Epizootology and experimental infection of Yokose virus in bats

Mutations in the 3' non-coding region of a no-known vector flavivirus Yokose virus increased its replication ability in mosquito C6/36 cells

Yokose virus (YOKV) is a bat-associated no-known vector flavivirus group member. We investigated the replication ability of YOKV in mosquito-derived C6/36 cells. YOKV grew in C6/36 cells, but its kinetics of YOKV was markedly slower than those of other mosquito-borne flaviviruses. Transmission electron microscopy indicated an extremely small number of viral particles in YOKV-infected C6/36 cells. Mosquito-borne Japanese encephalitis virus prM-E-bearing chimeric YOKV failed to propagate efficiently in C6/36 cells. We isolated C6/36-adapted YOKV and identified nucleotide mutations in the adapted YOKV. Mutations detected in the 3' non-coding region of the adapted YOKV were critical for the enhanced proliferation ability of the virus. Moreover, the growth of the original and adapted YOKV in C6/36 cells was remarkably increased by shifting the culture temperature from 28 to 36 °C. Thus, our results demonstrate the potential of YOKV to propagate in mosquito cells and support its classification as a mosquito-borne flavivirus.

Update on Potentially Zoonotic Viruses of European Bats

Bats have been increasingly gaining attention as potential reservoir hosts of some of the most virulent viruses known. Numerous review articles summarize bats as potential reservoir hosts of human-pathogenic zoonotic viruses. For European bats, just one review article is available that we published in 2014. The present review provides an update on the earlier article and summarizes the most important viruses found in European bats and their possible implications for Public Health. We identify the research gaps and recommend monitoring of these viruses.

Genetic diversity of the Yokose virus, XYBX1332, isolated from bats (Myotis daubentonii) in China

BACKGROUND

Yokose virus was first isolated from bats (Miniopterus fuliginosus) collected in Yokosuka, Japan, in 1971, and is a new member of the family Flaviviridae, genus Flavivirus. In this study, we isolated a Yokose virus from a serum sample of Myotis daubentonii (order Chiroptera, family Vespertilionidae) collected in Yunnan province, China in 2013.

METHODS

The serum specimens of bat were used to inoculate in BHK-21 and Vero E6 cells for virus isolation. Then the viral complete genome sequence was obtained and was used for phylogenetic analysis performed by BEAST software package.

RESULTS

The virus was shown to have cytopathic effects in mammalian cells (BHK-21 and Vero E6). Genome sequencing indicated that it has a single open reading frame (ORF), with a genome of 10,785 nucleotides in total. Phylogenetic analysis of the viral genome suggests that XYBX1332 is a Yokose virus (YOKV) of the genus Flavivirus. Nucleotide and amino acid homology levels of the ORF of XYBX1332 and Oita-36, the original strain of YOKV, were 72 and 82%, respectively. The ORFs of XYBX1332 and Oita-36 encode 3422 and 3425 amino acids, respectively. In addition, the non-coding regions (5'- and 3'-untranslated regions [UTRs]) of these two strains differ in length and the homology of the 5'- and 3'-UTRs was 81.5 and 78.3%, respectively.

CONCLUSION

The isolation of YOKV (XYBX1332) from inland China thousands of kilometers from Yokosuka, Japan, suggests that the geographical distribution of YOKV is not limited to the islands of Japan and that it can also exist in the inland areas of Asia. However, there are large differences between the Chinese and Japanese YOKV strains in viral genome.

