Physical characterization of the genome of feline herpesvirus-1

The Latest Prevalence, Isolation, and Molecular Characteristics of Feline Herpesvirus Type 1 in Yanji City, China

Epidemiological surveys revealed that 33 of the 93 samples were positive for FHV-1, with the gD gene of these 33 samples exhibiting low variation, high homology, and no critical amino acid mutation. Feline herpesvirus type 1 (FHV-1), also known as feline viral rhinotracheitis (FVR) virus, is one of the main causes of URT disease in cats. All cats can become hosts of FHV-1, and the spread of this disease affects the protection of rare feline animals. Nasal swabs from cats with URT disease were collected at five veterinary clinics in Yanji City from 2022 to 2024. The purpose of this study was to isolate and investigate the epidemiology of FHV-1. The gD gene of the FHV-1 strain was cloned and inserted into the pMD-18T vector and transformed into a competent Escherichia coli strain. Subsequently, the gD gene of the positive samples was sequenced and phylogenetic analysis was performed to determine the genetic evolution relationship between the strains. We successfully isolated the FHV-1 strain YBYJ-1 in Yanji City for the first time. The diameter of the virus is approximately 150-160 nm. After 48 h of virus inoculation, the cells were round, isolated, and formed grape-like clusters. The gD gene of the virus was sequenced, and the length was 1125 bp, which proved the isolate was FHV-1. This study found that the genetic evolution of the FHV-1 gD gene was stable, expanding the molecular epidemiological data on FHV-1 in cats in Yanji City.

Immunogenicity evaluation of a bivalent vaccine based on a recombinant rabies virus expressing gB protein of FHV-1 in mice and cats

Feline viral rhinotracheitis (FVR) is caused by the feline herpesvirus-1 (FHV-1), which commonly results in upper respiratory symptoms, and can result in death in the kittens and weak cats. Rabies is an infectious disease with zoonotic characteristics highly relevant to public health and also poses a serious threat to cats. Vaccines are the most effective method to control the spread of both FHV-1 and RABV and have the advantage that they produce long-term specific immune responses. In this study, we constructed a bivalent vaccine against FHV-1 and rabies virus (RABV) simultaneously. The vaccine was constructed by cloning FHV-1 gB into a RABV based vector, and the recombinant RABV (SRV9-FHV-gB) expressing the FHV-1 gB protein was rescued. The growth characteristics of SRV9-FHV-gB were analyzed on NA and BSR cells. To assess the immunogenicity of the vaccine, mice and cats were immunized with SRV9-FHV-gB supplemented with Gel02 adjuvant. The SRV9-FHV-gB exhibited the same growth characteristics as the parent virus SRV9 in both BSR cells and NA cells. The safety of SRV9-FHV-gB was evaluated using 5-day-old and 14-day-old suckling mice. The results showed that mice infected with the SRV9-FHV-gB survived for longer than those in the SRV9 group. Mice immunized with inactivated SRV9-FHV-gB produced high titers of specific antibodies against FHV-1 and neutralizing antibodies against RABV. Cats that received three immunizations with SRV9-FHV-gB also produced neutralizing antibodies against both FHV-1 and RABV. This study represents the first time that a bivalent vaccine targeting FHV-1 and RABV has been constructed, laying the foundations and providing inspiration for the development of other multivalent vaccines.

Pathogenicity and immunogenicity of gI/gE/TK-gene-deleted Felid herpesvirus 1 variants in cats

BACKGROUND

Felid herpesvirus 1 (FHV-1) is a major pathogenic agent of upper respiratory tract infections and eye damage in felines worldwide. Current FHV-1 vaccines offer limited protection of short duration, and therefore, do not reduce the development of clinical signs or the latency of FHV-1.

