Detection of feline herpesvirus 1 transcripts in trigeminal ganglia of latently infected cats

Evaluation of compounded cidofovir, famciclovir, and ganciclovir for the treatment of feline herpesvirus ocular surface disease in shelter-housed cats

OBJECTIVE

To assess the efficacy of compounded cidofovir, famciclovir, and ganciclovir for the treatment of feline herpesvirus type 1 (FHV-1) ocular surface disease.

ANIMALS STUDIED

132 shelter-housed cats qPCR positive for FHV-1.

PROCEDURES

A masked placebo-controlled study design was utilized. Animals were enrolled in one of four treatment groups: topical ocular placebo + oral placebo (n = 32), compounded cidofovir 0.5% ophthalmic solution + oral placebo (n = 32), compounded famciclovir oral solution (90 mg/kg) + topical ocular placebo (n = 32), and compounded ganciclovir 0.15% ophthalmic solution + oral placebo (n = 36). Cats were treated with each medication twice daily for 7 days and were evaluated on Day 1 and Day 8 using an ocular scoring system, body weight, and qPCR for FHV-1 viral load.

RESULTS

Cidofovir significantly decreased viral load from Day 1 to Day 8 compared with placebo (p = .024). Neither famciclovir nor ganciclovir decreased viral load compared with placebo (p = .14, p = .41). There was no significant improvement of ocular scores for any drug group compared with placebo (p = .62). In all groups, 65%-75% of cats improved from Day 1 to Day 8. Juvenile cats had a significant increase in weight gain compared with placebo for cidofovir (p = .025) and ganciclovir (p = .023). All corneal ulcers in placebo animals failed to heal whereas 77% of ulcers in antiviral group animals healed.

CONCLUSIONS

Topical ophthalmic cidofovir significantly decreased ocular FHV-1 viral shedding and increased weight gain in juvenile cats. Ganciclovir increased weight gain in juvenile cats. Compounded famciclovir demonstrated limited efficacy for the treatment of FHV-1 ocular surface disease in shelter-housed cats.

Effects of physiologic concentrations of l-lysine on in vitro replication of feline herpesvirus 1

OBJECTIVE

To evaluate the effects of various concentrations of l-lysine on in vitro replication of feline herpesvirus 1 (FHV-1).

SAMPLE

Cultures of Crandell-Rees feline kidney (CRFK) cells.

PROCEDURES

CRFK cells were inoculated with FHV-1 and maintained in media with 20 combinations of l-arginine and l-lysine concentrations. Changes in cell viability were monitored by continuous measurement of electrical impedance of cultured cells and by observation of viral cytopathic effects. Viral load was determined by use of quantitative PCR assay in supernatants obtained from infected cultures at specified time points.

RESULTS

Increases in l-lysine concentration had no effect on the kinetics of cell death in FHV-1-infected cultures. There was also no significant effect (r(2) < 0.1) on viral DNA load for l-arginine concentrations ≥ 12 μg/mL There was a significant effect of increases in l-lysine concentration on viral DNA load in media supplemented with 6 μg of l-arginine/mL (mean ± SD slope, -4,641 ± 1,626 units; adjusted r(2) = 0.45). However, the difference between the lowest (1 × 10(6.28) copies/μL) and highest (1 × 10(6.86) copies/μL) FHV-1 DNA load in these media was < 1 logarithm.

CONCLUSIONS AND CLINICAL RELEVANCE

The difference in FHV-1 DNA load was unlikely to be biologically important. Various l-lysine concentrations did not inhibit in vitro replication of FHV-1 at l-arginine concentrations sufficient to maintain cell growth. This conclusion was consistent with results of other studies in which investigators have not detected a consistently beneficial effect when l-lysine is administered to FHV-1-infected cats.

