【病毒外文文獻】2004 Recommendations from workshops of the second international feline coronavirus_feline infectious peritonitis symposi

Recommendations from workshops of the second international feline coronavirus feline infectious peritonitis symposium Diane D Addie a Saverio Paltrinieri b Niels C Pedersen c a Department of Veterinary Pathology Companion Animal Diagnostics Institute of Comparative Medicine Bearsden Road Glasgow Scotland G61 1QH UK b Dip Patologia Animale Igiene e Sanita Pubblica Veterinaria Via Celoria 10 Milano I 20133 Italy c Department of Medicine and Epidemiology School of Veterinary Medicine University of California 2108 Tupper Hall Davis CA 95616 USA Accepted 3 December 2003 Summary In August 2002 scientists and veterinarians from all over the world met in Scotland to discuss feline coronavirus FCoV and feline infectious peritonitis FIP The conference ended with delegates dividing into three workshops to draw up recommendations for FCoV control diagnosis and treatment and future research The workshops were chaired by the three authors and the recommendations are presented in this paper 2004 ESFM and AAFP Published by Elsevier Ltd All rights reserved Recommendations for control of FCoV in catteries Pedersen Due to time limits the working group decided to concentrate on breeding and rescue catteries rather than veterinary practices shows or boarding catteries as recommendations for the former would apply to the latter We are using the generic term feline coronavirus for a common RNA containing virus in accordance with the guidelines set out in the Fifth International Symposium on Coronaviruses Laude 1994 Feline coronavirus FCoV is com prised of two closely related biotypes 1 a ubiqui tous form present in virtually all large multi cat environments which leads to seroconversion and causes very little disease known as feline enteric coronavirus FECV and 2 a much less common mutant form of FECV that has gained the ability to replicate in macrophages and causes feline infec tious peritonitis known as FIP virus FIPV Both biotypes exist in at least two strains types I and II with large numbers of genetic variants FIP is the major consequence of feline corona virus infection and because FIPV occurs as a mu tant of the common FCoV control of FIP must be directed first at control of its parent virus and should that fail at the FIPV itself Early weaning and isolation Isolation of queens 2 3 weeks prior to parturition strict quarantine of queen and kittens and early weaning at 4 6 weeks of age is one means to prevent FCoV infection This procedure is based on the findings that some queens do not shed the virus some queens will stop shedding after several weeks if not re exposed and that even if they do shed very young kittens have maternal resistance to the virus Addie and Jarrett 1992 Therefore if you can prevent outside infection you should be able to remove the kittens from the queen before they can be infected and then continue to raise them clear of the infection Early weaning and isolation is not Corresponding author Tel 44 141 3305777 E mail address D D Addie vet gla ac uk D D Addie Journal of Feline Medicine and Surgery 2004 6 125 130 1084 2756 04 see front matter 2004 ESFM and AAFP Published by Elsevier Ltd All rights reserved doi 10 1016 j jfms 2003 12 009 just a good idea for the control of FCoV but also for the control of feline calicivirus feline herpesvirus Bordetella bronchiseptica Microsporum spp and the many enteric infections to which kittens are susceptible Although straightforward in concept isolation of queens and early weaning is not as simple as it may seem The procedure requires quarantine rooms and procedures that absolutely ensure that new virus does not enter It also works best when the isolated queens are not shedding FCoV when they are shedding low levels or when they can clear the infection early after being isolated The single fac tor that most assures these conditions is the number of animals The success of early weaning and isolation in FCoV control depends on effective quarantine and low numbers of cats in the house hold preferably under 5 or 6 If there are less than 5 or 6 cats the chances of there being high or persistent shedders is low Also human abodes do not easily allow for adequate quarantine space for large numbers of queens and kittens and the time and money required to maintain quarantine goes up in proportion to the number of queens and litters under quarantine As examples of environment and cat numbers all kittens under 8 weeks old submit ted to a USA shelter were FCoV negative Pedersen et al 2003 These were kittens that largely came from one queen homes In contrast a Swiss study in large catteries demonstrated viral infection of kittens as young as 2 weeks old Lutz et al 2002 It is clear that low FCoV exposure will delay infec tion while high exposure can overcome maternally derived immunity at an early age There are two essential downsides of isolation and early weaning The first is that