# Successful in vitro propagation of feline coronavirus from clinically diagnosed feline infectious peritonitis cases using Vero cells: A potential model for future research

## TL;DR

Researchers successfully grew feline coronavirus in lab cells from cats with a deadly disease, offering a new tool for studying the virus and developing treatments.

## Contribution

The study demonstrates the first successful in vitro propagation of feline coronavirus using Vero cells from confirmed FIP cases.

## Key findings

- FCoV was successfully propagated in Vero cells, showing cytopathic effects from day 5 in the first passage.
- RT-qPCR confirmed active viral replication with decreasing Ct values across passages.
- The adapted cell culture system could support drug screening and vaccine development for FIP.

## Abstract

Feline coronavirus (FCoV) causes inapparent to progressive fatal feline infectious peritonitis (FIP) in domestic and wild cats, which affects multiple‐organ systems.

We investigated three clinically sick cats using different laboratory and molecular tests to diagnose and confirm FCoV and propagate the virus in Vero cell culture.

All the cats exhibited effusive FIP with multiple clinical signs. The haematology profiles revealed lymphopenia in all cases and leukopenia, neutropenia and regenerative left shift in one case. Serum biochemistry showed elevated creatine kinase, aspartate aminotransferase, hyperbilirubinaemia and hypoalbuminaemia in all the cases. Urinalysis revealed bilirubinuria in two cases and marked proteinuria in another. All effused samples showed a positive Rivalta test, and the cytology showed a mixed pyogranulomatous inflammatory exudate. Reverse transcription quantitative polymerase chain reaction (RT‐qPCR) confirmed that all the cats were infected with FCoV. The specific gene sequencing of three isolates clustered in the same clade of the phylogenetic tree, suggesting a closely related genotype associated with FIP in cats. Feline coronavirus induced cytopathic effects (CPEs) in Vero cells, first appearing on day 5 post‐infection (pi) in the primary passage. In the second passage, more distinct CPEs, including cell rounding, shrinkage, detachment and death, were evident from day 2 pi. Reverse transcription quantitative polymerase chain reaction confirmed active viral replication, with significantly decreasing Ct values across passages.

The adaptation and propagation of FCoV in a non‐feline cell line provide promising opportunities for future studies, including generating sufficient viral RNA for sequencing, evaluating antiviral resistance, and establishing a practical in vitro system for drug screening and vaccine development.