Feline herpesvirus

Herpesviruses: overview of systematics, genomic complexity and life cycle

Herpesviruses are double-stranded DNA viruses with distinct morphological features and are among the largest and most complex viruses. According to the International Committee on Taxonomy of Viruses (ICTV), in 2022, there were 133 herpesviruses classified into three families: Orthoherpesviridae, infecting mammals and birds; Malacoherpesviridae infecting marine molluscs; and Alloherpesviridae infecting fish and amphibians. Herpesviruses have a complex genomic architecture, characterised by unique regions flanked by repeated and inverted sequences. Unique regions can undergo rearrangements leading to the formation of genomic isomers, which could have important implications for the life cycle of the virus. Herpesviruses life cycle consists of two main phases: the lytic phase, during which viral genes are expressed and translated into viral proteins that regulate DNA replication, capsid formation and the production of new particles; and the persistence phase, in which the virus persists in the host without being eliminated by the immune system. This review offers an updated and comprehensive overview of the Herpesvirales order, detailing their morphological characteristics, providing an in-depth taxonomic classification, examining their genomic architecture and isomers, and describing their life cycle.

Presumed calcific band keratopathy in a 10-month-old domestic shorthair cat

OBJECTIVE

To describe a case of presumed band keratopathy in a young cat with no known history of corneal disease who was not receiving topical phosphate-based steroids.

ANIMAL STUDIED

A 10-month-old domestic shorthair cat was evaluated for severe ocular discomfort that did not improve despite the initiation of topical antibiotic treatment.

METHODS

A complete ophthalmic examination and ancillary tests such as biomicroscopy and corneal cytology were performed at the time of presentation. A superficial lamellar keratectomy was excised, and the corneal button was sent for histopathology. In addition to routine hematoxylin-eosin staining, sections were stained with Gram, PAS, von Kossa, and trichrome stains.

RESULTS

Biomicroscopic examination revealed an extensive corneal epithelial ulcer with a hard white plaque in the central area of the right cornea with associated superficial neovascularization. Ultrasound biomicroscopy showed a 0.63 mm, slightly hyperechoic band in the anterior corneal stroma. Corneal cytology evidenced numerous neutrophils with toxic changes and few macrophages. Histopathologic analysis excluded corneal sequestration as a differential diagnosis and confirmed superficial corneal mineralization. At the last follow-up, 16 months after surgery, corneal transparency had returned, and visual acuity was good with some corneal conjunctivalization.

CONCLUSIONS

In this case report, the presumptive diagnosis is calcific band keratopathy. To the best of the author's knowledge, this is the first presumed case in a cat not receiving topical phosphate-based steroids and without previous corneal damage. Lamellar keratectomy represents a curative approach that successfully resolved the clinical signs, with no reported recurrence.

Identification, Genetic Characterization, and Pathogenicity of Three Feline Herpesvirus Type 1 Isolates from Domestic Cats in China

(1) Background: Feline herpesvirus (FHV-1) is a significant pathogen in cats, causing respiratory and ocular diseases with consequential economic and welfare implications. (2) Methods: This study aimed to isolate and characterize FHV-1 from clinical samples and assess its pathogenicity. We collected 35 nasal and ocular swabs from cats showing symptoms of upper respiratory tract infection and FHV positivity detected by polymerase chain reaction (PCR). Viral isolation was carried out using feline kidney (F81) cell lines. Confirmation of FHV-1 presence was achieved through PCR detection, sequencing, electron microscopy, and indirect immunofluorescence assay. The isolated strains were further characterized by evaluating their titers, growth kinetics, and genetic characteristics. Additionally, we assessed the pathogenicity of the isolated strains in a feline model, monitoring clinical signs, viral shedding, and histopathological changes. (3) Results: Three strains of FHV-1 were isolated, purified, and identified. The isolated FHV-1 strains exhibited high homology among themselves and with domestic isolates and FHV-1 viruses from around the world. However, they showed varying degrees of virulence, with one strain (FHV-A1) causing severe clinical signs and histopathological lesions. (4) Conclusion: This study advances our understanding of the genetic and pathogenic characteristics of FHV-1 in China. These findings underscore FHV-A1 isolate as a potentially ideal candidate for establishing a challenge model and as a potential vaccine strain for vaccine development.

