High sensitivity polymerase chain reaction assay for active and latent feline herpesvirus-1 infections in domestic cats

Prevalence and characteristics of ocular diseases in Sphynx cats: A retrospective assessment (2012-2021) and comparison with non-Sphynx cats

PURPOSE

To describe the prevalence of ocular diseases in Sphynx cats, and compare disease characteristics with other feline breeds.

METHODS

Medical records of Sphynx cats presented to an ophthalmology referral center between 1/2012 and 4/2021 were examined. Cats of other breeds examined during the same period served as controls.

RESULTS

One hundred ten Sphynx cats were examined during the study period, diagnosed with corneal sequestrum (n = 42 cats), lower eyelid entropion (n = 25), presumed herpetic keratoconjunctivitis (n = 19), conjunctivitis (n = 7), corneal ulcers (n = 6), nasolacrimal duct atresia/obstruction (n = 6), corneal dystrophy (n = 3), eosinophilic keratitis (n = 2), uveitis (n = 2), non-ulcerative keratitis (n = 1), and cataract (n = 1). Corneal sequestrum was significantly more common in Sphynx versus non-Sphynx cats (odds ratio = 8.0, 95% CI = 5.3-12.2, p < .001), and age of diagnosis was significantly younger in Sphynx cats (2.0 ± 1.5 years vs. 5.9 ± 4.0 years, p < .001). Corneal sequestrum recurrence was noted in 19.4% Sphynx eyes and 6.4% non-Sphynx eyes undergoing surgery (p = .015). Lower eyelid entropion-most often bilateral (80%)-was significantly more common in Sphynx versus non-Sphynx cats (odds ratio = 4.1, 95% CI = 2.3-7.1, p < .001), and age of diagnosis was significantly younger in Sphynx cats (0.9 ± 1.4 years vs. 3.5 ± 3.3 years, p < .005).

CONCLUSIONS

Corneal sequestrum and entropion were overrepresented and diagnosed at an earlier age in Sphynx cats when compared with the general feline population. Given the high prevalence, early age of onset, and relatively high recurrence of corneal sequestrum in Sphynx cats, further studies are warranted to better understand etiopathogenesis and preferred therapies.

Quantitative real time polymerase chain reaction (qRT-PCR) and RNAscope in situ hybridization (RNA-ISH) as effective tools to diagnose feline herpesvirus-1-associated dermatitis

BACKGROUND

Felid herpesvirus type 1 (FHV-1)-associated dermatitis is characterized by facial and nasal involvement; clinical and histopathological manifestations may overlap with other dermatitides.

OBJECTIVE

To evaluate the realibility of qRT-PCR-2^{- ΔΔC q} and RNAscope in situ hybridization (RNA-ISH) methods to diagnose FHV-1-associated dermatitis, in formalin-fixed paraffin-embedded (FFPE) tissues.

ANIMALS

Sixteen FFPE samples from cats with facial dermatitis and four controls were studied.

METHODS AND MATERIALS

Based on histopathological features, cases were separated into: Group 1, samples with herpetic dermatitis (four); Group 2, samples with nonherpetic facial dermatitis (six); Group 3, samples with facial dermatitis of ambiguous nature (allergic or viral) (six); and Group 4, samples from healthy cats (four). A relative quantification using the 2^{- ΔΔC q} method was used to estimate the "upregulation" of each FHV-1 target viral gene copies (glycoprotein-B and thymidine-kinase) relative to reference gene. Detection of FHV-1 mRNA was performed using the RNAscope 2.5 detection kit.

RESULTS

By 2^{- ΔΔC q} analysis, upregulation of both FHV-1 genes was observed in all samples from Group 1 and two of six from Group 3. No upregulation was identified in samples from groups 2 and 4. Positive mRNA hybridization signal was observed in all cases from Group 1 and two cases of Group 3. No positivity was observed in samples from groups 2 and 4.

CONCLUSIONS AND CLINICAL IMPORTANCE

QRT-PCR 2^-ΔΔCq analysis and RNA-ISH can identify the FHV-1 genome as causative agent of the associated dermatitis, even where inclusion bodies are not detectable. Both techniques are functional in retrospective studies, have greater specificity than conventional PCR, and may be proposed for research and diagnostic purposes.

Feline corneal sequestra: outcome of corneoconjunctival transposition in 97 cats (109 eyes)

Case series summary A retrospective study was undertaken to review outcomes of keratectomy and corneoconjunctival transposition in cats with superficial and deep corneal sequestra. Information including pertinent history, signalment, ophthalmological findings and postoperative outcome was collected from medical records. Follow-up was obtained by clinical examination, contact with the referring veterinarians and review of medical records or telephone contact with owners. Ninety-seven cats (109 eyes) were included from 2005-2015. The most commonly affected breeds included Persian, Burmese and Himalayan. The mean age at the time of surgery was 6.8 years (median 6.5 years; range 8.0 months-18.0 years). A corneal sequestrum in the contralateral eye was diagnosed in 28 cats (28.9%). Recurrent corneal sequestration was diagnosed in eight cats (nine eyes), with recurrence occurring a mean of 703 days after surgery (range 29-1750 days). Age, sex, breed, depth of sequestration and concurrent ocular disease in the contralateral eye were compared between cats with and without recurrence, with no risk factors for recurrence identified. Relevance and novel information Excellent surgical outcomes have previously been described in a series of 17 cats with superficial and mid-stromal corneal sequestra. This paper adds further information to the literature by describing a larger series of cats, with corneal sequestra affecting the full range of corneal thickness, and good long-term postoperative outcomes.

