Deciphering Viral Replication Dynamics in Feline Infectious Peritonitis: A Quantitative Approach

Area of Science:

• Veterinary Virology
• Immunology
• Molecular Biology

Background:

• Feline infectious peritonitis (FIP) is a severe immune-mediated disease in cats, caused by feline coronavirus (FCoV).
• Understanding FCoV's viral factors, including virion composition and replication, is crucial but challenging.
• Previous research highlights the need to investigate viral gene expression in FIP pathogenesis.

Purpose of the Study:

• To investigate potential associations between feline coronavirus (FCoV) gene expression ratios and the development of feline infectious peritonitis (FIP).
• To compare viral gene expression in cats with FIP lesions versus FCoV-infected cats without FIP.

Main Methods:

• Analysis of tissue samples from 46 cats with FIP and 10 FCoV-infected cats without FIP.
• Utilized three RT-qPCR assays targeting RNA-dependent RNA polymerase (RdRp) and envelope (E) gene (sub)-genomic RNAs.
• Quantified viral RNA copy numbers and assessed gene expression patterns.

Main Results:

• Cats with FIP exhibited significantly higher viral RNA copy numbers for RdRp mRNA and combined RdRp gRNA/mRNA compared to E mRNA.
• Fewer viral RNA copies were detected in FCoV-infected cats without FIP, with some showing no or low-level gene expression.
• Consistent transcription of RdRp and E genes was observed in FIP lesions, but not in systemic FCoV infection alone.

Conclusions:

• Distinct viral gene expression patterns, particularly for RdRp and E genes, are associated with feline infectious peritonitis (FIP).
• The findings suggest that consistent viral gene transcription within lesions is a hallmark of FIP, differentiating it from systemic FCoV infection.