Nanoparticle ocular immunotherapy for herpesvirus surface eye infections evaluated in cat infection model

Ocular herpes simplex type 1 (HSV-1) infections can trigger conjunctivitis, keratitis, uveitis, and occasionally retinitis, and is a major cause of blindness worldwide. The infections are lifelong and can often recrudesce during periods of stress or immune suppression. Currently HSV-1 infections of the eye are managed primarily with anti-viral eye drops, which require frequent administration, can cause irritation, and may take weeks for full resolution of symptoms. We therefore evaluated the effectiveness of an ocular immune activating nanoparticle eye drop as a novel approach to treating HSV-1 infection, using a cat feline herpesvirus -1 (FHV-1) ocular infection model. In vitro studies demonstrated significant induction of both type I and II interferon responses by the liposome-dual TLR 3/9 agonist nanoparticles, along with suppression of FHV-1 replication. In cats with naturally occurring eye infections either proven or suspected to involve FHV-1, ocular nanoparticle treated animals experienced resolution of signs within several days of treatment, including resolution of keratitis and corneal ulcers. In a cat model of recrudescent FHV-1 infection, cats treated twice daily with immune nanoparticle eye drops experienced significant lessening of ocular signs of infection and significantly fewer episodes of viral shedding compared to control cats. Treatment was well-tolerated by all cats, without signs of drug-induced ocular irritation. We concluded therefore that non-specific ocular immunotherapy offers significant promise as a novel approach to treatment of HSV-1 and FHV-1 ocular infections.

First Report of Isolation and Molecular Characterization of Felid Herpesvirus-1 from Symptomatic Domestic Cats in Egypt

Feline herpesvirus 1 (FHV-1) is one of the main causes of upper respiratory tract infection in cats. Despite its veterinary importance, no previous studies investigated the occurrence of this virus in Egypt. In the present work, a total number of one hundred forty (N = 140) conjunctival and/or oropharyngeal swabs were collected from symptomatic cats during veterinary clinic visits located in two Egyptian provinces. Virus isolation was performed in the Chorioallantoic membranes (CAMs) of 12-days-old SPF eggs. Interestingly, the embryos showed stunting growth and abnormal feathering and infected CAMs showed edematous thickening and cloudiness with characteristic white opaque pock lesions. Polymerase chain reaction (PCR) amplification of the thymidine kinase gene (TK) was successful in 16/140 (11.4%) of the suspected cases. Two of the amplified genes were sequenced and the TK gene sequences of the FHV-1 isolates were highly similar to other reference strains in the GenBank database. Given the above information, the present study represents the first report of feline herpesvirus type 1 (FHV-1) in domestic cats in Egypt. Further studies on the causes of upper respiratory tract infections in cats as well as vaccine efficacy are needed.

Genomic analysis for virulence determinants in feline herpesvirus type-1 isolates

Feline herpesvirus type 1 (FHV-1) is a widespread cause of respiratory and ocular disease in domestic cats. A spectrum of disease severity is observed in host animals, but there has been limited prior investigation into viral genome factors which could be responsible. Stocks of FHV-1 were established from oropharyngeal swabs obtained from twenty-five cats with signs of infection housed in eight animal shelters around the USA. A standardized numerical host clinical disease severity scoring scheme was used for each cat from which an isolate was obtained. Illumina MiSeq was used to sequence the genome of each isolate. Genomic homogeneity among isolates was relatively high. A general linear model for fixed effects determined that only two synonymous single nucleotide polymorphisms across two genes (UL37/39) in the same isolate (from one host animal with a low disease severity score) were significantly associated (p ≤ 0.05) with assigned host respiratory and total disease severity score. No variants in any isolate were found to be significantly associated with assigned host ocular disease severity score. A concurrent analysis of missense mutations among the viral isolates identified three genes as being primarily involved in the observed genomic variation, but none were significantly associated with host disease severity scores. An ancestral state likelihood reconstruction was performed and determined that there was no evidence of a connection between host disease severity score and viral evolutionary state. We conclude from our results that the spectrum of host disease severity observed with FHV-1 is unlikely to be primarily related to viral genomic variations, and is instead due to host response and/or other factors.

