Protection against lethal equine herpes virus type 1 (subtype 1) infection in hamsters by immune stimulating complexes (ISCOMs) containing the major viral glycoproteins

Equine Herpesvirus-I Infection in Horses: Recent Updates on its Pathogenicity, Vaccination, and Preventive Management Strategies

Equine herpesvirus-1 (EHV-1) is one of the most common and ubiquitous viral pathogens infecting equines, particularly horses worldwide. The EHV-1 is known to induce not only humoral but also cellular immune responses in horses. Respiratory distress, abortion in pregnant mares, neurological disorders, and neonatal foal deaths represent EHV-1 infection. Despite the limited success of inactivated, subunit, live, and DNA vaccines, over the past few decades, vaccination remains the prime preventive option to combat EHV-1 infection in horses. However, current vaccines lack the potentiality to protect the neurological form of infections in horses. There is desperate necessity to search effectual EHV-1 vaccines that may stimulate not only mucosal and systemic cellular immunity but also humoral immunity in the horses. This review highlights the state of knowledge regarding EHV-1 biology, EHV-1 pathogenesis, and disparate vaccines studied in the past to prevent EHV-1 infection. The review also underlines the best management strategies which certainly need to be adopted by veterinarians in order to avoid and prevent EHV-1 infection and outbreak in horses in the future.

Diagnosis and prevention of equine infectious diseases: present status, potential, and challenges for the future

The frequent transfers of horses, whether on a permanent or temporary basis, make strict control of infectious diseases essential. Such control needs a reliable and rapid means to accurately diagnose the relevant diseases. Indirect diagnosis based on antibody detection remains certainly the best method to secure the epidemiologic surveillance of the diseases at regional, national, or even world level, while direct diagnosis is the only way to diagnose a new outbreak. New diagnostic methods resulting from advances in biochemistry, molecular biology, and immunology are now available. As far as antibody detection is concerned, the new methods are mainly based on immunoassays, especially ELISAs. Regarding the identification of the pathogens, while isolation is still of importance, much progress has been made with immunocapture tests including capture ELISA based on monoclonal antibodies. DNA probes and amplification tests such as PCR or RT-PCR are representing a real breakthrough. Factors common to all of these tests are specificity, sensitivity, rapid implementation, and quick results. Such tests are, however, often still at the development stage. They absolutely need to be validated under multicentric evaluations prior to being used on a larger scale. At the same time there is an obvious need for the standardization of the reagents used. The technical and economic impact of a false (either positive or negative) diagnosis justifies such an harmonization which could effectively be achieved worldwide under the aegis of the Office International des Epizooties (OIE), which is itself the primary source of disease information. Vaccines are also essential for the control of equine infectious diseases. Most vaccines used in the prevention of viral or bacterial diseases are inactivated adjuvanted vaccines, which may cause unacceptable side effects. Also, their efficacy can sometimes be questioned. Subunit vaccines, when available, represent significant advances especially with regards to safety. Greater progress is expected from the use of new technologies taking advantage of recent developments in molecular biology (recombinant DNA technology) and in immunology (immunomodulators). Significant results have been obtained with subunit vaccines or with live vectored vaccines using recombinant DNA technology. Good results are on the way to be achieved with genetic (or naked-DNA) vaccines. It is therefore possible to expect the availability of a new generation of vaccines in the rather short term. Such vaccines will not only be safer and more efficacious, but they will also make it possible to differentiate vaccinated from infected animals, which will contribute to better control of the infection. Whatever the quality of the vaccines of the future may be, vaccination alone will never be sufficient to control infectious diseases. It is therefore essential to keep on making the animal owners and their veterinarians aware of the importance of the management and the hygiene in the diseases control and to organize them under "Common Codes of Practice."

