Feline morbillivirus, a previously undescribed paramyxovirus associated with tubulointerstitial nephritis in domestic cats

Abstract

We describe the discovery and isolation of a paramyxovirus, feline morbillivirus (FmoPV), from domestic cat (Felis catus). FmoPV RNA was detected in 56 (12.3%) of 457 stray cats (53 urine, four rectal swabs, and one blood sample) by RT-PCR. Complete genome sequencing of three FmoPV strains showed genome sizes of 16,050 bases, the largest among morbilliviruses, because of unusually long 5' trailer sequences of 400 nt. FmoPV possesses identical gene contents (3'-N-P/V/C-M-F-H-L-5') and is phylogenetically clustered with other morbilliviruses. IgG against FmoPV N protein was positive in 49 sera (76.7%) of 56 RT-PCR-positive cats, but 78 (19.4%) of 401 RT-PCR-negative cats (P < 0.0001) by Western blot. FmoPV was isolated from CRFK feline kidney cells, causing cytopathic effects with cell rounding, detachment, lysis, and syncytia formation. FmoPV could also replicate in subsequent passages in primate Vero E6 cells. Infected cell lines exhibited finely granular and diffuse cytoplasmic fluorescence on immunostaining for FmoPV N protein. Electron microscopy showed enveloped virus with typical "herringbone" appearance of helical N in paramyxoviruses. Histological examination of necropsy tissues in two FmoPV-positive cats revealed interstitial inflammatory infiltrate and tubular degeneration/necrosis in kidneys, with decreased cauxin expression in degenerated tubular epithelial cells, compatible with tubulointerstitial nephritis (TIN). Immunohistochemical staining revealed FmoPV N protein-positive renal tubular cells and mononuclear cells in lymph nodes. A case-control study showed the presence of TIN in seven of 12 cats with FmoPV infection, but only two of 15 cats without FmoPV infection (P < 0.05), suggesting an association between FmoPV and TIN.

Fig. 1.

Genome organization of FmoPV and other morbilliviruses. The genes are shown as boxes that are drawn to scale. For P gene, the brown line above the orange box represents the region of V CDS and the red line represents the C CDS.

Fig. 2.

Phylogenetic analysis of N, P, M, F, A, and L amino acid sequences of FmoPV. The trees were constructed by maximum likelihood method with bootstrap values calculated from 1,000 trees and rooted on midpoint. The scale bars indicates the branch length that corresponds to 0.5 substitutions per site. Three strains from FmoPV were named as 761U, 776U, and M252A. Names and accession numbers of the other viruses are listed in Table S5.

Fig. 3.

(A) CPEs of FmoPV on CRFK cells. Red squares show the formation of giant cells. (B and C) Indirect immunofluorescent antigen detection in uninfected and infected CRFK cells using serum from guinea pig immunized with recombinant N protein of FmoPV, showing specific apple green cytoplasmic fluorescence in FmoPV-infected CRFK cells. (D) EM examination of infected CRFK cell culture supernatant showing enveloped virus with burst envelope and typical herringbone appearance of helical N in paramyxoviruses.

Fig. 4.

(A and B) Histological section of kidneys stained by H&E from a stray cat with FmoPV detected in urine and a normal cat, showing aggregates of inflammatory cells in the interstitium and renal tubular degeneration in the infected cat. (C and D) Immunohistochemical staining of kidney sections of stray cat with FmoPV detected in urine using guinea pig serum positive for anti-FmoPV N protein antibody and preimmune guinea pig serum, showing positive renal tubular cells. (E and F) Immunohistochemical staining of lymph node sections of stray cat positive for FmoPV using guinea pig serum positive for anti-FmoPV N protein antibody and preimmune guinea pig serum, showing positive mononuclear cells.