METHODS

To address these shortcomings, we constructed FHV ∆gIgE-eGFP, FHV ∆TK mCherry, and FHV ∆gIgE/TK eGFP-mCherry deletion mutants (ΔgI/gE, ΔTK, and ΔgIgE/TK, respectively) using the clustered regularly interspaced palindromic repeats (CRISPR)/CRISP-associated protein 9 (Cas9) system (CRISPR/Cas9), which showed safety and immunogenicity in vitro. We evaluated the safety and efficacy of the deletion mutants administered with intranasal (IN) and IN + subcutaneous (SC) vaccination protocols. Cats in the vaccination group were vaccinated twice at a 4-week interval, and all cats were challenged with infection 3 weeks after the last vaccination. The cats were assessed for clinical signs, nasal shedding, and virus-neutralizing antibodies (VN), and with postmortem histological testing.

RESULTS

Vaccination with the gI/gE-deleted and gI/gE/TK-deleted mutants was safe and resulted in significantly lower clinical disease scores, fewer pathological changes, and less nasal virus shedding after infection. All three mutants induced virus-neutralizing antibodies after immunization.

CONCLUSIONS

In conclusion, this study demonstrates the advantages of FHV-1 deletion mutants in preventing FHV-1 infection in cats.

Use of feline herpesvirus as a vaccine vector offers alternative applications for feline health

Herpesviruses are attractive vaccine vector candidates due to their large double stranded DNA genome and latency characteristics. Within the scope of veterinary vaccines, herpesvirus-vectored vaccines have been well studied and commercially available vectored vaccines are used to help prevent diseases in different animal species. Felid alphaherpesvirus 1 (FHV-1) has been characterised as a vector candidate to protect against a range of feline pathogens. In this review we highlight the methods used to construct FHV-1 based vaccines and their outcomes, while also proposing alternative uses for FHV-1 as a viral vector.

miR-101 inhibits feline herpesvirus 1 replication by targeting cellular suppressor of cytokine signaling 5 (SOCS5)

Feline viral rhinotracheitis is a prevalent disease among cats caused by feline herpesvirus 1 (FHV-1). microRNAs (miRNAs), which serve as important regulatory factors in the host, participate in the regulation of the host innate immune response to virus infection. However, the roles of miRNAs in the FHV-1 life cycle remain unclear. In this study, we found that a new miRNA, miR-101, could suppress FHV-1 replication. FHV-1 infection upregulated the expression level of miR-101 in a cGAS-dependent manner. Furthermore, miR-101 could significantly enhance type I interferon antiviral signaling by targeting suppressor of cytokine signaling 5 (SOCS5), a negative regulator of the JAK-STAT pathway. Likewise, knockdown of cellular SOCS5 also suppressed FHV-1 replication due to the enhancement of IFN-I-induced signaling cascades. Taken together, our data demonstrated a new strategy for miR-101-mediated defense against FHV-1 infection by enhancing IFN-I antiviral signaling and increased the knowledge of miRNAs regulating innate immune signaling pathways.

Antibody response to feline herpesvirus-1 vaccination in healthy adult cats

OBJECTIVES

Vaccination against feline herpesvirus-1 (FHV-1) is recommended for all cats. However, it is unknown how adult healthy cats with different pre-vaccination antibodies respond to FHV-1 vaccination in the field. The aim of the study was to determine the prevalence of neutralising antibodies against FHV-1 in healthy adult cats and the response to FHV-1 vaccination within 28 days of vaccination.

METHODS

One hundred and ten cats (⩾1 year of age) that had not received a vaccination within the past 12 months were vaccinated with a combined FHV-1 vaccine. Antibodies against FHV-1 were determined before vaccination (day 0), on day 7 and day 28 by serum neutralisation test. Uni- and multivariate statistical analyses were used to determine factors associated with the presence of pre-vaccination antibodies and response to vaccination.

