Detection of active and latent feline herpesvirus 1 infections using the polymerase chain reaction

Performance and overview of clinically relevant areas of application of saliva testing in the cat

Introduction

The cat represents an important model in order to investigate basic physiological knowledge of salivary secretion as well as pharmacokinetics of active substances.

Objective

The aim of the study was to review in which diagnostic application areas saliva testing is routinely used and in which areas it could be further explored in the future.

Materials and methods

Literature relevant to the research question was collected in March 2022 using the Pubmed database.

Results

The diagnosis of infectious diseases in cat saliva is one of the most important fields of application. Saliva diagnostics may also indicate dental diseases, allergies or kidney and other metabolic diseases. Sexual and stress hormones can also be measured in cat saliva. A number of clinically relevant allergens in cat saliva that may cause allergies in humans has been investigated and described, in addition to infectious agents that can be transmitted from cats to humans.

Conclusions

Saliva testing in cats can be useful in many areas, including the detection of infectious diseases, allergies and dental disease. However, it is far from being used to its full potential within veterinary medicine.

Prevalence and risk factors for common respiratory pathogens within a cohort of pet cats in the UK

OBJECTIVES

Feline herpesvirus (FHV), feline calicivirus (FCV) and Chlamydia felis are common causes of upper respiratory tract disease (URTD) in cats. Their prevalence in the UK pet cat population has not been reported and little is known regarding the risk factors for their oral carriage.

METHODS

Total nucleic acid was extracted from owner-collected buccal swabs (n=600) from cats enrolled in a self-selected longitudinal cohort study. Duplex quantitative PCRs for the detection of FHV and C. felis genomic DNA and reverse-transcriptase quantitative PCRs for the detection of FCV genomic RNA were performed. Duplicates, swabs with insufficient host DNA/RNA, and cats with missing data were excluded. Selected epidemiological data were interrogated using univariable and multi-variable logistic regression modelling to identify risk factors.

RESULTS

Data from 430 cats were included in the final statistical model. Of these, 2.1% (n=9/430; 95% CI 1.0% to 3.9%) were positive for FHV, 13.3% (n=57/430; 95% CI 10.2% to 16.8%) positive for FCV and 1.2% (n=5/430; 95% CI 0.4% to 2.7%) positive for C. felis. FCV co-infection was present in five (44%) FHV-positive cats and three (60%) C. felis-positive cats. FCV carriage was more frequent in purebred cats (odds ratio 2.48; 95% CI 1.37 to 4.49) and in cats with current or historical clinical signs compatible with URTD (odds ratio 2.98; 95% CI 1.22 to 7.27).

CLINICAL SIGNIFICANCE

FCV was the most frequently encountered URTD pathogen in this sample of cats; this should be noted for disinfectant choice. In cats suspected of having FHV or C. felis infection, assessment for co-infection with FCV is recommended.

Internal reference genes with the potential for normalizing quantitative PCR results for oral fluid specimens

In basic research, testing of oral fluid specimens by real-time quantitative polymerase chain reaction (qPCR) has been used to evaluate changes in gene expression levels following experimental treatments. In diagnostic medicine, qPCR has been used to detect DNA/RNA transcripts indicative of bacterial or viral infections. Normalization of qPCR using endogenous and exogenous reference genes is a well-established strategy for ensuring result comparability by controlling sample-to-sample variation introduced during sampling, storage, and qPCR testing. In this review, the majority of recent publications in human (n = 136) and veterinary (n = 179) medicine did not describe the use of internal reference genes in qPCRs for oral fluid specimens (52.9% animal studies; 57.0% human studies). However, the use of endogenous reference genes has not been fully explored or validated for oral fluid specimens. The lack of valid internal reference genes inherent to the oral fluid matrix will continue to hamper the reliability, reproducibility, and generalizability of oral fluid qPCR assays until this issue is addressed.

