The growth profiles of three types of canine distemper virus on Vero cells expressing canine signaling lymphocyte activation molecule

Comparison of Growth Characteristics and Genomics of Two Canine Distemper Virus Strains Isolated From Minks in China

Canine distemper (CD), caused by the CDV variant strain with H^I542N/Y549H, has become an epidemic in fur-bearing animals in China since 2012. To well understand the genomic and replicated characteristics of the CDV variants, we determined the viral growth kinetics and completed the genome sequences of two CDV strains, namely SDZC(17)M2 and LNDL(17)M4, isolated from CDV-infected minks from Shandong and Liaoning province in China, in 2017. SDZC(17)M2 showed higher viral titers and extensive syncytia in BHK-minkSLAM (BMS) cells than LNDL(17)M4. Although both two strains belong to the Asia-1 genotype and clustered an independent clade in the phylogenetic tree, SDZC(17)M2, harboring I542N/Y549H substitutions in the H protein, shared high identity (99.3–99.6% nt) with the other variant strains, whereas LNDL(17)M4, with the only Y549H substitution, shared a lower identity (97.7%–97.9% nt) with the other variant strains. Furthermore, a novel R223K substitution was identified in the conserved cleavage site (RRQRR → RRQKR) of the F protein in the SDZC(17)M2 strain. However, it which did not significantly affect the cell to cell fusion activity when combined with the CDV H/minkSLAM in BHK-21 cells. The key variations in the genome contributed to the virulence and the evolutionary trend need to be determined in the future.

Virus isolation and full-length genome sequencing of a representative canine distemper virus wild type strain of the South America 2 clade

Canine Distemper Virus (CDV) is a highly contagious pathogen of dogs that causes severe respiratory, gastrointestinal and nervous signs. Although vaccines have been used to prevent infections, CDV has been reported worldwide, even in vaccinated animals. In the present study, a representative wild type CDV strain (Arg24) was isolated from a sick vaccinated dog and its genome was completely sequenced using Illumina technology. This strain produced a strong cytopathic effect in Vero SLAM (Signaling Lymphocyte Activation Molecule) cells with a higher titer of 1.1 × 10⁵ Median Tissue Culture Infectious Dose (TCID₅₀/mL) at 32 h post infection, in cell-associated virus. The Arg24 strain genome, showed values of 97.1, 90.3, 96.7, 90.6, 89.8 and 97.3 % of amino acid identity with respect to the Onderstepoort vaccine strain (Nucleoprotein, Phosphoprotein, Matrix, Fusion, Hemagglutinin and Large polymerase, respectively). Focusing on the Hemagglutinin gene, which is the target for genetic characterization, Arg24 showed four additional potential glycosylation sites, with respect to the Onderstepoort. The availability of Arg24 strain, which can be easily grown in Vero SLAM cells, is an important tool to perform immunological and antigenic comparative studies, between wild type and vaccine CDV strains.

Epidemiology, pathological aspects and genome heterogeneity of feline morbillivirus in Italy

Feline morbillivirus (FeMV) is an emerging morbillivirus first described in cats less than a decade ago. FeMV has been associated with chronic kidney disease of cats characterized by tubulointerstitial nephritis (TIN), although this aspect is still controversial and not demonstrated with certainty. To investigate FeMV prevalence and genomic characteristics, an epidemiological survey was conducted in a total number of 127 household cats originating from two Italian regions, Abruzzi and Emilia-Romagna. A total number of 69 cats originating from three feline colonies were also enrolled for the study. Correlation with TIN was investigated by employing a total number of 35 carcasses. Prevalence of FeMV RNA was higher in urine samples collected from cats of colonies (P = 31.8%, CI 95% 22.1-43.6) compared to household cats (P = 8.66%, CI 95% 4.9-14.9) and in young and middle-aged cats while prevalence of FeMV Abs was higher in old cats. Sequences obtained straight from infected biological samples, either partial or complete, cluster into two clades within FeMV genotype 1, distantly related to FeMV genotype 2. Immunohistochemistry analysis of kidney sections of FeMV RNA positive cats revealed immunoreactivity within epithelial cells of renal tubuli and inflammatory cells. However, statistically significant association between FeMV and renal damages, including TIN, was not demonstrated (p= 0.0695, Fisher exact test). By virus histochemistry performed with FeMV-negative feline tissues and a FeMV isolate, tropism for different cellular types such as inflammatory cells residing in blood vessels of kidney and brain, airway epithelial cells, alveolar macrophages and to a lesser extent, the central nervous system, was demonstrated. Additional studies are warranted in order to establish viral tropism and immune response during the early phases of infection and to disentangle the role of FeMV in co-infection processes.