Seroprevalence of canine herpesvirus-1 and Brucella canis in Finnish breeding kennels with and without reproductive problems

We compared the serological status of Brucella canis and canine herpesvirus-1 (CHV-1) in Finnish breeding kennels with and without reproductive problems. Dogs from kennels with reproductive problems had significantly higher CHV-1 titres than dogs from kennels having no reproductive problems (p < 0.001). In dogs from kennels with reproductive problems 100% (32/32) had positive titres, whereas in dogs from kennels without reproductive problems 65% (22/34) had positive titres. The median titre for dogs from kennels with reproductive problems was 1 : 160 and for dogs from kennels without reproductive problems 1 : 80. The high prevalence of positive CHV-1 titres in this study indicates that prevention of the disease is difficult and reinforces the need to minimize the reproductive problems caused by CHV-1. All 388 dogs from 94 kennels had negative B. canis titres.

Effect of topical ophthalmic application of cidofovir on experimentally induced primary ocular feline herpesvirus-1 infection in cats

OBJECTIVE

To evaluate the efficacy of twice-daily ophthalmic application of 0.5% cidofovir solution in cats with experimentally induced primary ocular feline herpesvirus-1 (FHV-1) infection.

ANIMALS

Twelve 6-month-old sexually intact male cats.

PROCEDURES

Cats were randomly assigned to either a treatment or control group. Ocular infection with FHV-1 was induced (day 0) in all cats via inoculation of both eyes with 10(4) plaque-forming units of a plaque-purified FHV-1 field strain. Twice daily for 10 days beginning on day 4 after virus inoculation, the treatment group received 1 drop of 0.5% cidofovir in 1% carboxymethylcellulose in both eyes, and the control group received 1 drop of 1% carboxymethylcellulose in both eyes. A standardized scoring method was used to evaluate clinical signs of FHV-1 infection in each cat once daily for 24 days. The amount of ocular viral shedding was assessed by use of a quantitative real-time PCR procedure every 3 days during the study period. Clinical scores and viral quantification were averaged over the pretreatment (days 0 to 3), treatment (days 4 to 14), and posttreatment (days 15 to 24) periods for each cat.

RESULTS

During the treatment period, clinical scores and amount of viral ocular shedding were significantly lower in the treatment group, compared with findings in the control group.

CONCLUSIONS AND CLINICAL RELEVANCE

Twice-daily application of 0.5% cidofovir solution in both eyes significantly decreased the amount of viral shedding and the severity of clinical disease in cats with experimentally induced ocular FHV-1 infection.

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

OBJECTIVE

To use PCR assays to determine the prevalence of feline herpesvirus 1 (FHV-1), Chlamydophila felis, and Mycoplasma spp DNA in conjunctival cells collected from cats with and without conjunctivitis; to compare results of conventional and real-time fluorogenic PCR assays for amplification of FHV-1 DNA; and to determine whether copy numbers of FHV-1 DNA are correlated with conjunctivitis.

ANIMALS

55 cats with active conjunctivitis, 39 healthy cats that never had conjunctivitis, and 32 cats with a history of conjunctivitis that had been resolved for at least 3 months.

PROCEDURES

Samples were obtained by rolling cotton-tipped applicators on the ventral conjunctiva of awake cats treated topically with proparacaine. The DNA was extracted from the swab specimens and assessed in PCR assays to detect DNA of FHV-1 (fluorogenic PCR assay and conventional PCR assay), Mycoplasma spp (conventional PCR assay), and C felis (conventional PCR assay).

RESULTS

Overall prevalence rates of FHV-1, C felis, and Mycoplasma spp as assessed by the conventional PCR assays were 6.7%, 3.2%, and 9.6%, respectively. Percentage concordance between conventional PCR and fluorogenic PCR assays for FHV-1 was 92.5%. There were no significant differences among the 3 groups of cats for the mean copy number of FHV-1 divided by the copy number of glyceraldehyde-3-phosphate dehydrogenase.

CONCLUSIONS AND CLINICAL RELEVANCE

Mycoplasma spp were the most prevalent organism detected and was associated with conjunctivitis. This study could not confirm that there are increased copy numbers of FHV-1 DNA in cats with conjunctivitis, compared with the copy numbers for cats without conjunctivitis.

