Comparison of the Performance of Bioresonance, Electrophoresis and RT-PCR in the Diagnosis of Feline Infectious Peritonitis.

Feline infectious peritonitis (FIP) continues to be one of the most researched infectious diseases of cats. The diagnosis of FIP is challenging, and diverse techniques have been developed for its accurate diagnosis. However, they have some limitations. The present study was conducted to investigate the efficacy of specific modulation frequency (SMF), compared to other routine diagnostic methods for detecting feline coronavirus. Blood samples were collected from 30 diseased cats suspected of having FIP based on clinical signs. Electrophoresis, polymerase chain reaction (PCR), and SMF tests were performed for each sample. The sensitivity and specificity of each test, as well as the agreement between the tests and the gold standard (the combination of PCR, electrophoresis, and bioresonance results), were calculated using the Kappa coefficient method. The sensitivity and specificity of electrophoresis, PCR, and SMF for the diagnosis of FIP were 70.6%, 70.6%, 100%, and 100%, 72.7%, 81.8%, respectively. According to the findings of the present study, SMF is effective and safe in FIP diagnosis, which is a challenge in veterinary medicine diagnosis.

Structural-based virtual screening and in vitro assays for small molecules inhibiting the feline coronavirus 3CL protease as a surrogate platform for coronaviruses.

Feline infectious peritonitis (FIP) which is caused by feline infectious peritonitis virus (FIPV), a variant of feline coronavirus (FCoV), is a member of family Coronaviridae, together with severe acute respiratory syndrome coronavirus (SARS-CoV), Middle East respiratory syndrome coronavirus (MERS-CoV), and SARS-CoV-2. So far, neither effective vaccines nor approved antiviral therapeutics are currently available for the treatment of FIPV infection. Both human and animal CoVs shares similar functional proteins, particularly the 3CL protease (3CLpro), which plays the pivotal role on viral replication. We investigated the potential drug-liked compounds and their inhibitory interaction on the 3CLpro active sites of CoVs by the structural-bases virtual screening. Fluorescence resonance energy transfer (FRET) assay revealed that three out of twenty-eight compounds could hamper FIPV 3CLpro activities with IC50 of 3.57 ± 0.36 µM to 25.90 ± 1.40 µM, and Ki values of 2.04 ± 0.08 to 15.21 ± 1.76 µM, respectively. Evaluation of antiviral activity using cell-based assay showed that NSC629301 and NSC71097 could strongly inhibit the cytopathic effect and also reduced replication of FIPV in CRFK cells in all examined conditions with the low range of EC50 (6.11 ± 1.90 to 7.75 ± 0.48 µM and 1.99 ± 0.30 to 4.03 ± 0.60 µM, respectively), less than those of ribavirin and lopinavir. Analysis of FIPV 3CLpro-ligand interaction demonstrated that the selected compounds reacted to the crucial residues (His41 and Cys144) of catalytic dyad. Our investigations provide a fundamental knowledge for the further development of antiviral agents and increase the number of anti-CoV agent pools for feline coronavirus and other related CoVs.

In silico and in vitro analysis of small molecules and natural compounds targeting the 3CL protease of feline infectious peritonitis virus.

The computational search of chemical libraries has been used as a powerful tool for the rapid discovery of candidate compounds. To find small molecules with anti-feline infectious peritonitis virus (FIPV) properties, we utilized a virtual screening technique to identify the active site on the viral protease for the binding of the available natural compounds. The protease 3CL (3CLpro) plays an important role in the replication cycle of FIPV and other viruses within the family Coronaviridae. The 15 best-ranked candidate consensus compounds, based on three docking tools, were evaluated for further assays. The protease inhibitor assay on recombinant FIPV 3CLpro was performed to screen the inhibitory effect of the candidate compounds with IC50 ranging from 6.36 ± 2.15 to 78.40 ± 2.60 µM. As determined by the cell-based assay, the compounds NSC345647, NSC87511, and NSC343256 showed better EC50 values than the broad-spectrum antiviral drug ribavirin and the protease inhibitor lopinavir, under all the test conditions including pre-viral entry, post-viral entry, and prophylactic activity. The NSC87511 particularly yielded the best selective index (>4; range of SI = 13.80-22.90). These results indicated that the natural small-molecular compounds specifically targeted the 3CLpro of FIPV and inhibited its replication. Structural modification of these compounds may generate a higher anti-viral potency for the further development of a novel therapy against FIP.

