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.     

Herpesviruses of carnivores.

This review focuses on felid herpesvirus 1 (FHV-1), the most studied of the carnivore herpesviruses. Canid herpesvirus (CHV-1) and phocid (seal) herpesvirus 1 (PhHV-1) are also included where information is available. FHV-1 is a member of the Varicellovirus genus of the Alphaherpesvirinae, which appears to be closely related phylogenetically to both CHV-1 and PhHV-1. FHV-1 infects both domestic and some wild Felidae, such as cheetahs, and is predominantly a respiratory pathogen of cats. As in other herpesviruses, infection with FHV-1 is characterised by a latent carrier state, during which intermittent shedding of infectious virus may occur. Typical of an alphaherpesvirus, the primary site of FHV-1 latency is neurological tissue (trigeminal ganglion), though recent studies using the polymerase chain reaction have suggested that some latency may occur in non-neurological sites. Latently infected carriers are epidemiologically important as sources of infection for susceptible animals. Though conventional modified live and inactivated vaccines have been available for a number of years, they do not protect against infection nor the development of latency. Recently, work has focused on molecular characterisation of FHV-1, detecting genes such as glycoproteins or regulatory genes. Such work will enable better understanding of the interaction of FHV-1 with the natural host. Deletion mutants of some of these genes may also have potential as vaccine strains.     

Feline herpesvirus.

Feline herpesvirus infection is extremely common and may lead to recurring ocular disease in the adult cat. Recognition of the history and clinical signs that are consistent with FHV-1 infection is critical because diagnostic tests may be negative. Although a variety of treatment options are available, no one therapy is successful in every cat, and a small percentage of cats respond poorly to any treatment.     

Update on pathogenesis, diagnosis, and treatment of feline herpesvirus type 1

Feline herpesvirus type 1 (FHV-1) infection, but not necessarily chronic or recurrent disease, is common throughout domestic cat populations worldwide. Knowledge of a few essential virological facts permits practitioners to provide appropriate advice to owners of individual pet cats infected with this virus and to assist in the management of shelters and other multicat households in which the virus is enzootic. This article discusses pathogenesis, diagnostic techniques, and clinical signs considered characteristic of infection with FHV-1. Treatment options are considered under the broad categories of supportive care, antiviral agents, and adjunctive therapies.     

Use of serologic tests to predict resistance to feline herpesvirus 1, feline calicivirus,and feline parvovirus infection in cats

OBJECTIVE: To determine whether detection of virus-specific serum antibodies correlates with resistance to challenge with virulent feline herpesvirus 1 (FHV-1), feline calicivirus (FCV), and feline parvovirus (FPV) in cats and to determine percentages of client-owned cats with serum antibodies to FHV-1, FCV, and FPV. DESIGN: Prospective experimental study. ANIMALS: 72 laboratory-reared cats and 276 client-owned cats. PROCEDURES: Laboratory-reared cats were vaccinated against FHV-1, FCV, and FPV, using 1 of 3 commercial vaccines, or maintained as unvaccinated controls. Between 9 and 36 months after vaccination, cats were challenged with virulent virus. Recombinant-antigen ELISA for detection of FHV-1-, FCV-, and FPV-specific antibodies were developed, and results were compared with results of hemagglutination inhibition (FPV) and virus neutralization (FHV-1 and FCV) assays and with resistance to viral challenge. RESULTS: For vaccinated laboratory-reared cats, predictive values of positive results were 100% for the FPV and FCV ELISA and 90% for the FHV-1 ELISA. Results of the FHV-1, FCV, and FPV ELISA were positive for 195 (70.7%), 255 (92.4%), and 189 (68.5%), respectively, of the 276 client-owned cats. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that for cats that have been vaccinated, detection of FHV-1-, FCV-, and FPV-specific antibodies is predictive of whether cats are susceptible to disease, regardless of vaccine type or vaccination interval. Because most client-owned cats had detectable serum antibodies suggestive of resistance to infection, use of arbitrary booster vaccination intervals is likely to lead to unnecessary vaccination of some cats.     

