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H J Field

Publications and source records attributed to H J Field.

At least 73 records · Page 4Linked to original sources
PubMed1990

The pathogenesis of equine herpesvirus type 1 in the mouse: a new model for studying host responses to the infection.

An infection was established in adult BALB/c mice by means of intranasal inoculation of the AB4 strain of equine herpesvirus type 1 (EHV-1). The acute infection was confined to the respiratory tract and blood. Virus was shown to replicate in the nasal mucosa, trachea and lung for several days producing clinical signs of disease. Viraemia was also detected and a small proportion of peripheral blood cells contained virus at the peak of the infection. Histological and electron microscopic evidence were obtained which proved that productive virus replication occurred in the ciliated epithelial cells lining the bronchi and in pneumocytes in the lung, resulting in the destruction of these cells. Both humoral and cell-mediated responses to the infection were detected and monitored. By means of immunoprophylaxis or chemotherapy it was possible to modify the course of the infection. This infection model has many striking features in common with that observed in the natural host and the observations suggest that the mouse is a convenient and relevant model in which to study both host responses to EHV-1 infection and modification of the pathogenesis by means of immunoprophylaxis or therapy.

Animals↗
PubMed1990

Effective chemotherapy of equine herpesvirus 1 by phosphonylmethoxyalkyl derivatives of adenine demonstrated in a novel murine model for the disease.

Equine herpesvirus 1 was established in adult mice by means of intranasal inoculation. A disease developed that showed several features closely resembling the infection in the natural host. These included the restriction of virus replication to the respiratory tract and blood, the replication of virus in ciliated mucosa, and development of viremia for several days during the acute phase of the infection. Infected mice were treated with the antiviral agent (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine. A marked effect was observed on virus replication in the respiratory tract when chemotherapy was commenced 1 day before virus inoculation; it also cleared the viremia and reversed the progression of clinical signs. When chemotherapy was commenced 1 day after virus inoculation, a moderate, though less marked effect was observed. The efficacy of this drug in the murine infection correlated with activity of the drug against equine herpesvirus 1 in cell cultures. The prospects for chemotherapy in the natural host are discussed in the light of these findings.

Adenine↗
PubMed1989

Persistent herpes simplex virus infection and mechanisms of virus drug resistance.

Herpes simplex virus (HSV) is susceptible to a variety of antiviral compounds, most of which are nucleoside analogues that interfere with DNA metabolism involving the virus enzymes DNA-polymerase and thymidine kinase. Single mutations in the virus genome give rise to resistant mutants following selection in vitro in the presence of a particular drug, and in this respect HSV is similar to several other viruses. Such mutants have been invaluable research tools. HSV is responsible for a variety of lesions which tend to be recurrent, owing to the special ability of the virus to remain latent in and reactivate from neural tissue. The consequences of this upon clinical resistance are discussed in the present review. In fact, clinical resistance in HSV infections has not yet become widespread but does appear to be especially important in immunocompromised patients, including those suffering from AIDS. HSV is proposed as an important model for the investigation of drug resistance in other, more complex organisms, and with respect to antiviral strategies against the human immunodeficiency virus.

Antiviral Agents↗
PubMed1989

Antiviral drug resistance.

Recently the first report of zidovudine-resistant human immunodeficiency virus obtained from AIDS patients was published. Resistance to antiviral agents may result from single point mutations in the virus genome. Several mechanisms of resistance have already been elucidated at the biochemical level but the clinical significance of drug resistance is much more difficult to establish. Most attention is now focused on the immunocompromised host where clinically important resistance has been encountered most frequently. Hugh Field and Siân Goldthorpe describe the mechanisms of resistance in viruses that are currently targets for chemotherapy and discuss the likely future role of drug-resistant virus infections in man.

Antiviral Agents↗
PubMed1989

Animal models for antiviral chemotherapy.

Traditionally animal models have formed a vital part of the preclinical evaluation of new forms of antiviral therapy. A variety of models used in the past or potentially useful in the future are considered in this short review. Several valuable and complex questions concerning virus-drug interactions in vivo have been successfully addressed by means of animal models. Better understanding of drug modes of action and virus pathogenesis in the models enable even more accurate predictions to be made for the outcome of antiviral therapy in man. The complexity of virus infections in man is such that animals are likely to remain an important part in drug evaluation for many years. To this end, new developments such as improved techniques in the production of transgenic animals are opening up a variety of completely novel methods for studying inhibitors of a wider group of viruses in vivo including the human immunodeficiency virus. However, the correct interpretation of animal data requires the critical evaluation of animal models. This review will identify several important difficulties which confront those working on antiviral chemotherapy in animals and which must continue to be addressed if confidence in animal data is to be maintained.

