Proceedings of the International Congress of the Italian Association of Companion Animal Veterinarians

www.ivis.org Proceedings of the International Congress of the Italian Association of Companion Animal Veterinarians June 8-10, 2012 - Rimini, Italy Next SCIVAC Congress: Mar. 8-10, 2013 Pisa, Italy SCIVAC International Congress Canine Leishmaniasis and other Vector-Borne diseases. Current State of Knowledge Reprinted in the IVIS website with the permission of the Congress Organizers http://www.ivis.org

73 CONGRESSO INTERNAZIONALE MULTISALA SCIVAC RIMINI, 8-10 GIUGNO 2012 Feline keratoconjunctivitis clinical signs & the latest on diagnosis and therapy (Feline Herpesvirus, Chlamydia Felis, and Mycoplasma Spp.) David Maggs DVM, BVSc, Dipl ACVO, USA INTRODUCTION Feline herpesvirus is a ubiquitous virus that varies very little worldwide; i.e. strains do not vary greatly in their clinical virulence. And yet, we see a huge range of clinical signs in cats infected with this virus. There are probably a large number of reasons for this; however principle among these is likely the host s response to this virus. FHV-1-naïve kittens infected in the first few weeks of life against a backdrop waning maternal immunity almost inevitably get severe upper respiratory and ocular disease with high morbidity but rare mortality. By contrast, adult cats can undergo viral reactivation with viral shedding and can infect in-contact cats; all without demonstrating clinical signs themselves. These two scenarios represent just the two extremes of infection; within your clinic you see cats with a huge diversity of clinical signs in between. For this reason, I like to consider clinical signs associated with FHV-1 under one of three broad categories: primary infection, recrudescent infections, and FHV-1-associated syndromes. PRIMARY HERPETIC DISEASE Primary ocular FHV-1 infection is characterized by blepharospasm, conjunctival hyperemia, serous ocular discharge that becomes purulent by day 5-7 of infection, mild to moderate conjunctival swelling, and often conjunctival ulcers. Corneal involvement is not reliable; however some cats develop corneal ulcers which are transiently dendritic at the very earliest phase only. These dendrites quickly coalesce to become geographic ulcers. The ocular signs are seen in association with typical signs of upper respiratory infection. The uncomplicated clinical course is typically 10-14 days; however it is critical to realize that almost all cats become latently infected within ganglia for life. Reactivation from latency is likely in at least 50% of cats, sometimes with viral shedding. RECRUDESCENT FHV-1 SYNDROMES Despite the frequency with which latently infected cats undergo viral reactivation at the ganglia and viral shedding at peripheral epithelial sites, recrudescent disease occurs in a minority of these. Further, disease severity and tissue involvement can range very widely between individuals and even between episodes in the same cat. Recrudescent conjunctivitis is usually milder than in acute infections, but can become chronic and smoldering. Although recrudescent conjunctivitis is usually nonulcerative, substantial conjunctival thickening and hyperemia can occur secondary to inflammatory cell infiltration. Corneal involvement is relatively frequent in recrudescent disease compared to primary infection and may involve the corneal epithelium or stroma. With epithelial involvement, dendritic and later geographic corneal ulceration may be seen just as in primary infections. Corneal stromal disease is typically immunopathological (i.e., immune-mediated, but not necessarily autoimmune) in origin and includes stromal neovascularization, edema, stromal cell infiltration, and ultimately fibrosis usually under an intact epithelium. Consensus has not been reached regarding the antigens responsible for the subepithelial immunological response within cornea and/or conjunctiva. Some believe the process is driven by viral antigens, while others are suspicious that altered self antigens are the focus of the immunological response. FHV-1-ASSOCIATED DISEASE SYNDROMES The following diseases have been associated with detection of FHV-1 in affected tissues; however the causative role of the virus in each syndrome has been variably proven. Symblepharon. There is little question that symblepharon can be a sequela to severe primary FHV-1 infection. It is commonly seen in young animals, and presumably occurs as a result of widespread ulceration with exposure of the conjunctival substantia propria and sometimes also the corneal stroma. FHV-1 is almost certainly the predominant cause of symblepharon formation in cats and other infectious agents are unlikely to cause symblepharon formation. Corneal sequestration. Experimentally, FHV-1 inoculation (in cats receiving corticosteroids) can result in corneal sequestration. However, the prevalence of detectable FHV-1 328