it is not easy to do and will fail if conditions are not proper Second some breeders believe that early weaning exacts a social price on the kittens In recognition of both concerns the group recommended that early weaning not be undertaken without careful con sideration FCoV free households would not be required to undertake routine isolation and early weaning Where kittens are isolated with their queen extra care must be taken during the 2 7 weeks of age period to socialise the kittens The success of early weaning should also be measured and not continued in situations where it is not working Kittens that have been successfully reared free of the FCoV should be antibody nega tive at 12 weeks of age If they are antibody posi tive it means that they have been infected with the virus Even if kittens can be raised free of FCoV it is clear that they may become infected sooner or later The virus is very widespread even among outdoor cats and it is easily carried on clothes hair hands shoes etc Pedersen et al 1981 Therefore the objective of isolation and early weaning should not be to prevent infection forever but to delay it It is known that immunity to FIPV does not develop until around 16 weeks of age based on experience with Primucell vaccine Pfizer reviewed by Pedersen et al 1995 We also have anecdotal evidence that FIPV infection in shelter and cattery kittens occurs in the first 2 months or so of life even though the actual disease may not appear outwardly for many weeks months and sometimes years Measurement of antibody titres and viral load FCoV serology also known as FIP serology can be of some value but only if it is performed accurately and expressed as an endpoint titre Lutz et al 2002 For instance cats with very low titres 1 25 or below are often shedding no or low levels of virus Addie and Jarrett 2001 and will frequently stop shedding when isolated Cats with high titres 1 400 are almost always shedding high levels of virus Some of these cats will stop shedding upon isolation and this will be demonstrated by a decrease in their titre to low or negligible levels If a cat is persistently shedding virus the titre will always remain high If laboratories cannot offer accurate antibody testing than the alternative is for commercial laboratories to make available quantitative RT PCR to measure viral load PCR based tests would be a direct measure of virus shedding Veterinarians would be supplied with a faecal swab in a tube and a bar code This would allow for accurate submission of samples Genetic markers in the cat We know that three groups of FCoV shedders exist 1 those that shed high levels of virus all of the time about 10 15 2 those that seem to be immune to the virus and never shed less than 5 and 3 those that continuously lose and re acquire the infection about 70 80 Addie and Jarrett 2001 Foley et al 1997 Do high shedders or resistant cats have genetic markers for either state Susceptibility to FCoV infection is likely to be different to susceptibility to the mutant FIPV We know that the heritability of FIP is about 50 susceptible cats being approximately twice as likely to develop FIP as other cats Foley and Pedersen 1996 That is why we do not recommend breeding 126 D D Addie et al cats that have thrown kittens that later developed FIP This would be especially true of toms which can sire so many more kittens and therefore have a greater genetic influence on the bloodline Genetic markers of the virus Are some FCoV strains more likely to mutate and thus cause FIP We see some households without any cat deaths despite endemic FCoV while other households suffer many cases of FIP Vaccination A FCoV vaccine may well be different from an FIPV vaccine just as immunity to the two biotypes of the virus may differ However doubt was expressed about the possibility of ever developing a successful vaccine to the non mutated form of FCoV or FECV because no vaccine can work better than natural infection Most infected cats develop immunity but the immunity disappears when the virus is controlled and the cats are then reinfected Most cats are repeatedly infected with the same strain of FCoV as well as by different strains Addie et al 2003 Panleucopenia vaccines work well because most cats in nature recover from the infection Where hosts do not have good immunity we often do not have good vaccines e g feline calicivirus Shelters Forty percent of young cats in the USA are now coming from shelters Previously people acquired kittens from newspaper advertisements and word of mouth Pedersen et al 2004 found that admis sion into a rescue cattery resulted in high levels of shedding of feline calicivirus herpesvirus and coronavirus All of these viruses can cause long term consequences in an infected cat Shelters need to optimise facilities and husbandry so they can be cleaned easily and minimise virus spread It is essential to decrease viral load and stress levels in shelters Recommendations for diagnosing FIP especially with regard to RT PCR tests and