Cytoplasmic Translocation of Nucleolar Protein NOP53 Promotes Viral Replication by Suppressing Host Defense

NOP53 is a tumor suppressor protein located in the nucleolus and is translocated to the cytoplasm during infection by vesicular stomatitis virus (VSV) and herpes simplex virus type 1 (HSV-1), as shown in our previous study. Cytoplasmic NOP53 interacts with the retinoic acid-inducible gene I (RIG-I) to remove its K63-linked ubiquitination, leading to attenuation of type I interferon IFN-β. In the present study, we found no obvious translocation of NOP53 in infection by a mutant virus lacking ICP4 (HSV-1/d120, replication inadequate). Blocking cytoplasmic translocation of NOP53 by the deletion of its nuclear export sequence (NES) abrogated its ability to support viral replication. These results demonstrated that NOP53 redistribution is related to viral replication. It is interesting that treatment with poly (I:C) or RIG-I-N (a constitutively-active variant) directly induced NOP53 cytoplasmic translocation. To better assess the function of cytoplasmic NOP53 in viral replication, the NOP53-derived protein N3-T, which contains a human immunodeficiency virus (HIV)-derived cell-penetrating Tat peptide at the C-terminal region of N3 (residues 330–432), was constructed and expressed. The recombinant N3-T protein formed trimers, attenuated the expression of IFN-β and IFN-stimulated genes, as well as decreased the phosphorylation level of interferon regulatory factor 3 (IRF3). Furthermore, N3-T promoted the efficient replication of enveloped and non-enveloped DNA and RNA viruses belonging to 5 families. Our findings expand the understanding of the mechanism by which viruses utilize the nucleolar protein NOP53 for optimal viral replication.

Cellular protein GLTSCR2: A valuable target for the development of broad-spectrum antivirals

Viral infection induces translocation of the nucleolar protein GLTSCR2 from the nucleus to the cytoplasm, resulting in attenuation of the type I interferon IFN-β. Addressing the role of GLTSCR2 in viral replication, we detect that knocking down GLTSCR2 by shRNAs results in significant suppression of viral replication in mammalian and chicken cells. Injection of chicken embryo with the GLTSCR2-specific shRNA-1370 simultaneously or 24 h prior to infection with Newcastle disease virus (NDV) substantially reduces viral replication in chicken embryo fibroblasts. Injection of shRNA-1370 into chicken embryo also reduces the replication of avian influenza virus (AIV). In contrast, GLTSCR2-derived protein G4-T, forming α-helical dimers, increases replication of seven various DNA and RNA viruses in cells. Our studies reveal that alteration of the function of cellular GLTSCR2 plays a role in supporting viral replication. GLTSCR2 should be seriously considered as a therapeutic target for developing broad spectrum antiviral agents to effectively control viral infection.

Relationship between growth behavior in vero cells and the molecular characteristics of recent isolated classified in the Asia 1 and 2 groups of canine distemper virus

Ten recent isolates of canine distemper virus (CDV) strains were classified according to the growth ability and development of syncytial cytopathic effects (CPE) in Vero cells. Strains P94S, Ac96I, S124C, MD231, MS232, MSA5 and 095Cr were classified as Type 1 and exhibited hardly and did not develop CPE in Vero cells. Strains 007Lm, 009L and 011C were classified as Type 2 as grew well but failed to develop a syncytial CPE in Vero cells. A comparison of the phylogenetic trees of the H and P genes showed that all Type 1 strains belonged to the Asia 1 group and all Type 2 strains belonged to the Asia 2 group. Our findings suggest that the recent Asia 2 isolated of CDV in Japan, but not Asia 1 may grow in Vero cells, and their growth ability may be related with their molecular characteristics.

First isolation and characterization of canine distemper virus in Vietnam with the immunohistochemical examination of the dog

Canine distemper caused by canine distemper virus (CDV) is a contagious, incurable, often fatal, multisystemic viral disease that affects the respiratory gastrointestinal and central nervous system. Strains Vn86 and Vn99 of CDV were isolated, we believe for the first time, in Vietnam from two 4-month-old autopsied dogs pathologically showing non-suppurative encephalitis with pneumonia, lymphoid depletion and severe gastroenteritis. These strains caused syncytium cytopathic effect in Vero cells and Vero cells expressing canine signaling lymphocyte activation molecules. The titers of cell-associated viruses of both strains were higher than for released viruses. Molecular analysis showed that both new isolates of CDV joined to the group of classic type that is far from the Asia 1 and Asia 2 groups. These results indicated that first isolation and characterization of canine distemper virus in Vietnam with the immunohistochemical examination of the dog.