in samples collected from cats with sequestra has varied widely in the clinical setting and the link between FHV-1 and sequestra has not been shown to be causative. It seems likely that sequestration is a non-specific response to stromal exposure or damage and that FHV-1 is just one possible cause of this disease. This is borne out in a study by Nasisse et al who reported identification of FHV-1 DNA in 86 of 156 (55%) of sequestra analyzed (compared with only 6% of clinically normal corneas). A lower prevalence of FHV-1 DNA was found in corneas of Persian and Himalayan cats with sequestration, suggesting that other non-viral causes of sequestration are more likely to be operative in these breeds. We will mention this further in the corneal conundrums lecture. Eosinophilic keratitis. Prior clinical studies have suggested a link between FHV-1 infection and eosinophilic keratitis. PCR testing of corneal scrapings from cats with cytology-confirmed eosinophilic keratitis has revealed 76% (45/59) of cases to be FHV-1 positive. However, PCR performed on tears collected onto a STT was negative in 10 cats with cytologically proven eosinophilic keratitis. As with corneal sequestra, the role of the virus in the initiation or exacerbation of this disease has not been determined; however anecdotally some patients with this syndrome improve with antiviral therapy alone. We will mention this further in the corneal conundrums lecture. Uveitis. HSV-1 is a well-documented cause of uveitis in humans. Given the shared biological behavior of the alphaherpesviruses, we examined the role of FHV-1 in feline uveitis. The PCR assay was used to demonstrate FHV-1 DNA in the aqueous humor of 12/86 cats; all but one of which had uveitis. The same study also used ELISA to examine FHV-1-specific antibody concentrations in aqueous humor and serum. While seropositivity did not vary among cats, intraocular antibody production, as determined by a Goldman-Witmer coefficient (C-value) > 1, was detected only in cats with uveitis. Additionally, a Cvalue > 8, which is frequently quoted as a more clinically useful indicator of intraocular antibody production, was found only in cats with idiopathic uveitis. This information suggests that FHV-1 can infect the intraocular compartment and that, at least in some cats, it stimulates a specific and local antibody response. Because the trigeminal nerve supplies the uveal tract, it is possible that virus may reactivate spontaneously or via induction and arrive in the uvea (and aqueous humor) by the round trip theory, as for surface ocular disease. Viral pathogenic mechanisms similar to those reported in surface disease are therefore plausible explanations for the uveal pathology seen. That is, virally mediated cytolysis and immunopathological responses directed at auto or viral antigens are both possible. However, proving a casual association remains difficult. Dermatitis. Periodically, FHV-1 has been identified as a cause of dermatological lesions, particularly those surrounding the eyes and involving nasal skin of domestic and wild felidae. This is not surprising when one considers the marked epithelial tropism of this virus and the reliability with which HSV-1 causes dermal lesions. We have recently examined the diagnostic utility of FHV-1 PCR for this disease. FHV-1 DNA was detected in all 9 biopsy specimens from 5 cats with herpetic dermatitis but in 1 of 17 biopsy specimens from the 14 cats with nonherpetic dermatitis, and was not detected in any of the 21 biopsy specimens from the 8 cats without dermatitis. This is in sharp contrast to the use of this technique in ocular tissues where the extent of viral shedding in normal animals dramatically reduces the sensitivity of a positive test in affected animals. When results of histologic examination were used as the gold standard in this study of cats with dermatitis, sensitivity and specificity of the PCR assay were 100% and 95%, respectively. We concluded that FHV-1 DNA can be detected in the skin of cats with herpetic dermatitis, that the virus may play a causative role in the disease, and that this PCR assay may be useful in confirming a diagnosis of herpetic dermatitis. DIAGNOSING CATS WITH KERATOCONJUNCTIVITIS One of my least favorite questions is What is the best laboratory test for cats with corneal or conjunctival disease?. In reality there is not one. Explaining this position requires an understanding of an essential fact about feline herpesvirus (FHV-1) - clinically normal cats (and lots of them) can shed FHV-1 at their ocular surface. Because PCR is more sensitive than IFA or VI, this assay exacerbates this problem. In fact, in some humane shelter-based populations, about half of all normal cats are shedding FHV-1 DNA as determined by PCR. Therefore, in some circumstances, the number of false positive test results we can expect is extraordinarily high and we may be better to flip a coin than to run that PCR assay! Given the predictably high rate of false positive (particularly with serology and PCR) and negative test results (particularly with VI and IFA), I now no longer conduct laboratory tests for FHV-1 or Chlamydia felis (previously Chlamydia psittaci and, before that, Chlamydophila felis) in individual cats with keratoconjunctivitis. Rather, I resort to good old fashioned clinical acumen. My diagnostic tests