Risk of Feline Immunodeficiency Virus (FIV) Infection in Pet Cats in Australia is Higher in Areas of Lower Socioeconomic Status

Simple Summary

Some diseases are known to occur at a higher frequency in Australia in areas of social and economic disadvantage. Identification of these diseases is important for effective infection control strategies. We investigated whether an association existed between socioeconomic factors and three infectious diseases in cats (feline immunodeficiency virus, FIV; feline calicivirus, FCV; and feline herpesvirus-1, FHV-1) in Australia. Disease cases that were reported to a voluntary veterinary disease surveillance system (Disease WatchDog) between January 2010 and July 2017 were extracted and analysed. Postcodes of the owners of these cats were compared to four government-published indexes measuring socioeconomic disadvantage and advantage. An association between socioeconomic status and FIV infection, but not FCV and FHV-1 infection, was found. FIV infection was more commonly reported in areas of socioeconomic disadvantage according to all four indexes. Prevention strategies targeting lower socioeconomic communities may help to reduce the overall prevalence of FIV infection in Australia.

Abstract

Feline immunodeficiency virus (FIV), feline calicivirus (FCV), and feline herpesvirus (FHV-1) are common viral infections of domestic cats in Australia. A study was performed to investigate the possible effect of area-based socioeconomic factors on the occurrence of FIV, FCV, and FHV-1 infection in Australian client-owned cats. A total of 1044 cases, reported to a voluntary Australian online disease surveillance system between January 2010 and July 2017, were analysed with respect to their postcode-related socioeconomic factors using the Socio-Economic Indexes For Areas (SEIFA). SEIFA consists of four different indexes which describe different aspects of socioeconomic advantage and disadvantage. Signalment details including age, sex, neuter status, and breed were also considered. A significant correlation was observed between areas of lower socioeconomic status and a higher number of reported cases of FIV infection for all four SEIFA indexes (p ≤ 0.0002). Postcodes with SEIFA indexes below the Australian median (“disadvantaged” areas) were 1.6–2.3 times more likely to have reported cases of FIV infection than postcodes with SEIFA indexes above the median (“advantaged” areas). In contrast, no correlation was observed between the number of reported cases of FCV or FHV-1 infection and any of the four SEIFA indexes (p > 0.05). When signalment data were analysed for the three infections, FIV-infected cats were more likely to be older (p < 0.00001), male (p < 0.0001), neutered (p = 0.03), and non-pedigree (p < 0.0001) compared to FCV and FHV-1 infected cats. Results from this study suggest that area-based disease control strategies, particularly in areas of social disadvantage, might be effective in reducing the prevalence of FIV infection in pet cats in Australia.

Cat flu: Broad spectrum polymeric antivirals

Feline herpesvirus type 1 (FHV-1) and feline calicivirus (FCV) are considered as main causes of feline upper respiratory tract disease and the most common clinical manifestations include rhinotracheitis, conjunctivitis, and nasal/facial ulcerations. While the primary infection is relatively mild, secondary infections pose a threat to young or immunocompromised cats and may result in a fatal outcome. In this study, we made an effort to evaluate antiviral potency of poly(sodium 4-styrenesulfonates) (PSSNa) as potent FHV-1 and FCV inhibitors for topical use. Mechanistic studies showed that PSSNa exhibits a different mechanism of action depending on target species. While PSSNa acts directly on FHV-1 particles blocking their interaction with the host's cell and preventing the infection, the antiviral potency against FCV is based on inhibition at late stages of the viral replication cycle. Altogether, PSSNa polymers are promising drug candidates to be used in the treatment and prevention of the viral upper respiratory tract disease (URTD), regardless of the cause.

Feline Herpesvirus Pneumonia: Investigations Into the Pathogenesis

Feline herpesvirus type 1 (FeHV-1) is one of the etiological agents of feline respiratory disease. FeHV-1 is an epitheliotropic and cytopathic virus that mainly causes rhinitis and conjunctivitis, although pneumonia is also occasionally seen. In this study, the authors investigated the pathogenesis of FeHV-1-associated pneumonia, comparing natural cases with viral infection of tracheal ring and cell cultures in vitro, using histology, immunohistology, double immunofluorescence, and transmission electron microscopy as investigative tools. The results confirm that FeHV-1 targets both respiratory epithelial cells and pneumocytes and indicate that FeHV-1 pneumonia is the consequence of continuous cell-to-cell viral spread from the upper airways via the trachea into the lungs. They provide strong evidence that FeHV-1–infected cells die primarily via apoptosis, following loss of cell-to-cell contact, rounding, and detachment. However, virus-induced lesions in vivo are dominated by marked neutrophil infiltration and extensive necrosis with less prominent apoptosis; in the airways, the tissue necrosis can extend into the submucosa. The necrosis appears to result from virus-induced neutrophil influx and release of proteolytic enzymes, such as matrix metalloproteinase-9, from the neutrophils.