A Review of Flaviviruses that Have No Known Arthropod Vector

Most viruses in the genus Flavivirus are horizontally transmitted between hematophagous arthropods and vertebrate hosts, but some are maintained in arthropod- or vertebrate-restricted transmission cycles. Flaviviruses maintained by vertebrate-only transmission are commonly referred to as no known vector (NKV) flaviviruses. Fourteen species and two subtypes of NKV flaviviruses are recognized by the International Committee on Taxonomy of Viruses (ICTV), and Tamana bat virus potentially belongs to this group. NKV flaviviruses have been isolated in nature almost exclusively from bats and rodents; exceptions are the two isolates of Dakar bat virus recovered from febrile humans and the recent isolations of Sokoluk virus from field-collected ticks, which raises questions as to whether it should remain classified as an NKV flavivirus. There is evidence to suggest that two other NKV flaviviruses, Entebbe bat virus and Yokose virus, may also infect arthropods in nature. The best characterized bat- and rodent-associated NKV flaviviruses are Rio Bravo and Modoc viruses, respectively, but both have received limited research attention compared to many of their arthropod-infecting counterparts. Herein, we provide a comprehensive review of NKV flaviviruses, placing a particular emphasis on their classification, host range, geographic distribution, replication kinetics, pathogenesis, transmissibility and molecular biology.

Experimental inoculation of Artibeus jamaicensis bats with dengue virus serotypes 1 or 4 showed no evidence of sustained replication

Dengue is the most important mosquito-borne viral disease to humans. Bats are potential reservoirs for flaviviruses, including dengue virus (DENV). In this work, Artibeus jamaicensis bats were inoculated with two serotypes of DENV using different routes. For experimental inoculations (EI) 1 and 2, bats were inoculated subcutaneously or intraperitoneally with DENV-4; for EI-3 bats were inoculated intraperitoneally with DENV-1. Mock inoculated bats were kept as controls. In EI-4, bats were bitten by Aedes aegypti mosquitoes infected with DENV-1 or 4. Reverse transcription-polymerase chain reaction assays in plasma and spleen tissue collected from Day 1 to Days 9-17 after inoculation failed to reveal the presence of viral RNA in any of the samples. No evidence of circulating NS1 or specific anti-DENV IgG was detected in the plasma of the inoculated bats. These results indicate that A. jamaicensis bats are incapable of sustaining dengue virus replication and are unlikely to act as reservoirs for this virus.

Experimental infection of Artibeus intermedius bats with serotype-2 dengue virus

Dengue fever is caused by a flavivirus that primarily infects humans and Aedes sp. mosquitoes. However, viral replication in wild animals other than non-human primates has been scarcely studied. In this report, the susceptibility of Artibeus intermedius frugivorous bat to serotype-2 dengue virus (DENV-2) infection was tested. Twenty-three bats were intraperitoneally inoculated with different viral loads of DENV-2 (New Guinea-C strain). Forty-three percent of the infected bats developed bruises on the chest or on the wings. Histological analyses showed structural alterations in the spleen and bleeding in liver and intestine, but the virus was not detected by RT-PCR in any of the analyzed tissues, and it was found in only one bat (kidney) by semi-nested RT-PCR. In sera, the viral RNA was detected by semi-nested RT-PCR in 39% of bats, but only 8% of bats seroconverted. Overall, these data indicate that DENV-2 replicates poorly in these bats, suggesting they are not suitable hosts to this virus.

Detection of a new bat gammaherpesvirus in the Philippines

A new bat herpesvirus was detected in the spleen of an insectivorous bat (Hipposideros diadema, family Hipposideridae) collected on Panay Island, the Philippines. PCR analyses were performed using COnsensus-DEgenerate Hybrid Oligonucleotide Primers (CODEHOPs) targeting the herpesvirus DNA polymerase (DPOL) gene. Although we obtained PCR products with CODEHOPs, direct sequencing using the primers was not possible because of high degree of degeneracy. Direct sequencing technology developed in our rapid determination system of viral RNA sequences (RDV) was applied in this study, and a partial DPOL nucleotide sequence was determined. In addition, a partial gB gene nucleotide sequence was also determined using the same strategy. We connected the partial gB and DPOL sequences with long-distance PCR, and a 3741-bp nucleotide fragment, including the 3′ part of the gB gene and the 5′ part of the DPOL gene, was finally determined. Phylogenetic analysis showed that the sequence was novel and most similar to those of the subfamily Gammaherpesvirinae.