Relationship between Uveal Inflammation and Viral Detection in 30 Cats with Feline Infectious Peritonitis

Abstract

Feline infectious peritonitis (FIP) virus is the most common infectious cause of uveitis in cats. Confirmatory diagnosis is usually only reached at postmortem examination. The relationship between the histologic inflammatory pattern, which depends on the stage of the disease, and the likelihood of detection of the viral antigen and/or RNA has not been investigated. We hypothesized that viral detection rate by either immunohistochemistry, in situ hybridization or RT-qPCR is dependent upon the predominant type of uveal inflammatory response (i.e., pyogranulomatous vs. plasmacytic). Thus, the aims of this study were to evaluate cases of FIP-induced uveitis, localize the viral antigen and RNA, and assess the relationship between the inflammatory pattern (macrophage- vs. plasma cell-rich) and the likelihood of detecting the FIP antigen and/or RNA. We evaluated 30 cats with FIP-induced uveitis. The viral antigen and/or RNA were detected within uveal macrophages in 11/30 cases, of which 8 tested positive by RT-qPCR. Correlation analysis determined a weak to moderate but significant negative correlation between the degree of plasmacytic uveal inflammation and the likelihood of detecting the FIP antigen and RNA. This study suggests that predominance of plasmacytic inflammation in cases of FIP uveitis reduces the odds of a confirmatory diagnosis through the viral detection methods available.

Feline Infectious Peritonitis: European Advisory Board on Cat Diseases Guidelines

“…A study describing the ocular lesions in 15 cats with FIP found effusions in 13 cats and no effusion in only 2 cats [ 32 ], although other authors have found a low prevalence of effusions in cats with FIP-associated uveitis [ 244 ]. Ocular manifestations of FIP comprise anterior and/or posterior uveitis [ 15 , 35 , 45 , 233 , 243 ] ( Figure 8 , Figure 9 and Figure 10 ), with anterior uveitis being more common [ 245 ]. The uveitis is unilateral or bilateral [ 244 ].…”

“…Eyes enucleated as a result of uveitis-associated intractable glaucoma or pain can also be submitted for histopathology and IHC [ 174 ]. However, ocular tissues characterised by heavy plasmacytic inflammation in FIP are less likely to be IHC-positive for FCoV antigens [ 245 ]. The samples most likely to be useful are those that are affected by the disease process, and this can be guided by the results of diagnostic testing (e.g., imaging results, pyogranulomatous inflammation on FNA cytology) as well as clinical signs.…”

“…One study has described the use of ISH to detect FCoV sequences in fixed samples prepared from enucleations of cats with FIP [ 245 ]; the technique had a similar diagnostic performance to IHC and RT-PCR. More studies are required to evaluate the use of ISH in the diagnosis of FIP.…”

A Combined Method Based on the FIPV N Monoclonal Antibody Immunofluorescence Assay and RT-nPCR Method for the Rapid Diagnosis of FIP-Suspected Ascites

“…Detecting an FIPV antigen within an efusion macrophage can be a good approach for viral antigen detection, and those involved mostly choose to target the nucleocapsid (N) protein due to its high-yield production in infected cells [2]. IHC is considered the "gold standard" for FIP diagnosis [5,13,43]. However, IHC is a time-consuming and complex procedure that requires specialized personnel and equipment [44,45].…”

“…FIPV can efciently and continuously replicate in monocytes and macrophages [12]. Monocyte/ macrophage-tropic FIPV typically manifests as either efusive (wet form) or nonefusion (dry form) [13,14]. Te wet form is characterized by immune-mediated, fbrinous-granulomatous serositis, often with protein-rich efusions in the thoracic or abdominal cavities [15].…”