RESULTS

Pre-vaccination neutralising antibody titres (⩾10) were present in 40.9% of cats (45/110; 95% confidence interval [CI] 32.2-50.3); titres were generally low (range 10-640). Antibody response to vaccination (⩾four-fold titre increase) was observed in 8.3% (9/109; 95% CI 4.2-15.1). Cats ⩾2 years of age were more likely to have pre-vaccination neutralising antibodies than cats aged between 1 and 2 years (odds ratio [OR] 24.619; P = 0.005). Cats from breeders were more likely to have pre-vaccination neutralising antibodies than privately owned cats (OR 7.070; P = 0.007). Domestic shorthair cats were more likely to have an at least four-fold titre increase vs purebred cats (OR 11.22; P = 0.027).

CONCLUSIONS AND RELEVANCE

Many cats have no detectable neutralising antibodies against FHV-1 despite previous vaccinations and fail to develop a ⩾four-fold titre increase after vaccination. This is likely because older cats and cats with a higher FHV-1 exposure risk are more likely to get infected with FHV-1 and thus to have FHV-1 neutralizing antibodies. Purebred cats more often fail to develop a ⩾four-fold titre increase after vaccination.

Felid herpesvirus type 1 infection in cats: a natural host model for alphaherpesvirus pathogenesis

Feline herpesvirus 1 (FeHV-1) is an alphaherpesvirus that causes feline viral rhinotracheitis, an important viral disease of cats on a worldwide basis. Acute FeHV-1 infection is associated with both upper respiratory and ocular signs. Following the acute phase of the disease lifelong latency is established, primarily in sensory neuronal cells. As is the case with human herpes simplex viruses, latency reactivation can result in recrudescence, which can manifest itself in the form of serious ocular lesions. FeHV-1 infection in cats is a natural host model that is useful for the identification of viral virulence genes that play a role in replication at the mucosal portals of entry or are mediators of the establishment, maintenance, or reactivation of latency. It is also a model system for defining innate and adaptive immunity mechanisms and for immunization strategies that can lead to better protection against this and other alphaherpesvirus infections.

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.

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

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

Aetiology of corneal ulcers assume FHV-1 unless proven otherwise

OVERVIEW

Feline ulcerative keratitis is a common presenting complaint and is frequently a sequela of feline herpesvirus 1 (FHV-1) infection; so much so, in fact, that it is fair to assume an FHV-1 aetiology until proven otherwise. Other potential causes of ulceration are trauma or underlying eyelid abnormalities (entropion, ectropion, agenesis, dermoids, neoplasia), lash abnormalities (ectopic cilia, trichiasis), tear film abnormalities or neurological deficiencies (trigeminal nerve paralysis, facial nerve paralysis).

CLINICAL CHALLENGES

The management of corneal ulceration in cats is frequently challenging, and treatment needs to be tailored carefully to the individual cat, its temperament, and the disease process present.

EVIDENCE BASE

The scientific literature on feline ulcerative keratitis is extensive, particularly that related to FHV-1 infection. The aim of this article is to review the aetiology and diagnosis of corneal ulceration in cats with particular reference to the evidence base available.

PATIENT GROUP

All age groups and breeds can suffer with ulcerative keratitis. Breed predispositions are present for some forms of corneal ulceration, and these are discussed.

Use of interfering RNAs targeted against feline herpesvirus 1 glycoprotein D for inhibition of feline herpesvirus 1 infection of feline kidney cells

OBJECTIVE

To evaluate the use of RNA interference targeted against feline herpesvirus 1 (FHV-1) glycoprotein D for inhibition of FHV-1 infection of feline kidney cells.

SAMPLE POPULATION

Crandell-Rees feline kidney cells.

PROCEDURES

Crandell-Rees feline kidney cells were transfected with small interfering RNAs (siRNAs) that were designed to inhibit expression of FHV-1 glycoprotein D. The effectiveness of the treatment was determined via measurement of amounts of glycoprotein D mRNA, intracellular glycoprotein D, and glycoprotein D expressed on the surface of infected cells and comparison with appropriate control sample data.