Silicone-acyclovir controlled release devices suppress primary herpes simplex virus-2 and varicella zoster virus infections in vitro

Following initial infection, herpesviruses retreat into a permanent latent state with periodic reactivation resulting in an enhanced likelihood of transmission and clinical disease. The nucleoside analogue acyclovir reduces clinical symptoms of the three human alpha herpesviruses, HSV-1, HSV-2, and VZV. Long-term administration of acyclovir (ACV) can reduce the frequency and severity of reactivation, but its low bioavailability and short half-life require a daily drug regimen. Our lab is working to develop a subcutaneous delivery system to provide long-lasting, sustained release of ACV. Previously, we demonstrated that an implantable silicone (MED-4050) device, impregnated with ACV protected against HSV-1 both in vitro and in vivo. Here, we extend our in vitro observations to include protection against both HSV-2 and VZV. We also demonstrate protection against HSV-2 in vitro using MED-4750, a silicone polymer designed for long-term use in humans. When release of ACV from MED-4750 is quantitated on a daily basis, an initial burst of 5 days is observed, followed by a long period of slow release with near-zero-order kinetics, with an average daily release of 1.3923 ± 0.5908 μg ACV over days 20–60. Development of a slow-release implant has the potential to significantly impact the treatment of human alpha herpesvirus infections.

Effects of topical ocular administration of high doses of human recombinant interferon alpha-2b and feline recombinant interferon omega on naturally occurring viral keratoconjunctivitis in cats

OBJECTIVE

To determine whether 14-day topical ocular administration of high doses of feline recombinant interferon omega (FelFN) or human recombinant interferon alpha-2b (HulFN) solution improves clinical disease and decreases virus shedding in cats with naturally acquired viral keratoconjunctivitis.

ANIMALS

36 cats with upper respiratory tract disease and ocular involvement.

PROCEDURES

Cats received 1 drop of FelFN solution (1 × 10(6) U/mL), HulFN solution (1 × 10(6) U/mL), or saline (0.9% NaCl) solution (12 cats/group) in each eye twice daily for 14 days (beginning day 1). Oropharyngeal and conjunctival swab samples were collected from each cat before (day 0) and on day 14 of treatment for virus isolation (VI) and real-time quantitative PCR (RT-qPCR) testing to detect feline herpesvirus-1 and feline calicivirus. Subjective clinical scores were recorded on days 0, 3, 7, 10, and 14.

RESULTS

The number of cats for which feline herpesvirus-1 was detected via VI or RT-qPCR assay was generally (albeit not always significantly) lower on day 14, compared with day 0 findings; however, findings on days 0 or 14 did not differ among groups. The number of cats for which feline calicivirus was detected via VI or RT-qPCR assay did not differ significantly between days 0 and 14 for any group. Clinical scores significantly decreased over the 14-day period but did not differ among groups.

CONCLUSIONS AND CLINICAL RELEVANCE

In cats with naturally occurring viral keratoconjunctivitis, bilateral ocular administration of high doses of FelFN or HulFN twice daily for 14 days did not improve clinical disease or virus shedding, compared with treatment with saline solution.

Lingual Lesions in the Dog and Cat: Recognition, Diagnosis, and Treatment

The tongue plays many vital roles in the oral cavity of the dog and cat. Consequently, lingual lesions can have devastating effects on an animal's overall health. This article provides a review of tongue anatomy as well as a review of the etiology, gross appearance, and diagnostic procedures indicated for a wide variety of lingual lesions. Lingual pathologic conditions that are reviewed include traumatic, metabolic, idiopathic, infectious, immune-mediated, hereditary, and neoplastic lesions. This article also describes current concepts in the medical management of lingual lesions.

Treatment of corneal ulcers: when is surgery indicated?

PRACTICAL RELEVANCE

While corneal ulcers in cats frequently arise secondarily to feline herpesvirus (FHV-1) infection, and thus medical therapy is often indicated, other causes include trauma, eyelid abnormalities (agenesis, entropion, dermoids and neoplasia), tear film abnormalities and neurological deficiencies (trigeminal nerve paralysis or facial nerve paralysis). In some such cases, surgery is required. Treatment always needs to be tailored carefully according to the depth and progression of the ulcer, any concurrent ophthalmic disease, the patient's general health and demeanour, and owner compliance and financial circumstances.

