Phylogenetic Analysis of Feline Coronavirus Strains in an Epizootic Outbreak of Feline Infectious Peritonitis

Abstract

Background: Feline coronavirus (FCoV) infection is common. In a small percentage of cats, FCoV infection is associated with the fatal disease feline infectious peritonitis (FIP). Genetically distinct virulent and avirulent strains of FCoV might coexist within a cat population.Objectives: To determine whether the strains of FCoV in FIP-affected cats are closely related or genetically distinct from the fecally derived strains of FCoV in contemporary-asymptomatic cats during an epizootic outbreak of FIP.Animals: Four cats euthanized because of FIP and 16 asymptomatic cats.Methods: This prospective outbreak investigation was initiated during an outbreak of FIP in cats within or rehomed from a rescue/rehoming center. Postmortem samples were collected from cats with FIP and contemporaneous fecal samples from asymptomatic cats. RNA was purified from tissue and fecal samples, FCoV gene fragments were reverse transcribed, PCR-amplified using novel primers, and sequenced. Sequences were aligned with ClustalW and compared with published FCoV sequences.Results: FCoV RNA was detected in all 4 FIP cat postmortem samples and in 9 of the 16 fecal samples from contemporary-asymptomatic cats. Novel primers successfully amplified fragments from 4 regions of the genome for all FCoV-positive samples. Phylogenetic analysis showed that the FIP-associated strains of FCoV from the outbreak were very closely related to the fecally derived strains of FCoV from contemporary-asymptomatic cats.Conclusions and Clinical Importance: Sequence analysis provided no evidence that genetically distinct virulent and avirulent strains of FCoV were present during this FIP outbreak.

An update on feline infectious peritonitis: Virology and immunopathogenesis

“…Additional studies on a large population of cats, taking into consideration genetic differences related to geographic origins, also failed to find evidence for the 'two virus' theory or any significant genetic differences between FIPVs and FECVs from the same environments (Pedersen et al, 2012). A phylogenetic analysis of fecal and tissue coronaviruses from an outbreak of FIP in a group of 20 cats also confirmed that strains of FIP-associated feline coronaviruses were very closely related to viruses identified in the feces of healthy cats in the same environment (Barker et al, 2013). This study also provided no evidence that genetically distinct virulent (FIPV) and avirulent (FECV) strains of feline coronavirus were present during this outbreak.…”

“…There is a general consensus that FIPVs arise by internal mutation from FECVs in the same environment (Pedersen et al, , 2012Harley et al, 2013). Except in unusual circumstances , the causative mutations occur independently within each cat and each FIPV strain has unique genetic features (Pedersen et al, , 2012Chang et al, 2012;Barker et al, 2013;Licitra et al, 2013). Currently, three different genes have been associated with the FECV-to-FIPV mutation or biotype conversion.…”

Feline Coronaviruses

“…The authors claimed that cats develop FIP only upon infection with the virulent FCoV type. However, this hypothesis has failed to receive any backing, and since then additional experiments and further analyses have strengthened the "internal mutation" theory (Bank-Wolf et al, 2014; Barker et al, 2013;Chang et al, 2010Chang et al, , 2011Chang et al, , 2012Lewis et al, 2015;Licitra et al, 2013;Pedersen et al, 2012;Porter et al, 2014). It is now widely accepted that FIPV emerges during persistent infection through mutations from the harmless FECV.…”

Characterization of amino acid substitutions in feline coronavirus 3C-like protease from a cat with feline infectious peritonitis treated with a protease inhibitor

“…However, a small number of cats may develop feline infectious peritonitis (FIP), a highly fatal, systemic disease, following enteric coronavirus infection (Pedersen, 2009(Pedersen, , 2014. The detailed mechanism of FIP development is still elusive, but it is believed that FIP arises in individual cats through altered viral tropism that allows viral replication in the macrophages (Barker et al, 2013;Chang et al, 2012;Licitra et al, 2013;Pedersen et al, 2009Pedersen et al, , 2012 in the presence of inadequate cellular immunity of the affected cats (Pedersen, 2014). FIP are commonly described as wet or dry forms based on the presence or absence of effusion, respectively, but these forms may switch as the disease progresses in some cats.…”