Chinese hamster ovary (CHO) cells manifesting striking cytopathogenic changes in culture were investigated to determine the causative agent. Electron microscopic analyses revealed viral particles of about 40 nm in diameter, displaying typical calicivirus morphology. To date, this virus, designated isolate 2117, exclusively replicates in CHO cells, achieving only moderate titres. After cloning, the coding region of 7928 nucleotides, the 39 non-coding region and the poly(A) tail were sequenced. The genome consists of three open reading frames (ORFs), with the first and second ORF having the same reading frame. The overall genomic organization as well as the nucleotide sequence of isolate 2117 is most similar to that of a recently described canine calicivirus, but also shows significant similarity to the sequences of mink calicivirus and other caliciviruses within the genus Vesivirus. In Western blots, using antibodies against the viral protease, a stable, unprocessed 3CD protein of 68 kDa was identified in homogenates of 2117-infected CHO cells. Furthermore, antibodies raised against ORF 3 reacted with the respective protein in 2117-virions, demonstrating that this predicted 9 kDa protein is a minor structural component of the virion. In addition, an RT-PCR assay was established to detect 2117 viral RNA in biological products such as foetal bovine serum, which will aid the discovery of the origin and host of the virus.
INTRODUCTIONThe isolation of caliciviruses from diverse species has been reported by many investigators. These viruses have been classified into four genera: Vesivirus, e.g. vesicular exanthema of swine virus (VESV), feline calicivirus (FCV) and San Miguel sea lion virus (SMSV); Lagovirus, e.g. rabbit haemorrhagic disease virus (RHDV) and European brown hare syndrome virus (EBHSV); the human genera Norovirus and Sappovirus (Capucci et al., 1996; Green et al., 1994Green et al., , 2000Ohlinger et al., 1990;Schaffer et al., 1980, Smith et al., 1979Studdert, 1978;Wirblich et al., 1994). In addition, caliciviruses have been isolated from mink, dog, cattle and non-human primates (Dastjerdi et al., 1999(Dastjerdi et al., , 2000Guo et al., 2001; Liu et al., 1999a;Mochizuki et al., 1993;Smith et al., 1985).In humans, caliciviruses represent the main cause of non-bacterial gastroenteritis (Clarke & Lambden, 1997b), whereas animal caliciviruses can cause vesicular lesions in swine and sea lions, respiratory illness and conjunctivitis in cats, and severe haemorrhagic liver diseases in rabbits and hares (Neill et al., 1998;Smith et al., 1973). While VESV, SMSV or FCV can easily be propagated in cell culture and cause a cytopathogenic effect within a few hours (Studdert, 1978), there is no cell culture system available for lagoviruses or human caliciviruses (Konig et al., 1998; White et al., 1996). Caliciviruses consist of non-enveloped virions 32-40 nm in diameter. Electron microscopy has revealed that several, but not all species, display typical cup-shaped surface depressions, the characteristic 'calyx' morph...