RESULTS

2 of 6 siRNAs tested were highly effective in reducing expression (ie, knockdown) of glycoprotein D mRNA; there were 77% and 85% reductions in mRNA in treated samples, compared with findings in the control samples. The knockdown of glycoprotein D mRNA resulted in reduced glycoprotein D protein production, as evidenced by 27% and 43% decreases in expression of glycoprotein D on the surface of siRNA-treated, FHV-1-infected cells and decreased expression of the protein within infected cells, compared with control samples. Treatment with these siRNAs also resulted in inhibition of FHV-1 replication, with reductions of 84% and 77% in amounts of virus released into cell culture supernatant, compared with findings in control samples.

CONCLUSIONS AND CLINICAL RELEVANCE

2 chemically produced siRNAs that targeted the glycoprotein D gene significantly reduced FHV-1 titers in treated cells, suggesting that glycoprotein D is necessary for production of infective virions. This gene is a potential target for RNA interference as a means of inhibition of FHV-1 infection of feline cells.

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.

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.

Efficient expression of the envelope protein of feline immunodeficiency virus in a recombinant feline herpesvirus type 1 (FHV-1) using the gC promoter of FHV-1

We constructed two recombinant feline herpesvirus type 1 (FHV-1) expressing the envelope (Env) protein of feline immunodeficiency virus (FIV). One recombinant, designated dlTK-env, has the whole FIV env gene inserted at a thymidine kinase (TK) deletion site. The second recombinant, designated dlTK(gCp)-env, has a cassette containing a partial FIV env gene fused with the signal sequence of the gC protein of FHV-1 (under the control of the gC promoter) inserted at the same site. Growth kinetics of both the recombinants in Crandell feline kidney (CRFK) cells were similar to that of the parent strain of FHV-1. By indirect immunofluorescence assays and immunoblot analyses, we confirmed the expression of the FIV Env protein in CRFK cells infected with both recombinants. Enzyme-linked immunosorbent assays showed that the maximum Env expression level achieved by dlTK(gCp)-env was more than four times higher than that observed for dlTK-env. Flow cytometric analyses revealed that the Env protein produced by both recombinants was efficiently expressed on the cell surface. The dlTK(gCp)-env reported here may thus be a promising candidate for a live recombinant vaccine to protect against FIV infection.

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.

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.

Properties and functions of feline herpesvirus type 1 glycoproteins

Feline herpesvirus type 1 (FHV-1) is a causative agent of feline viral rhinotracheitis and belongs to the subfamily Alphaherpesvirinae of the family Herpesviridae. Since first isolated in 1958 by Crandell and Maurer, FHV-1 is distributed worldwide and is the most clinically significant agent for respiratory infections in cats. In this review, we describe the recent findings with properties and functions of FHV-1 glycoproteins, especially hemagglutinins.

Further development of a recombinant feline herpesvirus type 1 vector expressing feline calicivirus immunogenic antigen

We previously reported the attenuation of thymidine kinase (TK) deficient mutant (C7301dlTK) of feline herpesvirus type 1 (FHV-1) in cats and the construction of a recombinant FHV-1 (C7301dlTK-Cap) inserted a precursor capsid gene of feline calcivirus (FCV) into the TK deletion locus of the C7301dlTK. In this study, we constructed a further improved recombinant FHV-1 (dlTK(gCp)-Cap) carrying a putative FHV-1 gC promoter sequence upstream of the FCV precursor capsid gene of the C7301dlTK-Cap. Growth kinetics of the dlTK(gCp)-Cap in cell cultures was similar to those of C7301dlTK and C7301dlTK-Cap. A strong expression of FCV immunogenic antigen by dlTK(gCp)-Cap was confirmed by indirect immunofluorescence and enzyme-linked immunosorbent assays. In addition, one vaccination with dlTK(gCp)-Cap protected cats more effective against subsequent virulent FCV challenge than that with C7301dlTK-Cap.

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.

