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FELINE INFECTIOUS PERITONITIS: HOW CAN WE GET A DIAGNOSIS? Dr Emi Barker BSc BVSc PhD MRCVS Senior Clinical Training Scholar in Small Animal Medicine. Dr Séverine Tasker BSc BVSc PhD DSAM Dip ECVIM-CA PGCert HE MRCVS RCVS Specialist in Feline Medicine, University of Bristol.

Feline infectious peritonitis (FIP) is Concurrently viral RNA is variably switch permitting the replication in usually regarded as an incurable detectable in mesenteric lymph nodes, liver, monocytes / macrophages, and the disease and an important cause of lungs and other organs, typically within subsequent development of FIP, arises specialised resident macrophages in the from nucleotide mutation(s) in less death in young cats caused by feline absence of pathology, providing potential pathogenic FCoVs in individual infected coronavirus (FCoV). FCoV infection sources for recurrent viraemia and persistent cats; known as the “internal mutation” is endemic amongst cats worldwide. infection. Infections are usually hypothesis (Pedersen 2009). In the UK, around 40% of the domestic asymptomatic or result in transient mild An alternative “virulent/avirulent” cat population has been infected gastrointestinal disease (e.g. diarrhoea). hypothesis had been proposed, which with FCoV and in multi-cat Viral particles are shed in the faeces and stated that distinct populations of enteric subsequently ingested by a susceptible households this figure increases to and FIP FCoV strains are circulating in cat cat. Risk factors for the development of populations, and that these are almost 90% (Addie 2000, Addie and the disease are multifactorial (see Fig. 1), independently acquired (Brown and Jarrett 1992, Hartmann 2005, Sparkes but a detailed discussion of these risk others 2009). Recently whole genome 1992). FIP usually arises sporadically factors and their management are sequencing data identified a genetic and unpredictably, with only a small beyond the scope of this article. mutation, common to the >90% FIP percentage of cats developing FIP In a small number of individual cats the tissue-derived FCoVs, and present in within the first three years of infecting FCoV becomes capable of none of the asymptomatic faeces-derived replicating extensively within monocytes/ FCoVs, (Chang and others 2012). entering a seropositive household. macrophages leading to pathological This genome mutation provides a very Rarely FIP can arise as an ‘outbreak’ in changes that culminate in vasculitis and useful potential future target for FIP a group of cats over a short period of granuloma development in organs (Kipar diagnostics but does not completely time (Pedersen 2009, Potkay and others and others 2005). In the early stages of confirm the “internal mutation” 1974). FIP is extremely distressing to disease the clinical signs may be hypothesis and exclude the possibility of vaguesigns consistent with a systemic deal with, for both cat owners and other explanations in other situations. This inflammatory response, such as lethargy, veterinary surgeons, because of the is because the FCoV genome mutation pyrexia and weight loss, are often rate is rapid, meaning that this genome difficulties in achieving an ante mortem present. Subsequently the vasculitis can mutation should be generated many diagnosis, the fatal nature of the disease, result in the peritoneal pleural and times over during the course of a typical and the difficulties of control of FCoV pericardial effusions seen in the ‘wet’ FCoV infection in a cat. However FIP only infection. form of the disease. In contrast the ‘dry’ arises sporadically in FCoV-infected cats, form of the disease is characterised by suggesting that factors other than the What Causes FIP? the organ system most affected by the described genetic mutation also play a During natural FCoV infection the virus granuloma formation e.g. neurological role in the development of FIP. Host replicates within enterocytes, particularly dysfunction with central nervous system factors are likely to play a role in this. of the colon and to a lesser extent the involvement, uveitis with ocular involvement. small intestine (Kipar and others 2010). It has been proposed that the molecular

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HYGIENE, clean kittens, spotless litter trays Fig. 1:Sm Riskall factors involved in Feline Infectious Peritonitis development and their management. stable groups 10

Control Separate other isolation and diseases kittening DELAY units REHOMING

Modulate immune response avoid same pair matings?

Fig. 1: Risk factors involved in Feline Infectious Peritonits development and their management.