now are (i) the history and clinical exam findings followed by (ii) response to therapy. This requires acceptance of a couple of critical facts: first I have to be willing to be wrong when making an educated guess regarding the etiological diagnosis and, second, I have to use the absolute best therapeutic trial and demand excellent owner compliance in executing that trial. DIAGNOSING KERATOCONJUNCTIVITIS USING CLINICAL SIGNS AS YOUR GUIDE Using clinical signs of surface ocular disease as a diagnostic assay requires a philosophical approach that I liken to adding pebbles to one of two sides of an old-fashioned scale or balance. I start with the paradigm that feline keratoconjunctivitis is infectious till proven otherwise and that by far and away the most commonly implicated infectious organisms are FHV-1 and Chlamydia felis. I then consider 329

the clinical signs outlined in the table. Using each feature as a discerning feature I aim to place one of my diagnostic pebbles on the herpetic or chlamydial sides of the balance, thereby making a clinical judgment at the end of the examination as to which of these 2 organisms is more likely to be the cause of the disease seen. Table. Clinical observations as a means to differentiate chlamydial and herpetic ocular surface disease Clinical Signs FHV-1 C. felis Conjunctival hyperemia +++ ++ Chemosis + +++ Conjunctival ulceration +/- - Keratitis +/- - Dendrites Pathognomonic - Respiratory signs/malaise ++ +/- Note that both agents cause some of the signs and that it is a weighted assessment. This introduces a notable element of subjectivity into the assessment. I unashamedly tell clients this and explain that I still believe that this is better than wasting their money on a laboratory test. I also use this time to introduce the concept that the clients themselves will form the critical next step in the diagnostic process response to therapy. We will discuss this more fully in the next session. ANTIVIRAL THERAPY If we are to use response to therapy as a diagnostic test, then we must choose the optimum therapeutic approach possible for each cat. This requires knowledge regarding: 1. General features of the antiviral drug class 2. Specific in vitro susceptibility of FHV-1 to each drug 3. How well tolerated and how safe each drug is in cats 4. Which tissues are reached following topical or systemic therapy 5. The owner preferences Some general comments. Although a large variety of antiviral agents exists for oral or topical treatment of cats infected with feline herpesvirus type 1 (FHV-1), some general comments regarding these agents are possible: No antiviral agent has been developed for FHV-1; although many have been tested for efficacy against this virus. Agents highly effective against closely-related human herpesviruses are not necessarily or predictably effective against FHV-1 and all should be tested in vitro before they are administered to cats. No antiviral agent has been developed for cats; although some have been tested for safety in this species. Agents with a reasonable safety profile in humans are not always or predictably nontoxic when administered to cats and all require safety and efficacy testing in vivo. Many antiviral agents require host metabolism before achieving their active form. These agents are not reliably or predictably metabolized by cats and pharmacokinetic studies in cats are required. Antiviral agents tend to be more toxic than do antibacterial agents since viruses are obligate intracellular organisms and co-opt or have close analogues of the host s cellular machinery. This limits many antiviral agents to topical (ophthalmic) rather than systemic use. All antiviral agents currently used for cats infected with FHV-1 are virostatic. Therefore, they typically require frequent administration to be effective. The following antiviral agents have been studied to varying degrees for their efficacy against FHV-1, their pharmacokinetics in cats, and/or their safety and efficacy in treating cats infected with FHV-1. Trifluridine (TFU or trifluorothymidine) is too toxic to be administered systemically but topically administered trifluridine is considered one of the most effective drugs for treating HSV-1 keratitis. This is in part due to its superior corneal epithelial penetration. It is also one of the more potent antiviral drugs for FHV-1. It is commercially available in the USA as a 1% ophthalmic solution that should be applied to the affected eye 5-6 times daily. Unfortunately, it is expensive and is often not well tolerated by cats, presumably due to a stinging reaction reported in humans. Idoxuridine (IDU) is a nonspecific inhibitor of DNA synthesis, affecting any process requiring thymidine. Therefore, host cells are similarly affected, systemic therapy is not possible, and corneal toxicity can occur. It has been used as an ophthalmic 0.1% solution or 0.5% ointment. This drug is reasonably well tolerated by most cats and seems efficacious in many. It is no longer commercially available in the USA but can be obtained from a compounding pharmacist. It should be applied to the affected eye 5-6 times