidence of Genogroup I and II in the Upper Respiratory Tract

“…Surprisingly, the library_D5 showed sequences for nine different GI clones. This high number of PBV contigs per sample is perhaps not surprising, given the extreme sequence diversity displayed by genogroup 1 PBVs in mammals [ 19 , 27 , 28 ]. However, there is also a possibility that this finding might be due to contamination of the blood with faeces strains.…”

“…From the 71 deer that both blood and faeces were collected and screened by PCR, serum/faeces-positive amplification was found only for PBV GI, with identical sequences found in one of them (N308). Given the extreme sequence diversity within the PBV GI, which has been reported previously [ 19 , 27 , 28 ], a more complete analysis of this genogroup might be found if future studies were to use a more long-read sequencing platform such as the Oxford nanopore technology [ 42 ].…”

“…No amplification of PBV sequences was detected in the lung or spleen, suggesting the absence of chronic systemic infection in the wild deer sampled for this study. Since PBVs have been mostly detected in faeces/gut contents of animals and humans with or without diarrhoea, they were considered as opportunistic enteric pathogens of mammals [ 4 , 28 ]. In fact, the detection of identical PBV in the trachea and nasal swabs of the same animal, with no amplification in the lung, may indicate an active replication and infection of the upper respiratory tract.…”

“…Interspecies transmission events, including zoonoses, have been proposed for PBV GI [ 4 , 5 , 11 , 19 , 26 ], based on sequence identities and phylogenetic analysis; however, the use of partial gene segment-2 sequences in several of these studies make these findings inconclusive. Moreover, until the true host/s of PBVs are proven, caution should be exercised when interpreting PBV interspecies transmission events [ 28 ].…”