Synergistic antiviral effect of Galanthus nivalis agglutinin and nelfinavir against feline coronavirus.

Feline infectious peritonitis (FIP) is a fatal disease in domestic and nondomestic felids caused by feline coronavirus (FCoV). Currently, no effective vaccine is available for the prevention of this disease. In searching for agents that may prove clinically effective against FCoV infection, 16 compounds were screened for their antiviral activity against a local FCoV strain in Felis catus whole fetus-4 cells. The results showed that Galanthus nivalis agglutinin (GNA) and nelfinavir effectively inhibited FCoV replication. When the amount of virus preinoculated into the test cells was increased to mimic the high viral load present in the target cells of FIP cats, GNA and nelfinavir by themselves lost their inhibitory effect. However, when the two agents were added together to FCoV-infected cells, a synergistic antiviral effect defined by complete blockage of viral replication was observed. These results suggest that the combined use of GNA and nelfinavir has therapeutic potential in the prophylaxis and treatment of cats with early-diagnosed FIP.

Type IV hypersensitivity in the pathogenesis of FIPV-induced lesions.

In focal lesions of feline infectious peritonitis (FIP), the cells involved in the delayed-type hypersensitivity were identified in formalin-fixed paraffin-embedded and frozen samples taken from 35 affected cats. The clinical diagnosis of FIP was confirmed by necropsy, histology and direct immunofluorescence against the coronaviruses on cryostatic sections. The immune cells were detected immunohistochemically by the Avidin-Biotin-Complex (ABC) method using either polyclonal antibodies against lymphoid antigens (CD3) or monoclonal antibodies against lymphoid (PAN-T, CD4, CD8) and myeloid antigens (MAC387). Better identification of T cells and macrophages was found on formalin-fixed paraffin-embedded sections than on cryostatic ones, while T lymphocyte subpopulations could be differentiated only in cryostatic sections. Type IV hypersensitivity was detected in focal feline infectious peritonitis virus (FIPV)-induced lesions from progressive activation of T lymphocytes, mainly CD4+, and the presence of granulocytes and macrophages. The FIPV-induced lesions could be studied as examples of granulomas caused by unconventional antigens, such as viruses or immune complexes.

Detection of feline infectious peritonitis virus infection in cell cultures and peripheral blood mononuclear leukocytes of experimentally infected cats using a biotinylated cDNA probe.

A dot blot hybridization assay, using a biotinylated cDNA probe, was able to detect feline infectious peritonitis virus (FIPV) RNA in Felis catus whole fetus (fcwf-4) cells infected with the FIPV isolates DF2, 79-1146, UCD1, and UCD2. The probe cross-hybridized in the dot blot assay with nucleic acid of a closely related feline coronavirus, feline enteric coronavirus (FEVC)-79-1683. To construct the probe, a 2.5 kilobase cDNA, prepared from FIPV-DF2 genomic RNA, was molecularly cloned. The recombinant cDNA clone was digested with the restriction endonuclease Rsa I, and an 870 basepair Rsa I fragment was isolated from vector DNA by agarose electrophoresis and glass-milk purification. This fragment was complementary to the 3' three fourths of the nucleocapsid gene. The hybridization probe was prepared by random primed labeling in the presence of biotin-11-dUTP. Using an avidin-alkaline phosphatase conjugate and chemiluminescent substrate detection system, virus could be detected in as few as 3000 infected cells. In an in vivo study, the probe was used to detect FIPV RNA in peripheral blood mononuclear leukocytes (PBML) isolated at various post-infection days (PID) from cats experimentally infected with the FIP-producing coronavirus isolate FIPV-79-1146 or FIPV-DF2. Viral RNA could be detected in as few as 12,000 PBML isolated from cats at PID 7 and in 50,000 PBML at PID 22. There was no consistent pattern, however, between hybridization results and prognosis or severity of disease at the time of sampling. Despite some cross-hybridization with FECV RNA, this probe should be useful for diagnosis of FIP, because cats infected with FECV most likely do not become viremic.