Recombinase Polymerase Amplification Assay-A Simple, Fast and Cost-Effective Alternative to Real Time PCR for Specific Detection of Feline Herpesvirus-1

Feline herpesvirus 1 (FHV-1), an enveloped dsDNA virus, is one of the major pathogens of feline upper respiratory tract disease (URTD) and ocular disease. Currently, polymerase chain reaction (PCR) remains the gold standard diagnostic tool for FHV-1 infection but is relatively expensive, requires well-equipped laboratories and is not suitable for field tests. Recombinase polymerase amplification (RPA), an isothermal gene amplification technology, has been explored for the molecular diagnosis of infectious diseases. In this study, an exo-RPA assay for FHV-1 detection was developed and validated. Primers targeting specifically the thymidine kinase (TK) gene of FHV-1 were designed. The RPA reaction was performed successfully at 39°C and the results were obtained within 20 min. Using different copy numbers of recombinant plasmid DNA that contains the TK gene as template, we showed the detection limit of exo-RPA was 10² copies DNA/reaction, the same as that of real time PCR. The exo-RPA assay did not cross-detect feline panleukopenia virus, feline calicivirus, bovine herpesvirus-1, pseudorabies virus or chlamydia psittaci, a panel of pathogens important in feline URTD or other viruses in Alphaherpesvirinae, demonstrating high specificity. The assay was validated by testing 120 nasal and ocular conjunctival swabs of cats, and the results were compared with those obtained with real-time PCR. Both assays provided the same testing results in the clinical samples. Compared with real time PCR, the exo-RPA assay uses less-complex equipment that is portable and the reaction is completed much faster. Additionally, commercial RPA reagents in vacuum-sealed pouches can tolerate temperatures up to room temperature for days without loss of activity, suitable for shipment and storage for field tests. Taken together, the exo-RPA assay is a simple, fast and cost-effective alternative to real time PCR, suitable for use in less advanced laboratories and for field detection of FHV-1 infection.

An Immunohistochemical and Polymerase Chain Reaction Evaluation of Feline Plasmacytic Pododermatitis

Sections of 14 skin biopsies of cats with plasmacytic pododermatitis and a clinical follow-up of 12–36 months were stained with a polyclonal anti- Mycobacterium bovis (Bacille Calmette-Guerin = BCG) antibody cross-reactive to a broad spectrum of fungi and bacteria. All sections were negative for organisms within the actual footpad tissue with the anti-BCG antibody stains. Polymerase chain reaction (PCR) assays that amplify the DNA of Bartonella spp., Ehrlichia spp., Anaplasma phagocytophilum, Chlamydophila felis, Mycoplasma spp., Toxoplasma gondii, and feline herpesvirus 1 (FHV-1) were applied to tissue digests. DNA of those pathogens assessed was not amplified from tissue.

Prevalence of selected infectious disease agents in stray cats in Catalonia, Spain

Objectives

The objective of the current study was to investigate the prevalence rates of the following infectious agents in 116 stray cats in the Barcelona area of Spain: Anaplasma phagocytophilum, Bartonella species, Borrelia burgdorferi, Chlamydia felis, Dirofilaria immitis, Ehrlichia species, feline calicivirus (FCV), feline herpesvirus-1 (FHV-1), feline leukaemia virus (FeLV), feline immunodeficiency virus (FIV), haemoplasmas, Mycoplasma species and Rickettsia species.

Methods

Serum antibodies were used to estimate the prevalence of exposure to A phagocytophilum, Bartonella species, B burgdorferi, Ehrlichia species and FIV; serum antigens were used to assess for infection by D immitis and FeLV; and molecular assays were used to amplify nucleic acids of Anaplasma species, Bartonella species, C felis, D immitis, Ehrlichia species, FCV, FHV-1, haemoplasmas, Mycoplasma species and Rickettsia species from blood and nasal or oral swabs.

Results

Of the 116 cats, 63 (54.3%) had evidence of infection by Bartonella species, FeLV, FIV or a haemoplasma. Anaplasma species, Ehrlichia species or Rickettsia species DNA was not amplified from these cats. A total of 18/116 cats (15.5%) were positive for FCV RNA (six cats), Mycoplasma species DNA (six cats), FHV-1 DNA (three cats) or C felis DNA (three cats).

Conclusions and relevance

This study documents that shelter cats in Catalonia are exposed to many infectious agents with clinical and zoonotic significance, and that flea control is indicated for cats in the region.

Ocular and neural distribution of feline herpesvirus-1 during active and latent experimental infection in cats

BACKGROUND

Herpes simplex virus 1 (HSV-1) and varicella zoster virus (VZV) cause extensive intra-ocular and neural infections in humans and are closely related to Felid herpes virus 1 (FeHV-1). We report the extent of intra-ocular replication and the extent and morphological aspects of neural replication during the acute and latent phases of FeHV-1 infection. Juvenile, SPF cats were inoculated with FeHV-1. Additional cats were used as negative controls. Cats were euthanized on days 6, 10, and 30 post-inoculation.

RESULTS

FeHV-1 was isolated from the conjunctiva, cornea, uveal tract, retina, optic nerve, ciliary ganglion (CG), pterygopalatine ganglion (PTPG), trigeminal ganglion (TG), brainstem, visual cortex, cerebellum, and olfactory bulb of infected cats during the acute phase, but not the cranial cervical ganglion (CCG) and optic chiasm. Viral DNA was detected in all tissues during acute infection by a real-time quantitative PCR assay. On day 30, viral DNA was detected in all TG, all CCG, and 2 PTPG. Histologically mild inflammation and ganglion cell loss were noted within the TG during acute, but not latent infection. Using linear regression, a strong correlation existed between clinical score and day 30 viral DNA copy number within the TG.

CONCLUSIONS

The correlation between clinical score and day 30 viral DNA copy number suggests the severity of the acute clinical infection is related to the quantity of latent viral DNA. The histologic response was similar to that seen during HSV-1 or VZV infection. To the author's knowledge this is the first report of FeHV-1 infection involving intraocular structures and autonomic ganglia.

