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Disease features in horses with induced equine monocytic ehrlichiosis (Potomac horse fever).
Abstract: Fifty-five horses were inoculated IV and/or SC with materials containing Ehrlichia risticii, ie, infected whole blood, buffy coat cells, or cell culture, to study clinical and hematologic features of equine monocytic ehrlichiosis (Potomac horse fever). Major clinical and hematologic features of induced E risticii infection were biphasic increase in rectal temperature with peak increases of 38.9 C and 39.3 C on postinoculation days (PID) 5 and 12, respectively; depression; anorexia; decreased WBC count (maximal decrease of 47% on PID 12); and diarrhea from PID 14 to PID 18. Increased WBC count was an inconsistent feature, with a maximal increase of 51.5% on PID 20. During times of decreased and increased WBC counts, lymphocyte/neutrophil ratios remained fairly constant. However, not all horses had all clinical and hematologic features, and these features were present in different degrees among horses. Increased rectal temperature, depression, anorexia, and decreased WBC count were more consistent features, whereas diarrhea developed in 73% of the horses. Of 55 horses, 39 (71%) had all clinical and hematologic features of the disease (classic disease), whereas 16 (29%) horses did not have greater than or equal to 1 of these features (nonclassic disease). The E risticii titer in the blood (ehrlichemia) was maximum during the peak increase in rectal temperature. In 55 horses, mortality was 9%. Significant differences (P greater than 0.5) in clinical and hematologic features were not detected between horses that survived and those that died of E risticii infection.
Publication Date: 1988-10-01 PubMed ID: 3189992 The Equine Research Bank provides access to a large database of publicly available scientific literature. Inclusion in the Research Bank does not imply endorsement of study methods or findings by Mad Barn.
- Journal Article
- Research Support
- Non-U.S. Gov't
Summary
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The researchers conducted a study on 55 horses that were intentionally infected with Ehrlichia risticii to investigate the physical and blood-related effects of equine monocytic ehrlichiosis, also known as Potomac horse fever. The major findings included two phases of increased body temperature, loss of appetite, decrease in white blood cell count, depression, and diarrhea, though the exact symptoms and severity varied between horses. Out of these, 71% exhibited the full set of symptoms while the remainder showed a subset. Despite this, there were no significant differences in symptoms between horses that survived and those that didn’t.
Research Methodology
- The research was carried out on 55 horses.
- The horses were inoculated either intravenously (IV) or subcutaneously (SC) with Ehrlichia risticii, explaining that it was present in infected whole blood, buffy coat cells or cell culture.
Clinical and Hematologic Features
- The induced infection resulted in a biphasic increase in rectal temperature with peak increases of 38.9 C and 39.3 C on post-inoculation days (PID) 5 and 12, respectively.
- Other symptomatology included depression, appetite loss or anorexia, a decreased white blood cell (WBC) count (the most significant drop, 47%, occurring on PID 12) and diarrhea, which manifested from PID 14 to PID 18.
- Increased WBC count was found to be inconsistent, with the highest recorded increase being 51.5% on PID 20.
- Through periods of decreased and increased WBC counts, the ratios of lymphocytes to neutrophils remained more or less constant.
Variability in Disease Presentation
- Not all horses showed the same clinical and hematologic features, and these varied in degrees among different horses.
- Increased rectal temperature, depression, anorexia, and a decrease in WBC count were more consistent features across all the horses, while 73% developed diarrhea.
- Out of the 55 horses, 39 (71%) showed all clinical and hematologic features (termed as classic disease), while 16 (29%) did not demonstrate one or more of these features (labelled as nonclassic disease).
- The Ehrlichia risticii titer in the blood (ehrlichemia) was found to be at its highest during the peak increase in rectal temperature.
Survival and Mortality Rates
- The mortality rate was found to be 9% among the 55 horses.
- No significant differences were found in clinical and hematologic features between the horses that survived and those that succumbed to E risticii infection.