Animals↗
PubMed1989

Analysis of the bovine herpesvirus type 1 thymidine kinase (TK) gene from wild-type virus and TK-deficient mutants.

Five thymidine kinase (TK)-deficient mutants (B1 to B5) of bovine herpesvirus type 1 (BHV-1) were isolated by selection for resistance to the nucleotide analogue bromovinyldeoxyuridine. The genetic lesion in mutant B1 was localized in a 2.7 kb SalI-SalI subfragment (fTK2.7) which maps between 0.456 and 0.475 within the HindIII A fragment of the BHV-1 genome. The tk genes from wild-type and the TK-mutants B1 to B5 were cloned and sequenced using eight unique synthetic primers designed from a published sequence. The BHV-1 tk gene sequence for the strain 6660 contained some differences compared with that published previously for strain LA. Alignment of the predicted amino acid sequence of the BHV-1 TK polypeptide with different herpesvirus TKs revealed five strongly conserved regions and also identified putative functional relationships with other enzymes. Several interesting features were apparent in the tk gene sequences from the TK- mutants. The TK mutant B1 was a typical frameshift and chain termination mutant due to the deletion of a single base. The tk gene sequence of mutant B2 revealed the deletion of three bases resulting in the loss of valine at amino acid residue 174 of the TK polypeptide. The tk genes of mutants B3 to B5 contained an identical change of a single base addition resulting in frameshift and premature chain termination. In contrast to wild-type BHV-1, the TK-defective mutants were incapable of adsorbing TK-neutralizing antibodies from serum.

Amino Acid Sequence↗
PubMed1988

Genomic localization and sequence analysis of the putative bovine herpesvirus-1 DNA polymerase gene.

The bovine herpesvirus-1 (BHV-1) genome was analysed by Southern blot hybridization using the herpes simplex virus type 1 (HSV-1) DNA polymerase gene as a probe. A 2.5 kilobase region which hybridized specifically to the HSV-1 DNA polymerase gene was identified within the Hind III G fragment at approximate map units 0.334-0.352. In order to provide further evidence that this is the location of the BHV-1 DNA polymerase gene, the 2.5 kilobase region was cloned and part of it sequenced. An uninterrupted stretch of over 800 nucleotides was obtained and an open reading frame spanning the entire sequence was identified. The amino acid sequence that it encodes shows striking homology to a region within the C-terminal half of other herpesvirus DNA polymerases.

Amino Acid Sequence↗
PubMed1988

Application of cloned fragments of equine herpesvirus type-1 DNA for detection of virus-specific DNA in equine tissues.

Tissue specimens obtained from equine herpesvirus-1 (EHV-1), subtype 1-infected aborted foetuses were analysed for the presence of virus DNA by means of Southern blot and dot blot hybridisations. The specificity of the methods was confirmed although the sensitivity was inferior to classical techniques such as virus isolation. However, the possibility of detecting the state of the virus DNA and the ability to distinguish between subtypes were important features, and the dot blot method was shown to have potential for a rapid diagnostic test. This report demonstrates some potential practical applications of hybridisation methods for studying the pathogenesis and epidemiology of EHV-1 but also reveals limitations of the techniques.

Abortion, Veterinary↗
PubMed1987

The inhibition of bovine herpesvirus-1 by methyl 2-pyridyl ketone thiosemicarbazone and its effects on bovine cells.

Methyl 2-pyridyl ketone thiosemicarbazone (MPKT) was found to inhibit bovine herpesvirus-1 (BHV-1) at an ED50 concentration of approximately 5-10 microM. Several virus strains were shown to have similar sensitivity to the drug and serial passage of virus in the presence of MPKT failed to yield resistant progeny. There was evidence for toxic effects on cells at drug concentrations similar to those required to inhibit virus and passage of cells in low concentrations of MPKT gave results suggesting cumulative toxicity. Pre-incubation of cells in the presence of MPKT produced a residual antiviral effect. Taken together, these observations cast doubt on the selectivity of the drug for BHV-1, at least in the bovine system under test.

Animals↗
PubMed1987

Critical determinants of antiherpes efficacy of buciclovir and related acyclic guanosine analogs.

Buciclovir is an example of an antiherpes, acyclic guanosine analog activated by the viral thymidine kinase and inhibiting viral DNA synthesis in infected cells. An investigation of closely related buciclovir-analogs with similar antiherpes activities in cell cultures and similar, or identical, modes of action but with disparate effects in vivo, revealed the following critical determinants of antiherpes efficacy. (1) The accumulation of guanosine analog-triphosphates in infected cells, which is cell-type-specific and analog-dependent. (2) The potencies of the triphosphates as inhibitors of the viral DNA polymerase. (3) The plasma kinetics of the analogs, which are widely different despite the similar structures. (4) The penetration into nervous tissue relative to penetration into non-nervous tissues, of importance in connection with the neurotropic behavior of the virus. (5) The concentration of the antagonist thymidine in certain tissues. (6) The difference in pathogenesis between primary infections and recurrent infections, exemplified in the different efficacies of topically applied drugs in cutaneous and genital HSV-2 infections in guinea pigs.