daily. Vidarabine (VDB) interferes with DNA polymerase and, like idoxuridine, is non-selective in its effect and so is associated with notable host toxicity if administered systemically. Because it affects a viral replication step different from that targeted by idoxuridine, vidarabine may be effective in patients whose disease seems resistant to idoxuridine. As a 3% ophthalmic ointment, vidarabine often appears to be better tolerated than many of the antiviral solutions. Where it is not available commercially, it can be obtained from a compounding pharmacist. Like idoxuridine, it should be applied to the affected eye 5-6 times daily. Acyclovir (ACV) has relatively low antiviral potency against FHV-1, poor bioavailability, and is potentially toxic when systemically administered to cats. Oral administration of 50 mg/kg acyclovir to cats was associated with peak plasma levels of only approximately one third required for this virus. Common signs of toxicity are referable to bone marrow suppression. However, acyclovir is also available as a 3% ophthalmic ointment in some coun- 330

tries. In one study in which a 0.5% ointment was used 5 times daily, the median time to resolution of clinical signs was 10 days. Cats treated only 3 times daily took approximately twice as long to resolve and did so only once therapy was increased to 5 times daily. Taken together, these data suggest that very frequent topical application of acyclovir may produce concentrations at the corneal surface that do exceed the reported concentration required for this virus but are not associated with toxicity. There are also in vitro data suggesting that interferon exerts a synergistic effect with acyclovir that could permit an approximately 8- fold reduction in acyclovir dose. In vivo investigation and validation of these data are needed. Valacyclovir (VCV) is a prodrug of acyclovir that, in humans and cats, is more efficiently absorbed from the gastrointestinal tract compared with acyclovir and is converted to acyclovir by a hepatic hydrolase. Its safety and efficacy have been studied in cats. Plasma concentrations of acyclovir that surpass the IC50 for FHV-1 can be achieved after oral administration of this drug. However, in cats experimentally infected with FHV-1, valacyclovir induced fatal hepatic and renal necrosis, along with bone marrow suppression, and did not reduce viral shedding or clinical disease severity. Therefore, despite its superior pharmacokinetics, valacyclovir should never be used in cats. Ganciclovir (GCV) appears to be at least 10-fold more effective against FHV-1 compared with acyclovir. It is available for systemic (IV or PO) and intravitreal administration in humans, where it is associated with greater toxicity than acyclovir. Toxicity is typically evident as bone marrow suppression. It has just been released as a new topical antiviral gel in humans. There are no reports of its safety or efficacy in cats as a systemic or topical agent. Penciclovir (PCV) is available as a dermatologic cream for humans that should not be applied to the eye. We have some preliminary data in which we administered PCV intravenously to cats, but this was done largely to assist with our ongoing investigations of the penciclovir prodrug famciclovir (unpublished data). In vivo studies of penciclovir s safety or efficacy in cats are lacking and at this time, its use in cats cannot be recommended. Famciclovir (FCV) is a prodrug of penciclovir; however metabolism of famciclovir to penciclovir is complex and requires di-deacetylation followed by oxidation to penciclovir by a hepatic aldehyde oxidase. Unfortunately, hepatic aldehyde oxidase activity is nearly absent in cats. This necessitates cautious extrapolation to cats of data generated in humans. Our data to date in normal and experimentally infected cats suggest that the pharmacokinetics of this drug are extremely complex and likely result from nonlinear famciclovir absorption, metabolism, or a combination of the two. Despite this, there is mounting evidence that suggests famciclovir is very effective in some cats with experimentally induced (90 mg/kg TID) or suspected spontaneous herpetic disease. Further studies of this drugs pharmacokinetics, safety and efficacy are required before dose rates and frequency can be recommended; however we have recently demonstrated that cats receiving 40 or 90 mg famciclovir/kg TID achieve similar plasma penciclovir concentrations. Therefore, it seems likely that 40 mg/kg PO TID might be expected to be as effective as 90 mg/kg PO TID. By comparison the plasma penciclovir concentration following oral administration of 15 mg/kg was only approximately onethird that achieved with 40 or 90 mg/kg. There is also a report of this drug being administered to a small number of clientowned cats with good results. In no study to date have any signs of toxicity been noted. Finally, we have shown that 40mg/kg PO TID produced tear penciclovir concentrations likely to be effective against FHV-1 for approximately 4 hours after oral administration. Cidofovir (CDV) is commercially available only in injectable form in the USA but has been