treatment Paltrinieri Serology and RT PCR At the present time FIP cannot be diagnosed solely by serology or on a positive RT PCR test In par ticular no specific data regarding the pathogenic role of some mutated genes or proteins detectable by RT PCR or serology have been published in independent peer reviewed scientific journals The diagnosis of FIP is based on the history of the animal the history of the disease signs on gross clinical abnormalities and a number of suggestive but not specific abnormal laboratory findings Immunohistochemistry to identify viral proteins in macrophages within lesions can be used on tissues taken at biopsy or necropsy Positive immunohisto chemical staining of macrophages within lesions is considered the most definitive test for FIP How ever the possibility of detecting replicating FCoVs within circulating monocytes by RT PCR was pre sented at this meeting and looks promising Simons et al 2002 Based on the assumption that only mutated FCoV can replicate within monocytes this test or other future tests based on biologic behaviour of mutated FCoVs might have a high diagnostic significance More detailed descriptions of diagnostic tests are given below Recommended tests for diagnosing FIP The most important tests for FIP are not laboratory but rather historical Most cats with FIP are from 6 months to 3 years of age come from shelters or catteries and show signs of cyclical antibiotic resistant fevers and specific physical manifes tations depending on the form of the disease and location of lesions A second tier of test findings include characteristic analysis of peritoneal or pleural effusions elevated white blood cell counts with neutrophilia and lymphopenia elevated globulin levels and non regenerative anaemia of chronic disease and hypoalbuminemia and elevated fibrinogen Laboratory tests such as the serology and RT PCR should comprise a third tier of diagnostics Because a wide range of tests is quite expensive it is prudent to start with basic tests first and add additional procedures only if prelimi nary testing justifies them For these reasons we recommend starting with a laboratory approach only when the clinical signs are strongly suggestive of FIP and keeping in mind a list of possible differ ential diagnoses This might help to choose the best panel of tests to apply to your case Analysis of the effusion In the case of suspect effusive FIP the analysis of the effusions remain the best diagnostic method although it can be supported by other clinico pathological changes In particular protein and globulin determination cytology and bacterial cul tures should be performed These tests might strongly support the diagnosis of FIP when high Recommendations from workshops 127 proteins and or globulin concentrations are found in a sterile effusion with cytologic signs of a non specific inflammatory process In any case they will rule out septic effusions and neoplasia mainly lymphomas but might not be enough to differen tiate FIP from for example cholangiohepatitis The detection of FCoVs in the effusion is the only conclusive test in these cases To do this immu nocytologic techniques immunofluorescence immunohistochemistry are preferable to the detection of FCoV genome by RT PCR although RT PCR might easily detect FCoV in the effusions Kita et al 2002 as previously stated it is a very sensitive technique and can detect any small amount of virus that might extravasate from blood to the effusion during every inflammatory process in cats with circulating FCoVs In contrast immu nocytology detects only large amounts of virus and moreover allows identification of macrophages as the cells carrying the FCoVs A positive result using these techniques can thus confirm the diagnosis of FIP while an eventual negative result does not exclude the disease Hartmann et al 2002 In these cases as in dry forms the detection of other clinico pathological changes is needed to support the clinical diagnosis of FIP Non effusive FIP In dry forms a list of possible differential diagnoses must also be considered to suggest the best diag nostic approach It is not possible in this report to list all possible differential diagnoses due to the extreme variability in clinical signs detectable in dry forms This list however should include any possible cause of fever of unknown origin FUO uveitis neurological alterations hepatic or renal failure The panel of tests to be used should be decided based on these symptoms and should always include a complete CBC non regenerative anaemia neutrophilic leukocytosis and in particu lar lymphopenia might have a high diagnostic value for FIP the determination of the albumin globulin ratio eventually followed by a serum protein elec trophoresis in the case of high globulins afii9825 2 and afii9828 globulins are expected to be elevated during FIP and the measurement of afii9825 1 acid glycoprotein levels high concentrations of this protein although not specific might be strongly suggestive of FIP Duthie et al 1997 