Search

Background: A mycovirus previously identified in brown discolored fruiting bodies of the cultivated mushroom Flammulina velutipes was characterized. We tentatively named the virus the F. velutipes browning virus (FvBV)., Results: Purified FvBV particles contained two dsRNA genomes (dsRNA1 and 2). The complete sequence of dsRNA1 was 1,915 bp long, containing a single open reading frame (ORF) that encoded 580 amino acids of a putative 66-kDa RNA-dependent RNA polymerase (RdRp). dsRNA2 was 1,730 bp long containing a single ORF encoding 541 amino acids of a putative 60-kDa coat protein (CP1). Phylogenetic analysis of the RdRp sequences revealed FvBV to be a Partitivirus, most closely related to Chondrostereum purpureum cryptic virus. An RT-PCR assay was developed for the amplification of a 495-bp cDNA fragment from dsRNA encoding the CP1. When wild F. velutipes isolated from various parts of Japan were examined by RT-PCR assay, three isolates from the central region of Japan contained FvBV. One wild strain infected with FvBV was isolated in Nagano prefecture, where brown discoloration of white cultivated strains has occurred. Fruiting bodies produced by virus-harboring and virus-free F. velutipes were compared., Conclusions: Cap color of the fruiting bodies of F. velutipes that contained Partitivirus FvBV was darker than FvBV-free fruiting bodies. The use of RT-PCR enabled association of FvBV and dark brown color of the fruiting body produced by F. velutipes strains.

One hundred fourteen field isolates of the Ibaraki virus (IBAV), a member of the epizootic hemorrhagic disease virus serotype 2 (EHDV-2), were isolated from blood samples of affected and apparently healthy cattle and Culicoides biting midges and from blood samples of dams and internal organs of aborted fetuses during an outbreak of Ibaraki disease in the southern part of Japan in 1997. In this outbreak, 242 cattle showed typical symptoms of the disease, and several hundred dams had miscarriages or stillbirths. The viruses that induced typical Ibaraki disease and reproductive problems among cattle were identical and were antigenically closely related to but distinct from previous isolates of IBAV and EHDV-2. The virus was considered to be a putative agent of this outbreak. Reverse transcription-PCR based on segment 3 of the RNA genome of EHDV-2 and restriction fragment length polymorphism analysis of the PCR products were conducted to compare the genomes of the viruses. The results suggested that the virus isolated in 1997 was a variant of IBAV and might be exotic.

Various combinations of G type and P type were observed in 76 bovine rotavirus (BRV) strains isolated from 235 diarrheal calves in three prefectures of Japan in 1992-1994. The most prevalent combination was G6:P5 (46/76, 60.5%), followed by G10:P11 (13/76, 17.1%), G6:P11 (7/76, 9.2%) and G10:P5 (5/76, 6.6%). No G6:P1 strain of BRV was recognized from the isolates in the present study, though this type of BRV is well known as a suitable vaccine strain against BRV infection.