Whole genome characterization of a chelonian orthoreovirus strain identifies significant genetic diversity and may classify reptile orthoreoviruses into distinct species

Genetic diversity among reptilian orthoreoviruses isolated from pet snakes and lizards

Reovirus infections in reptiles are frequently detected and associated with various clinical diseases; yet, our knowledge about their genetic diversity and evolutionary relationships remains limited. In this study, we characterize at the genomic level five reptile origin orthoreovirus strains isolated from exotic snakes and lizards in Hungary and Germany. The genomic organization of the study strains was similar to that of the representative strains of reptile origin reoviruses belonging to species Reptilian orthoreovirus and Testudine orthoreovirus. Additionally, all five study strains clustered with the bush viper origin reference Reptilian orthoreovirus strain, 47/02. The nucleotide sequence divergence among strains fell from 56.64 to 99.36%. Based on genome segment constellations two well separated groups were observed, which may represent two genetic lineages of reptilian orthoreoviruses we tentatively referred here as genogroups, classifying two squamata origin strains with available whole genome sequences into genogroup I (GGI) and four strains into genogroup II (GGII). The representative GGI and GGII Reptilian orthoreovirus strains are characterized by moderate-to-high nucleotide and amino acid similarities within genogroups (range, 69.45 to 99.36% and 74.64 to 100.00%), whereas lower nucleotide and amino acid similarities (range, 56.64 to 77.24% and 54.53 to 93.85%) and different structures of the bicistronic S1 segment were found between genogroups. Further studies are needed to explore the genomic diversity among reptilian reoviruses of squamata origin; this would be critical to establish a robust classification system for these viruses and to see if interaction among members of distinct lineages may result in viable progenies with novel genetic features.

Diagnostics of Infectious Respiratory Pathogens in Reptiles

Methods for the detection of pathogens associated with respiratory disease in reptiles, including viruses, bacteria, fungi, and parasites, are constantly evolving as is the understanding of the specific roles played by various pathogens in disease processes. Some are known to be primary pathogens with high prevalence in captive reptiles, for example, serpentoviruses in pythons or mycoplasma in tortoises. Others are very commonly found in reptiles with respiratory disease but are most often considered secondary, for example, gram-negative bacteria. Detection methods as well as specific pathogens associated with upper- and lower-respiratory disease are discussed.

Genomic characterization of avian and neoavian orthoreoviruses detected in pheasants

Avian reoviruses are well-known pathogens seriously affecting the productivity of poultry industry. Game birds represent a small segment of the agricultural sector and much remained to be learnt about factors affecting productivity. Here we show that reovirus infections might occur in pheasants and demonstrate that reoviruses of pheasants are of diverse origin. The complete or coding-complete genomic sequences of two Hungarian reovirus strains, D1996/2/1 and Reo/HUN/Pheasant/216/2015, have been determined in this study. The strain D1996/2/1 was isolated in 2012 from birds with gizzard erosion, whereas the other strain was isolated in 2015 from diarrheic pheasant poults. Phylogenetic analyses showed that none of the Hungarian isolates shared common origin with a pheasant reovirus detected recently in the United States. Additionally, we found that Reo/HUN/Pheasant/216/2015 is a multi-reassortant reovirus within the species Avian orthoreovirus that shared genetic relationship with turkey reoviruses (σC), partridge reoviruses (λA, σB), and chicken reoviruses (λB, λC, μA, σA, and σNS), in the respective gene phylogenies, whereas two genes (μB and μNS) did not reveal any possible common ancestors. The other isolate, D1996/2/1, was found to be distantly related to previously described reoviruses raising the possibility that it might represent a novel orthoreovirus species or a new genogroup within the newly accepted species, Neoavian orthoreovirus. The genetic diversity among pheasant reoviruses could raise challenges for virus classification as well as for development of molecular diagnostic tools and vaccine based prevention and control measures.