Safety and Efficacy of Felid Herpesvirus-1 Deletion Mutants in Cats

Felid herpesvirus-1 (FeHV-1) is an important respiratory and ocular pathogen of cats and current vaccines are limited in duration and efficacy because they do not prevent infection, viral nasal shedding and latency. To address these shortcomings, we have constructed FeHV-1 gE-TK- and FeHV-1 PK- deletion mutants (gE-TK- and PK-) using bacterial artificial chromosome (BAC) mutagenesis and shown safety and immunogenicity in vitro. Here, we compare the safety and efficacy of a prime boost FeHV-1 gE-TK- and FeHV-1 PK- vaccination regimen with commercial vaccination in cats. Cats in the vaccination groups were vaccinated at 3-week intervals and all cats were challenge infected 3 weeks after the last vaccination. Evaluations included clinical signs, nasal shedding, virus neutralizing antibodies (VN), cytokine mRNA gene expression, post-mortem histology and detection of latency establishment. Vaccination with gE-TK- and PK- mutants was safe and resulted in significantly reduced clinical disease scores, pathological changes, viral nasal shedding, and viral DNA in the trigeminal ganglia (the site of latency) following infection. Both mutants induced VN antibodies and interferons after immunization. In addition, after challenge infection, we observed a reduction of IL-1β expression, and modulation of TNFα, TGFβ and IL10 expression. In conclusion, this study shows the merits of using FeHV-1 deletion mutants for prevention of FeHV-1 infection in cats.

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.

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.

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.

Sampling sites for detection of feline herpesvirus-1, feline calicivirus and Chlamydia felis in cats with feline upper respiratory tract disease

OBJECTIVES

Feline herpesvirus-1 (FHV-1), feline calicivirus (FCV) and Chlamydia felis are involved in feline upper respiratory tract disease (FURTD). Clinical signs caused by these agents can overlap, and the involvement of certain pathogens is often unpredictable. The objectives of this study were to compare detection rates of FHV-1, FCV and C felis at different sampling sites, and to investigate the correlation between positive test results and clinical signs in cats with FURTD.

METHODS

Swabs were taken from the nose, pharynx, tongue and conjunctiva of 104 cats with signs of FURTD. Real-time PCR was performed on all samples for the detection of FHV-1, FCV and C felis.

RESULTS

Infectious agents were identified in 93 (89.4%) cats. Of these, 55.8% were positive for FHV-1, 50.0% for FCV and 35.6% for C felis. FCV was found more frequently in the oropharynx (92.3% of FCV-positive cats) and on the tongue (90.4%) than the conjunctiva (38.5%) (P <0.001). There was no significant difference between the four sampling sites for the detection of FHV-1 and C felis. If nasal samples had also been taken, 94.9% of FHV-1-positive cats, 96.2% of FCV-positive cats and 81.1% of C felis-positive cats would have been detected.

CONCLUSIONS AND RELEVANCE

The oropharynx can be recommended as the preferred single sampling site for the detection of FCV, FHV-1 and C felis if only one sample can be taken; however, taking samples at different sites significantly increases the detection rate for all pathogens studied. Interestingly, sampling from a site with FURTD-associated lesions did not increase the likelihood of detecting the infectious agents.

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.

Uterine adenocarcinoma with feline leukemia virus infection

Feline endometrial adenocarcinomas are uncommon malignant neoplasms that have been poorly characterized to date. In this study, we describe a uterine adenocarcinoma in a Persian cat with feline leukemia virus infection. At the time of presentation, the cat, a female Persian chinchilla, was 2 years old. The cat underwent surgical ovariohystectomy. A cross-section of the uterine wall revealed a thickened uterine horn. The cat tested positive for feline leukemia virus as detected by polymerase chain reaction. Histopathological examination revealed uterine adenocarcinoma that had metastasized to the omentum, resulting in thickening and the formation of inflammatory lesions. Based on the histopathological findings, this case was diagnosed as a uterine adenocarcinoma with abdominal metastasis. To the best of our knowledge, this is the first report of a uterine adenocarcinoma with feline leukemia virus infection.

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.

Evidence of feline herpesvirus-1 DNA in the vestibular ganglion of domestic cats

In humans, herpes simplex virus type-1 has recently been detected in the vestibular ganglion (VG) and labyrinth (VL) and may be associated with vestibular signs. Feline herpesvirus-1 (FHV-1) is widespread amongst cat populations and affects many different tissues. The aim of this pilot study was to investigate the presence of FHV-1 DNA in the VG and VL of randomly selected domestic cats using PCR. FHV-1 DNA was detected in the VG of 14% of the cats. There was no detectable FHV-1 DNA in the VL of any cat. None of the infected cats had vestibular signs related to the VG infection.

