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Journal of clinical microbiology1998; 36(2); 506-512; doi: 10.1128/JCM.36.2.506-512.1998

Association of deficiency in antibody response to vaccine and heterogeneity of Ehrlichia risticii strains with Potomac horse fever vaccine failure in horses.

Abstract: Ehrlichia risticii is the causative agent of Potomac horse fever (PHF), which continues to be an important disease of horses. Commercial inactivated whole-cell vaccines are regularly used for immunization of horses against the disease. However, PHF is occurring in large numbers of horses in spite of vaccination. In a limited study, 43 confirmed cases of PHF occurred between the 1994 and 1996 seasons; of these, 38 (89%) were in horses that had been vaccinated for the respective season, thereby clearly indicating vaccine failure. A field study of horses vaccinated with two PHF vaccines indicated a poor antibody response, as determined by immunofluorescence assay (IFA) titers. In a majority of horses, the final antibody titer ranged between 40 and 1,280, in spite of repeated vaccinations. None of the vaccinated horses developed in vitro neutralizing antibody in their sera. Similarly, one horse experimentally vaccinated three times with one of the vaccines showed a poor antibody response, with final IFA titers between 80 and 160. The horse did not develop in vitro neutralizing antibody or antibody against the 50/85-kDa strain-specific antigen (SSA), which is the protective antigen of the original strain, 25-D, and the variant strain of our laboratory, strain 90-12. Upon challenge infection with the 90-12 strain, the horse showed clinical signs of the disease. The horse developed neutralizing antibody and antibody to the 50/85-kDa SSA following the infection. Studies of the new E. risticii isolates from the field cases indicated that they were heterogeneous among themselves and showed differences from the 25-D and 90-12 strains as determined by IFA reactivity pattern, DNA amplification finger printing profile, and in vitro neutralization activity. Most importantly, the molecular sizes of the SSA of these isolates varied, ranging from 48 to 85 kDa. These studies suggest that the deficiency in the antibody response to the PHF vaccines and the heterogeneity of E. risticii isolates may be associated with the vaccine failure.
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Publication Date: 1998-02-18 PubMed ID: 9466767PubMed Central: PMC104568DOI: 10.1128/JCM.36.2.506-512.1998Google Scholar: Lookup
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  • Journal Article

Summary

This research summary has been generated with artificial intelligence and may contain errors and omissions. Refer to the original study to confirm details provided. Submit correction.

The research article examines the ineffectiveness of vaccines used in combating Potomac horse fever (PHF) in horses due to the deficiency in antibody response to the vaccines and the inconsistencies of the Ehrlichia risticii (causative pathogen) strains.

Research Overview

  • The research was instigated by the observation that a large number of horses were contracting PHF even though they had been vaccinated against the disease. To quantify this, a study was conducted between 1994 and 1996, where it was found that 89% of the confirmed PHF cases were in horses that had been vaccinated for the respective season.
  • The study was then extended to the horses vaccinated with two types of PHF vaccines, where it was found that these vaccines induced a poor antibody response as was determined by immunofluorescence assay (IFA) titers.
  • An experimental horse was given vaccinations three times, but it showed a poor antibody response and did not develop neutralizing antibodies. When the horse was infected with a strain of E. risticii, it presented PHF clinical signs, further demonstrating the vaccine’s failure.

Vaccine Failure and Antibody Response

  • The study discovered that none of the vaccinated horses developed in vitro neutralizing antibody in their sera – this suggests that the vaccines were failing to stimulate an effective immune response.
  • There was an observed poor antibody response – the final antibody titer ranged from 40 to 1,280, despite repeated vaccinations.
  • The experimentally vaccinated horse also showed a deficient antibody response and did not develop any neutralizing antibody. However, this horse developed the neutralizing antibody after being infected with the E. risticii strain, indicating that the disease triggered the appropriate antibody response.

Heterogeneity of Ehrlichia risticii Strains

  • New E. risticii isolates from the field cases were found to be variable and different from the original strain used for the vaccines.
  • The differences were seen in the IFA reactivity pattern, DNA amplification fingerprinting profile, and in vitro neutralization activity.
  • Interestingly, the molecular sizes of the strain-specific antigen (SSA) of these isolates varied, ranging from 48 to 85 kDa. The SSAs are the protective antigens.

Conclusion

  • The research concludes that the deficiency in antibody response and the diversity of the E. risticii strains may be associated with the observed vaccine failure. This suggests a need to adapt the vaccines to be more effective against the disease.

Cite This Article

APA
Dutta SK, Vemulapalli R, Biswas B. (1998). Association of deficiency in antibody response to vaccine and heterogeneity of Ehrlichia risticii strains with Potomac horse fever vaccine failure in horses. J Clin Microbiol, 36(2), 506-512. https://doi.org/10.1128/JCM.36.2.506-512.1998

Publication

Journal of clinical microbiology
ISSN: 0095-1137
NlmUniqueID: 7505564
Country: United States
Language: English
Volume: 36
Issue: 2
Pages: 506-512

Researcher Affiliations

Dutta, S K
  • Virginia-Maryland Regional College of Veterinary Medicine, University of Maryland, College Park 20742, USA.
Vemulapalli, R
    Biswas, B

      MeSH Terms

      • Animals
      • Antibodies, Bacterial / biosynthesis
      • Antibodies, Bacterial / immunology
      • Antigens, Bacterial / immunology
      • Blotting, Western
      • DNA, Bacterial / analysis
      • DNA, Bacterial / genetics
      • Ehrlichia / genetics
      • Ehrlichia / immunology
      • Ehrlichia / isolation & purification
      • Ehrlichiosis / immunology
      • Ehrlichiosis / prevention & control
      • Ehrlichiosis / veterinary
      • Fluorescent Antibody Technique
      • Horses
      • Neutralization Tests
      • Polymerase Chain Reaction
      • Rickettsial Vaccines / immunology
      • Treatment Failure
      • Vaccination
      • Vaccines, Inactivated / immunology

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      Citations

      This article has been cited 10 times.
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      2. McKenzie HC, Funk RA, Trager L, Werre SR, Crisman M. Immunogenicity of Potomac horse fever vaccine when simultaneously co-administered with rabies vaccine in a multivalent vaccine or as two monovalent vaccines at separate sites. Equine Vet J 2019 Nov;51(6):774-778.
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      3. Shaw SD, Stämpfli H. Diagnosis and Treatment of Undifferentiated and Infectious Acute Diarrhea in the Adult Horse. Vet Clin North Am Equine Pract 2018 Apr;34(1):39-53.
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