PATIENT GROUP

All age groups and breeds can suffer with ulcerative keratitis although some breeds are over-represented for some types of corneal ulceration.

EVIDENCE BASE

The scientific literature on feline ulcerative keratitis is extensive. This article reviews the surgical indications for corneal ulceration in cats with reference to the current evidence base.

Complete genomic sequence and an infectious BAC clone of feline herpesvirus-1 (FHV-1)

Infection with feline herpesvirus-1 (FHV-1) is a major cause of upper respiratory and ocular diseases in Felidae. We report the first complete genomic sequence of FHV-1, as well as the construction and characterization of a bacterial artificial chromosome (BAC) clone of FHV-1, which contains the entire FHV-1 genome and has the BAC vector inserted at the left end of U(L). Complete genomic sequences were derived from both the FHV-1 BAC clone and purified virion DNA. The FHV-1 genome is 135,797bp in size with an overall G+C content of 45%. A total of 78 open reading frames were predicted, encoding 74 distinct proteins. The gene arrangement is collinear with that of most sequenced varicelloviruses. The virus regenerated from the BAC was very similar to the parental C-27 strain in vitro in terms of plaque morphology and growth characteristics and highly virulent in cats in a preliminary in vivo study.

Occurrence, morphological characterization and antigen localization of felid herpesvirus-induced pneumonia in cats: a retrospective study (2000-2006)

The pathological findings in nine cases of pneumonia associated with infection by felid herpesvirus-1 (FeHV-1) are presented. The animals affected were five kittens, two subadult cats and two adult cats. The microscopical changes included fibrinonecrotic pneumonia and severe necrosis of the bronchial and bronchiolar epithelium. FeHV-1 antigen was detected immunohistochemically in pneumocytes, alveolar macrophages and necrotic bronchial and bronchiolar epithelial cells. In the youngest kitten viral antigen was also found in the liver. FeHV-1 infection should therefore be considered as a differential diagnosis in cats with fibrinonecrotic pneumonia and demonstration of viral antigen by immunohistochemistry is a useful diagnostic procedure in such cases.

Evaluation of different sampling methods and results of real-time PCR for detection of feline herpes virus-1, Chlamydophila felis and Mycoplasma felis in cats

OBJECTIVE

To investigate how different sampling techniques affect detection of DNA from feline herpes virus Type 1 (FHV-1), Chlamydophila felis and Mycoplasma felis and to study the correlation between positive test results and clinical signs in cats.

ANIMALS

Fifty-one cats; 24 with ocular signs and 27 healthy control cats.

PROCEDURES

Samples were collected from all cats using cotton swabs, conjunctival and corneal biopsies, and corneal scrapings. Samples were analyzed for presence of FHV-1, C. felis, M. felis, and feline DNA, defined by 28S rDNA, by using real-time PCR.

RESULTS

In affected cats, FHV-1 was detected in only one cat; C. felis and M. felis were not detected in any affected cats. None of the three organisms was detected in any control cats. Feline DNA was demonstrated in all conjunctival samples, in 82% of corneal swabs, 92% of corneal scrapings, and 100% of keratectomy samples.

CONCLUSIONS

Because of the generally low detection rate for FHV-1, C. felis, and M. felis DNA in this study, differences regarding sampling technique could not be determined and correlation between positive test results and degree of clinical signs could not be made. Detection of feline DNA in most samples irrespective of sampling technique, suggests a low prevalence of FHV-1, C. felis and M. felis in this population of cats.

Feline herpesvirus-1 down-regulates MHC class I expression in an homologous cell system

Cytotoxic T lymphocytes (CTLs) are an essential component of the immune defense against many virus infections. CTLs recognize viral peptides in the context of the major histocompatibility complex (MHC) class I molecules on the surface of infected cells. Many viruses have evolved mechanisms to interfere with MHC class I expression as a means of evading the host immune response. In the present research we have studied the effect of in vitro Feline Herpesvirus 1 (FeHV-1) infection on MHC class I expression. The results of this study demonstrate that FeHV-1 down regulates surface expression of MHC class I molecules on infected cells, presumably to evade cytotoxic T-cell recognition and, perhaps, attenuate induction of immunity. Sensitivity to UV irradiation and insensitivity to a viral DNA synthesis inhibitor, like phosphonacetic acid, revealed that immediate early or early viral gene(s) are responsible. Use of the protein translation inhibitor cycloheximide confirmed that an early gene is primarily responsible.