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.

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.

Pathogenesis of feline enteric coronavirus infection

Fifty-one specific pathogen-free (SPF) cats 10 weeks to 13 years of age were infected with a cat-to-cat fecal-oral passed strain of feline enteric coronavirus (FECV). Clinical signs ranged from unapparent to a mild and self-limiting diarrhea. Twenty-nine of these cats were FECV naïve before infection and followed sequentially for fecal virus shedding and antibody responses over a period of 8-48 months. Fecal shedding, as determined by real-time polymerase chain reaction (RT-PCR) from rectal swabs, appeared within a week and was significantly higher in kittens than older cats. FECV shedding remained at high levels for 2-10 months before eventually evolving into one of three excretion patterns. Eleven cats shed the virus persistently at varying levels over an observation period of 9-24 months. Eleven cats appeared to have periods of virus shedding interlaced with periods of non-shedding (intermittent or recurrent shedders), and seven cats ceased shedding after 5-19 months (average 12 months). There was no change in the patterns of virus shedding among cats that were excreting FECV at the time of a secondary challenge exposure. Four cats, which had ceased shedding, re-manifested a primary type infection when secondarily infected. Cats with higher feline coronavirus (FCoV) antibody titers were significantly more likely to shed virus, while cats with lower titers were significantly less likely to be shedding. Twenty-two kittens born to experimentally infected project queens began shedding virus spontaneously, but never before 9-10 weeks of age. Natural kittenhood infections appeared to be low grade and abortive. However, a characteristic primary type infection occurred following experimental infection with FECV at 12-15 weeks of age. Pregnancy, parturition and lactation had no influence on fecal shedding by queens. Methylprednisolone acetate treatment did not induce non-shedders to shed and shedders to increase shedding.

Canine and feline pregnancy loss due to viral and non-infectious causes: a review

Among the causes for pregnancy loss, viruses and non-infectious factors are among the most important. In both dogs and cats, research and clinical evidence provide proof that there is an increasing incidence of pregnancy loss associated with infectious diseases like herpesvirus, as well as the presence of toxicants or chemicals in the animal's diet and environment. Endocrine causes must be taken into consideration when dealing with pregnancy loss. This review will cover the most recent knowledge regarding viral and non-infectious of pregnancy losses in the dog and cat.

Subclinical infection with avian influenza A (H5N1) virus in cats

Infection without disease may occur under natural conditions after contact with infected birds.

Avian influenza A virus subtype H5N1 was transmitted to domestic cats by close contact with infected birds. Virus-specific nucleic acids were detected in pharyngeal swabs from 3 of 40 randomly sampled cats from a group of 194 animals (day 8 after contact with an infected swan). All cats were transferred to a quarantine station and monitored for clinical signs, virus shedding, and antibody production until day 50. Despite unfamiliar handling, social distress and the presence of other viral and nonviral pathogens that caused illness and poor health and compromised the immune systems, none of the cats developed clinical signs of influenza. There was no evidence of horizontal transmission to other cats because only 2 cats developed antibodies against H5N1 virus.

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.

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.

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.

Chronic Rhinitis in Cats

Chronic rhinitis is a common and important problem in cats potentially resulting from a number of intranasal or systemic disorders. Idiopathic chronic rhinosinusitis and nasal neoplasia are the most common causes of chronic nasal disease in cats. For most cats with chronic rhinitis, diagnostic imaging, endoscopic studies, and nasal biopsy will be required to establish a diagnosis. A discussion of some of the more common causes of chronic nasal disease is presented.

Isolation of feline herpesvirus-1 and feline calicivirus from healthy cats in Swedish breeding catteries

Feline calicivirus (FCV) could be isolated from four cats (2.6%) and feline herpesvirus-1 (FHV) from none of 152 clinically healthy cats from 22 Swedish breeding catteries. These cats had all previously shown signs of respiratory tract disease or conjunctivitis, although several years ago. The results suggest that carriers of FCV and FHV were uncommon in Swedish breeding catteries studied. Prevalence rates in other European countries and North America are usually higher, especially of FCV. The lower prevalence rates in our study might be explained by test group selection, differences in factors such as management, environment, or genetic constitution of the cats, or by sample handling. It was concluded that the presence of an FCV shedder in the cattery does not mean that all cats in the group are infected, but special measures are recommended to avoid infection of susceptible cats.