Infectious feline herpesvirus detected in distant bone and tendon following mucosal inoculation of specific pathogen-free cats

Emerging evidence suggests that cats infected with feline herpesvirus-1 (FHV-1) may experience a brief viremic phase. The objective of this study was to determine whether natural routes of FHV-1 inoculation could result in viremic transmission of infectious virus to connective tissues (cortical bone, tendon). Three specific pathogen-free cats were experimentally inoculated with FHV-1 via a combined mucosal (oronasal, ocular) route. Cats were euthanized at the peak of clinical signs to aseptically harvest tissues (cortical bone, tendon, trachea/tongue) for co-culture with a susceptible cell line to promote spread of infectious virus. Viral infection of Crandall-Rees feline kidney cells was microscopically visualized by cytopathic effect (CPE). Additionally, co-culture DNA was extracted either at the point of CPE or 16 days of culture without evidence of CPE, to amplify FHV-1 glycoprotein B gene using real-time PCR. Infectious virus was detected in distant cortical bone (two cats, moderate to severe clinical signs) and tendon (one cat, severe clinical signs). Direct infection of mucosal (trachea, tongue) tissues also was confirmed in these two cats. In contrast, all co-cultured tissues from the third cat (mild clinical signs) were negative for FHV-1 by CPE and PCR. Results of this study demonstrated that early primary FHV-1 viremia may be distributed to distant connective tissues.

Feline calicivirus: a neglected cause of feline ocular surface infections?

OBJECTIVE

To investigate the prevalence of feline calicivirus (FCV) infection in relation to ocular surface lesions in cats with upper respiratory tract diseases (URTD).

ANIMALS STUDIED

Ninety-nine cats with ocular surface infection and symptoms or recent history of URTD were examined at various rescue shelters and hospitals.

PROCEDURE

A complete general and ophthalmic examination was performed including Schirmer tear test, slit-lamp biomicroscopy, fluorescein and lissamine green staining. Clinical and ocular symptoms were scored and recorded. Conjunctival samples were collected using a cytobrush, and nucleic acid extraction using RT-PCR was carried out to analyze for the presence of various infectious agents.

RESULTS

RT-PCR detected either FCV, feline herpes virus type 1 (FHV-1), Chlamydophila felis or Mycoplasma spp. in 63/99 samples. 30/63 samples were positive for FCV, 23/63 for C. felis, 21/63 for Mycoplasma spp., and 16/63 for FHV-1. Out of the 30 FCV-positive samples, 11 were positive only for FCV and in 19 samples FCV was seen in combination with other agents. FCV infection was highest in animals examined at the rescue centers and in the age group of 0-2 months. Erosive conjunctivitis was an important ocular finding. Oral ulcers were detected in all FCV-infected cats.

CONCLUSION

Results indicate that FCV is highly prevalent in cats with URTD either as a sole infectious agent or in combination with other pathogens and therefore is a potential cause for ocular surface lesions during the URTD.

The in vitro effects of proxymetacaine, fluorescein, and fusidic acid on real-time PCR assays used for the diagnosis of Feline herpesvirus 1 and Chlamydophila felis infections

PURPOSE

To investigate the possible inhibition of qPCR assays used for the diagnosis of ocular infections in cats by proxymetacaine, fluorescein, and fusidic acid, which are commonly used in veterinary ophthalmology.

METHODS

Fluorescein, proxymetacaine, and fusidic acid were tested for possible inhibition of a triplex qPCR assay designed to detect Chlamydophila felis, Feline herpesvirus 1 (FHV-1), and the feline 28S ribosomal DNA (28S rDNA) gene by comparing threshold cycle (C(t) ) values of samples with and without the three products. A second experiment was carried out to measure the effects of various dilutions of fusidic acid.

RESULTS

No statistically significant differences were detected between the C. felis, FHV-1, and 28S rDNA C(t) values with and without proxymetacaine or fluorescein. However, there was a statistically significant increase in FHV-1 (P < 0.01), C. felis (P < 0.01), and 28S rDNA (P < 0.05) C(t) values when fusidic acid was used. When dilutions of fusidic acid were tested, the results revealed that only the 1:2 dilution caused a statistically significant increase (P < 0.01) in the FHV-1 Ct values.

CONCLUSION

Proxymetacaine and fluorescein did not interfere with our qPCR assays for the detection of C. felis and FHV-1. The presence of fusidic acid caused a small inhibitory effect of doubtful clinical significance. In vivo studies are required to establish the clinical relevance of this study and to confirm our findings.

Effects of dietary lysine supplementation on upper respiratory and ocular disease and detection of infectious organisms in cats within an animal shelter

OBJECTIVE

To determine within a cat shelter effects of dietary lysine supplementation on nasal and ocular disease and detection of nucleic acids of Chlamydophila felis, feline calicivirus (FCV), and feline herpesvirus (FHV-1).

ANIMALS

261 adult cats.

PROCEDURES

Cats were fed a diet containing 1.7% (basal diet; control cats) or 5.7% (supplemented diet; treated cats) lysine for 4 weeks. Plasma concentrations of lysine and arginine were assessed at the beginning (baseline) and end of the study. Three times a week, cats were assigned a clinical score based on evidence of nasal and ocular disease. Conjunctival and oropharyngeal swab specimens were tested for FHV-1, FCV, and C felis nucleic acids once a week.

RESULTS

Data were collected from 123, 74, 59, and 47 cats during study weeks 1, 2, 3, and 4, respectively. By study end, plasma lysine concentration in treated cats was greater than that in control cats and had increased from baseline. There was no difference between dietary groups in the proportion of cats developing mild disease. However, more treated cats than control cats developed moderate to severe disease during week 4. During week 2, FHV-1 DNA was detected more commonly in swab specimens from treated versus control cats.