Recombinant feline herpesvirus type 1 expressing immunogenic proteins inducible virus neutralizing antibody against feline calicivirus in cats

In this study, an entire open reading frame encoding the capsid protein of feline calicivirus (FCV) F4 strain was inserted into the deletion locus (SmaI site) of the thymidine kinase (TK) deficient mutant (C7301dlTK) of feline herpesvirus type 1 (FHV-1) and the resulting recombinant virus was designated as C7301dlTK-Cap. Expression of the FCV antigens by C7301dlTK-Cap was confirmed by indirect immunofluorescence assay and immunoblot analysis. To assess whether the recombinant virus can induce virus neutralizing (VN) antibody against FCV in the natural host, three cats were inoculated intranasally and orally with C7301dlTK-Cap (two cats) or C7301dlTK (one cat). As a result, sera collected from cats inoculated with the C7301dlTK-Cap possessed VN antibody against FCV. This recombinant virus is expected as a new polyvalent recombinant vaccine against FHV-1 and FCV infections.

Restriction endonuclease analysis of field isolates of feline herpesvirus type 1 and identification of heterogeneous regions

The genomic heterogeneity of 78 isolates of feline herpesvirus type 1 (FHV-1) recently isolated from cats suspected to have feline viral rhinotracheitis was analyzed by examining the digestion patterns found with restriction endonuclease MluI. The FHV-1 field isolates were classified into at least three genotypes, namely, the C7301, F2 (an attenuated vaccine strain), and C7805 types. The C7301 type seems to be a major type, since 64 of the 78 isolates belonged to this type. Eight and six isolates belonged to the F2 and C7805 types, respectively. Compared with the C7301 type, the heterogeneous region of the F2 type was localized to a 4.3-kbp EcoRI fragment within the US segment and the heterogeneous region of the C7805 type was localized to a 5.5-kbp XbaI fragment within the UL segment. Northern (RNA) blot analysis revealed no differences in the products transcribed from these regions. In addition, nucleotide sequence analysis showed that the MluI sites not found in the F2 and C7805 types were located in the regions homologous to the herpes simplex virus type 1 gI and UL5 genes, respectively.

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

A polymerase chain reaction (PCR) assay was developed to detect the thymidine kinase gene of feline herpesvirus 1 (FHV-1) and to study the active and latent carrier state in a group of naturally FHV-1 infected specific pathogen free (SPF) cats. The detection limit of PCR products on ethidium bromide stained gels was 390 fg or about 3 x 10(3) copies of the FHV-1 genome. The PCR was 25% more sensitive than conventional cell culture based virus isolation techniques in detecting FHV-1 in oral/ocular swabs and 100 times more sensitive in detecting virus in cell culture supernatants. Sites of FHV-1 latency in FHV-1 carriers as determined by PCR were mainly tissues of the head, especially the trigeminal ganglia, optic nerves, olfactory bulbs and corneas. Oral fauces, salivary glands, lacrimal glands, cerebellum and conjunctiva were less consistently positive. The cerebral cortex, thymus, trachea, lung, liver, spleen, kidney, and peripheral blood mononuclear cells were consistently negative for FHV-1 genome. The distribution of FHV-1 DNA in the tissues of the head was similar whether or not corticosteroid-induced virus shedding was occurring at the time the tissues were collected. Infectious virus was never recovered from tissue homogenates regardless of the PCR status of the tissues.