Tissue distribution of phocine herpesvirus-1 (PhHV-1) in infected harbour seals (Phoca vitulina) from the central Californian coast and a comparison of diagnostic methods

The polymerase chain reaction (PCR) was used to determine the tissue distribution of phocine herpesvirus-1 (PhHV-1) DNA in 20 stranded Pacific harbour seals (17 pups and three seals older than one year) that died during rehabilitation. The aim was to begin to define stages of infection and to investigate the relation between the presence of PhHV-1 in tissues, histological lesions and serology. PhHV-1 DNA was detected in a wide range of tissues from 10/17 pups and 3/3 subadults or adults. Different clinical patterns emerged from the examination of ante- and post-mortem samples. These patterns probably represented pups with active PhHV-1 infection, pups recovering from infection, and older harbour seals with chronic, reactivated infection. As PhHV-1 DNA was detected in tissues in the absence of typical histological lesions in seven seals and in the absence of PhHV-1 specific antibodies in four seals, it is clear that both histological examination and serology underestimate the presence of infection. These results showed that infection can occur in the absence of obvious disease and that seroconversion may be associated with clinical recovery.

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.

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.

Development of a reverse transcriptase-polymerase chain reaction assay to detect feline herpesvirus-1 latency-associated transcripts in the trigeminal ganglia and corneas of cats that did not have clinical signs of ocular disease

OBJECTIVE

To develop a reverse transcriptase-polymerase chain reaction (RT-PCR) assay to detect feline herpesvirus-1 (FHV-1) latency-associated transcripts (LATs) in the corneas and trigeminal ganglia of cats that did not have clinical signs of ocular disease.

SAMPLE POPULATION

Corneas and trigeminal ganglia obtained from 21 cats necropsied at the Indiana Animal Disease Diagnostic Laboratory and 25 cats euthanatized at a humane shelter; none of the cats had a recent history of respiratory tract or ocular disease, and all had normal results for ophthalmic examinations.

PROCEDURE

Both corneas and both trigeminal ganglia were harvested from each cat. An initial PCR assay detected FHV-1 DNA in the corneas and trigeminal ganglia. The RNA was then isolated from samples positive for FHV-1 DNA, and an RT-PCR assay was used to detect LATs.

RESULTS

FHV-1 DNA was detected in 45 of 92 (48.9%) corneas and 38 of 92 (41.3%) trigeminal ganglia. In many samples, the RNA had degraded and RT-PCR assay was not possible. Of the samples subjected to RT-PCR assay, none of the 39 corneas but 4 of 16 trigeminal ganglia had positive results when tested for LATs.

CONCLUSIONS AND CLINICAL RELEVANCE

Analysis of the results indicated that a high percentage of cats that did not have clinical signs of ocular disease had detectable FHV-1 DNA in their corneas and trigeminal ganglia. This study documents that the RT-PCR assay can successfully identify LATs and may serve as a tool to better understand the biologic characteristics of FHV-1 and its relationship to clinical disease.

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.

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.

Latency sites and reactivation of duck enteritis virus

Duck virus enteritis (DVE) is a contagious disease caused by herpesvirus in waterfowl populations. Recovered birds become carriers and shed the virus periodically. Reactivation of latent duck enteritis virus (DEV) has been implicated in outbreaks of DVE in domestic and migrating waterfowl populations. In this study, the sites for virus latency were determined in white Pekin ducks infected with the DEV-97 strain. At 3 wk postinfection, infectious virus was not detectable in tissues or cloacal swabs (CSs). At 7 and 9 weeks postinfection, the viral DNA was detected by polymerase chain reaction in the trigeminal ganglia (TG), suggesting that the virus is latent. Viral DNA was detected in the peripheral blood lymphocytes (PBL), spleen, thymus, bursa, and CSs only after in vitro cocultivation. In vivo virus reactivation was demonstrated when dexamethasone or a combination of dexamethasone and cyclophosphamide was inoculated in latently infected ducks. The reactivation of DEV occurred without any clinical evidence of the disease, but the virus was detected in PBL and CSs. We conclude from this study that DEV establishes latency in TG and lymphoid tissues including PBL.