CONCLUSIONS AND CLINICAL RELEVANCE

Dietary lysine supplementation in the amount used in our study was not a successful means of controlling infectious upper respiratory disease within a cat shelter. Rather, it led to increases in disease severity and the incidence of detection of FHV-1 DNA in oropharyngeal or conjunctival mucosal swab specimens at certain time points.

Feline herpesvirus infection. ABCD guidelines on prevention and management

OVERVIEW

Feline viral rhinotracheitis, caused by feline herpesvirus (FHV), is an upper respiratory tract disease that is often associated with feline calicivirus and bacteria. In most cats, FHV remains latent after recovery, and they become lifelong virus carriers. Stress or corticosteroid treatment may lead to virus reactivation and shedding in oronasal and conjunctival secretions.

INFECTION

Sick cats shed FHV in oral, nasal and conjunctival secretions; shedding may last for 3 weeks. Infection requires direct contact with a shedding cat.

DISEASE SIGNS

Feline herpesvirus infections cause acute rhinitis and conjunctivitis, usually accompanied by fever, depression and anorexia. Affected cats may also develop typical ulcerative, dendritic keratitis.

DIAGNOSIS

Samples consist of conjunctival, corneal or oropharyngeal swabs, corneal scrapings or biopsies. It is not recommended that cats recently vaccinated with a modified-live virus vaccine are sampled. Positive PCR results should be interpreted with caution, as they may be produced by low-level shedding or viral latency.

DISEASE MANAGEMENT

'Tender loving care' from the owner, supportive therapy and good nursing are essential. Anorexic cats should be fed blended, highly palatable food - warmed up if required. Mucolytic drugs (eg, bromhexine) or nebulisation with saline may offer relief. Broad-spectrum antibiotics should be given to prevent secondary bacterial infections. Topical antiviral drugs may be used for the treatment of acute FHV ocular disease. The virus is labile and susceptible to most disinfectants, antiseptics and detergents.

VACCINATION RECOMMENDATIONS

Two injections, at 9 and 12 weeks of age, are recommended, with a first booster 1 year later. Boosters should be given annually to at-risk cats. For cats in low-risk situations (eg, indoor-only cats), 3-yearly intervals suffice. Cats that have recovered from FHV-associated disease are usually not protected for life against further disease episodes; vaccination of recovered cats is therefore recommended.

Assessment of viremia associated with experimental primary feline herpesvirus infection or presumed herpetic recrudescence in cats

OBJECTIVE

To detect feline herpesvirus type 1 (FHV-1) in blood of cats undergoing experimental primary herpetic disease or with spontaneous disease presumed to be caused by FHV-1 reactivation.

ANIMALS

6 young specific-pathogen-free (SPF) cats and 34 adult cats from a shelter.

PROCEDURES

Conjunctiva and nares of SPF cats were inoculated with FHV-1, and cats were monitored for 21 days. Periodically, blood was collected for CBC, serum biochemical analyses, and detection of FHV-1 DNA via PCR assay. For shelter cats, a conjunctival swab specimen was collected for FHV-1 PCR assay, and blood mononuclear cells were tested via virus isolation (with or without hydrocortisone) and FHV-1 PCR assay.

RESULTS

All SPF cats developed clinical and clinicopathologic evidence of upper respiratory tract and ocular disease only. Via PCR assay, FHV-1 DNA was detected in blood of all SPF cats at least once between 2 and 15 days after inoculation. Feline herpesvirus type 1 DNA was detected in conjunctival swabs of 27 shelter cats; 25 had clinical signs of herpetic infection. However, virus was not isolated from mononuclear cell samples of any shelter cat regardless of passage number or whether hydrocortisone was present in the culture medium; FHV-1 DNA was not detected in any mononuclear cell sample collected from shelter cats.

CONCLUSIONS AND CLINICAL RELEVANCE

A brief period of viremia occurred in cats undergoing primary herpetic disease but not in cats undergoing presumed recrudescent herpetic disease. Viremia may be important in the pathogenesis of primary herpetic disease but seems unlikely to be associated with recrudescent disease.

Effects of dietary lysine supplementation in cats with enzootic upper respiratory disease

To determine the effectiveness of dietary lysine supplementation in cats with enzootic upper respiratory disease (URD), 50 cats were fed a ration containing 11 or 51 g lysine/kg diet for 52 days. Food intake, body weight, clinical signs, plasma amino acid concentrations and presence of Chlamydophila felis or feline herpesvirus (FHV)-1 DNA within the conjunctival fornix were assessed. Food and lysine intake of both dietary groups decreased between days 17 and 22, coinciding with peak disease and viral presence. Mean disease score for cats fed the supplemented ration (0.94) was higher than for those fed the basal diet (0.21); however, this could be attributed to a small subset of male cats which demonstrated fighting behavior that may have contributed to stress within that cage. FHV-1 DNA was detected on 12 occasions in six cats receiving the supplemented diet and on one occasion in one cat fed the basal diet. C felis DNA was never detected. Mean plasma arginine concentration was lower and plasma lysine concentration was higher in supplemented cats. Mean plasma arginine concentration declined throughout the study in both dietary groups. Data from the present study raise important questions but do not permit a definitive conclusion regarding the efficacy of dietary lysine supplementation in cats with enzootic URD.

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.

Feline herpes dermatitis treated with interferon omega

This case report describes the diagnosis, demonstration and treatment of feline herpes virus-induced facial dermatitis in a cat. The cat was successfully treated with interferon omega (IFN-omega).

