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Equine veterinary journal2019; 51(6); 774-778; doi: 10.1111/evj.13096

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.

Abstract: Potomac horse fever (PHF) is a potentially fatal enterocolitis of horses caused by Neorickettsia risticii. The disease was originally recognised almost 40 years ago in the state of Maryland in the US. It is now known to occur in many areas of North America, as well as having been described in South America and Europe. Monocomponent PHF vaccines are available, but clinical protection with vaccination has been reported to be inconsistent. Objective: This study was designed to assess the immunogenicity of a commercially available Potomac Horse Fever (PHF) vaccine when administered as either a monovalent PHF vaccine simultaneously co-administered with a separate monovalent Rabies vaccine or as a multivalent PHF/Rabies vaccine in horses. Methods: Randomised parallel group trial. Methods: Ninety-one client or University owned horses participated in this open-label randomised study, with 45 horses receiving the monovalent vaccines at separate sites and 46 receiving the multivalent vaccine at a single site. Serum PHF IFA titres were determined twice prior to vaccination and at 1, 2 and 3 months after vaccination. Results: Both vaccination protocols exhibited poor immunogenicity, with only one-third of all the animals demonstrating seroconversion, defined as an increase in titre of greater than 400 over baseline, at any time point after vaccination. The monovalent PHF vaccine exhibited significantly greater immunogenicity in terms of the number of horses exhibiting seroconversion, as compared to the multivalent vaccine, at one (20 vs. 11, P = 0.03) and two (18 vs. 9, p = 0.02) months post vaccination. The monovalent PHF vaccine also exhibited significantly greater immunogenicity in terms of the median (interquartile range) IFA titres, as compared to the multivalent vaccine, at one (800 [200-1600] vs. 400 [200-800], P = 0.009) and 2 months (400 [200-1600] vs. 400 [100-800], P = 0.02) post vaccination. There was no significant difference between groups at 3 months in either seroconversion rate or median IFA titers. Conclusions: This study did not assess the actual protective effects of PHF vaccination but rather used the serologic response to vaccination as a surrogate biomarker of immunity. Conclusions: The multivalent PHF/Rabies vaccine exhibited lower immunogenicity as compared to the monovalent PHF vaccine co-administered with a separate Rabies vaccine.
© 2019 The Authors. Equine Veterinary Journal published by John Wiley & Sons Ltd on behalf of EVJ Ltd.
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Publication Date: 2019-04-05 PubMed ID: 30859618PubMed Central: PMC6850380DOI: 10.1111/evj.13096Google Scholar: Lookup
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  • Journal Article
  • Randomized Controlled Trial
  • Veterinary

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 in this paper investigates the effectiveness of a vaccine for Potomac Horse Fever (PHF) in comparison to a multivalent PHF/Rabies vaccine. The study found that the single disease vaccine was more effective in stimulating an immune response in the horses tested.

Introduction

This research primarily centers around Potomac Horse Fever (PHF), a disease in horses caused by the bacterium Neorickettsia risticii. The disease, first identified forty years ago in Maryland, USA, is known to be prevalent in many regions across North America, and has also been documented in South America and Europe. While monovalent PHF vaccines are commercially available, their effectiveness in providing consistent clinical protection remains inconsistent and under question.

Objective and Methodology

  • The primary goal of this study was to assess and compare the immunogenicity – the ability to provoke an immune response – of a monovalent PHF vaccine and a combined multivalent PHF/Rabies vaccine in horses.
  • The research team used a randomized parallel group trial approach, with 91 client or University-owned horses participating in the study, which was also randomized.
  • The monovalent PHF vaccines were given to 45 horses at separate sites and another batch of 46 horses received the combined multivalent vaccine at a single site.
  • The horse’s serum PHF IFA (Immunofluorescence Assay) titres – a measure of the immune response – were recorded twice before vaccination and then at 1, 2, and 3 months post-vaccination.

Results

  • The results of the study showed that both vaccine protocols – monovalent and multivalent – demonstrated low immunogenicity, with only about a third of the animals showing seroconversion, or an increased titre of more than 400 over the baseline, at any point post-vaccination.
  • Interestingly, the monovalent PHF vaccine proved significantly more effective at eliciting an immune response – as measured by the number of horses showing seroconversion – compared to the multivalent vaccine, particularly at one and two months post-vaccination.
  • The trend was also visible in terms of median IFA titres, with the monovalent PHF vaccine generating significantly higher titres compared to the multivalent one at one and two months post-vaccination.
  • However, by the third month post-vaccination, there was no significant difference observed between the two groups in terms of either seroconversion rate or median IFA titers.

Conclusions

  • It’s important to clarify that the researchers did not directly examine the implication of these findings on actual protective immunity against PHF, but used the serologic response to vaccination as an indirect indicator of immunity.
  • Nonetheless, the key finding of this study indicates that a multivalent PHF/Rabies vaccine displayed lower immunogenicity as compared to when a single-disease PHF vaccine was co-administered with a separate Rabies vaccine. This outcome prompts several potential new avenues for further research into improving PHF vaccine effectiveness.

Cite This Article

APA
McKenzie HC, Funk RA, Trager L, Werre SR, Crisman M. (2019). 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, 51(6), 774-778. https://doi.org/10.1111/evj.13096

Publication

Equine veterinary journal
ISSN: 2042-3306
NlmUniqueID: 0173320
Country: United States
Language: English
Volume: 51
Issue: 6
Pages: 774-778

Researcher Affiliations

McKenzie, H C
  • Department of Large Animal Clinical Sciences, Virginia Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, Virginia, USA.
Funk, R A
  • Department of Large Animal Clinical Sciences, Virginia Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, Virginia, USA.
Trager, L
  • Department of Large Animal Clinical Sciences, Virginia Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, Virginia, USA.
Werre, S R
  • Laboratory for Study Design and Statistical Analysis, Department of Biomedical Sciences and Pathobiology, Virginia Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, Virginia, USA.
Crisman, M
  • Department of Large Animal Clinical Sciences, Virginia Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, Virginia, USA.

MeSH Terms

  • Anaplasmataceae Infections / microbiology
  • Anaplasmataceae Infections / prevention & control
  • Anaplasmataceae Infections / veterinary
  • Animals
  • Antibodies, Bacterial / blood
  • Female
  • Horse Diseases / microbiology
  • Horse Diseases / prevention & control
  • Horses
  • Immunogenicity, Vaccine
  • Male
  • Neorickettsia risticii
  • Rabies / prevention & control
  • Rabies / veterinary
  • Rabies Vaccines / immunology
  • Rickettsial Vaccines / immunology
  • Vaccination
  • Vaccines, Inactivated / immunology

Grant Funding

  • Zoetis, Inc.

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Citations

This article has been cited 2 times.
  1. Pinn-Woodcock TL, Aprea MS, Lejeune M, Tomlinson JE. Molecular detection of pathogens in an equine fever diagnostic panel: 2019-2023. Equine Vet J 2026 Mar;58(2):486-496.
    doi: 10.1111/evj.14527pubmed: 40384355google scholar: lookup
  2. Uzal FA, Arroyo LG, Navarro MA, Gomez DE, Asín J, Henderson E. Bacterial and viral enterocolitis in horses: a review. J Vet Diagn Invest 2022 May;34(3):354-375.
    doi: 10.1177/10406387211057469pubmed: 34763560google scholar: lookup
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