studied as a 0.5% solution applied topically twice daily to cats experimentally infected with FHV-1. Its use in these cats was associated with reduced viral shedding and clinical disease. Its efficacy at only twice daily (despite being virostatic) is believed to be due to the long tissue half-lives of the metabolites of this drug. There are occasional reports of its experimental topical use in humans being associated with stenosis of the nasolacrimal drainage system components and, as yet, it is not commercially available as an ophthalmic agent in humans. Therefore, at this stage there are insufficient data to support its long term safety as a topical agent in cats. LYSINE The literature regarding lysine has become very interesting recently with some data that at first glance appear contrary to earlier study outcomes which suggested efficacy. This requires a more detailed assessment. In Vitro efficacy against FHV-1. Lysine limits the in vitro replication of many viruses, including FHV-1. The antiviral mechanism is unknown; however, many investigators have demonstrated that concurrent depletion of arginine is essential for lysine supplementation to be effective. This finding suggests that lysine exerts its antiviral effect by antagonism of arginine. This is certainly true for FHV-1 where arginine is an essential amino acid for viral replication but, in the presence of small amounts of arginine, lysine supplementation reduces viral replication by about 50%. However, this effect was not seen in media containing higher arginine concentrations, suggesting that a high lysine: arginine ratio was critical for efficacy. In Vivo Research in Cats. Results of 2 early independent in vivo studies have supported the clinical use of l-lysine in cats. In the first of these studies, 8 FHV-1 naive cats were administered 500 mg of lysine per os q 12 hours beginning 6 hours before, and continuing for 3 weeks after, experimental inoculation with FHV-1. Lysine-treated cats had sig- 331

nificantly less severe conjunctivitis than cats that received placebo. In the second study, 14 latently infected cats received 400 mg of lysine per os q 24 hours. Viral shedding was monitored for 30 days. Lysine administration in these cats was associated with a statistically significant reduction in basal viral shedding compared with cats that received placebo. Since these cats were normal, latently infected carrier cats, little or no clinical disease was seen during the month-long study in the placebo or lysine group. In both studies, plasma arginine concentrations remained in the normal range, and no signs of toxicity were observed, despite notably elevated plasma lysine concentrations in treated cats. Importantly, both studies reported results of lysine administration to experimentally infected cats; therefore, the applicability of these data in naturally infected cats needed to be investigated. A subsequent study examined the effects of lysine in 144 cats in a shelter. Cats received oral boluses of 250 mg (kittens) or 500 mg (adult cats) of lysine once daily for the duration of their stay at the shelter and outcomes were compared with those of an untreated control group. No significant treatment effect was detected on the incidence of infectious upper respiratory disease (IURD), the need for antimicrobial treatment for IURD, or the interval from admission to onset of IURD. However it was not determined if and to what extent these cats were shedding or infected with FHV-1 or other pathogens. This study raised the concern that bolus administration of lysine to individual cats within multicat environments such as shelters, where FHV-1 is prevalent, may not only be ineffective but it is also plausible that twice daily handling of these cats may actually stimulate further viral reactivation through stress and cause transfer of pathogens between cats by shelter workers administering the lysine. Thus we became interested in studying the safety and efficacy of l-lysine incorporated into cat food. Results of an initial safety trial were encouraging. Cats fed a diet supplemented with up to 8.6% (dry matter) l-lysine showed no signs of toxicity, had normal plasma arginine concentrations, and had normal food intake. Mean plasma lysine concentration of these cats was increased to levels similar to that achieved with bolus administration. In a subsequent study, 50 cats with enzootic upper respiratory tract disease were fed a diet supplemented to approximately 1% (n = 25) or 5% (n = 25) lysine for 52 days while subjected to rehousing stress which is known to cause viral reactivation. Perhaps not unexpectedly, food (and therefore lysine) intake decreased coincident with peak disease and viral presence. As a result, cats did not receive lysine at the very time they needed it most. Analysis of the data revealed that disease in cats fed the supplemented ration was more severe than that in cats fed the basal diet. In addition, viral shedding was more frequent in cats receiving the supplemented diet. To further elucidate the efficacy of dietary lysine supplementation, we performed a similarly designed experiment in a local