Metagenomic analysis of viral diversity and a novel astroviruse of forest rodent

Astrovirus induced nonpurulent encephalomyelitis in sheep: First report from Türkiye by high-throughput sequencing

BACKGROUND

This study presents the case of non-purulent encephalomyelitis associated with astrovirus infection in a sheep from Eastern Anatolia, Türkiye.

METHODS

A necropsy was performed on a sheep showing nervous signs. Afterwards, brain tissue samples were taken and examined with histopathological, immunohistochemical and molecular techniques.

RESULTS

Neuropathologic changes included neuronal degeneration, diffuse gliosis, multifocal perivascular cuffing, neuronophagy and neuronal necrosis in the cerebrum, the cerebellum and the cervical spinal cord. Aerobic and anaerobic bacterial culture, selective culture for Listeria monocytogenes, and PCR analysis for rabies virus, tick-borne encephalitis virus, Türkiye encephalitis virus, small ruminant lentiviruses and border disease virus were negative. However, the presence of astrovirus RNA in cerebral, cerebellar and spinal cord samples was demonstrated by a pan-astrovirus RT-PCR. Immunohistochemical examinations revealed astrovirus antigens within the neuronal cytoplasm. High-throughput sequencing techniques identified the causative agent as a member of the genotype species Mamastrovirus 13 but representing a distinct genetic lineage with similarity to ovine astrovirus 1 in the open-reading frames (ORF)1ab region and muskox astrovirus in the ORF2 region.

CONCLUSION

This report provides evidence that astroviruses are potentially encephalitis-causing pathogens in ovine populations in Türkiye, featuring an astrovirus strain distinct from those previously identified in sheep.

Prevalence of Astroviruses in Different Animal Species in Poland

Astroviruses (AstVs) are small RNA viruses characterized by a high mutation rate, the ability to recombine, and interspecies transmission, which allows them to infect a multitude of hosts including humans, companion animals, and farmed animals as well as wildlife. AstVs are stable in the environment, and their transmission is usually through the fecal-oral route or via contaminated water and food. Although direct zoonotic transmission was not confirmed, interspecies transmission events have occurred or have been indicated to occur in the past between wild and domestic animals and humans. They cause large economic losses, mainly in the poultry sector, due to gastroenteritis and mortality. In young children, they are the second most common cause of diarrhea. This study involved 166 intestine samples and pools of spleen, lymph node, and kidney samples collected from 352 wild animals, 52 pigs, and 31 companion animals. Astroviruses were detected in the intestine samples and were separately detected in pools of tissue samples prepared for individual animals using a heminested RT-PCR protocol. Amplicons were subjected to Sanger sequencing, and a phylogenetic analysis of 320 nt RNA-dependent RNA polymerase (RdRp) fragments referring to known nt sequences of astroviruses was performed. Astroviral RNA was detected in the intestine samples and/or tissue pools of red foxes (nine positive intestines and six positive tissue pools), rats (two positive intestines and three positive tissue pools), a cat (one AstV detected in an intestine sample), pigs (eight positive tissue pools), and wild boars (two positive pools of spleens, kidneys, and lymph nodes). No astroviral RNA was detected in wild mustelids, dogs, or other small wild animals including rodents. A phylogenetic analysis revealed that the astroviruses detected during this study were mostly host-specific, such as porcine, canine, and rat astroviruses that were highly homologous to the sequences of reference strains. In one of two wild boars, an AstV distinct to porcine species was found with the highest nt identity to Avastroviruses, i.e., turkey astroviruses, which suggests potential cross-species transmission of the virus, as previously described. Here, we present the first detection of astroviruses in the population of wild animals, companion animals, and pigs in Poland, confirming that astroviruses are frequent pathogens circulating in animals in the field. Our study also suggests potential cross-species transmission of Avaastrovirus to wild boars; however, further molecular characterization is needed.

Evaluating the zoonotic potential of RNA viromes of rodents provides new insight into rodent-borne zoonotic pathogens in Guangdong, China

Emerging and re-emerging infectious diseases have been on the rise, with a significant proportion being zoonotic. Rodents, as the natural reservoirs of numerous diverse zoonotic viruses, pose a substantial threat to human health. To investigate the diversity of known and unknown viruses harbored by rodents in Guangdong (southern province of China), we conducted a comprehensive analysis of viral genomes through metagenomic sequencing of organs from 194 rodents. Our analysis yielded 2163 viral contigs that were assigned to 25 families known to infect a wide range of hosts, including vertebrates, invertebrates, amoebas, and plants. The viral compositions vary considerably among different organs, but not in rodent species. We also assessed and prioritized zoonotic potential of those detected viruses. Ninety-two viral species that are either known to infect vertebrates and invertebrates or only vertebrates were identified, among which 21 are considered high-risk to humans. The high-risk viruses included members of the Hantavirus, Picobirnaviruses, Astroviruses and Pestivirus. The phylogenetic trees of four zoonotic viruses revealed features of novel viral genomes that seem to fit evolutionarily into a zone of viruses that potentially pose a risk of transmission to humans. Recognizing that zoonotic diseases are a One Health issue, we approached the problem of identifying the zoonotic risk from rodent-transmitted disease in the Guangdong province by performing next-generation sequencing to look for potentially zoonotic viruses in these animals.