Article

Comparison of the efficacy of inactivated combination and modified-live virus vaccines against challenge infection with neuropathogenic equine herpesvirus type 1 (EHV-1)

Department of Microbiology and Immunology, College of Veterinary Medicine, Cornell University, Ithaca, NY 14853, USA.
Vaccine (Impact Factor: 3.49). 05/2006; 24(17):3636-45. DOI: 10.1016/j.vaccine.2006.01.062
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ABSTRACT Equine herpesvirus type 1 (EHV-1) is a ubiquitous alphaherpesvirus of horses which causes rhinopneumonitis, abortion and myeloencephalopathy. To test the efficacy of commercial vaccines in protection against neurological EHV-1 challenge, groups of five horses were immunized with modified-live virus or an inactivated vaccine, or received placebo. Horses were challenged by aerosol with a recent virus isolate obtained from a case of paralytic EHV-1. The duration of fever decreased significantly in the modified-live virus vaccine group. Three animals in each of the inactivate and control groups showed alterations in neurological status. When compared to the inactivated vaccine, the modified-live virus vaccine induced significantly lower virus-neutralizing antibodies over the course of the study. The modified-live virus vaccine resulted in low EHV-1-specific IgG(T)/IgGa and IgG(T)/IgGb ratios, suggesting a bias towards a cytotoxic immune response. Virus shedding from the nasopharynx was almost undetectable in the modified-live virus group, and was significantly lower when compared to that in the other groups. Normalized lymphocyte viral genome copies were similar for the three groups, although animals vaccinated with the modified-live virus vaccine were qPCR-positive on fewer days when compared to those of the other groups. Based on data from neurological signs, rectal temperatures, virus isolation from nasal swabs and immune response specificity, we concluded that protection induced by the modified-live virus vaccine is superior to that induced by the inactivated combination vaccine.

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    • "The MLV vaccine reduced virus shedding after challenge to almost undetectable levels. It also prevented neurological signs but only slightly reduced viremia (Goodman et al., 2006). In another study, the efficacy of the MLV vaccine was compared to an inactivated vaccine with high antigen content for abortion control (Pneumabort K, Pfizer) in an optimized 3-dose vaccination regimen. "
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    ABSTRACT: The equine herpesviruses type 1 (EHV-1) and 4 (EHV-4) are ubiquitous pathogens that affect horse populations on all continents. Despite widespread vaccination, EHV-1 and EHV-4 infections remain a permanent risk. While the two viruses share a high degree of genetic and antigenic similarity, they differ significantly in host range and pathogenicity. Compared to EHV-4, which mainly infects horses and causes respiratory disease, EHV-1 has a broader host range and can result in respiratory disease, abortions, neonatal death, and equine herpesvirusmyeloencephalopathy (EHM). Recent studies have elucidated a number of mechanisms that may, at least partly, explain the differential pathogenic potential of the two viruses. While both EHV-1 and EHV-4 can escape host immune responses and establish latent infection, there are differences with respect to virus entry and their ability to interfere with the innate immune response. Understanding the virus' repertoire of immunomodulatory mechanisms may lead the way to develop more efficient vaccines.
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    • "Indeed, we observed that isolates with the D 752 genotype had significantly more single EHV-1-infected cells below the BM than isolates with the N 752 genotype, at 48 h p.i. This is in agreement with several other studies, showing a more robust replication of neurovirulent D 752 isolates, as shown by a higher level of viraemia of infected cells in the blood (Allen & Breathnach, 2006; Goodman et al., 2006, 2007; Allen, 2008; Van de Walle et al., 2009). "
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    • "There are currently many variations of EHV-1 inactivated vaccines [3]. However, only one modified live vaccine (MLV) each is registered in the US and Europe for use in horses, although MLV's seem to have some advantages over the widely used inactivated combination vaccines [3] [4] [5]. "
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