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.

Mineralized corneal sequestrum in a cat

An 8-month-old 3-kg (6.6-lb) sexually intact male cat was evaluated for chronic refractory keratitis and a corneal plaque that developed after treatment with a corticosteroid-containing ophthalmic preparation. Pertinent ophthalmic findings included blepharospasm, conjunctivitis, corneal vascularization, and a tan raised corneal plaque with a dense and gritty composition. Lamellar keratectomy was performed to excise the plaque. The cornea healed with mild scarring. Histologic examination revealed extensive coagulation necrosis and mineralization of the corneal stroma with increased inflammatory cells, blood vessels, and fibrosis, which is compatible with a diagnosis of mineralized corneal sequestrum. The history suggested chronic feline herpesvirus-1 (FHV-1)-induced keratoconjunctivitis as the underlying cause. Topical corticosteroid administration may have potentiated the preexisting corneal necrosis and initiated mineralization. To our knowledge, mineralization of a corneal sequestrum in a cat has not been reported in a clinical case but has been reported in cats experimentally infected with FHV-1.

Experimental infection of European red foxes (Vulpes vulpes) with canine herpesvirus

We report on the pathogenicity of canine herpesvirus (CHV) for European red foxes. In the first experiment, we inoculated 10 adult foxes intravenously with a canine isolate of CHV. All foxes became infected and shed CHV in saliva and genital secretions for up to 14 days post-inoculation (p.i.) as evaluated by PCR and/or by virus isolation. All foxes developed clinical signs such as fever, lethargy and evidence of respiratory tract disease. Two foxes died on day 6 p.i., one on day 7 p.i., and one fox was euthanased on day 6 p.i. Tissues taken from the four dead foxes were positive for CHV by PCR. The remaining six foxes recovered after approximately 14 days p.i. Virus particles with morphology typical of herpesviruses were found by electron microscopy in the liver of an infected animal. All surviving foxes developed serum anti-CHV antibodies. In a second experiment, six foxes were dosed perorally with CHV and paired with six untreated controls. Neither the perorally dosed nor the in-contact control foxes developed clinical signs of disease. Infectious CHV was not isolated from any of the dosed or the in-contact foxes but all perorally-infected foxes and one of the in-contact foxes tested PCR-positive for CHV on several occasions p.i. All perorally-infected foxes, but none of the in-contact foxes, seroconverted. In summary, intravenous CHV inoculation caused a clinical disease in adult foxes much more severe than observed in experimentally-infected adult dogs. No clinical disease or virus spread was observed after peroral dosing although viral infection occurred as evidenced by seroconversion.

Ulcerative keratitis associated with qualitative tear film abnormalities in cats

Three cats with indolent corneal ulcers and one cat with bilateral corneal sequestration and normal aqueous tear production were found to have rapid tear break-up times (BUTs). Tear BUTs in clinically affected cats averaged 2.5 +/- 1.29 s and 2.33 +/- 0.58 s for the right and left eyes, respectively. Palpebral conjunctival biopsies were harvested from consistent sites from each eye of affected cats (n = 7 affected eyes), and age-and breed-matched controls (n = 2 unaffected eyes). Light microscopy revealed a marked decrease to complete absence of conjunctival goblet cells (average goblet cell (GC):epithelial cell (EC) density = 18:50), conjunctival epithelial dysplasia, squamous metaplasia, and neutrophilic and mononuclear cell submucosal infiltration in affected cats. Specimens from the control cats had an average GC:EC density of 34:50, and minimal submucosal inflammatory infiltrate. The corneas (n = 7 eyes) healed following surgical keratectomy with (n = 2 eyes) or without (n = 1 eye) conjunctival pedicle flaps, superficial keratectomy and striate keratotomy with (n = 2 eyes) or without (n = 2 eyes) third eyelid flaps, and mucinomimetic tear supplementation (n = 5 eyes). Goblet cell regeneration was confirmed after 5 months of mucinomimetic supplementation (n = 2 eyes). The etiology for these mucin deficiencies remains unknown.