Cite This Article
APA
Dutta SK, Penney BE, Myrup AC, Robl MG, Rice RM.
(1988).
Disease features in horses with induced equine monocytic ehrlichiosis (Potomac horse fever).
Am J Vet Res, 49(10), 1747-1751.
Publication
Researcher Affiliations
- College of Veterinary Medicine, University of Maryland, College Park 20742.
MeSH Terms
- Animals
- Anorexia / veterinary
- Body Temperature
- Diarrhea / veterinary
- Ehrlichia / growth & development
- Female
- Fever / veterinary
- Horse Diseases / blood
- Horse Diseases / mortality
- Horses
- Leukocyte Count / veterinary
- Male
- Rickettsiaceae Infections / blood
- Rickettsiaceae Infections / mortality
- Rickettsiaceae Infections / veterinary
Citations
This article has been cited 16 times.- 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.
- 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.
- Lin M, Bachman K, Cheng Z, Daugherty SC, Nagaraj S, Sengamalay N, Ott S, Godinez A, Tallon LJ, Sadzewicz L, Fraser C, Dunning Hotopp JC, Rikihisa Y. Analysis of complete genome sequence and major surface antigens of Neorickettsia helminthoeca, causative agent of salmon poisoning disease. Microb Biotechnol 2017 Jul;10(4):933-957.
- Baird JD, Arroyo LG. Historical aspects of Potomac horse fever in Ontario (1924-2010). Can Vet J 2013 Jun;54(6):565-72.
- Gibson K, Kumagai Y, Rikihisa Y. Proteomic analysis of Neorickettsia sennetsu surface-exposed proteins and porin activity of the major surface protein P51. J Bacteriol 2010 Nov;192(22):5898-905.
- 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.
- Dutta SK, Vemulapalli R, Biswas B. 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 1998 Feb;36(2):506-12.
- Vemulapalli R, Biswas B, Dutta SK. Pathogenic, immunologic, and molecular differences between two Ehrlichia risticii strains. J Clin Microbiol 1995 Nov;33(11):2987-93.
- Biswas B, Vemulapalli R, Dutta SK. Detection of Ehrlichia risticii from feces of infected horses by immunomagnetic separation and PCR. J Clin Microbiol 1994 Sep;32(9):2147-51.
- Dutta SK, Mattingly BL, Shankarappa B. Antibody response to Ehrlichia risticii and antibody reactivity to the component antigens in horses with induced Potomac horse fever. Infect Immun 1989 Oct;57(10):2959-62.
- Thaker SR, Dutta SK, Adhya SL, Mattingly-Napier BL. Molecular cloning of Ehrlichia risticii and development of a gene probe for the diagnosis of Potomac horse fever. J Clin Microbiol 1990 Sep;28(9):1963-7.
- Kaylor PS, Crawford TB, McElwain TF, Palmer GH. Passive transfer of antibody to Ehrlichia risticii protects mice from ehrlichiosis. Infect Immun 1991 Jun;59(6):2058-62.
- Dutta SK, Shankarappa B, Mattingly-Napier BL. Molecular cloning and analysis of recombinant major antigens of Ehrlichia risticii. Infect Immun 1991 Mar;59(3):1162-9.
- Biswas B, Mukherjee D, Mattingly-Napier BL, Dutta SK. Diagnostic application of polymerase chain reaction for detection of Ehrlichia risticii in equine monocytic ehrlichiosis (Potomac horse fever). J Clin Microbiol 1991 Oct;29(10):2228-33.
- Shankarappa B, Dutta SK, Mattingly-Napier B. Identification of the protective 44-kilodalton recombinant antigen of Ehrlichia risticii. Infect Immun 1992 Feb;60(2):612-7.
- Messick JB, Rikihisa Y. Presence of parasite antigen on the surface of P388D1 cells infected with Ehrlichia risticii. Infect Immun 1992 Aug;60(8):3079-86.
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