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Home / Equine Research Bank / Appl Environ Microbiol / An Ecotype of Neorickettsia risticii Causing Potomac Horse F...
Applied and environmental microbiology2016; 82(19); 6030-6036; doi: 10.1128/AEM.01366-16

An Ecotype of Neorickettsia risticii Causing Potomac Horse Fever in Canada.

Abstract: Neorickettsia (formerly Ehrlichia) risticii is an obligatory intracellular bacterium of digenetic trematodes. When a horse accidentally ingests aquatic insects containing encysted trematodes infected with N. risticii, the bacterium is transmitted from trematodes to horse cells and causes an acute and often fatal disease called Potomac horse fever (PHF). Since the discovery of N. risticii in the United States in 1984, using immunofluorescence and PCR assays, PHF has been increasingly recognized throughout North America and South America. However, so far, there exist only a few stable N. risticii culture isolates, all of which are from horses within the United States, and the strain diversity and environmental spreading and distribution of pathogenic N. risticii strains remain poorly understood. This paper reports the isolation of N. risticii from the blood of a horse with acute PHF in Ontario, Canada. Intracellular N. risticii colonies were detected in P388D1 cells after 47 days of culturing and 8 days after the addition of rapamycin. Molecular phylogenetic analysis based on amino acid sequences of major surface proteins P51 and Ssa1 showed that this isolate is distinct from any previously sequenced strains but closely related to midwestern U.S. strains. This is the first Canadian strain cultured, and a new method was developed to reactivate dormant N. risticii to improve culture isolation. Neorickettsia risticii is an environmental bacterium that lives inside flukes that are parasitic to aquatic snails, insects, and bats. When a horse accidentally ingests insects harboring flukes infected with N. risticii, the bacterium is transmitted to the horse and causes an acute and often fatal disease called Potomac horse fever. Although the disease has been increasingly recognized throughout North and South America, N. risticii has not been cultured outside the United States. This paper reports the first Canadian strain cultured and a new method to effectively culture isolate N. risticii from the horse blood sample. Molecular analysis showed that the genotype of this Canadian strain is distinct from previously sequenced strains but closely related to midwestern U.S. strains. Culture isolation of N. risticii strains would confirm the geographic presence of pathogenic N. risticii, help elucidate N. risticii strain diversity and environmental spreading and distribution, and improve diagnosis and development of vaccines for this dreadful disease.
Copyright © 2016, American Society for Microbiology. All Rights Reserved.
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Publication Date: 2016-09-16 PubMed ID: 27474720PubMed Central: PMC5038023DOI: 10.1128/AEM.01366-16Google Scholar: Lookup
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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 focuses on the discovery of a unique strain of Neorickettsia risticii in Canada, which is the cause of a severe equine disease called Potomac horse fever. The paper is also an exploration of a new method for culturing this bacterium for further studies.

Background of the Research

  • This study is centered around an infectious bacterium, Neorickettsia risticii, which is responsible for causing Potomac horse fever, a severe and often fatal illness in horses.
  • The bacterium lives inside flukes, parasitic organisms that infest aquatic animals like snails, insects, and bats. The transmission to horses occurs when these hosts, specifically insects, are accidentally ingested by the horse.
  • Although the disease has been prevalent in North and South America, all cultured isolates of this bacterium, to date, have originated from the United States. The study of strain diversity and ecological distribution is thus limited due to a lack of varied samples.

Discovery in Canada

  • The research marks the first successful cultivation of a Neorickettsia risticii strain from Canada. The isolate was extracted from the blood of a horse suffering from acute Potomac horse fever in Ontario.
  • The Canadian strain was found to be genetically distinct from previously analyzed strains but shared close relations to those found in midwestern U.S.
  • Intracellular colonies of N. risticii were detected in the horse blood sample after 47 days of culture and 8 days post addition of rapamycin, an antibacterial agent.

