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Detection of feline norovirus using commercial real-time RT-PCR kit for the diagnosis of human norovirus infection

Feline noroviruses (FNoVs) are potential clinical pathogens in cats. To perform an epidemiological study of FNoV infection, it is necessary to develop a simple and effective method for virus detection. We investigated whether a commercial human NoV quantitative RT-PCR kit for the detection of human NoVs used in medical practice can be applied for FNoV detection. This kit was capable of detecting the FNoV gene regardless of the genogroup (GIV and GVI) in experimental and field samples. Based on the above findings, it is possible to detect FNoVs using human NoV tests. The relationship between FNoV infection and gastroenteritis in cats may be clarified by applying these methods to an epidemiological survey of FNoVs.

Fecal samples collected from 2 GIV FNoV-infected cats (n=30) and 8 GVI FNoV-infected cats (n=30) were randomly selected, and the viral load was measured using qRT-PCR. The correlation between the values of viral load assessed using GIV FNoVspecific or GVI FNoV-specific qRT-PCR (FNoV qRT-PCR) and commercial human norovirus detective qRT-PCR (human NoV qRT-PCR) was investigated. FNoV qRT-PCR with the specific primers and probe ( Table 1) was performed as described previously [16]. The RNA copy number was calculated following the procedure described by Fronhoffs et al. [5]. Detection of FNoV RNA using a commercial human norovirus detection kit (TaKaRa ® qPCR Norovirus (GI/GII) Typing Kit; TaKaRa Bio, Kusatsu, Japan) was carried out according to the manufacturer's protocol. Based on the results of conventional RT-PCR, the primers and probe set to detect the GII human NoV gene were used in human NoV qRT-PCR. A correlation was noted between the viral loads determined using feline NoV qRT-PCR and human NoV qRT-PCR in the samples from GIV FNoV-infected cats (Fig. 1C, r 2 =0.9598). The samples from GVI FNoV-infected cats produced similar results (Fig. 1D, r 2 =0.9756).
A total of 100 fresh fecal samples in the litter boxes and on the ground in the animal shelter were collected from cats between 2016 and 2018 in Mie Prefecture were tested by universal Caliciviridae RT-PCR using P289d/P290d primer set and the human NoV qRT-PCR ( Table 2). Thirteen samples were positive by universal Caliciviridae RT-PCR, whereas four samples were positive by the human NoV qRT-PCR. All human NoV qRT-PCR-positive samples were positive on universal Caliciviridae RT-PCR. When the PCR products were subjected to sequencing analysis as described previously [17], all samples positive on both universal Caliciviridae RT-PCR and human NoV qRT-PCR were FNoV, whereas all samples positive on only universal Caliciviridae RT-PCR were FCV. When the genogroups of 4 FNoV-positive samples were investigated using feline NoV qRT-PCR, one sample was GIV FNoV and all others were GVI FNoV.
FNoV infection in cats has been confirmed in the USA, Italy, and Japan [3,13,15]. FNoV is considered to be the cause of gastroenteritis in cats, but no clear evidence has been reported. As a reason for that there are no established methods for FNoV detection. In this study, we demonstrated that the commercial human NoV detective kit is capable of detecting FNoV.
When the primers (COG2F+ALPF/COG2R) and probe set detecting the GII human NoV gene were used for conventional RT-PCR, all FNoVs were detected regardless of the genogroup. The ALPF primer was prepared based on the gene sequence of the GIV human NoV Alphatron strain [11]. For that reason, GIV FNoV and GVI FNoV, which are phylogenetically close to the NoV Alphatron strain, can be detected using the (COG2F+) ALPF-COG2R primer set.
Even though the human NoV qRT-PCR is applied to detect the HNoV, we were able to detect the FNoV using this kit. It was unclear why the human NoV qRT-PCR was able to detect the FNoV. If ALPF is used as the primer in this kit, FNoV will be detected as with conventional PCR. However, the sequences of primers and probe included in the human NoV qRT-PCR have not been published. We confirmed that FNoV was detected by qRT-PCR reported by Obara et al. [12] in our preliminary experiment. In this previous report, ALPF is used as a primer. We speculate that the human NoV qRT-PCR contains ALPF and FNoV have been detected.
The FCVs are detected in feline feces [10]. The conventional method to detect FNoV is universal Caliciviridae RT-PCR. It is difficult to distinguish FCV and FNoV using this method unless the gene sequencing of the PCR products. FCV (331 bp) and 805-808, 2021  FNoV (319 bp) can be distinguished based on the band position after electrophoresis on 6.5% polyacrylamide gel, but this is difficult for persons other than skilled researchers. Moreover, FCV and FNoV may be mixed in a singlet band on agarose gel. Therefore, the universal Caliciviridae RT-PCR may be inappropriate for an epidemiological survey of FNoV. Using the commercial human NoV qRT-PCR, FNoV was able to specifically detect. As the results of two tests were in correspondence, the commercial human NoV qRT-PCR is appropriate for an epidemiological survey of FNoV. Diarrhea is a common clinical sign in cats. There are many causative agents, but a number of cases are diagnosed with an unknown cause. Moreover, in clinical veterinary practice, the only viruses tested as a cause of diarrhea are feline coronavirus and feline panleukopenia virus [1]. On the other hand, FNoV has been reported to be related to diarrhea in cats, but this virus is not included as a target cause because there is no clear evidence of a correlation between diarrhea and FNoV infection in cats. Using methods for FNoV detection, such as that used in this study, the relationship between FNoV infection and diarrhea may be clarified. Furthermore, it is necessary to investigate whether canine NoV (CNoV), which has a genome sequence similar to FNoV, can be detected by human NoV qRT-PCR. CNoV is associated with viral gastroenteritis in dogs [4,9]. This kit will be useful for 805-808, 2021  epidemiological studies of norovirus infections in dogs.
We investigated whether qRT-PCR used to detect human NoVs in medical practice can be applied for FNoV detection [14]. Based on this finding, it is possible to detect FNoVs using human NoV tests. By applying this method to an epidemiological survey of FNoV, the relationship between FNoV infection and diarrhea may be clarified. FNoV researchers may be able to gather useful data using the commercial kit for virus detection.