Feline leukemia virus detection in corneal tissues of cats by polymerase chain reaction and immunohistochemistry

OBJECTIVES

To determine the presence of feline leukemia virus (FeLV) in the corneas of FeLV-infected cats.

ANIMALS STUDIED

Thirty-four random source cats.

PROCEDURES

Seventeen cats were found positive for FeLV serum p27 antigen by enzyme-linked immunosorbent assay (ELISA). Twelve ELISA positive cats were also positive on peripheral blood samples by immunofluorescent antibody (IFA) testing. Seventeen ELISA negative cats served as negative controls. Full thickness corneal specimens were collected from the left cornea of all cats and analyzed for FeLV proviral DNA and gp70 antigen by polymerase chain reaction (PCR) and immunohistochemical (IHC) testing, respectively.

RESULTS

Eleven (64.7%) positive corneal PCR results were obtained from 17 ELISA positive cats. Of 12 cats that were both ELISA and IFA positive on peripheral blood, 10 (83.3%) had positive corneal PCR results. All corneal tissues from ELISA negative cats were PCR negative. IHC staining of corneal sections revealed the presence of FeLV gp70 in corneal tissues of nine (52.9%) ELISA positive cats. Of the 12 cats that were both ELISA and IFA positive on peripheral blood, eight (66.7%) had positive corneal IHC results. Positive IHC staining was localized to the corneal epithelium. Corneal tissues of all ELISA negative cats and all IFA negative cats were negative on IHC testing.

CONCLUSIONS

FeLV antigens and proviral DNA are present in corneal tissues of some FeLV-infected cats. Screening corneal donors for FeLV infection is warranted.

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.

Feline infectious pneumonia: a short literature review and a retrospective immunohistological study on the involvement of Chlamydia spp. and distemper virus

A short literature review of feline infectious pneumonia, feline Chlamydia and Paramyxoviridae is presented. In a retrospective study (from 1987 to 1996) 245 cases of feline pneumonia or conjunctivitis/rhinitis were investigated: histological diagnoses and aetiologies were compared; all lungs were examined immunohistologically for the occurrence of chlamydia and of canine distemper virus (CDV), but neither pathogen could be demonstrated. The results confirm previous reports indicating that feline chlamydia is not a primarily pulmonary pathogen and that CDV is not a causative agent of pneumonia in cats as it is in large felids. The review provides a summary of the known causes and pathology of infectious pneumonia in cats (in order of frequency), although some remain aetiologically uncertain. It focuses on chlamydia and distemper virus - a recognized and as yet unknown cause of feline pneumonia. The role and especially the frequency of chlamydia as a cause of feline pneumonia are controversial but distemper virus, known to cause pneumonia in dogs and large felids, has not as yet been demonstrated in cats. The aims of the retrospective study were to determine the occurrence of chlamydia in 245 cases of feline pneumonia or conjunctivitis/rhinitis, and to investigate the presence of CDV in these lungs.

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.

Comparison of PCR, virus isolation, and indirect fluorescent antibody staining in the detection of naturally occurring feline herpesvirus infections

Cats with clinical signs suggestive of ocular infection with feline herpesvirus type 1 (FHV 1) and cats without such signs were assayed by 3 methods to detect FHV. Comparison of polymerase chain reaction (PCR), virus isolation, and indirect fluorescent antibody staining techniques for the detection of FHV demonstrated higher sensitivity of PCR in detecting this common infectious agent of cats. Compared with PCR, sensitivity and specificity for virus isolation was 49% and 100%, respectively, and those of indirect immunofluorescence were 29% and 96%, respectively. FHV was detected in 13.7% of client-owned cats with conjunctivitis and in 31% of shelter cats with no ocular signs. The use of FHV PCR as a diagnostic test for FHV-associated disease is limited because of the occurrence of healthy carriers.