human shelter with a more consistent background level of stress and with greater numbers enrolled compared to the initial rehousing study. We enrolled 261 cats; each for 4 weeks. Despite plasma lysine concentration in treated cats being greater than that in control cats, more treated cats than control cats developed moderate to severe disease during week 4. Meanwhile, during week 2, FHV-1 DNA was detected more commonly in swab specimens from treated than control cats. Taken together, these data suggest that approximately 5% dietary lysine supplementation is not a successful means of controlling infectious upper respiratory disease within large multicat populations in which IURD is enzootic. In fact, it can lead to an increase in disease severity and the presence of FHV-1 DNA on oropharyngeal or conjunctival mucosa at certain points. Indications and Course of Treatment. Lysine is now commercially available in veterinary formulations and is recommended by many veterinarians for cats infected with FHV-1. There are no published data on dose, frequency of administration, course of therapy, or timing of lysine administration relative to herpetic disease episodes in client-owned patients; thus, information on these issues is anecdotal or derived from the studies described above. I administer 500 mg lysine per os q 12 hours. I administer it therapeutically at the time of recrudescent disease and encourage owners of cats that have frequent recurrences to administer this same dose over the long term as a prophylactic measure. More recently I have strongly recommended that client-owned animals receive lysine as a twice daily bolus; not sprinkled on food. Unlike the protocol for HSV-1 infected humans, owners of cats receiving l-lysine for FHV-1 should not be advised to restrict their cat s arginine intake. THE INTERFERONS Interferons are a group of cytokines that have diverse immunological and antiviral functions. Interferons are divided into 4 groups; α, β, γ, and ω interferons, and numerous subtypes. Viral infection stimulates cells to secrete interferon (IFN) into the extracellular space where it binds to specific receptors on neighboring cells and, through mechanisms not fully understood, prevents or limits the spread of infection (i.e., it is not virucidal). Although interferons may play important physiological roles in the control of viral infections, in vitro and clinical trials investigating potential therapeutic applications have produced conflicting results. In in vitro studies, 1 x 105-5 x 105 IU/ml of recombinant human IFNα or recombinant feline IFNω significantly reduced FHV-1 titer and/or cytopathic effect while not producing any detectable cytotoxic changes in the feline corneal cell line or CRFK cells on which the virus was grown. At higher concentrations, the effect the recombinant feline IFNω was greater than that of IFNα. In a separate in vitro study, notable synergistic activity against FHV-1 was demonstrated when 10-62.5 μg/ml acyclovir was combined with 10 or 100 IU/mL of human recombinant IFNα. The combined use of the 2 compounds did not cause increased cytotoxicity but permitted a nearly eightfold reduction in the dose of acyclovir required to achieve maximal inhibition of FHV-1. Significant synergistic interactions 332

resulted when the IFNα was given before or after infection at the lower doses of acyclovir; however IFNα pretreatment was more effective. I know of very few peer-reviewed, placebo-controlled, prospective clinical trials of IFN administration in SPF cats experimentally infected with FHV-1. One study utilized 10,000 IU recombinant feline IFNω administered topically (OU) q 12 hours and 2,000 IU administered PO q 24 hours. Based on data generated in studies utilizing other viruses and knowledge of the mode of action of IFNs, IFN administration in this feline study was initiated 2 days prior to viral inoculation but was not continued after inoculation. No beneficial effects were shown. The effects of very high-dose systemic administration of IFNα prior to experimental FHV- 1 infection have also been studied; 108 IU/kg were administered subcutaneously BID on two consecutive days prior to inoculation. Although disease was not prevented, cumulative clinical scores were lower for cats treated with IFNα. An abstract has also been presented detailing preliminary low-dose oral data. Cats received 1, 5 or 25 IU/cat IFNα PO q 24 hrs 24 and 48 hours after inoculation. Scores for disease severity were significantly lower in cats receiving 5 or 25 units than in control cats. Given the lack of peer-reviewed, masked, placebocontrolled studies and the variability in methodology and outcome in the few studies to date, further research is necessary to determine dosage, timing, and efficacy of this group of compounds, especially in the more chronic or recrudescent syndromes seen most commonly by ophthalmologists. CONTRAINDICATED THERAPY Anti-inflammatory therapy has relative or, in some circumstances, absolute contraindications in cats with herpetic disease, especially those undergoing primary infection and use of such agents remains controversial in the management