Pilot study to evaluate the effect of oral supplementation of Enterococcus faecium SF68 on cats with latent feline herpesvirus 1

Feline herpesvirus 1 (FHV-1) infection is extremely common in cats and is frequently associated with morbidity because of recurrent ocular and respiratory clinical signs of disease. Enterococcus faecium strain SF68 is an immune-enhancing probiotic used as a dietary supplement. In this pilot study, 12 cats with chronic FHV-1 infection were administered either SF68 or a placebo, monitored for clinical signs of disease, monitored for FHV-1 shedding, and evaluated for FHV-1 specific humoral and cell-mediated immune responses and fecal microbiome stability. Fecal microbial diversity was maintained throughout the study in cats supplemented with SF68, but decreased in cats fed the placebo, indicating a more stable microbiome in cats fed SF68. While clinical results varied among individual cats, the overall findings suggest that administration of the probiotic lessened morbidity associated with chronic FHV-1 infection in some cats. Additional study is warranted to determine efficacy in a clinical setting.

Development of a quantitative real-time TaqMan PCR assay for testing the susceptibility of feline herpesvirus-1 to antiviral compounds

Feline herpesvirus-1 (FHV-1) is considered as the most common viral infection of domestic cats worldwide. It causes a disease characterized by upper respiratory and ocular clinical signs. Several attempts are currently underway to develop antiviral chemotherapy for treating FHV-1 infections. The availability of a rapid quantitative method for detecting FHV-1 would greatly facilitate prompt therapy, and hence enhance the success of any antiviral regime. In this study, a TaqMan real-time PCR assay was established for measuring FHV-1 DNA levels in culture supernatants. This assay was shown to be highly specific, reproducible and allows quantitation over a range of 2 to 2 x 10(8) copies per reaction. The assay was then applied to measure the reduction of FHV-1 DNA levels in the presence of increasing concentrations of acyclovir (ACV), penciclovir (PCV) and cidofovir (CDV). The 50% inhibitory concentrations (IC(50s)) obtained with the B927 laboratory strain of FHV-1 were 15.8 microM for ACV, 7.93 microM for CDV and 1.2 microM for PCV. The assay described here is sensitive, time-saving and does not involve prior titration of virus stocks or monitoring virus-induced cytopathic effects. Therefore, it is suitable for routine anti-FHV-1 drug susceptibility testing in veterinary clinics.

Detection of virulent feline herpesvirus-1 in the corneas of clinically normal cats

To evaluate the clinically normal feline cornea for the presence of virulent feline herpesvirus-1 (FHV-1), corneas from 31 cats (25 with normal eyes and six with active disease or corneal scarring) euthanased at a shelter were collected. Corneas from two specific pathogen-free cats were included as negative controls. Virus isolation (VI), fluorescent antibody (FA) staining and real-time polymerase chain reaction (rt-PCR) were performed on all samples. The presence or absence of dexamethasone in the media was evaluated for its effect on VI. VI was positive for FHV-1 in six corneas from five cats, all with clinically normal eyes. One cornea was positive for feline calicivirus (FCV) in addition to FHV-1, but only in media that included dexamethasone. Eight corneas were positive on rt-PCR for FHV-1, all from cats with clinically normal eyes. All positive VI samples were confirmed with FA staining. VI and rt-PCR were negative for FHV-1 and FCV in cats with active disease or corneal scarring. Data from this study indicate that virulent FHV-1 and FCV can be present in feline corneas that are clinically normal. Dexamethasone may enhance viral spread through a cell receptor mechanism.

In vitro effects of the active metabolite of leflunomide, A77 1726, on feline herpesvirus-1

OBJECTIVE

To determine whether the active metabolite of leflunomide, A77 1726 (A77), inhibits replication of feline herpesvirus-1 (FHV-1) in cell culture.

STUDY POPULATION

Crandell Rees feline kidney (CRFK) cell cultures.