Cytologic findings, and feline herpesvirus DNA and Chlamydophila felis antigen detection rates in normal cats and cats with conjunctival and corneal lesions

Samples were collected from 36 cats with feline herpesvirus (FHV-1)-related ocular disease (conjunctivitis, epithelial or stromal keratitis, or corneal sequestration), and 17 cats without ocular changes. Corneoconjunctival swabs, scrapings and biopsies were tested in various combinations for presence of FHV-1 DNA using single round (sr) polymerase chain reaction (PCR) and nested PCR (nPCR). Additional swabs from the inferior conjunctival fornix were tested by enzyme-linked immunosorbent assay for Chlamydophila felis antigen. Cytologic evaluation was carried out on conjunctival (cats with conjunctivitis) and corneal (cats with keratitis) cytobrush preparations. FHV-1 DNA was detected by PCR in 14 (39%) cats with ocular disease and 1 (6%) of the control group. Agreement between srPCR and nPCR results was significant (P < 0.01). FHV-1 DNA was detected in 3/7 cats with conjunctivitis, 5/6 cats with epithelial keratitis, 3/11 cats with stromal keratitis, and 3/12 cats with corneal sequestration. There was a significant association (P = 0.0027) between viral presence and epithelial keratitis. However, no significant association was found between viral presence and conjunctivitis (P = 0.059), stromal keratitis (P = 0.15), or corneal sequestration (P = 0.18). With respect to FHV-1 DNA detection, intersample agreement was significant (P < 0.03). No sampling technique seemed more likely than another to harvest detectable viral DNA, except for cats with corneal sequestrum in which viral DNA was not detected using corneoconjunctival swabs. FHV-1 DNA was detected in 6/9 samples with intranuclear inclusion bodies and in 6/7 cats with eosinophils on cytologic examination. All samples tested negative for C. felis antigen.     

Experimental infection of recent field isolates of feline herpesvirus type 1

Two field isolates of feline herpesvirus type 1 (FHV-1) designated as 00-015 and 00-035, were obtained from cats diagnosed as feline viral rhinotracheitis (FVR) in Japan. To analyze the character of recent FHV-1, these two isolates and our laboratory strain C7301 were inoculated experimentally to specific-pathogen-free cats. Although all cats showed typical FVR symptoms, more severe clinical symptoms were observed on cats infected with the isolates 00-015 and 00-035 compared with those of C7301-infected cats. Severe ocular lesions including conjunctivitis were found in the cats infected with the isolates, indicating that the recent FHV-1 has a potential to induce severe FVR symptoms including ocular lesions.     

Effects of L-lysine and L-arginine on in vitro replication of feline herpesvirus type-1

OBJECTIVE: To determine the effects of various concentrations of L-lysine and L-arginine on in vitro replication of feline herpesvirus type-1 (FHV-1). SAMPLE POPULATION: Cultured Crandell-Reese feline kidney (CRFK) cells and FHV-1 strain 727. PROCEDURE: Uninfected CRFK cells or CRFK cells infected with FHV-1 were cultured in Dulbecco's modified Eagle's medium or in 1 of 7 test media containing various concentrations of lysine and arginine. Viral titer and CRFK growth rate were assessed in each medium. RESULTS: Media depleted of arginine almost completely inhibited viral replication, whereas 2.5 or 5.0 microg of arginine/ml of media was associated with a significant increase in FHV-1 replication. In media with 2.5 microg of arginine/ml, supplementation with 200 or 300 microg of lysine/ml reduced viral replication by 34.2 and 53.9%, respectively. This effect was not seen in media containing 5.0 microg of arginine/ml. Growth rates of CRFK cells also were suppressed in media containing these concentrations of amino acids, but they were not significantly different from each other. CONCLUSIONS AND CLINICAL RELEVANCE: Arginine exerts a substantial growth-promoting effect on FHV-1. Supplementation of viral culture medium with lysine attenuates this growth-promoting effect in media containing low concentrations of arginine. Analysis of data from this study indicates that high concentrations of lysine reduce in vitro replication of FHV-1 but only in media containing low concentrations of arginine. Clinical trials will be necessary to determine whether supplemental administration of lysine, with or without arginine restriction, will be useful in the management of cats with FHV-1 infections.     

Efficacy of oral supplementation with L-lysine in cats latently infected with feline herpesvirus

