Existence of feline morbillivirus infection in Japanese cat populations

Basic biological characterization of feline morbillivirus

Feline morbillivirus (FmoPV) is an emerging virus that was recently discovered in domestic cats with chronic nephritis. Despite the potential role of FmoPV in chronic nephritis, little is known about its biological characteristics. In this study, we established a quantitative assay of FmoPV by using an indirect immunofluorescence technique. Viral titers of FmoPV were determined in one week. Treatment with polybrene^® or trypsin which was previously used in virus isolation did not augment the virus titers. FmoPV was notably stable at 4°C, retaining high titers for at least 12 days. Heat-treatment at 60°C and 70°C effectively inactivated FmoPV in 10 and 2 min, respectively. The biological characteristics of FmoPV reported here will be beneficial for establishing an efficient virus isolation method and will provide important information to take a measure to reduce the risk of FmoPV infection.

Identification of a natural recombination in the F and H genes of feline morbillivirus

Feline morbillivirus (FmoPV) has recently been identified in Hong Kong and Japan. FmoPV is considered to belong to the genus Morbillivirus, in the family Paramyxoviridae. In this study, the complete nucleotide sequences of three strains of FmoPV detected in cats in Japan were determined. Among the six genes in FmoPV; N, P/V/C, M, F, H and L, the P gene showed the highest polymorphism in the nucleotide and putative amino acid sequences among the FmoPV strains. There was no geographical association in terms of the FmoPV phylogeny; however, from extensive phylogenetic and recombination analyses, we found that one Japanese FmoPV strain, MiJP003, was a probable recombinant between two virus strains in the independent lineages found in Japan and Hong Kong, respectively. The recombination was considered to have occurred within the F and H genes. Such recombination is thought to be involved in the evolution of FmoPV.

Genetic diversity of feline morbilliviruses isolated in Japan

Feline morbillivirus (FmoPV) is an emerging virus in domestic cats and considered to be associated with tubulointerstitial nephritis. Although FmoPV was first described in China in 2012, there has been no report of the isolation of this virus in other countries. In this report, we describe the isolation and characterization of FmoPV from domestic cats in Japan. By using reverse transcription (RT)-PCR, we found that three of 13 urine samples from cats brought to veterinary hospitals were positive for FmoPV. FmoPV strains SS1 to SS3 were isolated from the RT-PCR-positive urine samples. Crandell-Rees feline kidney (CRFK) cells exposed to FmoPV showed cytopathic effects with syncytia formation, and FmoPV N protein was detected by indirect immunofluorescence assays. In addition, pleomorphic virus particles with apparent glycoprotein envelope spikes were observed by electron microscopy. By sequence analysis of FmoPV H and L genes, we found that FmoPVs showed genetic diversity; however, signatures of positive selection were not identified.