PROCEDURES

Cell cultures were inoculated with FHV-1 and treated simultaneously with concentrations of A77 ranging from 0 to 200microM. The antiviral effect of A77 was determined by use of conventional plaque reduction assays. The effect of A77 on viral load was determined via real-time PCR analysis, and transmission electron microscopy was used to evaluate the effect of A77 on viral morphology. To determine whether the antiviral effect was attributable to alterations in CRFK cell viability and number, CRFK cells were treated with various concentrations of A77 and stained with Annexin V and propidium iodide to assess apoptosis and a mitochondrial function assay was used to determine cell viability.

RESULTS

Concentrations of A77 > or = 20microM were associated with substantial reduction in plaque number and viral load. Concentrations > or = 100microM were associated with complete suppression of plaque formation. At low concentrations of A77, clusters of intracytoplasmic virus particles that appeared to lack tegument and an external membrane were detected. Treatment of uninfected CRFK cell monolayers with A77 was associated with reduction in mitochondrial function with minimal evidence of apoptosis.

CONCLUSIONS AND CLINICAL RELEVANCE

Leflunomide may be an alternative to current calcineurin-based immunosuppressive protocols used in feline organ transplantation because of its antiherpesviral activity.

Feline herpesvirus

Feline herpesvirus (FHV-1; felid herpesvirus 1 (FeHV-1)) is an alphaherpesvirus of cats closely related to canine herpesvirus-1 and phocine herpesvirus-1. There is only one serotype of the virus and it is relatively homogenous genetically. FeHV-1 is an important cause of acute upper respiratory tract and ocular disease in cats. In addition, its role in more chronic ocular disease and skin lesions is increasingly being recognised. Epidemiologically, FeHV-1 behaves as a typical alphaherpesvirus whereby clinically recovered cats become latently infected carriers which undergo periodic episodes of virus reactivation, particularly after a stress. The primary site of latency is the trigeminal ganglion. Conventional inactivated and modified-live vaccines are available and protect reasonably well against disease but not infection, although viral shedding may be reduced. Genetically engineered vaccines have also been developed, both for FeHV-1 and as vector vaccines for other pathogens, but none is as yet marketed.

Felid herpesvirus 1 glycoprotein G is a structural protein that mediates the binding of chemokines on the viral envelope

Glycoprotein G (gG) orthologues have been described in several alphaherpesviruses. gG is expressed both as a membrane-anchored form on infected cells and as a secreted form. Recently, we reported that both forms of gG encoded by alphaherpesviruses infecting large herbivores and by Felid herpesvirus 1 (FeHV-1) bind with high affinity to a broad range of CXC, CC and C-chemokines. Based on the viral species, gG has been reported either as a structural or a non-structural protein. To date, the incorporation of FeHV-1 gG into virions has never been tested, nor the property of alphaherpesvirus structural gG to bind chemokines on the virion surface. In the present study, to address these questions, various FeHV-1 gG recombinant strains were produced using an original technique based on an infectious FeHV-1 BAC clone and restriction endonuclease mediated recombination. Using the recombinants produced, we were able to determine that FeHV-1 gG is a structural protein that acts as a chemokine-binding protein on the virion surface. In the light of these results, putative roles of gG in alphaherpesvirus infections are discussed, and an evolutionary scenario is proposed to explain the structural versus non-structural property of gG amongst alphaherpesviruses.

Herpesvirus latency and therapy—From a veterinary perspective

This short review considers how the human herpesviruses were among the first viruses to be effectively treated by means of antiviral therapy although the ability of alphaherpsviruses to establish neuronal latency with reactivation remains the major obstacle to achieving a cure. Laboratory animals played an essential role in the development of herpes antivirals including our understanding of the complexity of the neurological infection in relation to chemotherapy. The existence of natural herpesvirus infections in domestic species also contributes to our understanding of latency and reactivation relevant to antiviral therapy although the use of antivirals to treat or prevent virus infections in veterinary species has been minimal, to date. The review briefly focuses on herpes infections in the horse and cat where some progress has already been achieved in the veterinary antiviral field.