OBJECTIVE: To examine the effects of orally administered L-lysine on clinical signs of feline herpesvirus type 1 (FHV-1) infection and ocular shedding of FHV-1 in latently infected cats. ANIMALS: 14 young adult, FHV-1-naive cats. PROCEDURE: Five months after primary conjunctival inoculation with FHV-1, cats were rehoused and assigned to receive 400 mg of L-lysine in food once daily for 30 days or food only. On day 15, all cats received methylprednisolone to induce viral reactivation. Clinical signs of infection were graded, and viral shedding was assessed by a polymerase chain reaction assay throughout our study. Peak and trough plasma amino acid concentrations were assessed on day 30. RESULTS: Fewer cats and eyes were affected by conjunctivitis, and onset of clinical signs of infection was delayed on average by 7 days in cats receiving L-lysine, compared with cats in the control group; however, significant differences between groups were not demonstrated. Significantly fewer viral shedding episodes were identified in the treatment group cats, compared with the control group cats, after rehousing but not following corticosteroid-induced viral reactivation. Mean plasma L-lysine concentration was significantly increased at 3 hours but not at 24 hours after L-lysine administration. Plasma arginine concentration was not significantly altered. CONCLUSIONS AND CLINICAL RELEVANCE: Once daily oral administration of 400 mg of L-lysine to cats latently infected with FHV-1 was associated with reduced viral shedding following changes in housing and husbandry but not following corticosteroid administration. This dose caused a significant but short-term increase in plasma L-lysine concentration without altering plasma arginine concentration or inducing adverse clinical effects.     

Clinical improvement in feline herpesvirus 1 infected cats by oral low dose of interleukin-12 plus interferon-gamma

Feline herpesvirus 1 (FHV-1) is a widespread cat pathogen inducing rhinitis, conjunctivitis and corneal ulcers. To alleviate acute FHV-1-induced disease, antiviral agents are used often with antibiotics. But sometimes, these treatments, as well as conventional doses of cytokines have moderate efficacy and/or collateral effects. Herein we have investigated the effects of low dose interleukin (IL)-12 plus interferon (IFN)-gamma, prepared by Sequential Kinetic Activated (SKA), on the treatment of FHV-1 infection. Twenty-five, unvaccinated FHV-1-positive cats were recruited into a prospective, randomized, placebo-controlled, double-blinded clinical trial. Fifteen cats were treated for 6 months with oral low doses of SKA IL-12 plus IFN-gamma and 10 cats were treated with placebo. At 1, 6 and 12 months (follow-up) after the beginning of treatment, clinical assessment, PCR assay and blood count were carried out. At follow-up, in treated group, we observed significant (p < 0.05) improvements in clinical signs and PCR became negative in 12/15 cats (80%). In placebo, 10/10 cats were PCR-positive, with improvements (30%) or worsening (70%) in clinical signs. Blood values were normal in both groups.Our results show that the low dose therapy, based on activated solutions of IL-12 plus IFN-gamma, represents a novel approach to treat FHV-1 infection in cats.     

Culture of feline corneal epithelial cells and infection with feline herpesvirus-1 as an investigative tool

OBJECTIVE: To isolate and characterize pure cultures of feline corneal epithelial cells and to assess the extent and nature of feline herpesvirus (FHV)-1 infection in these cells. SAMPLE POPULATION: Healthy eyes from 23 recently euthanatized cats. PROCEDURE: Stroma and epithelium of the rostral portion of the cornea were surgically isolated, and epithelial cells were detached from the stroma by enzymatic incubation. Epithelial cells were cultured in hormone-supplemented media. Cells were passaged, and cytokeratin expression was assessed. Cells were then infected with FHV-1, and cytopathic effects were determined. RESULTS: Cell cultures were readily established from samples obtained from each eye and could be maintained through 6 passages. Cultured cells expressed cytokeratins 3 and 12 but not other cytokeratins. Infection with FHV-1 was rapid and caused widespread cytopathic effects. CONCLUSIONS AND CLINICAL RELEVANCE: Feline corneal cells cultured in vitro during multiple passages maintain consistent morphologic characteristics and intermediate filament expression. They are susceptible to infection with FHV-1 and may provide a useful in vitro model for investigation of ocular drugs.     

Prevalence of Chlamydophila felis and feline herpesvirus 1 in cats with conjunctivitis in northern Italy

The prevalence of Chlamydophila felis and feline herpesvirus 1 (FHV-1) infection in cats with conjunctivitis in northern Italy was investigated by conventional polymerase chain reaction (PCR) testing. In cats with conjunctivitis, C felis and FHV-1 were detected in 14 of 70 (20%) and in 23 of 70 (33%) animals, respectively. None of the 35 control cats were positive for C felis, whereas 7 (20%) of these cats were positive for FHV-1. Mixed infections were present in 5 of 70 cats (7%). Cats positive for C felis were significantly younger than control animals (P = .02), whereas no significant age differences were observed between FHV-1-positive cats and control cats (P = .41) or between FHV-1-positive animals and C felis-positive animals (P = .16). Cats sampled during acute-phase conjunctivitis were also investigated for the presence of C felis by conjunctival scrapings. In this acute phase, substantial agreement was found when comparing the results of the 2 methods (K = .80). The association between PCR results and conjunctivitis was evaluated for the 2 pathogens. The presence of C felis was significantly associated with conjunctivitis (P = .004), whereas the detection of FHV-1 did not significantly correlate with the clinical sign (P = .25), suggesting that, by itself. PCR is not suitable for the diagnosis of FHV-1-related conjunctivitis.     

