Objective: This study aimed to investigate the clinical and laboratory characteristics of naturally occurring feline infectious peritonitis (FIP) and estimate the median survival time of FIP cats treated with prednisolone to guide further therapeutic planning. Materials and Methods: In this retrospective study, data from a total of 116 cats with effusion were fully recorded. Forty-five FIP-diagnosed cats were enrolled for analysis. Results: The study findings indicate that FIP was a disease affecting cats aged 1–2 years and was highly prevalent among male cats. Clinical manifestations of FIP affected the digestive (60%), hematological (53.3%), respiratory (33.3%), neurological (6.7%), and ocular (4.4%) systems. Blood profiles revealed mild anemia, lymphopenia, thrombocytopenia, hypoalbuminemia, hyperglobulinemia, and an albumin to globulin ratio of 0.4. Fluid analysis and cytology of FIP cats demonstrated a transparent yellow fluid with a protein content of 6 gm/dl and a total nucleated cell count of approximately 5,000–10,000 cells. During the observation period, FIP cats treated with prednisolone exhibited a median survival time of 31 days. Conclusion: Confirming FIP cases can be challenging; therefore, a tentative diagnosis of FIP must be made with care. This study provided practical diagnostic tools to diagnose FIP based on clinical signs and multiple abnormalities, which allowed for more efficient and rapid detection.

Background and Aim: Feline infectious peritonitis (FIP) is an infectious, immune-mediated, and fatal disease in cats caused by a mutant feline coronavirus (FCoV) infection. Feline immunodeficiency virus (FIV) and feline leukemia virus (FeLV) are two common retroviruses that play a role in reducing feline immune function with opportunistic retrovirus infection being a predisposing factor for the development of FIP. This study aimed to evaluate the clinicopathological parameters of FIP in cats with and without retrovirus coinfection. Materials and Methods: In total, 62 cats presenting with pleural and/or peritoneal effusion at the Kasetsart University Veterinary Teaching Hospital, Bangkok, Thailand, were selected for the study. Effusion samples were collected and a reverse transcriptase-polymerase chain reaction (RT-PCR) assay was performed on all samples using the 3' untranslated region primer. All FCoV-positive cats were tested for retrovirus infection using a commercial kit (Witness FeLV-FIV [Zoetis]; United States). Clinical signs, hematological, and biochemical parameters of these cats were investigated and grouped. Results: Of the 62 cats with pleural and/or peritoneal effusion, FCoV was detected in 32, of which 21 were highly suspicious for FIP. The cats suspected of FIP were divided into three subgroups following viral detection. A total of 14 had only FCoV infection (Group A), four had FCoV and FeLV infection (Group B), and three had FCoV, FeLV, and FIV infection (Group C). Of the rest, 11 had definitive diagnoses, which included three being FCoV and FeLV-positive (Group D), and eight were retrovirus-negative (Group E). Mild anemia and lymphopenia were found in cats infected with these three viruses. An albumin-to-globulin ratio lower than 0.5 was found in FIP cats with only FCoV infection. Conclusion: Typically, cats with clinical effusion and FIP, with and without retrovirus coinfection, had similar hematological findings. Clinical signs, blood parameters, fluid analysis with cytological assessment, and RT-PCR assays could identify better criteria to diagnose FIP with and without retrovirus coinfection. Keywords: effusion, feline leukemia virus, feline infectious peritonitis, feline immunodeficiency virus, reverse transcriptase-polymerase chain reaction.

Feline infectious peritonitis (FIP) is a progressive and often fatal disease caused by a virulent biotype of feline coronavirus (FCoV). Although antiviral treatments are now available, relapse and resistance remain ongoing concerns. This study investigates the therapeutic potential of P. indusiatus, a medicinal mushroom, for its antiviral and anti-inflammatory activities against FIP. The main protease (FIPV M^pro) of feline infectious peritonitis virus (FIPV) was recombinantly expressed and purified to facilitate enzyme inhibition screening. P. indusiatus exhibited the strongest FIPV M^pro inhibitory activity among the 17 mushroom extracts tested (69.2%), showing a notable level of inhibition relative to standard antiviral agents such as lopinavir and ritonavir. To assess its anti-inflammatory potential, PBMCs derived from healthy cats and FIP-associated effusions (FIP fluid) were cultured and stimulated with LPS to induce inflammation. In healthy PBMCs, P. indusiatus significantly reduced nitrite levels, with effects similar to dexamethasone. However, PBMCs from FIP fluid, already in an activated state, showed no additional response. Notably, this study is the first to successfully isolate and culture PBMCs from FIP fluid, providing a new platform for future immunological research. These findings suggest that P. indusiatus possesses both antiviral and anti-inflammatory properties, positioning it as a potential dual-action therapeutic candidate for FIP. Further investigation into cytokine signaling pathways is warranted to clarify its mechanisms of action and advance future therapeutic development.

Feline infectious peritonitis (FIP) is a fatal disease driven by feline coronavirus induced immune dysregulation and excessive inflammatory cytokine production. Immunomodulatory agents capable of rebalancing this response are therefore of increasing interest. Phallus indusiatus (P. indusiatus), an edible mushroom containing diverse bioactive compounds, has previously demonstrated antiviral and anti-inflammatory potential. This study investigated the immunomodulatory effects of P. indusiatus extract on peripheral blood mononuclear cells (PBMCs) from healthy cats and FIP cats and characterized its chemical constituents using liquid chromatography coupled with tandem mass spectrometry (LC–MS/MS). PBMCs were isolated from whole blood and FIP fluid. Cytotoxicity screening identified 19 µg/mL as a non-toxic concentration for subsequent assays. Cytokine responses (IL-1β, IFN-γ, and IL-10) were evaluated following LPS stimulation in PBMCs from whole blood and under basal conditions in PBMCs from FIP fluid after treatment with P. indusiatus extract and dexamethasone. LC–MS/MS profiling combined with STITCH analysis was used to identify bioactive metabolites and their predicted molecular targets. PBMCs derived from FIP fluid exhibited markedly elevated IL-1β and IFN-γ, indicating strong baseline immune activation. P. indusiatus significantly reduced IL-1β and IFN-γ in PBMCs from FIP fluid and suppressed LPS-induced IL-1β and IL-10 in whole-blood PBMCs, demonstrating immunomodulatory patterns comparable to dexamethasone. LC–MS/MS analysis identified compounds including adenosine, phenylalanine, tyrosine, cystathionine, arginine, and sialic acid, which were linked to inflammatory signaling. Overall, the extract exhibited context-dependent modulation of pro- and anti-inflammatory cytokines, suggesting that P. indusiatus may serve as a promising natural adjunctive candidate for managing immune imbalance in cats with FIP.