Effects of a single dose of an intranasal feline herpesvirus 1, calicivirus, and panleukopenia vaccine on clinical signs and virus shedding after challenge with virulent feline herpesvirus 1

The objective of this study was to determine whether intranasal administration of a commercially available FVRCP vaccine to kittens lessened clinical signs and feline herpesvirus 1 (FHV-1) viral shedding when compared to unvaccinated control kittens after FHV-1 challenge. Three groups of 10 unvaccinated kittens were administered one dose of vaccine 6 days (group 1), 4 days (group 2), or 2 days (group 3) before challenge, respectively. One group was maintained as unvaccinated controls (group 4). FHV-1 challenge was then induced and the kittens were observed for 14 days. When the grouped vaccinated kitten results (groups 1-3) were compared to group 4 results, clinical scores following challenge were significantly lower (P<0.05) and significantly lower body temperatures (P<0.05) were detected on days 0, 5 and 9 post-challenge. When evaluated by individual group, group 1 and group 2 kittens had significantly lower clinical scores (P<0.05) than group 4 kittens post-challenge. In addition, FHV-1 shedding was lower in group 1 kittens when compared to group 4 kittens on day 6 after challenge (P<0.05). Administration of this vaccine within several days prior to exposure lessened clinical signs of disease and FHV-1 shedding compared to unvaccinated kittens.

Both soluble and membrane-anchored forms of Felid herpesvirus 1 glycoprotein G function as a broad-spectrum chemokine-binding protein

Recently, glycoprotein G (gG) of several alphaherpesviruses infecting large herbivores was shown to belong to a new family of chemokine-binding proteins (vCKBPs). In the present study, the function of Felid herpesvirus 1 (FeHV-1) gG as a vCKBP was investigated and the following conclusions were reached: (i) FeHV-1 secreted gG is a high-affinity broad-spectrum vCKBP that binds CC, CXC and C chemokines; (ii) gG is the only vCKBP expressed by FeHV-1 that binds CCL3 and CXCL1; (iii) secreted gG blocks chemokine activity by preventing their interaction with high-affinity cellular receptors; (iv) the membrane-anchored form of gG expressed on the surface of infected cells is also able to bind chemokines; and (v) the vCKBP activity is conserved among different field isolates of FeHV-1. Altogether, these data demonstrate that FeHV-1 gG is a new member of the vCKBP-4 family. Moreover, this study is the first to demonstrate that gG expressed at the surface of FeHV-1-infected cells can also bind chemokines.

NEUTRALIZING ANTIBODIES AGAINST FELINE HERPESVIRUS TYPE 1 IN CAPTIVE WILD FELIDS OF BRAZIL

Feline herpesvirus type 1 infection affects domestic cats, causing mainly upper respiratory tract diseases. Although this infection has been described in captive and free-ranging wild felids from Europe, Asia, North America, and Africa, no information is available on its occurrence among wild felids of Brazil. In this study, 250 serum samples of six species of Brazilian captive wild felids (Leopardus tigrinus, Leopardus wiedii, Herpailurus yaguarondi, Puma concolor, Leopardus pardalis, and Panthera onca) were examined for neutralizing antibodies to feline herpesvirus type 1. Positive sera were found in 72% of L. tigrinus samples, 15% of L. wiedii, 6% of L. pardalis, 8% of H. yaguarondi, 18% of P. concolor, and 14% of P. onca. The relatively low percentages of seropositivity and low antibody titers found among the last five species suggest that feline herpesvirus type 1 does not circulate extensively among these animals. Nevertheless, quarantine, serologic screening, and vaccination of newly introduced felids is recommended in zoos in order to prevent virus transmission and outbreaks of the disease among wild felids kept in captivity.

Feline Corneal Disease

The cornea is naturally transparent. Anything that interferes with the cornea's stromal architecture, contributes to blood vessel migration, increases corneal pigmentation, or predisposes to corneal edema, disrupts the corneas transparency and indicates corneal disease. The color, location, and shape and pattern of a corneal lesion can help in determining the underlying cause for the disease. Corneal disease is typically divided into congenital or acquired disorders. Congenital disorders, such as corneal dermoids are rare in cats, whereas acquired corneal disease associated with nonulcerative or ulcerative keratitis is common. Primary ocular disease, such as tear film instability, adenexal disease (medial canthal entropion, lagophthalmus, eyelid agenesis), and herpes keratitis are associated with the majority of acquired corneal disease in cats. Proliferative/eosinophilic keratitis, acute bullous keratopathy, and Florida keratopathy are common feline nonulcerative disorders. Nonprogressive ulcerative disease in cats, such as chronic corneal epithelial defects and corneal sequestration are more common than progressive corneal ulcerations.