Diagnosing FIP Blood Tests Additional serum testing FIP can be difficult to definitively diagnose Haematology and serum biochemistry l Protein electrophoresis despite a high degree of clinical suspicion can support a diagnosis of FIP, and • increased α2- globulins (mostly based on history, clinical signs and routine although changes are largely non-specific haptoglobin). laboratory tests. they can used to increase the index of • increased γ-globulins History & Clinical Signs suspicion. l Raised α1-acid glycoprotein (>0.48 The wide range of clinical signs makes Haematology mg/ml is abnormal but levels in FIP cases FIP a differential in many different clinical l Lymphopenia (55-77% of cases). are often markedly elevated at >1.5 mg/ml) cases. However, history and clinical signs l Neutrophilia (39-55% of cases). can be used to increase the index of suspicion. l Mild to moderate normocytic, normochromic anaemia (37-54% l FIP is most common in young cats (<3 of cases). years), but a smaller peak also occurs in older cats (>10 years). Serum Biochemistry l Pedigree cats and cats from multicat l Hyperproteinaemia households are at increased risk. (up to 60% of cases). l A recent history of stress (rehoming, • hyperglobulinaemia. neutering, introduction of new cats, • low or low-normal serum albumin. vaccination) may be apparent. • albumin: globulin (A:G) ratio. l Typical clinical signs of FIP: lethargy, low (< 0.4) = FIP very likely. anorexia, weight loss, pyrexia, jaundice, high (> 0.8) = FIP very unlikely. ascites (see Fig. 2) and/or pleural effusion and/or pericardial effusion, neurological • Hyperbilirubinaemia (21-36% of signs and/or ocular changes etc. cases; especially in effusive cases; magnitude increases as NB: FIP is a progressive disease: clinical the disease progresses). signs change over time so it is important • Liver enzymes (ALT, ALP & to repeat clinical (including ophthalmic GGT) often normal or only Fig. 2: British Shorthair with ‘wet’ FIP showing and neurological) examinations. mildly or moderately elevated. abdominal distension consistent with ascites. www.felineupdate.co.uk Feline INFECTIOUS PERITONITIS: HOW CAN WE GET A DIAGNOSIS?