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.     

Effects of temperature and time in transit on polymerase chain reaction detection of feline herpesvirus DNA.

The purpose of this study was to report methods currently recommended by commercial laboratories for collecting, shipping, and processing of samples for feline herpesvirus type 1 (FHV-1) testing using polymerase chain reaction (PCR) and to determine the effect of temperature and time on the ability of 1 PCR method to detect FHV-1 DNA in experimental and clinical samples. Eleven laboratories offering FHV-1 PCR were surveyed. There was notable variation in sample types and shipping conditions recommended and PCR protocols used by these laboratories. Subsequently, using a single PCR method, FHV-1 DNA was detected in samples exposed to various temperatures within the laboratory. Finally, FHV-1 PCR was performed on paired clinical samples collected from 25 cats and shipped at ambient temperatures via US Postal Service (USPS) or with an ice pack via a courier. Samples sent by USPS were exposed to significantly longer transit time and arrived at significantly higher temperature than did samples sent by courier. Despite this, all sample pairs yielded concordant results when tested for FHV-1 DNA using this PCR method. Although it may not be necessary for samples collected for detection of FHV-1 DNA using this PCR method to be shipped under the most expedient or temperature-controlled conditions, this should be verified for a variety of PCR assays and sample types.     

Detection of feline herpesvirus-specific antibodies and DNA in aqueous humor from cats with or without uveitis.

OBJECTIVE: To determine whether uveitis in cats was associated with intraocular production of feline herpesvirus type 1 (FHV-1)-specific antibodies or with detection of FHV-1 DNA in aqueous humor (AH). ANIMALS: 44 cats with idiopathic uveitis, 29 cats with uveitis attributed to Toxoplasma gondii infection, 13 FHV-1 seropositive cats without uveitis, and 9 FHV-1 seronegative cats without uveitis. PROCEDURE: ELISA were used to detect FHV-1-specific antibodies and total IgG antibodies in serum and AH, and the Goldmann-Witmer coefficient (C-value) for intraocular antibody production was calculated. A polymerase chain reaction assay was used to detect FHV-1 DNA in AH. RESULTS: FHV-1 seroprevalence among cats with uveitis was not significantly different from seroprevalence among cats without uveitis. Intraocular FHV-1 antibodies were never detected in cats without uveitis. Significantly more cats with idiopathic uveitis (22/44) or with toxoplasmic uveitis (11/29) had evidence of intraocular antibody production (C-value > 1) than did cats without uveitis. Only cats with idiopathic uveitis had FHV-1 C-values > 8. Among cats with evidence of intraocular antibody production, cats with idiopathic uveitis had a significantly higher median FHV-1 C-value (9.61) than did cats with toxoplasmic uveitis (2.56). Overall, FHV-1 DNA was detected in AH from 12 cats, 11 of which had uveitis. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that FHV-1 can infect intraocular tissues of cats and that intraocular FHV-1 infection may be associated with uveal inflammation in some cats.     

Feline Herpesvirus 1 and Mycoplasma spp. Conventional PCR Assay Results From Conjunctival Samples From Cats in Shelters With Suspected Acute Ocular Infections

Signs of ocular infections like discharge and conjunctivitis occur commonly in cats in shelters and feline herpesvirus 1 (FHV-1), Chlamydia felis, Mycoplasma spp, and feline calicivirus (FCV) are thought to be the most common causes. While molecular assays are available to amplify nucleic acids of each of these agents as single tests or in panels, additional information is needed concerning whether the assay results can be used to predict response to treatment. The objectives of this study were to report results for conventional polymerase chain reaction (PCR) assays that amplify nucleic acids of FHV-1, Mycoplasma spp., C. felis, and FCV from cats with signs of acute ocular and upper respiratory infections in an animal shelter and to determine whether the results are associated with treatment responses to topical administration of cidofovir (anti-FHV-1) or oxytetracycline (anti-Mycoplasma spp. and C. felis). Conjunctival samples were collected from both eyes of 60 cats with ocular signs of disease. Total deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) were extracted from each sample and assayed for DNA of FHV-1, Mycoplasma spp., and C. felis and RNA of FCV by conventional PCR assays. Cats were randomized to be administered either oxytetracycline ointment or cidofovir drops in both eyes and a standardized ocular disease score system was used to determine a total ocular score for each cat prior to treatment on Day 0 and on Day 7. Nucleic acids of one or more agents were amplified from one or both eyes from 39 of 60 cats (65%). FHV-1 DNA (21 cats), Mycoplasma spp. DNA (25 cats) or FCV RNA (2 cats) were amplified most commonly. After treatment for 7 days, 32 of 60 cats (53.3%) were considered improved with 27 of 32 cats (84.4%) having ocular scores of 0 (21 cats) or 1 (6 cats). When the results of the FHV-1 PCR assay were compared to cidofovir treatment responses, the positive and negative predictive values of the assay were shown to be 29.4% and 60%, respectively. When the results of the Mycoplasma spp. PCR assay were compared to oxytetracycline treatment responses, the positive and negative predictive values of the assay were shown to be 40% and 38.5%, respectively. The predictive value of conventional PCR assay results for FHV-1 or Mycoplasma spp. DNA was low, suggesting that performing these tests to formulate a treatment protocol has minimal clinical utility in cats with suspected acute ocular infections.     