Simian varicella virus expresses a latency-associated transcript that is antisense to open reading frame 61 (ICP0) mRNA in neural ganglia of latently infected monkeys

Simian varicella virus (SVV) and varicella-zoster virus (VZV) are closely related alphaherpesviruses that cause varicella (chickenpox) in nonhuman primates and humans, respectively. After resolution of the primary disease, SVV and VZV establish latent infection of neural ganglia and may later reactivate to cause a secondary disease (herpes zoster). This study investigated SVV gene expression in neural ganglia derived from latently infected vervet monkeys. SVV transcripts were detected in neural ganglia, but not in liver or lung tissues, of latently infected animals. A transcript mapping to open reading frame (ORF) 61 (herpes simplex virus type 1 [HSV-1] ICP0 homolog) was consistently detected in latently infected trigeminal, cervical, and lumbar ganglia by reverse transcriptase PCR. Further analysis confirmed that this SVV latency-associated transcript (LAT) was oriented antisense to the gene 61 mRNA. SVV ORF 21 transcripts were also detected in 42% of neural ganglia during latency. In contrast, SVV ORF 28, 29, 31, 62, and 63 transcripts were not detected in ganglia, liver, or lung tissues of latently infected animals. The results demonstrate that viral gene expression is limited during SVV latency and that a LAT antisense to an ICP0 homolog is expressed. In this regard, SVV gene expression during latency is similar to that of HSV-1 and other neurotropic animal alphaherpesviruses but differs from that reported for VZV.

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.

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.

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.

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.

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.

Ocular manifestations of feline herpesvirus

Feline herpesvirus-1 (FHV-1) infection is ubiquitous in the domestic cat population worldwide. The most common clinical ocular manifestations of infection with FHV-1 are conjunctivitis and keratitis. This paper reviews the pathogenesis of feline herpesvirus-1 and discusses the various clinical ocular manifestations, diagnostic techniques and treatment of FHV-1-induced diseases. Ocular manifestations include: conjunctivitis, keratitis, stromal keratitis, keratoconjunctivitis sicca, ophthalmia neonatorium, symblepharon, corneal sequestrum, eosinophilic keratitis and anterior uveitis. Diagnostic techniques discussed include: virus isolation, fluorescent antibody testing, serum neutralising titers, ELISA and polymerase chain reaction. Various therapies are also discussed.

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.

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.

Latency-associated transcripts of equine herpesvirus type 4 in trigeminal ganglia of naturally infected horses

Equine herpesvirus type 4 (EHV-4) is a major respiratory pathogen of horses. Unlike most other members of the Alphaherpesvirinae, EHV-4 was regarded as non-neurotropic. Here, neural and lymphoid tissues of 17 horses have been analysed post-mortem. EHV-4 DNA was detected in 11 cases (65%) by PCR, exclusively in the trigeminal ganglia. In order to define the transcriptional activity, RNA preparations of 10 EHV-4 DNA-positive ganglia were investigated by nested RT-PCR. EHV-4-specific transcripts derived from genes 63 [herpes simplex virus type 1 (HSV-1) ICPO gene homologue] and 64 (HSV-1 ICP4 gene homologue) were detected in six trigeminal ganglia. In one other case, only gene 64-specific transcripts were present. All of the transcripts proved to be antisense orientated when a strand-specific RT-PCR was applied. Type-specific primers for gene 33 (encoding glycoprotein B) served to detect transcripts of an acute EHV-4-infection, which were found in only one of the six ganglia positive for gene 63- and gene 64-specific transcripts. Overall, these studies clearly demonstrate that EHV-4 is latent in trigeminal ganglia.

In situ hybridization with riboprobes: an overview for veterinary pathologists

In situ hybridization using nonradioactively-labeled RNA probes is a technique that combines understanding of basic molecular biology and histopathologic interpretation. Recombinant or PCR technology can be used to produce probes that hybridize with a wide variety of cellular genes and infectious agents. Hybridization conditions can be optimized for each probe/target combination.