Tracheal organ cultures as a useful tool to study Felid herpesvirus 1 infection in respiratory epithelium

Felid herpesvirus 1 (FeHV-1) is an important feline pathogen of the upper respiratory tract which can be identified in clinical cases by virus isolation and PCR. Studies on the effect and mode of spread of FeHV-1 in the respiratory epithelium, however, have previously only been performed in infected cats. Feline tracheal organ cultures which were inoculated with FeHV-1 at varying multiplicity of infection (MOI) were established. A dose-dependent response was observed. Low MOIs induced multifocal infection in the otherwise viable respiratory epithelium, which allowed monitoring of viral growth over several days. Therefore, tracheal organ cultures represent a suitable model for further study of the morphological and functional effects of FeHV-1 on respiratory epithelium, mimicking the in vivo situation.

The 2006 American Association of Feline Practitioners Feline Vaccine Advisory Panel Report

Vaccination is a medical procedure, and the decision to vaccinate should be based on a risk-based assessment for each cat and each vaccine.

Detection of feline herpesvirus 1 DNA in skin biopsy specimens from cats with or without dermatitis

OBJECTIVE

To compare detection rates of feline herpesvirus 1 (FHV-1) DNA in skin biopsy specimens from cats with herpetic dermatitis, cats with nonherpetic dermatitis, and cats without dermatitis.

DESIGN

Prevalence survey. Animals-5 cats (9 biopsy specimens) with herpetic ulcerative dermatitis, 14 cats (17 biopsy specimens) with nonherpetic ulcerative dermatitis, and 8 cats (21 biopsy specimens) without clinically apparent skin lesions.

PROCEDURES

A single-phase PCR assay was used to detect FHV-1 DNA in biopsy specimens. Assay results were compared with results of histologic examination.

RESULTS

FHV-1 DNA was detected in all 9 biopsy specimens from the 5 cats with herpetic dermatitis and in 1 of 17 biopsy specimens from the 14 cats with nonherpetic dermatitis, but was not detected in any of the 21 biopsy specimens from the 8 cats without dermatitis. When results of histologic examination were used as the gold standard, sensitivity and specificity of the PCR assay were 100% and 95%, respectively.

CONCLUSIONS AND CLINICAL RELEVANCE

Results confirmed that FHV-1 DNA can be detected in the skin of cats with herpetic dermatitis and suggest that the virus may play a causative role in the disease. In addition, the PCR assay may be useful in confirming a diagnosis of herpetic dermatitis.

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.

ASSESSMENT OF VIRAL PRESENCE IN SEMEN AND REPRODUCTIVE FUNCTION OF FROZEN-THAWED SPERMATOZOA FROM PALLAS' CATS (OTOCOLOBUS MANUL) INFECTED WITH FELINE HERPESVIRUS

Although herpesviruses are known to contaminate the semen of several mammalian species, the occurrence of feline herpesvirus type 1 (FHV-1) in semen of infected cats has not been reported. Our objectives in this study were to investigate the presence of FHV-1 DNA in seminal fluid and frozen-thawed spermatozoa from FHV-1 infected Pallas' cats (Otocolobus manul) and assess the functionality of their frozen-thawed spermatozoa in vitro. Over a 3-yr period, semen (n = 33 ejaculates) was collected periodically via electroejaculation from four Pallas' cats chronically infected with FHV-1. Spermic ejaculates were frozen by pelleting on dry ice and stored in liquid nitrogen. After thawing, sperm motility and acrosome status were assessed over time during in vitro culture. For vitro fertilization (IVF), viable domestic cat (Felis silvestris catus) oocytes were inseminated with frozen-thawed Pallas' cat spermatozoa and evaluated for embryo cleavage. For FHV-1 polymerase chain reaction (PCR) analysis, DNA was extracted from seminal fluid, frozen-thawed spermatozoa, inseminated oocytes, heterologous IVF embryos, and conjunctival biopsies and analyzed for presence of a 322-base pair region of the FHV-1 thymidine kinase gene. Immediately post-thaw, sperm motility and percentage of intact acrosomes were decreased (P < 0.05) compared to fresh samples, and declined further (P < 0.05) during culture. However, all frozen-thawed IVF samples were capable of fertilizing domestic cat oocytes (overall, 46.1 +/- 6.0% cleavage). PCR analysis did not identify FHV-1 DNA in any reproductive sample despite the repeated detection of FHV-1 DNA in conjunctival biopsies. These results suggest that semen collected from Pallas' cats infected with FHV-1 does not contain cell-associated or non-cell-associated virus and that frozen-thawed spermatozoa exhibit adequate function for potential genetic rescue with minimal risk of FHV-1 transmission.

Corneal ulceration associated with naturally occurring canine herpesvirus-1 infection in two adult dogs

CASE DESCRIPTION

An 8-year-old Labrador Retriever with diabetes mellitus in which bilateral phacoemulsification had been performed 3 weeks earlier was evaluated for acute onset of blepharospasm, and a 7-year-old Miniature Schnauzer with chronic immune-mediated thrombocytopenia was reevaluated for keratoconjunctivitis sicca that had been diagnosed 4 weeks earlier.

CLINICAL FINDINGS

Dendritic corneal ulcerations were detected in both dogs. Canine herpesvirus-1 (CHV-1) was isolated from corneal swab specimens obtained during the initial evaluation of each dog and during recheck examinations performed until the ulcerations were healed. Canine herpesvirus-1 serum neutralization titers were detected in both dogs. Results of virus isolation from oropharyngeal and genital swab specimens were negative for both dogs. The isolated viruses were identified as CHV-1 via immunofluorescence, transmission electron microscopy, PCR assay, and gene sequencing. Negative controls for PCR assay and virus isolation included conjunctival swab specimens from 50 dogs without extraocular disease and corneal swab specimens from 50 dogs with corneal ulcers, respectively.