Feline herpesvirus ocular disease

Infection by FHV-1 is one of the most common ophthalmic diseases of domestic cats worldwide. Although the usual manifestations are conjunctivitis and keratitis, infection with this virus has been linked to a variety of other ophthalmic syndromes of cats, including keratoconjunctivitis sicca and corneal sequestration. Ocular FHV-1 infection of cats provides a significant diagnostic challenge to the practicing veterinarian because, in chronic cases, antigen detection tests often yield negative results. Although therapy for FHV-1 infections of cats is often difficult, the recent development of nontoxic antiviral drugs that demonstrate considerable efficacy against FHV-1 offers hope for improved therapeutic success in the future.     

Prevalence of feline herpesvirus 1, Chlamydophila felis, and Mycoplasma spp DNA in conjunctival cells collected from cats with and without conjunctivitis

OBJECTIVE: To use PCR assays to determine the prevalence of feline herpesvirus 1 (FHV-1), Chlamydophila felis, and Mycoplasma spp DNA in conjunctival cells collected from cats with and without conjunctivitis; to compare results of conventional and real-time fluorogenic PCR assays for amplification of FHV-1 DNA; and to determine whether copy numbers of FHV-1 DNA are correlated with conjunctivitis. ANIMALS: 55 cats with active conjunctivitis, 39 healthy cats that never had conjunctivitis, and 32 cats with a history of conjunctivitis that had been resolved for at least 3 months. PROCEDURES: Samples were obtained by rolling cotton-tipped applicators on the ventral conjunctiva of awake cats treated topically with proparacaine. The DNA was extracted from the swab specimens and assessed in PCR assays to detect DNA of FHV-1 (fluorogenic PCR assay and conventional PCR assay), Mycoplasma spp (conventional PCR assay), and C felis (conventional PCR assay). RESULTS: Overall prevalence rates of FHV-1, C felis, and Mycoplasma spp as assessed by the conventional PCR assays were 6.7%, 3.2%, and 9.6%, respectively. Percentage concordance between conventional PCR and fluorogenic PCR assays for FHV-1 was 92.5%. There were no significant differences among the 3 groups of cats for the mean copy number of FHV-1 divided by the copy number of glyceraldehyde-3-phosphate dehydrogenase. CONCLUSIONS AND CLINICAL RELEVANCE: Mycoplasma spp were the most prevalent organism detected and was associated with conjunctivitis. This study could not confirm that there are increased copy numbers of FHV-1 DNA in cats with conjunctivitis, compared with the copy numbers for cats without conjunctivitis.     

Establishment and Application of Quantitative Real-time PCR Detection Method for Feline Infectious Rhinotracheitis Virus

Feline herpesvirus type 1 (FHV-1) is the pathogeny of feline infectious rhinotracheitis.Based on the sequence of gD gene of FHV-1, one pair of primers(FHV-1F and FHV-1R) and FHV-1Probe were designed for the quantitative Real-time PCR detection method.The results showed that the method could detect FHV-1 DNA specifically and the sensitivity was 75 fg/μL.The reaction efficiency reached 107%, and the R² value was 0.9965.The coefficient of variance(CV) was below 2%.And the method was more sensitive than common PCR.It was specific, stable, and suitable for clinical diagnosis, detection and epidemiological investigation.Using this method, the Shanghai area pet clinic censorship suspected FHV-1 infected samples were detected, and the positive rate reached 27.78%, which indicated that the incidence of FHV-1 in Shanghai area was at a high level.