Immune responses and protective efficacy of recombinant baculovirus-expressed glycoproteins of equine herpesvirus 1 (EHV-1) gB, gC and gD alone or in combinations in BALB/c mice

Baculovirus-expressed glycoproteins of EHV-1 gB, gC and gD alone or in combination evoked antibody responses and protected vaccinated mice against a challenge with EHV-1. gB, gD, gB + gC, gB + gD and gC + gD elicited very high levels of ELISA antibodies while gC and gC + gD elicited high levels of virus neutralising antibodies. Western blotting demonstrated that the antibodies produced were not only specific for the baculovirus-expressed glycoproteins gB, gC and gD, but also highly specific for each EHV-1 glycoprotein. Vaccination of mice with gB or gD prevented clinical signs of infection in mice challenged with EHV-1 and all vaccinated groups of mice except controls showed a rapid clearance of virus from the lungs and a reduction in lesions characteristic of herpesviruses in the lungs post-challenge. Notably, the lungs of mice vaccinated with gB, gD or gB + gD and challenged with EHV-1 showed prominent peribronchiolar and perivascular aggregations of mononuclear cells, predominantly lymphocytes. Immunocytochemical staining of these sections showed large numbers of T cells, suggesting an active role for these cells at the site of virus replication post-challenge.

Transforming growth factor-beta induced by live or ultraviolet-inactivated equid herpes virus type-1 mediates immunosuppression in the horse

Up to 21 days after exposure to live or ultraviolet-inactivated equid herpesvirus type-1 (EHV-1) autologous serum from ponies caused an immunosuppressive effect if incorporated into T-cell proliferation assays to EHV-1. The suppressive factor in the sera of ponies also inhibited T-cell response to phytohaemagglutinin. Increased levels of circulating activated transforming growth factor-beta 1 (TGF-beta 1) were detected, and the suppressive activity of the serum could be reversed by antibody to TGF-beta 1. In a challenge experiment the ponies which exhibited circulating TGF-beta 1 activity succumbed to infection while the ones with similar magnitudes of T-cell responses, but no TGF-beta 1 activity, were protected. A definition of this immunosuppressive mechanism and its mode of induction must be central to the design of vaccines and to an understanding of the pathogenesis of EHV-1.

Response of ponies to adjuvanted EHV-1 whole virus vaccine and challenge with virus of the homologous strain

Five yearling ponies were vaccinated with inactivated Equid herpesvirus type 1 (EHV-1) in Freund's complete adjuvant as a double emulsion and revaccinated 6 weeks later with EHV-1 in Freund's incomplete adjuvant. These ponies and three age-matched controls were challenged intra-nasally after a further 6 weeks with homologous live virus and monitored clinically, biologically and serologically. After challenge, clinical signs were mild in both groups. No cell-associated viraemias were detected in vaccinated ponies. Vaccination induced high levels of complement-fixing (CF) and virus-neutralizing (VN) antibody, and elicited a response to all major viral glycoproteins as shown by western blot analysis.

Comparison of 24 different adjuvants for inactivated HIV-2 split whole virus as antigen in mice. Induction of titres of binding antibodies and toxicity of the formulations

The objective of this study was the comparison of the quantity and quality of the humoral immune response against inactivated whole human immunodeficiency virus type 2. Twenty-four different adjuvants were tested. The toxicity of these preparations was determined. Due to the large number of experiments, the animal model used was the NMRI mouse. Sera were assayed for the presence of antibodies by ELISA and Western blot. The toxicity of the adjuvants was determined by observing lethal side-effects occurring within two days after injection of the immunogenic preparations. The results show that polymethylmethacrylate nanoprticles were the best overall adjuvant, inducing the highest titres of antibodies compared with other adjuvants as well as producing a significantly better immune response against a number of individual HIV-2 antigens without any observable toxic side-effects. However, this adjuvant did not induce antibodies against the outer envelope protein gp120, whereas such antibodies were induced by aluminium compounds, Freund's complete and incomplete adjuvants, and fumed silica (Aerosil). This result suggests the necessity of using vaccines with two or more different adjuvants in order to induce the required immune response against physically different antigens.

Responses of ponies to equid herpesvirus-1 ISCOM vaccination and challenge with virus of the homologous strain

An experimental (ISCOM) vaccine previously shown to protect hamsters from lethal challenge with equid herpesvirus-1 (EHV-1), was tested in horses. Vaccination with EHV-1 ISCOMs induced serum antibodies to the major virus glycoproteins gp10, 13, 14, 17, 18 and 21/22a, whereas antibody responses to gp2 were weak or absent. High levels of virus neutralising antibody of long duration were induced, but did not prevent challenge infection with virus of the homologous strain. However, in the vaccinated ponies there was a significant reduction in clinical signs, nasal virus excretion and cell associated viraemia compared with age-matched unvaccinated controls. There was a strong correlation between pre-challenge levels of serum virus neutralising antibody and the duration and total amount of virus excreted from the nasopharynx.