Acyclovir↗
PubMed1987

Immunogenicity versus pathogenicity after anterior chamber inoculation of an acyclovir-induced double mutant of HSV-1.

The acyclovir-induced herpes simplex virus Type 1 (HSV-1) strain, R9C2, a double mutant in thymidine kinase (TK) and DNA polymerase (DNA pol), and its parental strain SC16 were compared for their effects on ocular pathology and systemic immunity after unilateral inoculation into the anterior chamber (AC) of BALB/c mouse eyes. Although AC-injected R9C2 produced no retinal necrosis (0/18 eyes), this mutant induced active suppression (33-87%) of anti-HSV delayed type hypersensitivity similar to that induced by another HSV strain, KOS. AC-injected parental strain, SC16, caused fatal disease within 7-10 days, and induced bilateral retinal necrosis and suppression of DTH in 100% of the mice. Preimmunization with R9C2 protected mice in a dose-dependent fashion from the pathologic and lethal effects of AC-injected parental virus. These data suggest that the immunogenicity of the TK and DNA pol double mutant remains intact despite the decreased ocular and systemic pathogenicity observed after intracameral inoculation.

Acyclovir↗
PubMed1986

Detection of herpes simplex virus-specific DNA sequences in latently infected mice and in humans.

Herpes simplex virus-specific DNA sequences have been detected by Southern hybridization analysis in both central and peripheral nervous system tissues of latently infected mice. We have detected virus-specific sequences corresponding to the junction fragment but not the genomic termini, an observation first made by Rock and Fraser (Nature [London] 302:523-525, 1983). This "endless" herpes simplex virus DNA is both qualitatively and quantitatively stable in mouse neural tissue analyzed over a 4-month period. In addition, examination of DNA extracted from human trigeminal ganglia has shown herpes simplex virus DNA to be present in an "endless" form similar to that found in the mouse model system. Further restriction enzyme analysis of latently infected mouse brainstem and human trigeminal DNA has shown that this "endless" herpes simplex virus DNA is present in all four isomeric configurations.

Adult↗
PubMed1986

Pathogenicity of herpes simplex virus mutants containing drug resistance mutations in the viral DNA polymerase gene.

Three herpes simplex virus mutants that contain drug resistance mutations in the DNA polymerase gene exhibited no significant reduction in replication in the ears of mice compared with the wild type after inoculation at that site but were attenuated for pathogenicity after intracerebral inoculation. Cataracts were common sequelae in mice that survived mutant infections.

Acyclovir↗
PubMed1985

Chemotherapy of Aujeszky's disease (pseudorabies) in the mouse by means of nucleoside analogues: bromovinyldeoxyuridine, acyclovir, and dihydroxypropoxymethylguanine.

Pseudorabies virus (PRV) infection was established in mice by means of inoculating the ear flap. The infection was universally fatal once clinical signs appeared. Bromovinyldeoxyuridine (BVDU) was a potent inhibitor of PRV in vitro, but this drug failed to protect mice and produced only marginal reductions in virus titre and slight prolongation of survival. Acyclovir (ACV) and dihydroxypropoxymethylguanine (DHPG) were both less active than BVDU when tested against the virus in BHK cells, yet DHPG therapy was extremely effective in mice; it reduced virus titres markedly and resulted in the long-term survival of mice given a potentially lethal infection. When ACV and DHPG were tested in vitro using murine rather than hamster cells, these compounds, especially DHPG, were shown to be much more active against PRV.

Acyclovir↗
PubMed1984

Characterization of latent infections in mice inoculated with herpes simplex virus which is clinically resistant to acyclovir.

Mice were inoculated into the ear pinna with herpes simplex virus (HSV) using a strain which is resistant to acyclovir (ACV) chemotherapy. The original inoculum was resistant to ACV because it contained a proportion of thymidine kinase-defective (TK-) virions. This had been obtained previously by passage of an HSV type 1 strain in mice undergoing suboptimal therapy. The cervical dorsal root ganglia were subsequently explanted from the infected mice and the presence of latent virus therein revealed by reactivation in vitro. These explant cultures yielded both TK+ and TK- viruses on reactivation. The establishment of latent infections was not affected by chemotherapy during the acute infection. One TK- ganglion isolate when studied in detail was found to be attenuated and thus resembled previously examined TK- strains which had been selected in vitro for ACV-resistance.

Acyclovir↗