Immunohistochemical demonstration of the putative canine distemper virus receptor CD150 in dogs with and without distemper

Signaling lymphocyte activation molecule (SLAM) or CD150 can function as a receptor for the canine distemper virus (CDV) in vitro. The expression of SLAM was studied using immunohistochemistry in order to evaluate the presence and distribution of the receptor in dogs in vivo. Additionally, receptor expression was assessed after experimental infection of dogs with CDV. In 7 control dogs without distemper virus, the receptor was found in various tissues, mostly on cells morphologically identified as lymphocytes and macrophages. In 7 dogs with early distemper lesions characterized by presence of the virus, higher numbers of SLAM-expressing cells were found in multiple tissues recognized as targets of CDV compared with those in control dogs. These findings suggest that SLAM, a putative distemper receptor, is expressed in dogs in vivo. Additionally, virus infection is associated with up-regulation of SLAM, potentially causing an amplification of virus in the host.

Development of a challenge-protective vaccine concept by modification of the viral RNA-dependent RNA polymerase of canine distemper virus

We demonstrate that insertion of the open reading frame of enhanced green fluorescent protein (EGFP) into the coding sequence for the second hinge region of the viral L (large) protein (RNA-dependent RNA polymerase) attenuates a wild-type canine distemper virus. Moreover, we show that single intranasal immunization with this recombinant virus provides significant protection against challenge with the virulent parental virus. Protection against wild-type challenge was gained either after recovery of cellular immunity postimmunization or after development of neutralizing antibodies. Insertion of EGFP seems to result in overattenuation of the virus, while our previous experiments demonstrated that the insertion of an epitope tag into a similar position did not affect L protein function. Thus, a desirable level of attenuation could be reached by manipulating the length of the insert (in the second hinge region of the L protein), providing additional tools for optimization of controlled attenuation. This strategy for controlled attenuation may be useful for a "quick response" in vaccine development against well-known and "new" viral infections and could be combined efficiently with other strategies of vaccine development and delivery systems.

Host range and receptor utilization of canine distemper virus analyzed by recombinant viruses: Involvement of heparin-like molecule in CDV infection

We constructed recombinant viruses expressing enhanced green fluorescent protein (EGFP) or firefly luciferase from cDNA clones of the canine distemper virus (CDV) (a Japanese field isolate, Yanaka strain). Using these viruses, we examined susceptibilities of different cell lines to CDV infection. The results revealed that the recombinant CDVs can infect a broad range of cell lines. Infectivity inhibition assay using a monoclonal antibody specific to the human SLAM molecule indicated that the infection of B95a cells with these recombinant CDVs is mainly mediated by SLAM but the infection of 293 cell lines with CDV is not, implying the presence of one or more alternative receptors for CDV in non-lymphoid tissue. Infection of 293 cells with the recombinant CDV was inhibited by soluble heparin, and the recombinant virus bound to immobilized heparin. Both F and H proteins of CDV could bind to immobilized heparin. These results suggest that heparin-like molecules are involved in CDV infection.

Stability of canine distemper virus (CDV) after 20 passages in Vero-DST cells expressing the receptor protein for CDV

Isolates 007Lm, S124C and Ac96I and a Vero cell-adapted Onderstepoort strain of canine distemper viruses (CDV) were examined for stability after passages in Vero cells expressing the canine signaling lymphocyte activation molecule (dogSLAM, the intrinsic receptor to CDV). These viruses passage once in Vero cells expressing dogSLAM (Vero-DST) cells (original) and after 20 passages (20p) were compared by using sequence analyses and growth characteristics. All four strains of 20p grew well and were slightly better than their originals. The 20p viruses developed a cytopathic effect slightly lower than the original strains. A few changes in amino acids in the H gene were between the 20p and the original viruses, but the sites of changes were not specific. Fragments of P, M and L genes of all strains showed no nucleotide changes after the passages. These results showed that: (1) passages of CDVs in Vero-DST cells induced amino acid changes only in the H gene, not in the P, M and L genes, unlike in a previous study with Vero cells; (2) passages did not markedly affect the growth characteristics of every viral strain. These results indicate that Vero cells expressing canine SLAM allow the isolation and passaging of CDV without major changes in viral genes.