Although none of the above men tioned changes is per se suggestive of FIP the presence of multiple alterations in cats with symptoms suggestive of FIP might highly increase the probability of correctly diagnosing the disease Other tests might also be considered in pure neurologic forms for example diagnostic imaging can exclude the presence of intracranial tumours and antibody titre in CSF can be evaluated and compared to those in blood a high CSF blood ratio might be detected during FIP based on the assump tion that antibodies are produced within the CNS but the results of this test must be carefully con sidered since alterations of the blood brain barrier BBB are often present during FIP The presence of a BBB damage can be excluded by measuring the serum CSF ratio of antibodies against other infectious agents e g herpes viruses The cost benefit ratio of such a compli cated panel of tests however strongly reduces its practical use The detection of histologic lesions consistent with FIP has been considered the only conclusive test for FIP for a long time Barlough and Stoddart 1998 and the finding of viral antigen in the lesions using immunofluorescence or immuno histochemistry again RT PCR is too sensitive allows further confirmation of the diagnosis Unfor tunately surgical biopsies cannot be taken fre quently during FIP due to the poor general conditions of the affected cats The probability of detecting histologic lesions or positive macro phages in ultrasound guided tru cut biopsies TCB or in fine needle aspiration biopsies FNA is very low and negatively correlated with the extension of the pyogranulomatous foci Paltrinieri manuscript in preparation Based on the general health status the clinician should then decide among the following three diagnostic approaches expose the cat to the risk of anaesthesia and laparoscopy laparotomy to obtain surgical biopsies and gather a conclusive diagnosis of FIP perform a non invasive bioptic technique TCB FNA with the possibility of a false negative result obtain only a presumptive diagnosis based on clinico pathological changes A presumptive diagnosis however would be not enough to subject the cat to any treatment In conclusion the only conclusive diagnosis of FIP must be obtained by the detection of FCoVs within macrophages in the effusions or within the lesions detected in surgical biopsies If such an approach cannot be followed the presence of mul tiple clinico pathological changes might support the clinical diagnosis of FIP in both wet and dry forms Serology and RT PCR are much more useful in the cattery management than in the diagnosis of the disease Recommendations on treatment of FIP No therapies have been proved to be effective for FIP and the use of alternative treatments and so called immunosuppressive or immunomodulat ing drugs should be suspect Although encouraging 128 D D Addie et al results obtained using feline recombinant feline interferon have been presented at this meeting Ishida et al 2004 further data are needed before recommendation of extensive use of this treat ment The best treatment at the present time is to stage the disease and treat symptomatically As long as the cat is eating feeling relatively well and not losing weight affected animals should be fed a high quality diet and kept as stress free as possible In contrast if the cat is losing condition is suffering from specific debilitating signs of the disease and has a poor quality of life treatment should be counselled against Severely affected animals should then be euthanased due to short survival expectation Even in cats with mild initial disease signs the ultimate mortality is over 95 However miracle cures do happen from time to time and miracles cannot happen unless they are allowed time to happen Recommendations for priority areas of future FCoV research Addie 1 In the absence of an effective vaccine it was considered a priority to prevent cats becoming infected with FCoV at all It was considered important to look at ways of minimising virus dose Existing cat litters need to be checked for their ability to limit FCoV transmission by bio cidal action and or good clumping The effect of flushing litter trays on FCoV spread needs to be investigated 2 The ideal vaccine should protect against FIP give good mucosal immunity to prevent infec tion and reduce virus shedding Development of a therapeutic vaccine should also be con sidered both to treat cats with FIP and to attempt to stop carrier cats from shedding For the latter it is essential to establish where the virus is in carrier cats the ileum and colon are the most likely areas so that immune clear ance of virus from this area is taken into consideration in vaccine development 3 The group was concerned about antibody dependent enhancement ADE being a labora tory artefact Addie et al 1995 and that experimental vaccines which might have worked perfectly well in the field had been rejected because in experimental infections they caused ADE A reasonable challenge virus nee