Transmission of Ehrlichia risticii, the agent of Potomac horse fever, using naturally infected aquatic insects and helminth vectors: preliminary report.
Abstract: Ehrlichia risticii, the agent of Potomac horse fever (PHF), has been recently detected in trematode stages found in snail secretions and in aquatic insects. Based on these findings, horses could conceivably be exposed to E. risticii by skin penetration with infected cercariae, by ingestion of infected cercariae in water or via metacercariae in a second intermediate host, such as an aquatic insect. In order to test this hypothesis, horses were challenged with infectious snail secretions and aquatic insects collected from a PHF endemic region in northern California. Two horses stood with their front feet in water harbouring E. risticii-infected cercariae, 2 horses drank water harbouring E. risticii-infected cercariae, and 6 horses were fed pools of different aquatic insects harbouring E. risticii-infected metacercariae. In this preliminary study, only the one horse infected orally with mature caddisflies (Dicosmoecus gilvipes) developed the clinical and haematological disease syndrome of PHF. The agent was isolated from the blood of the infected horse in a continuous cell line and identified as E. risticii by characterisation of the 16S rRNA gene. Therefore, E. risticii is maintained in nature in a complex aquatic ecosystem and transmission to horses can occur through accidental ingestion of insects such as caddisflies containing infected metacercariae. At present, the small number of horses used in this study does not exclude other insects and free trematode stages as potential sources of infection.
Publication Date: 2000-08-22 PubMed ID: 10952374DOI: 10.2746/042516400777032219Google Scholar: Lookup
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- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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The research investigates how the Potomac horse fever agent, Ehrlichia risticii, is transmitted through naturally infected aquatic insects and helminth vectors, with results indicating that transmission to horses can occur through accidental ingestion of certain infected insects.
Introduction to the Research
- This research focuses on transmission of Ehrlichia risticii, the agent causing Potomac horse fever (PHF). The infection has previously been found in the trematode stages in snail secretions and aquatic insects.
- It was hypothesized that horses could catch the infection through skin penetration or ingestion of infected water, or by eating infected insects.
- A study was conducted where horses were exposed to these potential sources of infection.
Research Methodology
- The experiment involved ten horses exposed to different,
potentially infectious sources. - Two horses stood in water containing E. risticii-infected cercariae, two horses drank such water, and six were fed an assortment of aquatic insects carrying E. risticii-infected metacercariae.
- The aquatic organisms were collected from a PHF endemic region in Northern California.
Research Findings
- Out of the ten horses used in this experiment, only the one that consumed mature caddisflies developed clinical and haematological symptoms of PHF.
- The E. risticii agent was successfully isolated from the blood of the infected horse, reinforcing the hypothesis that the transmission occurred via ingestion of the infected insect.
- Interestingly, there was no evidence of infection in horses exposed to the other potential sources of infection (infected water and other insects), though the study acknowledges that the small sample size does not rule out other possible transmission routes.
Conclusion of the Research
- The findings suggest that E. risticii is maintained in complex aquatic ecosystems and can infect horses through accidental caddisfly ingestion.
- Although the study provides a possible transmission route for PHF, it also emphasizes that larger studies are needed to explore potential alternative sources of infection.
Cite This Article
APA
Madigan JE, Pusterla N, Johnson E, Chae JS, Pusterla JB, Derock E, Lawler SP.
(2000).
Transmission of Ehrlichia risticii, the agent of Potomac horse fever, using naturally infected aquatic insects and helminth vectors: preliminary report.
Equine Vet J, 32(4), 275-279.
https://doi.org/10.2746/042516400777032219 Publication
Researcher Affiliations
- Department of Medicine and Epidemiology, School of Veterinary Medicine, University of California, Davis 95616, USA.
MeSH Terms
- Animals
- Cell Line
- Disease Vectors
- Ehrlichia / genetics
- Ehrlichiosis / transmission
- Ehrlichiosis / veterinary
- Female
- Horse Diseases / etiology
- Horse Diseases / microbiology
- Horses
- Insect Vectors
- Insecta / microbiology
- Macrophages / microbiology
- Male
- Mice
- RNA, Bacterial / chemistry
- RNA, Ribosomal, 16S / chemistry
- Snails / parasitology
- Trematoda / microbiology
Citations
This article has been cited 14 times.- 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.
- 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.
- Willette JA, Kopper JJ, Kogan CJ, Seguin MA, Schott HC. Effect of season and geographic location in the United States on detection of potential enteric pathogens or toxin genes in horses ≥6-mo-old. J Vet Diagn Invest 2022 May;34(3):407-411.
- 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.
- 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).
- Xiong Q, Bekebrede H, Sharma P, Arroyo LG, Baird JD, Rikihisa Y. An Ecotype of Neorickettsia risticii Causing Potomac Horse Fever in Canada. Appl Environ Microbiol 2016 Oct 1;82(19):6030-6.
- Durán MC, Marqués FJ. Detection of Neorickettsia risticii, the agent of Potomac horse fever, in a Gypsy Vanner stallion from Manitoba. Can Vet J 2016 Mar;57(3):293-5.
- Kang YJ, Diao XN, Zhao GY, Chen MH, Xiong Y, Shi M, Fu WM, Guo YJ, Pan B, Chen XP, Holmes EC, Gillespie JJ, Dumler SJ, Zhang YZ. Extensive diversity of Rickettsiales bacteria in two species of ticks from China and the evolution of the Rickettsiales. BMC Evol Biol 2014 Jul 30;14:167.
- Baird JD, Arroyo LG. Historical aspects of Potomac horse fever in Ontario (1924-2010). Can Vet J 2013 Jun;54(6):565-72.
- Heller MC, McClure J, Pusterla N, Pusterla JB, Stahel S. Two cases of Neorickettsia (Ehrlichia) risticii infection in horses from Nova Scotia. Can Vet J 2004 May;45(5):421-3.
- Mott J, Muramatsu Y, Seaton E, Martin C, Reed S, Rikihisa Y. Molecular analysis of Neorickettsia risticii in adult aquatic insects in Pennsylvania, in horses infected by ingestion of insects, and isolated in cell culture. J Clin Microbiol 2002 Feb;40(2):690-3.
- Haywood LMB, Sheahan BJ. A Review of Epithelial Ion Transporters and Their Roles in Equine Infectious Colitis. Vet Sci 2024 Oct 7;11(10).
- Rinaldi G, Paz Meseguer C, Cantacessi C, Cortés A. Form and Function in the Digenea, with an Emphasis on Host-Parasite and Parasite-Bacteria Interactions. Adv Exp Med Biol 2024;1454:3-45.
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