Nested polymerase chain reaction and in situ hybridization for diagnosis of canine herpesvirus infection in puppies

The usefulness of two nucleic acid detection systems in suspected cases of spontaneous canine herpesvirus (CHV) infection in puppies was evaluated. Formalin-fixed, paraffin-embedded tissues from seven 1-3-week-old naturally infected puppies with lesions characteristic of CHV infection were investigated in a retrospective study. Nested polymerase chain reaction (PCR) and nonradioactive in situ hybridization (ISH) were used to detect nucleotide sequences of the CHV thymidine kinase (TK) gene. According to the original necropsy reports, CHV was isolated in four of the seven puppies using primary canine lung and/or kidney cells. In all seven puppies, gross and histologic lesions consisted of disseminated focal necroses and hemorrhages predominantly in kidneys, lung, liver, and spleen. In addition, few small amphophilic intranuclear inclusion bodies were detected by light microscopy mainly in epithelial cells of kidney, lung, and liver. ISH was performed with a 111-base-pair (bp) digoxigenin-labeled double-stranded DNA probe. Viral DNA was detected in the nuclei of cells near and within lesions. Various cell types, including bronchiolar and alveolar epithelial cells, hepatocytes, renal tubular epithelial cells, neurons, fibrocytes, cardiac myocytes, and endothelial cells, were positive for viral DNA. PCR amplification products of the expected length of 168 bp containing the expected cleavage site for the restriction enzyme EcoRI, derived from paraffin blocks containing lung, kidney, and liver tissues, were detected in all seven puppies. The specificity of the obtained amplicon was further confirmed by Southern blot analysis. ISH and PCR are both useful methods for diagnosing CHV infection in formalin-fixed, paraffin-embedded tissues and are highly specific and sensitive methods for further investigations of the pathogenesis of CHV-induced lesions.

Detection of latency-associated transcripts of equid herpesvirus 1 in equine leukocytes but not in trigeminal ganglia

Results from Southern hybridization and PCR amplification experiments using a randomly synthesized reverse transcription-PCR product showed that peripheral blood leukocytes from horses showing no clinical signs of disease expressed a putative latency-associated transcript antisense to and overlapping the 3' end of the equid herpesvirus 1 (EHV-1) immediate-early gene (gene 64). A PCR product derived from this transcript has > or =96% identity with the published EHV-1 sequence. In situ hybridization studies of equine bronchial lymph nodes corroborated these findings and are consistent with reactivation data (D. A. Smith, A. Hamblin, and N. Edington, unpublished data), indicating that EHV-1 latency is established predominantly in CD5+/CD8+ leukocytes.

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.

Biosynthesis of glycoproteins E and I of feline herpesvirus: gE-gI interaction is required for intracellular transport

The biosynthesis of glycoproteins E and I of feline herpesvirus was studied by using the vaccinia virus vTF7-3 expression system. gE and gI were synthesized as N-glycosylated, endoglycosidase H (EndoH)-sensitive precursors with Mrs of 83,000 and 67,000, respectively. When coexpressed, gE and gI formed sodium dodecyl sulfate-sensitive hetero-oligomeric complexes that were readily transported from the endoplasmic reticulum (ER). Concomitantly, the glycoproteins acquired extensive posttranslational modifications, including O glycosylation, leading to an increase in their apparent molecular weights to 95,000 and 80,000 to 100,000 for gE and gI, respectively. In the absence of gE, most gI remained EndoH sensitive. Only a minor population became EndoH resistant, but these molecules were processed aberrantly as indicated by their Mrs (100,000 to 120,000). By immunofluorescence microscopy, gI was detected primarily in the ER but also at the plasma membrane. gE, when expressed by itself, remained EndoH sensitive and was found only in the ER and the nuclear envelope. These results were corroborated by studying the biosynthesis of gE in feline herpesvirus (FHV)-infected cells. In cells infected with wild-type FHV, gE acquired the same co- and posttranslational modifications as during vTF7-3-driven expression. However, an FHV mutant lacking gI failed to produce mature gE. We conclude that gE is retained in the ER, presumably by associating with molecular chaperones, and becomes transport competent only when in a complex with gI.