Identification and nucleotide sequence of a gene in feline herpesvirus type 1 homologous to the herpes simplex virus gene encoding the glycoprotein H

A gene encoding the glycoprotein H (gH) homologue of feline herpesvirus type 1 was identified and sequenced. It was located immediately downstream of the thymidine kinase gene within an EcoRI 6.6 kbp fragment. In addition, a partial UL21 homologous gene was located downstream of the gH homologous gene. The primary translation product of the gH homologous gene is predicted to consist of 821 amino acids with a molecular weight of 92.5 kDa. It possesses several characteristics typical of transmembrane glycoproteins, including a N-terminal hydrophobic signal sequence, C-terminal transmembrane domain, and putative N-linked glycosylation sites. Analysis of this protein revealed amino acid sequence homologies of 33.1% with equine herpesvirus type 1 (EHV-1) gH, 32.6% with EHV-4 gH, 29.1% with varicella-zoster virus gIII, 28.5% with pseudorabies virus gH, and 25.1% with herpes simplex virus type 1 gH. By Northern blot analysis, one of the transcripts specific for the gH homologous gene might be a mRNA of approximately 3.0 kb.

Identification and nucleotide sequence of a gene in feline herpesvirus type 1 homologous to the herpes simplex virus gene encoding the glycoprotein B

The nucleotide sequence of the glycoprotein B (gB) homologous gene of feline herpesvirus type 1 (FHV-1) was determined. The gene was found to be located within a 9.6 kbp SalI fragment by Southern-blot hybridization with a probe derived from the herpes simplex virus type 1 (HSV-1) gB DNA sequence. Furthermore, the predominant portion of the coding sequences was mapped to a 1.9 kbp Hin cII-EcoRI and its flanking 2.7 kbp Eco RI-Eco RI subfragments in the 9.6 kbp SalI fragment. The entire nucleotide sequence revealed that the FHV-1 gB homologous gene is capable of encoding a polypeptide of 948 amino acids. The predicted precursor polypeptide derived from this open reading frame could have a calculated M(r) of 106 kDa in unglycosylated form and contains ten potential N-linked glycosylation sites and a probable internal proteolytic cleavage site. By Northern-blot analysis using portions of the open reading frame as a probe, 3.9 and 3.3 kb RNA transcripts were identified in FHV-1 infected cells. The alignment of the amino acid sequence of the FHV-1 gB homologue with those of 14 other herpesviruses revealed that 10 cysteine residues were completely conserved. Meanwhile, when evolutionary trees were generated among these herpesvirus gB counterparts, the FHV-1 gB homologous nucleotide sequence seems to be closely related to equine herpesvirus type 4 and its amino acid sequence to pseudorabies virus.

The simian varicella virus and varicella zoster virus genomes are similar in size and structure

Simian varicella virus (SVV) DNA was purified from viral nucleocapsids and the molecular structure of the SVV genome was determined. SVV DNA was analyzed by agarose gel electrophoresis of BamHI, BglII, EcoRI, and PstI restriction endonuclease digests. SVV and varicella zoster virus (VZV) DNAs were demonstrated to have distinct restriction endonuclease profiles. Summation of the sizes of individual restriction endonuclease fragments indicate the size of SVV DNA is congruent to 121 kilobase pairs (kbp) or congruent to 76.8 megadaltons (Md). Electron microscopy, lambda exonuclease analysis, and Southern blot DNA hybridizations were utilized to determine the molecular structure of the SVV genome and to construct restriction endonuclease maps. The results indicate that SVV DNA consists of a long component (L, congruent to 100 kbp) covalently linked to a short component (S, congruent to 20 kbp) which is composed of a unique short sequence (Us, 5.3 +/- 0.7 kbp) bracketed by inverted repeat sequences (TRs and IRs, congruent to 7.2 kbp). The presence of 0.5 M PstI restriction endonuclease fragments indicates that the S component may invert relative to the L component and that the genome exists in two major isomeric forms. The findings demonstrate that the SVV and VZV genomes are similar in size and structure.

[Herpesviridae: classification and structure in 1991]

In 1981, herpesviruses were classified by the International Committee of Taxonomy of Viruses (ICTV, 1) inside the herpesviridae family. Progress in biotechnology and molecular biology during the last 10 yr, has permitted the characterization of new viruses and genomic structures. The objective of this paper is to collect the data found in the literature since 1981, to actualize the description of herpesviridae family.