FCoV Serology (e.g. lymphoma) and bacterial peritonitis mortem. Histopathology has been used as Commercial testing of serum FCoV can produce abdominal effusions of a similar the ‘‘gold standard’’ diagnostic test for the antibodies typically use enzyme-linked nature to FIP; remember that cytology diagnosis of FIP (Hartmann and others, 2003). immunosorbent assays (ELISAs) or (neoplastic cells and large numbers of [septic] However, routine histopathology is not indirect immunofluroescence antibody neutrophils respectively) may help 100% sensitive: lesions may be missed (IFA) tests. They only test for the presence differentiate the latter two diagnoses, whilst due to their multifocal distribution e.g. if of antibodies against any type of CoV and lymphocytic cholangitis will be accompanied small samples are taken, or if non- cannot differentiate antibodies induced by at least moderate increases in liver affected organs being sampled (Giordano by FIP-causing FCoVs from those not enzymes (esp. ALP and GGT). and others 2005). Immunostaining for associated with disease. Methodology Reverse-transcriptase (RT-) polymerase FCoV antigen (see below) can be used to and antibody titre results can differ between chain reaction (PCR) for detecting FCoV further confirm a diagnosis of FIP, and can be used in cases that have an different laboratories (so one cannot RT-PCR can detect viral FCoV RNA in absence of classical histopathology directly compare results). A positive blood, effusions, faeces (to detect FCoV changes (Giori and others 2011). FCoV antibody test only indicates that shedders) or tissue samples. Current the cat has been infected with an FCoV PCR assays detect any FCoV and are not Immunological staining of FCoV antigen and has seroconverted. Seroconversion specific for those associated with FIP. Immunohistopathology or immuno- takes 2-3 weeks. Although cases of FIP The use of RT-PCR to detect FCoV in cytology staining of formalin-fixed tissues tend to have higher antibody titres than blood samples showed promise in some or effusion cytology samples, respectively, non-FIP cases, the degree of overlap studies, although the level of FCoV in the has been used to identify FCoV antigen makes interpretation in an individual cat blood of cats affected with FIP can be associated with pathology in tissues or in the difficult. Indeed, most seropositive cats very low. RT-PCR on effusion or tissue cells of an effusion. Positive immunological will never develop FIP, and around 10% of samples is potentially more helpful. staining of tissues is said to confirm a cats with FIP are seronegative. Recent studies suggest that FCoV RNA diagnosis of FIP (i.e. it is very specific), can be amplified by RT-PCR from the vast although a negative result does not Effusion samples (usually peritoneal majority of FIP effusion samples tested, exclude FIP as FCoV antigens may be or pleural) are very helpful in the but not from non-FIP effusions (Held and variably distributed within lesions diagnosis of FIP. They may be classified others 2011, Tsai and others 2011). Work (Giordano and others 2005). as exudates based on their high protein at the University of Bristol has found Immunostaining of effusion samples has concentration (>35 g/l) but are more of similar RT-PCR results using effusion also shown variable sensitivity: a false a modified transudate based on samples, and also of tissue samples, negative result may be obtained if the their low cell counts although non-invasive collection of tissue effusion is cell-poor (i.e. few macrophages (usually <10 x109 cells/l). samples is obviously more difficult. In the in the sample), or if the FCoV antigen is future RT-PCR performed on tissue samples complexed by FCoV antibodies in the Body Cavity Effusions collected by minimally invasive techniques effusion. An abstract at a recent Identification and analysis of effusions e.g. Tru-Cut biopsy, may become a useful conference (Held and others 2011) reported can be very useful in the diagnosis of FIP. diagnostic test as it is quicker to perform that two of 50 cats without FIP had Ascites is the most commonly than histopathology. However, further positive immunostaining on their effusions. encountered body cavity effusion; studies are required to assess the However, immunostaining is a useful adjunct however, pleural effusion and / or sensitivity and specificity of RT-PCR, as test in the diagnosis of FIP. It is available pericardial effusion may be present in the cats with intestinal FCoV infection in the from the Veterinary Laboratory Services, presence or absence of ascites. Repeated absence of FIP can also be viraemic, School of Veterinary Science, University imaging (especially ultrasonography) can whilst those with FIP can have low blood of Liverpool, United Kingdom. be useful to detect subtle effusions and copy numbers and the tissues biopsied Conclusions direct fluid sampling. Characteristics of may not contain granulomatous lesions. Many features of a cat’s history, clinical FIP effusions include: To date there are no commercial RT-PCR signs and laboratory testing can increase tests for the detection of the FCoV l They are usually clear, viscous and our suspicion of a diagnosis of FIP, genome mutation associated with the straw-yellow in colour. potentially to the point that a FIP-phenotype (Chang and others 2012), l Typically they have a total protein presumptive diagnosis of FIP can be but this shows promise for future concentration of >35 g/l and a made, particularly in the face of owner diagnostic tests for FIP. predominance (>50%) of globulins. financial constraints or clinical Histopathological examination of tissues l Similar biochemical changes to those deterioration. A definitive diagnosis can found in the serum exist in effusions: Routine histopathology be made in the majority of cats with i.e. low A:G ratios, increased α2 Historically a definitive diagnosis of FIP using histopathology and immunostaining. However, no test is globulins and γ-globulins, and relied on histopathological examination of 100% sensitive or specific and it is markedly elevated α1-acid affected tissues and the identification of important not to interpret any clinico- glycoprotein levels. characteristic changes (pyogranulomatous parenchymal foci, perivascular mono- pathology results in isolation. RT-PCR l They are often (but not always) nuclear infiltrates, fibrinous polyserositis). shows promise as an additional non- poorly cellular. Cell counts are usually Samples of tissue, typically from invasive test for the diagnosis of FIP but <10, (but occasionally counts higher mesenteric lymph nodes, liver, kidney further work is required to fully 9 than 25 x10 /l have been reported). and spleen or less commonly from the determine its sensitivity and specificity. The cell types most frequently are thorax (these are harder to obtain), can Detection of the FCoV genome mutation non-degenerate neutrophils, be collected ante mortem (by ultrasound- associated with the FIP-phenotype may macrophages and lymphocytes. guided percutaneous Tru-Cut biopsy, have the potential to increase the NB: Lymphocytic cholangitis, malignancy laparoscopy or laparotomy) or at post- specificity of RT-PCR in the future. www.felineupdate.co.uk Feline INFECTIOUS PERITONITIS: HOW CAN WE GET A DIAGNOSIS?