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

The discovery and characterization of novel arthropod-borne viruses provide valuable information on their genetic diversity, ecology, evolution and potential to threaten animal or public health. Arbovirus surveillance is not conducted regularly in Romania, being particularly very scarce in the remote and diverse areas like the Danube Delta. Here we describe the detection and genetic characterization of a novel orbivirus (Reoviridae: Orbivirus) designated as Letea virus, which was found in grass snakes (Natrix natrix) during a metagenomic and metatranscriptomic survey conducted between 2014 and 2017. This virus is the first orbivirus discovered in reptiles. Phylogenetic analyses placed Letea virus as a highly divergent species in the Culicoides-/sand fly-borne orbivirus clade. Gene reassortment and intragenic recombination were detected in the majority of the nine Letea virus strains obtained, implying that these mechanisms play important roles in the evolution and diversification of the virus. However, the screening of arthropods, including Culicoides biting midges collected within the same surveillance program, tested negative for Letea virus infection and could not confirm the arthropod vector of the virus. The study provided complete genome sequences for nine Letea virus strains and new information about orbivirus diversity, host range, ecology and evolution. The phylogenetic associations warrant further screening of arthropods, as well as sustained surveillance efforts for elucidation of Letea virus natural cycle and possible implications for animal and human health.

Fusogenic Reoviruses and Their Fusion-Associated Small Transmembrane (FAST) Proteins

With no limiting membrane surrounding virions, nonenveloped viruses have no need for membrane fusion to gain access to intracellular replication compartments. Consequently, nonenveloped viruses do not encode membrane fusion proteins. The only exception to this dogma is the fusogenic reoviruses that encode fusion-associated small transmembrane (FAST) proteins that induce syncytium formation. FAST proteins are the smallest viral membrane fusion proteins and, unlike their enveloped virus counterparts, are nonstructural proteins that evolved specifically to induce cell-to-cell, not virus-cell, membrane fusion. This distinct evolutionary imperative is reflected in structural and functional features that distinguish this singular family of viral fusogens from all other protein fusogens. These rudimentary fusogens comprise specific combinations of different membrane effector motifs assembled into small, modular membrane fusogens. FAST proteins offer a minimalist model to better understand the ubiquitous process of protein-mediated membrane fusion and to reveal novel mechanisms of nonenveloped virus dissemination that contribute to virulence.

Isolation and complete genome characterization of novel reassortant orthoreovirus from common vole (Microtus arvalis)

A novel mammalian orthoreovirus (MRV) strain was isolated from the lung tissue of a common vole (Microtus arvalis) with Tula hantavirus infection. Seven segments (L1-L3, M2-M3, S2, and S4) of the Hungarian MRV isolate MORV/47Ma/06 revealed a high similarity with an MRV strain detected in bank vole (Myodes glareolus) in Germany. The M1 and S3 segment of the Hungarian isolate showed the closest relationship with the sequence of a Slovenian human and a French murine isolate, respectively. The highest nucleotide and amino acid identity values were above 90 and 95% in all of the comparisons to the reference sequences in GenBank, except for the S1 with a maximum of 69.6% nucleotide and 75.4% amino acid identity. As wild rodents are among the main sources of zoonotic infections, the reservoir role of these animals and zoonotic potential of rodent origin MRVs need to be further investigated.

Lineage diversification, homo- and heterologous reassortment and recombination shape the evolution of chicken orthoreoviruses

The near complete genome sequences of ten field avian orthoreovirus (ARV) strains collected from young chicken between 2002 and 2011 in Hungary have been determined in order to explore the genetic diversity and evolutionary mechanisms affecting ARVs in this region. Sequence analyses and phylogenetic calculations revealed similar geographic distribution and distinct evolution in case of eight studied strains that were closely related to the recently described Hungarian strain T1781. The remaining two strains showed the highest similarity with the US origin AVS-B. The topology of the phylogenetic trees of certain segments was affected by several potential homologous reassortment events between strains of Hungarian, Chinese and US origin. Analyzing the μB gene a possible heterologous reassortment event was identified in three Hungarian strains. Recombination events were detected in as much as a dozen cases implying that beside point mutations and reassorment this mechanism also plays an important role in the diversification of ARVs. All these mechanisms in concert may explain the reduced effectiveness of immunization using commercial vaccine strains.