Restriction endonuclease mapping of the genome of feline herpesvirus type 1

Restriction endonuclease mapping was used to determine the molecular structure of feline herpesvirus type 1 (FHV-1) strain B 927. FHV-1 DNA purified from infected cells by pulsed field gel electrophoresis was partially restricted with Sau 3A to generate a series of overlapping fragments of 10-20 kb. EMBL 4 DNA was digested with Bam HI and Sal I and viral DNA was inserted into the "stuffer" region. Recombinant phage were selected on E. coli strain Q359. Single and double digestions with the enzymes Eco RI, Bam HI, Sal I, Sst I and Xho I enabled construction of physical maps of the genome. The FHV-1 genome is approximately 126 kbp in length and is composed of a long unique region of 99 kbp and a short region of 27 kbp comprising an unique sequence of 8-9 kbp flanked by inverted repeats of 7-8.5 kbp.

The diversity and unity of Herpesviridae

The family herpesviridae contains over 100 viruses endogenous to humans and to a wide variety of eukaryotic organisms. Inclusion in the family is based on architecture of the virion. The viruses differ significantly with respect to base composition and sequence arrangements of their DNAs, but share many biologic properties including the ability to remain latent in their hosts. On the basis of their biologic properties the herpesviruses have been classified into three subfamilies, i.e. alphaherpesvirinae, betaherpesvirinae and gammaherpesvirinae. The members of each subfamily share many properties including greater conservation and colinear arrangements of their genes. As a rule, more than one herpesvirus has been isolated from animals of economic importance and both humans have yielded viruses belong to all three subfamilies of the herpesviridae.

Recombinant feline herpesviruses expressing feline leukemia virus envelope and gag proteins

We constructed recombinant feline herpesviruses (FHVs) expressing the envelope (env) and gag genes of feline leukemia virus (FeLV). Expression cassettes, utilizing the human cytomegalovirus immediate-early promoter, were inserted within the thymidine kinase gene of FHV. The FeLV env glycoprotein expressed by recombinant FHV was processed and transported to the cell surface much as in FeLV infection, with the exception that proteolytic processing to yield the mature gp70 and p15E proteins was less efficient in the context of herpesvirus infection. Glycosylation of the env protein was not affected; modification continued in the absence of efficient proteolytic processing to generate terminally glycosylated gp85 and gp70 proteins. A recombinant FHV containing the FeLV gag and protease genes expressed both gag and gag-protease precursor proteins. Functional protease was produced which mediated the proteolytic maturation of the FeLV gag proteins as in authentic FeLV infection. Use of these recombinant FHVs as live-virus vaccines may provide insight as to the role of specific retroviral proteins in protective immunity. The current use of conventional attenuated FHV vaccines speaks to the wider potential of recombinant FHVs for vaccination in cats.

Immunological relationship between feline herpesvirus type 1 (FHV-1) and canine herpesvirus (CHV) as revealed by polyvalent and monoclonal antibodies

Polyvalent and monoclonal antibodies were used to demonstrate serological and antigenic relationships between feline herpesvirus type 1 (FHV-1) and canine herpesvirus (CHV). Using virus neutralization tests, enzyme-linked immunosorbent and indirect immunofluorescence assays, and immunoblotting analysis, reciprocal cross-reactivities to the heterologous virus were observed with some polyvalent and monoclonal antibodies. One monoclonal antibody against CHV neutralized FHV-1 infectivity and one monoclonal antibody against FHV-1 inhibited the hemagglutination activity of CHV as well as FHV-1-infected mouse serum. The major cross-reacting proteins were identified as the 143/108 kDa and 60 kDa glycoproteins of FHV-1 and the 145/112 kDa and 41 kDa glycoproteins of CHV. Previously, we have identified the 60 kDa and 41 kDa glycoproteins as the hemagglutinins of FHV-1 and CHV, respectively. The present results indicated the presence of shared antigenic determinants among these proteins.