Significance of the Research

  • This discovery amplifies the understanding of the geographical presence of pathogenic N. risticii. This knowledge helps uncover elements about the strain diversity and spread of this bacterium.
  • A new method of culture isolation was developed during the study for reactivation of dormant bacteria. This technique can prove pivotal in facilitating future laboratory research and development of potential vaccines against the disease.
  • The researchers conducted a molecular phylogenetic analysis based on amino acid sequences of major surface proteins P51 and Ssa1 of the bacterium which further contributed to the understanding of its genetic diversity.

Imminent Research Directions

  • The successful culture of a Canadian strain propels the need for more extensive sampling from different geographic locations. This will facilitate a better understanding of the bacterium’s strain diversity, environmental spread, and distribution.
  • Further research could also delve into the development of diagnostic tools and vaccines to prevent Potomac horse fever.

Cite This Article

APA
Xiong Q, Bekebrede H, Sharma P, Arroyo LG, Baird JD, Rikihisa Y. (2016). An Ecotype of Neorickettsia risticii Causing Potomac Horse Fever in Canada. Appl Environ Microbiol, 82(19), 6030-6036. https://doi.org/10.1128/AEM.01366-16

Publication

Applied and environmental microbiology
ISSN: 1098-5336
NlmUniqueID: 7605801
Country: United States
Language: English
Volume: 82
Issue: 19
Pages: 6030-6036

Researcher Affiliations

Xiong, Qingming
  • Laboratory of Molecular, Cellular, and Environmental Rickettsiology, Department of Veterinary Biosciences, College of Veterinary Medicine, Columbus, Ohio, USA.
Bekebrede, Hannah
  • Laboratory of Molecular, Cellular, and Environmental Rickettsiology, Department of Veterinary Biosciences, College of Veterinary Medicine, Columbus, Ohio, USA.
Sharma, Pratibha
  • Laboratory of Molecular, Cellular, and Environmental Rickettsiology, Department of Veterinary Biosciences, College of Veterinary Medicine, Columbus, Ohio, USA.
Arroyo, Luis G
  • Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada.
Baird, John D
  • Department of Clinical Studies, Ontario Veterinary College, University of Guelph, Guelph, Ontario, Canada.
Rikihisa, Yasuko
  • Laboratory of Molecular, Cellular, and Environmental Rickettsiology, Department of Veterinary Biosciences, College of Veterinary Medicine, Columbus, Ohio, USA Rikihisa.1@osu.edu.

MeSH Terms

  • Anaplasmataceae Infections / blood
  • Anaplasmataceae Infections / microbiology
  • Anaplasmataceae Infections / veterinary
  • Animals
  • Antigens, Bacterial / blood
  • Bacteriological Techniques / veterinary
  • Ecotype
  • Horse Diseases / blood
  • Horse Diseases / microbiology
  • Horses
  • Male
  • Neorickettsia risticii / genetics
  • Neorickettsia risticii / immunology
  • Neorickettsia risticii / isolation & purification
  • Ontario
  • Phylogeny
  • Sequence Analysis, DNA / veterinary
  • Treatment Outcome

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Citations

This article has been cited 5 times.
  1. Budachetri K, Lin M, Yan Q, Chien RC, Hostnik LD, Haanen G, Leclère M, Waybright W, Baird JD, Arroyo LG, Rikihisa Y. Real-Time PCR Differential Detection of Neorickettsia findlayensis and N. risticii in Cases of Potomac Horse Fever. J Clin Microbiol 2022 Jul 20;60(7):e0025022.
    doi: 10.1128/jcm.00250-22pubmed: 35695520google scholar: lookup
  2. Arroyo LG, Moore A, Bedford S, Gomez DE, Teymournejad O, Xiong Q, Budachetri K, Bekebrede H, Rikihisa Y, Baird JD. Potomac horse fever in Ontario: Clinical, geographic, and diagnostic aspects. Can Vet J 2021 Jun;62(6):622-628.
    pubmed: 34219771
  3. Teymournejad O, Lin M, Bekebrede H, Kamr A, Toribio RE, Arroyo LG, Baird JD, Rikihisa Y. Isolation and Molecular Analysis of a Novel Neorickettsia Species That Causes Potomac Horse Fever. mBio 2020 Feb 25;11(1).
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  4. 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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    pubmed: 38046433
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