TREATMENT AND OUTCOME

Lesions resolved in both dogs after topical administration of idoxuridine or trifluridine and discontinuation of topically administered immunosuppressive medications.

CLINICAL RELEVANCE

To the authors' knowledge, this is the first report of corneal ulcerations associated with naturally occurring CHV-1 infection and may represent local ocular recrudescence of latent CHV-1 infection. The viruses isolated were identified as CHV-1, and the morphology, antigenicity, and genotype were similar to those for CHV-1 isolates obtained from a puppy that died from systemic CHV-1 infection.

Assessment of infectious organisms associated with chronic rhinosinusitis in cats

OBJECTIVE

To determine detection rates for feline herpesvirus type 1 (FHV-1), Mycoplasma spp, fungi, and bacteria in flush samples and biopsy specimens from the nasal cavities of cats with and without chronic rhinosinusitis (CRS).

DESIGN

Prospective study.

ANIMALS

10 CRS-affected cats and 7 cats without signs of respiratory tract disease.

PROCEDURES

Nasal flush samples and biopsy specimens were collected from all cats for bacterial (aerobic and anaerobic), fungal, and mycoplasmal cultures; additional biopsy specimens were collected for virus isolation and polymerase chain reaction (PCR) assay (to detect FHV-1 DNA).

RESULTS

Aerobic bacteria were detected in flush samples from 5 of 7 control cats; culture of flush samples from CRS-affected cats yielded aerobic bacteria (9/10 cats), anaerobic bacteria (3/10), and Mycoplasma spp (2/10). No fungal organisms were isolated from any cat. Potential pathogens were isolated significantly more often from CRS-affected cats than from control cats. Bacterial culture of biopsy specimens yielded aerobic bacteria (2/7 control cats and 4/10 CRS-affected cats) and anaerobic bacteria (2/10 CRS-affected cats). Although FHV-1 was not detected in nasal biopsy specimens from control or CRS-affected cats, FHV-1 DNA was detected via PCR assay in specimens from 4 of 7 control cats and 3 of 10 CRS-affected cats.

CONCLUSIONS AND CLINICAL RELEVANCE

Compared with findings in control cats, anaerobic bacteria, Mycoplasma spp, and a variety of potentially pathogenic organisms were detected more commonly in samples from cats with CRS. In both groups, FHV-1 was detected via PCR assay as a nonviable organism or in noncultivable amounts.

Relative sensitivity of polymerase chain reaction assays used for detection of feline herpesvirus type 1 DNA in clinical samples and commercial vaccines

OBJECTIVE

To determine relative detection rates and detection limits for 6 published polymerase chain reaction (PCR) assays used for detection of feline herpesvirus type 1 (FHV-1) DNA.

SAMPLE POPULATION

5 vaccines licensed for use in preventing FHV-1-associated disease; 15 conjunctival biopsy specimens collected from cats with keratitis, conjunctivitis, or both; and a plaque-purified field isolate of FHV-1 cultured in vitro.

PROCEDURE

Vaccines and clinical samples were assessed for FHV-1 DNA by use of all 6 assays. Detection rates were calculated by assuming that any sample in which FHV-1 DNA was detected was a true-positive result. Detection limits were estimated by use of serial dilutions of DNA extracted from cultured FHV-1 and 1 clinical sample.

RESULTS

Testing by use of all 6 assays resulted in detection of FHV-1 DNA in all 5 vaccines. Testing by use of all 6 assays yielded concordant results for 9 of 15 conjunctival biopsy specimens (8 with negative results and 1 with a positive result). Calculated detection rates for clinical samples ranged from 29% to 86%. Assay sensitivity was ranked similarly by use of detection rate or detection limit.

CONCLUSIONS AND CLINICAL RELEVANCE

Testing by use of all assays was equally likely to detect vaccine virus. Therefore, a positive PCR result in a cat may reflect vaccine virus rather than wild-type virus. Test sensitivity as assessed by detection limits and detection rates varied greatly. Because FHV-1 can be shed in clinically normal animals, high detection rate will not necessarily correlate with high diagnostic sensitivity.

Feline herpesvirus type-1 transcription is associated with increased nasal cytokine gene transcription in cats

The etiopathogenesis of chronic nasal discharge in the cat is poorly understood. The objective of this study was to investigate alterations in transcription of genes for cytokines and chemokines in association with feline herpesvirus-1 (FHV-1) mRNA transcription. Nasal samples from 21 cats were submitted for FHV-1 virus isolation (VI), traditional endpoint polymerase chain reaction (PCR) detection of FHV-1 DNA, and quantitative real-time TaqMan PCR analysis of cytokines and chemokines (interleukin [IL]-4, IL-5, IL-6, IL-10, IL-12p40, IL-16, IL-18, interferon [IFN]-gamma, tumor necrosis factor [TNF]-alpha, and regulated on activation normal T cell expressed and secreted protein [RANTES]) and of FHV-1 mRNA and DNA. Co-infection with feline calicivirus or Chlamydophila spp. was excluded in all cats. Gene transcription in nasal samples from four specific pathogen free (SPF) cats served as the calibrator for cytokines. FHV-1 was detected by VI in 14 of 21 samples, by traditional PCR in 18 of 21 samples, and by quantitative PCR in 13 (mRNA+) and 18 (DNA+) samples. Nasal samples from cats positive for FHV-1 mRNA displayed significantly increased transcription of IL-6, IL-10, IL-12p40, IL-18, IFN-gamma, TNF-alpha, and RANTES (P<0.05) in comparison to samples from cats negative for FHV-1 mRNA. The cycle threshold for FHV-1 DNA was significantly higher in cats with detectable FHV-1 mRNA (P<0.05). Increased transcription of cytokines/chemokines in cats with detectable mRNA for FHV-1 suggests a role for FHV-1 in nasal inflammation.