Polymerase chain reaction amplification of pseudorabies virus DNA from acutely and latently infected cells

A characteristic of alphaherpesviruses, including pseudorabies virus (PRV), is that the acute phase of the disease is followed by lifelong latency. Latently infected animals are asymptomatic but can transmit reactivated virus. Corticosteroid administration, tissue explanation, blot- and in situ hybridizations have been used to demonstrate the presence of latent PRV infections. The use of blot hybridization as a convenient method for defining the incidence of PRV infections in swine herds has been hampered by the detection limit of this method. The objective of this study was to increase this sensitivity of blot hybridization by polymerase chain reaction (PCR) amplification of target sequences. Two sets of 20-mer primers were synthesized and used to amplify gX and gII glycoprotein gene sequences in two different strains of PRV. The specificity of the amplification was verified by Southern blot hybridization and restriction endonuclease analysis of the amplified fragments. Amplification of target sequences by PRC increased their detection limit by a factor of at least 10(5). Porcine ganglion samples, in which latency had been demonstrated by in vitro explanation, were analyzed by PCR together with positive and negative controls. Duplicate slot blot analyses of a portion of the amplified products were used to demonstrate latency in seven of eight samples. It was concluded that blot hybridization of PCR amplified DNA appears to be both a sensitive and convenient method for the detection of PRV induced latency.

Homology between feline herpesvirus-1 and canine herpesvirus

The purpose of this study was to determine the extent of the relatedness between feline herpesvirus-1 (FHV-1) and canine herpesvirus (CHV). Immunoprecipitation studies using antisera to FHV-1 and CHV revealed that both share virion glycoprotein antigens with apparent molecular weights of approximately 60 and 68 kDa. Two non-glycosylated, virion-associated antigens of each virus also displayed weaker cross reactivity. Southern blot hybridization experiments indicated that restriction fragments which represented approximately 51% of the FHV-1 genome hybridized to CHV DNA under conditions which allowed less than 7% base pair mismatch. This is the first molecular characterization of cross-reactivity between FHV-1 and another herpesvirus.

Identification of the thymidine kinase gene of feline herpesvirus: use of degenerate oligonucleotides in the polymerase chain reaction to isolate herpesvirus gene homologs

Feline herpesvirus 1 (FHV) is the causative agent of viral rhinotracheitis in cats. Current vaccination programs employing attenuated live and killed FHV vaccines have been effective in reducing the incidence of this disease. As an initial step in the development of recombinant FHVs for use in the vaccination of cats, we have identified the thymidine kinase (TK) gene of this feline-specific alphaherpesvirus. Comparisons of the amino acid sequences of other herpesvirus TK proteins have shown that these proteins are highly divergent, sharing only short regions of imperfect amino acid identity. We have used the polymerase chain reaction method of DNA amplification to increase the specificity associated with the use of short, highly degenerate oligonucleotide probes derived from regions of imperfect amino acid conservation. These methods were used to isolate the TK gene of FHV and should prove to be useful in the identification of new members of other viral and cellular gene families. A recombinant FHV bearing a deletion in the identified TK gene was constructed and shown to possess the expected TK- phenotype. The FHV TK gene is located at a position of approximately 40% in the long unique component of the FHV genome. The location of the TK gene and the location and orientation of flanking FHV genes, homologs of herpes simplex virus type 1 UL24 and UL22, are conserved among alphaherpesviruses.

New approaches to animal vaccines utilizing genetic engineering

Control of infectious diseases in livestock is an important determinant in the success of a nation's effort to efficiently meet its need for animal products. Genetic engineering offers many new options in the design of animal vaccines. Monoclonal antibodies, DNA cloning, recombination, and transfection are examples of techniques that facilitate innovative strategies in antigen identification, production, and delivery. This article reviews the use of genetic engineering in the production of vaccines directed against foot-and-mouth disease virus and other important pathogens of animals. The advantages and disadvantages of vaccines produced through the use of genetic engineering are discussed.