References aspiration biopsies of liver and kidney for of granulomatous vasculitis in feline Addie, D. D. (2000) Clustering of feline diagnosis of feline infectious peritonitis. infectious peritonitis. Veterinary coronaviruses in multicat households. Veterinary Clinical Pathology 34, 368-374. Pathology 42, 321-330. Veterinary Journal 159, 8-9. Giori, L., Giordano, A., Giudice, C., Grieco, Kipar, A., Meli, M. L., Baptiste, K. E., Bowker, L. J. & Lutz, H. (2010) Sites of feline Addie, D. D. & Jarrett, O. (1992) A study V. & Paltrinieri, S. (2011) Performances of coronavirus persistence in healthy cats. of naturally occurring feline coronavirus different diagnostic tests for feline infectious Journal of General Virology 91, 1698-1705. infections in kittens. Veterinary Record peritonitis in challenging clinical cases. 130, 133-137. Journal of Small Animal Practice 52, 152-157. Pedersen, N. C. (2009) A review of feline infectious peritonitis virus infection: Addie, D. D., Toth, S., Murray, G. D. & Hartmann, K. (2005) Feline infectious 1963-2008. Journal of Feline Medicine and Jarrett, O. (1995) The risk of typical and peritonitis. Veterinary Clinics of North Surgery 11, 225-258. antibody enhanced feline infectious America Small Animal Practice 35, 39-79 peritonitis among cats from feline Hartmann, K., Binder, C., Hirschberger, J., Potkay, S., Bacher, J. D. & Pitts, T. W. coronavirus endemic households. Cole, D., Reinacher, M., Schroo, S., Frost, (1974) Feline infectious peritonitis in a Feline Practice 23, 24-26. J., Egberink, H., Lutz, H. & Hermanns, W. closed breeding colony. Laboratory Animal Sciences 24, 279-289. Brown, M. A., Troyer, J. L., Pecon-Slattery, (2003) Comparison of different tests to J., Roelke, M. E. & O’Brien, S. J. (2009) diagnose feline infectious peritonitis. Sparkes, A. H., Gruffydd-Jones, T. J., Genetics and pathogenesis of feline Journal of Veterinary Internal Medicine Howard, P. E., Harbour, D. A. (1992) infectious peritonitis virus. Emerging 17, 781-790. Coronavirus Serology in Healthy Pedigree Infectious Diseases 15, 1445-1452. Held, D., König, M., Hamann, H. P., Senge, Cats. Veterinary Record 131, 35-36. R., Hüllermeier, E. & Neiger, R. (2011) Chang, H. W., Egberink, H. F., Halpin, R., Tsai, H. Y., Chueh, L. L., Lin, C. N. & Su, B. Accuracy of diagnostic tests for feline Spiro, D. J. & Rottier, P. J. (2012) Spike L. (2011) Clinicopathological findings infectious peritonitis (FIP) in cats with protein fusion peptide and feline and disease staging of feline infectious bodycavity effusion. In: ECVIM Forum. coronavirus virulence. Emerging peritonitis: 51 cases from 2003 to 2009 in Journal of Veterinary Internal Medicine, Infectious Diseases 18, 1089-1095. Taiwan. Journal of Feline Medicine and Seville, Spain. p 1505. Surgery 13, 74-80. Giordano, A., Paltrinieri, S., Bertazzolo, Kipar, A., May, H., Menger, S., Weber, M., W., Milesi, E. & Parodi, M. (2005) Leukert, W. & Reinacher, M. (2005) Sensitivity of Tru-cut and fine needle Morphologic features and development

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