Diagnosis of ovine chlamydial abortions by PCR-RFLP performed on vaginal swabs

Ovine enzootic abortion is an infectious and contagious disease clinically characterized by abortion and weak neonates, affecting sheep and goats. The etiological agent is Chlamydophila (C.) abortus, which is considered one of the most common animal pathogens of small ruminants; it has important economic implications and represents a significant zoonotic risk. Clinical diagnosis is often difficult because the clinical signs and the pathological lesions are not specific for C. abortus infection, in fact they can also be observed as a result of infections with other abortifacient agents. Moreover, the involvement of the laboratory is necessary to perform the definitive diagnosis. One hundred and seventeen vaginal swabs from sheep with clinical signs related to chlamydial infection were examined by a PCR-RFLP assay that demonstrated high specifity and sensitivity. Six samples were positive for C. abortus. Vaginal swabs are easy to handle and allow to deal with biohazardous material in safety conditions.

Methodology in diagnostic virology

Selection of proper assays and appropriate interpretation of results can be a challenge to the veterinary clinician. Assays vary in methodology, sensitivity, and specificity. These assays can be invaluable in attaining the correct diagnosis, but a clear understanding of the assay and the results is essential. To this end, communication with the laboratory personnel is crucial. Optimal sample selection, shipping recommendations, assay selection, and interpretation should be discussed with the laboratory staff.

A novel nested PCR for the diagnosis of calicivirus infections in the cat

A novel nested PCR (nPCR) assay is reported on the diagnosis of the feline calicivirus (FCV) infection. The test was performed on 47 ocular and 40 pharyngeal swabs collected from 47 cats with respiratory syndrome; among the 87 samples examined, 18 ocular and 23 pharyngeal swabs were positive in nPCR. The nPCR sensitivity was compared to other diagnostic techniques such as virus isolation on cell culture and reverse transcriptase-polymerase chain reaction (RT-PCR). The nPCR was more sensitive than the virus isolation and RT-PCR; therefore, it can be used for calicivirosis diagnosis in cats.

Optimization of in situ hybridization protocols for detection of feline herpesvirus 1

In situ hybridization (ISH) protocol including microwaving pre-treatment regimes was developed and compared with protease digestion as a pre-treatment regime for its effects on detecting feline herpesvirus 1 (FHV-1) in formalin fixed, paraffin embedded tissue. We found that optimum results were obtained using microwave pre-treatment. The results showed that the use of microwave irradiation would be recommended as a means of supplementing ISH methods, especially when using long-term formalin fixed, paraffin-embedded tissue.

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.

Effects of bovine lactoferrin on in vitro replication of feline herpesvirus

OBJECTIVE

To investigate the effects of bovine lactoferrin on in vitro replication of feline herpes virus (FHV-1) and to determine at what points during viral replication these effects occur.

SAMPLE POPULATION

Cultured Crandell-Reese feline kidney (CRFK) cells and FHV-1 strain 727.

PROCEDURE

Five concentrations of bovine lactoferrin (0.5, 1, 2, 5, and 10 mg/mL) were added at one or more of three time points during conventional plaque reduction assays: (a) uninfected CRFK cells were incubated in lactoferrin-containing medium for 30 min prior to viral adsorption; (b) virus was suspended in lactoferrin-containing medium prior to and during adsorption, or (c) CRFK cells were incubated with lactoferrin-containing medium for 48 h following viral adsorption. Plaques were counted and antiviral effect expressed as percent inhibition relative to control medium that contained no lactoferrin.

RESULTS

Exposure of CRFK cells to lactoferrin prior to or during viral adsorption inhibited FHV-1 replication by 87-96% (mean: 91%). Application of lactoferrin following viral adsorption had no appreciable effect on FHV-1 replication. No additive or synergistic effects were noted when lactoferrin was added at multiple steps. These effects were similar at all concentrations of lactoferrin tested. Cytotoxic effects of lactoferrin on CRFK cells were not observed at any concentration tested.

CONCLUSIONS AND CLINICAL RELEVANCE

Bovine lactoferrin has a notable inhibitory effect on the in vitro replication of FHV-1 prior to and during, but not following viral adsorption. These findings strongly suggest that lactoferrin inhibits FHV-1 adsorption to the cell surface and/or penetration of the virus into the cell. Clinical effects of topical lactoferrin in acute or recrudescent herpetic episodes in cats warrant investigation.

Concurrent oral shedding of feline calicivirus and feline herpesvirus 1 in cats with chronic gingivostomatitis

Oral mucosal salivary samples were collected from 25 cats with chronic gingivostomatitis and 24 cats with periodontal disease. Viral culture and isolation of feline calicivirus and feline herpesvirus 1 were performed. Eighty-eight per cent of cats with chronic gingivostomatitis were shedding both viruses, compared to 21% of cats without chronic oral inflammatory disease. Cats with chronic gingivostomatitis are significantly more likely to concurrently shed both feline calicivirus and feline herpesvirus 1 than are cats with classical periodontal disease.

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.