of FHV-1 infections. However, a return to basic virology and a review of the literature makes some general comments possible. FHV-1 produces disease by at least 2 very different mechanisms that require markedly different (in fact, almost opposite) therapeutic approaches. Cytolytic infection represents active viral replication and is often ulcerative. Immunomodulation at this point is almost certainly contraindicated. By contrast, immunopathological (or immune-mediated) injury is mediated by host inflammatory responses and driven by persistent viral antigen and/or autoimmunity. Systemic administration of corticosteroids is a wellestablished and reliable means of inducing viral reactivation from latency. This must be considered whenever these drugs are considered in the clinical management of FHV-1-infected cats. The ability of locally-administered corticosteroids to exacerbate self-limiting primary conjunctival infection and to sometimes induce chronic herpetic keratitis has also been well established. Complications seen in corticosteroid treated eyes included deeper and more persistent corneal ulcers, corneal edema, corneal vascularization, sequestrum or band keratopathy formation, and protracted viral shedding. Topical corticosteroids are therefore contraindicated in primary ocular FHV-1 infection. The potential complications from using corticosteroids have prompted interest in the use of nonsteroidal antiinflammatory drugs (NSAIDs) for managing the inflammatory effects of ocular FHV-1 infection. Although there are no studies of their effects in cats infected with FHV-1, they are known to have similar negative effects to corticosteroids in humans and experimental studies investigating HSV-1. Cyclosporine is capable of suppressing inflammatory events operative in viral stromal keratitis, but also impairs viral clearance from the eye and suppresses some beneficial immune responses. In vitro, cyclosporine exerts a dose dependent effect on HSV-1 replication. In some experimental model systems, however, cyclosporine therapy resulted in more severe and persistent keratitis. In a recent clinical trial, cyclosporine and trifluridine were used in combination to treat HSK in humans with good results. Use of cyclosporine in chronic feline herpetic disease has been inadequately studied and I am unaware of any studies examining the effects of tacrolimus on ocular herpetic infections in any species. This suggests that use of these agents should, as a minimum, be restricted by the same principles that govern the use of corticosteroids in HSK. ANTICHLAMYDIAL THERAPY Chlamydia felis is also common cause of feline conjunctivitis; sometimes with mild rhinitis but without keratitis. Cats harbor and shed C. felis from non-ocular sites and systemic doxycycline is more effective at decreasing clinical signs and shedding of C. felis than topical therapy with a tetracycline-containing ophthalmic ointment alone. Azithromycin has good efficacy against chlamydial and mycoplasmal organisms and studies in humans show that antichlamydial concentrations are maintained in conjunctiva for 14 days and in tears for 4 days following a single oral administration. A feline pharmacokinetic study using a single oral dose of 5mg/kg showed reasonably rapid absorption, adequate bioavailability, and ocular concentrations that were detectable for at least 3 days. Based on these data and clinical reports from other ophthalmologists, I began using azithromycin at 5 mg/kg PO twice weekly for 3 weeks. I also treated all in-contact cats since silent harboring of C. felis is possible. This regimen is usually associated with adequate resolution of the chronic smoldering conjunctivitis for which C. felis is blamed; however it seemed that this effect was somewhat unpredictable in its duration following cessation of therapy. Repeat courses were often necessary. A recent experimental drug trial revealed that clinical disease was controlled approximately equally by doxycycline and azithromycin for about 20 days. However, while doxycycline-treated cats rapidly ceased to shed (day 7) and remained negative throughout the study, azithromycin-treated cats ceased shedding by day 6 but then shed Chlamydophila sporadically throughout the study. This suggests azithromycin decreases shedding but does not clear the 333

organism or that dosing more frequently than twice weekly is necessary. Therefore, I sometimes use an informed diagnostic (and therapeutic) trial of azithromycin because it is usually safe and relatively easy for clients to administer, particularly in multi-cat households. If this is successful but signs return in all or some cats, I usually recommend a 3 week course of doxycycline (10 mg/kg PO SID) for all cats. The usual precautions regarding esophageal stricture apply. I also use a topical tetracycline or erythromycin if conjunctivitis is severe so as to guarantee high drug concentrations at this site and to provide some surface ocular lubrication. Note that triple antibiotic is not effective against C. felis and that topically or systemically-administered corticosteroids are contraindicated as for FHV-1. 334