Vaccine efficacy of recombinant feline herpesvirus type 1 expressing immunogenic proteins of feline calicivirus in cats

We previously constructed a recombinant feline herpesvirus type 1 (FHV1), C7301dlTK-Cap, which contains an entire open reading frame encoding the capsid protein of feline calicivirus (FCV) F4 strain in the deleted locus of the thymidine kinase (TK) deficient mutant (C7301dlTK) of FHV1. In this report, we carried out in vivo experiments to assess the vaccine efficacy of the recombinant C7301dlTK-Cap against FCV and FHV1 infections in cats. As a result, two vaccinations with the C7301dlTK-Cap by intraocular, intranasal and oral routes protected cats to a significant degree against subsequent virulent challenges with both parent FCV F4 and FHV1 C7301 strains. The results are applicable for the further development of a new genetically engineered polyvalent vaccine for cats.

Detection of animal pathogens by using the polymerase chain reaction (PCR)

The polymerase chain reaction (PCR) is a nucleic acid-based technique that enables the rapid and sensitive detection of specific micro-organisms. Although this technique is widely used in veterinary research, it has not yet found applications in routine microbiological analysis of veterinary clinical samples. However, advances in sample preparation together with the increasing availability of specific gene sequences will probably lead to the more widespread diagnostic use of PCR in the future. PCR is likely to have a strong impact in the epidemiology, treatment and prevention of animal infectious diseases.

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

A polymerase chain reaction (PCR) assay was developed and used to detect feline herpesvirus-1 (FHV-1) in conjunctival and oropharyngeal swabs, and in latently infected tissues (trigeminal ganglia, optic nerves, optic chiasma, olfactory bulbs and corneas) collected from 10 experimentally infected cats. There was good agreement between parallel tests of the swab specimens by PCR and virus isolation assay during the phase of acute, latent and recurrent disease episodes (kappa = 0.63, P < 0.001). The PCR reliably detected < or = 240 copies of FHV-1 template DNA, significantly improving upon previously published PCR assays for the agent.

Detection of canine herpesvirus 1 in a wide range of tissues using the polymerase chain reaction

Canine herpesvirus 1 (CHV-1), a member of the alphaherpesvirus sub-family, is known to cause fatal infections in litters of puppies and may also be involved in infertility, abortion, and stillbirths in adult dogs. The purpose of this study was to determine the presence of CHV-1 DNA using the polymerase chain reaction (PCR) in twelve key sites that have been associated with latency for the other herpesviruses. A 605 base pair portion of the viral glycoprotein B (gB) gene was amplified using degenerate primers, cloned, and sequenced. Conventional 20 mer primers were designed using this sequence information to amplify a 120 bp fragment of gB situated between the original degenerate primers. The specificity of amplification was confirmed by Southern Blot hybridisation using an internal oligonucleotide probe. DNA was extracted from tissue samples taken from twelve dogs at post mortem and from twenty-four blood samples. Nine out of twelve dogs showed evidence of infection with CHV-1; the tissues most commonly affected were lumbo-sacral ganglia (5/12 dogs), tonsil (5/12), parotid salivary gland (4/9), and liver (4/9). No positive results were detected within the twenty-four blood samples. These results indicate that exposure to CHV-1 may be much more common than previously suggested.

Detection of feline herpesvirus 1 DNA by the nested polymerase chain reaction

The thymidine kinase region of feline herpesvirus 1 (FHV 1) genome in ocular/nasal swabs from cats with clinical manifestations of upper respiratory disease was amplified by nested polymerase chain reaction (nested PCR). Two primer pairs were prepared for nested PCR. FHV 1 DNA in ocular/nasal swabs was extracted using instaGene-DNA purification matrix. Nested PCR for the FHV 1 culture supernatants was ten times as sensitive as single PCR. On comparing viral isolation with single PCR and nested PCR for the detection of FHV 1 in ocular/nasal secretions, of 5 samples that yielded infectious virus in cell culture, 3 (60%) were positive in single PCR and 5 (100%) were positive in nested PCR. When 22 ocular/nasal swabs that did not yield FHV 1 were assayed, 3 were negative in both single PCR and nested PCR, 2 were positive in both single and nested PCR and 17 were positive in only nested PCR. Thus, FHV 1 was detected in 19/22 (86.4%) by the nested PCR and in 2/22 (9%) by single PCR. These results show that nested PCR is 4.8 (24 positive samples/5 positive samples) times as sensitive as single PCR.