Quantification of feline herpesvirus 1 DNA in ocular fluid samples of clinically diseased cats by real-time TaqMan PCR

A fluorogenic PCR was established for the quantification of feline herpesvirus 1 (FeHV-1) DNA in ocular fluid samples of clinically diseased cats. The new assay was specific for FeHV-1 and sensitive. The 100% detection rate ranged from 0.6 to 6 50% tissue culture infective doses per sample. When spiked samples with known quantities of virus were used, infectious virus titers and quantification of viral DNA by PCR correlated to each other in a linear fashion (R(2) = 0.9858) over a range of 4 orders of magnitude. Within this range, it was possible to calculate the FeHV-1 DNA content from a given infectious dose, and vice versa. The new diagnostic procedure was applied to ocular fluid samples from cats experimentally infected with FeHV-1 and specific FeHV-1-free cats. A good correlation between virus titer and quantitative PCR was observed, although only early in infection. In a second stage, the titer of infectious virus collapsed, while the PCR signal remained high. A constantly decreasing PCR signal accompanied by negative virus isolation was characteristic for a final stage of the infection. Finally, clinical samples from 20 cats that were suspected to suffer from FeHV-1 infection were analyzed. By comparing virus titers and quantitative PCR signals, it was possible to determine the current stage of the ongoing infection. Based on these findings, comparison of the results of consecutive samples allows the tracking of the course of the infection. Therefore, the new method combines the advantages of the two previously established conventional methods, qualitative PCR and virus isolation and titration.

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.

A study of feline upper respiratory tract disease with reference to prevalence and risk factors for infection with feline calicivirus and feline herpesvirus

A cross-sectional survey of a convenience sample of cats was carried out to determine the prevalence of and risk factors for respiratory tract disease, feline calicivirus (FCV) infection and feline herpesvirus (FHV) infection. Seven hundred and forty cats were studied; samples for isolation of FCV and FHV were obtained from 622 (84%). Data on individual cat and household variables were obtained by questionnaire for each cat and analysed using univariable and logistic regression analysis. Thirty-eight percent (282/740) of cats surveyed had respiratory tract disease. Eighteen of 24 predictor variables were found to be significantly (P<0.05) associated with the presence of respiratory tract disease in a cat on univariable analysis. Following logistic regression, several factors retained significance including isolation of FCV and FHV, younger cats (4-11 months of age) and multiple cat households. A negative association was found with breeding catteries and other types of household in comparison with rescue catteries. Overall, feline calicivirus was isolated from 162/622 (26%) of cats sampled; 33% of the cats with respiratory tract disease were FCV positive compared to 21% of healthy cats. Variables significantly associated with FCV isolation on logistic regression were the presence of respiratory tract disease and contact with dogs with and without respiratory tract disease. Feline herpesvirus was isolated from 30/622 (5%) of all cats sampled; 11% of cats with respiratory tract disease were FHV positive compared to 1% of healthy cats. Variables significantly associated with FHV isolation on univariable analysis included age, gender, and the presence of respiratory tract disease. Vaccination showed a negative association. Logistic regression analysis of the data for FHV was limited by the sample size and the low prevalence of FHV.

Diagnosis of feline herpesvirus infection by immunohistochemistry, polymerase chain reaction, and in situ hybridization

An adult domestic shorthair cat had severe chemosis due to purulent and necrotizing blepharitis and conjunctivitis. Purulent rhinitis, necrotizing glossitis, and dermatitis were also diagnosed. The cat was positive for feline immunodeficiency virus and feline leukemia virus. Histologically, intranuclear Cowdry type A inclusions were found within numerous epithelial cells adjacent to the lesions in skin, conjunctiva, and tongue. Electron microscopic examination revealed herpesviral particles within the lesions. Paraffin-embedded skin and tongue tissues were processed in a polymerase chain reaction, using primers to amplify a 306-bp region of the thymidine kinase gene of feline herpesvirus type 1, resulting in a distinct amplification product of the predicted size. The distribution of feline herpesvirus was demonstrated by immunohistochemistry and nonradioactive in situ hybridization. Positive immunostaining was found in nuclei and cytoplasm of numerous epithelial cells within and next to the lesions, whereas in situ hybridization, performed with a digoxigenin-labeled double-stranded DNA probe, revealed hybridization signal only in nuclei of intact epithelial cells. Neither immunohistochemistry nor in situ hybridization showed feline herpesvirus type 1 in tissues of lungs, liver, spleen, intestine, or brain.

Feline herpesvirus 1-associated facial and nasal dermatitis and stomatitis in domestic cats

Feline herpesvirus-associated dermatitis has rarely been reported. Recently we documented a unique ulcerative and often persistent facial dermatitis or stomatitis syndrome associated with feline herpesvirus 1. We believe this syndrome is relatively common, with the 10 cases in our series diagnosed between 1996 and 1997. The syndrome is associated with epithelial cell necrosis, eosinophilic inflammation, and intraepithelial herpesvirus inclusion bodies. The prevalence of eosinophilic inflammation and low number of inclusion bodies may lead to the misdiagnosis of allergic dermatitis or a lesion within the eosinophilic granuloma complex group of disorders. Feline herpesvirus 1 can be identified in lesional tissue by PCR methodology. Most of our cases developed under circumstances suggesting reactivation of latent herpesvirus infection, and previous glucocorticoid therapy or stress from overcrowding may have played a role in lesion development. Cats with ulcerative dermatitis, especially of the face and nose, and cats with stomatitis should be evaluated for the presence of feline herpesvirus. Treatment options include surgical excision, topical or systemic antibiotic therapy to treat secondary bacterial infection, and oral alpha interferon.

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.

The role of polymerase chain reaction and its newer developments in feline medicine

We give a brief overview on the principles of the polymerase chain reaction (PCR), reverse transcriptase PCR (RT-PCR), quantitative competitive PCR and real-time PCR (TaqMan technology). The literature dealing with PCR and its role in the diagnosis, pathogenesis and research of infectious diseases of the domestic cat is reviewed. Cross-contaminations which occasionally occur during handling of amplified DNA may be an important problem in the PCR laboratory. In many infectious diseases, PCR results are difficult to interpret as their predictive positive and negative values are not always known. Newer assays, such as TaqMan procedures, are becoming increasingly reliable and cost-effective. It can be expected that additional knowledge on how to interpret PCR results will soon be available.