West Nile virus encephalomyelitis in horses in Ontario: 28 cases.

Abstract: West Nile virus encephalomyelitis was diagnosed in 28 horses presented to the Ontario Veterinary College Veterinary Teaching Hospital between August 20 and October 15, 2002. The age range of affected horses was 5 months to 20 years (mean 6.9 years, median 6 years). Clinical signs were highly variable. Duration of hospitalization ranged from < 1 to 12 days (mean 5 days, median 5.4 days). Overall, 16 of the 28 (57%) horses were discharged and, of the 14 from which follow-up information was available, 13 (93%) were reported to be clinically normal 4 to 6 weeks following discharge, while the other horse had markedly improved. This pathogen is emerging as an important cause of neurological disease in Canada.
Publication Date: 2003-07-04 PubMed ID: 12839240PubMed Central: PMC340169
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  • Journal Article


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The research article discusses a study conducted on 28 horses in Ontario who were diagnosed with West Nile virus encephalomyelitis between August and October 2002. The study highlights the varying clinical signs, duration of hospitalization, and recovery rates, emphasizing that the West Nile virus is becoming a significant cause of neurological disease in Canada.

Study Overview

  • The research conducted at the Ontario Veterinary College Veterinary Teaching Hospital looked into 28 cases of horses suffering from West Nile virus encephalomyelitis.
  • The age of the diagnosed horses ranged from 5 months to 20 years, with an average age of 6.9 years and a median age of 6 years.
  • The study occurred between August 20 and October 15, 2002.

Clinical Symptoms and Hospitalization

  • A range of varying clinical signs were observed in the horses afflicted by the disease.
  • The length of hospital stays varied considerably, with durations anywhere from less than one day to 12 days.
  • The average hospital stay was 5 days, with a median stay of 5.4 days.

Recovery and Follow-up

  • From the total 28 cases, 16 horses (57%) were discharged from the hospital.
  • For 14 of these discharged horses, follow-up data was available. 13 of these 14 (93%) recovered to a point of exhibiting normal clinical behavior within a time frame of 4 to 6 weeks post discharge.
  • One horse, while not returning to normal, showed substantial improvement.

Significance of the Study

  • The study indicates that the West Nile virus is emerging as an increasingly important cause of neurological disease in Canadian horse populations.
  • This calls for increased vigilance, understanding, and prevention measures against the West Nile virus within veterinary practices.

Cite This Article

Weese JS, Baird JD, DeLay J, Kenney DG, Staempfli HR, Viel L, Parent J, Smith-Maxie L, Poma R. (2003). West Nile virus encephalomyelitis in horses in Ontario: 28 cases. Can Vet J, 44(6), 469-473.


ISSN: 0008-5286
NlmUniqueID: 0004653
Country: Canada
Language: English
Volume: 44
Issue: 6
Pages: 469-473

Researcher Affiliations

Weese, J Scott
  • Department of Clinical Studies, Ontario Veterinary College, Guelph, Ontario N1G 2W1. jsweese@uoguelph.ca
Baird, John D
    DeLay, Josepha
      Kenney, Daniel G
        Staempfli, Henry R
          Viel, Laurent
            Parent, Joane
              Smith-Maxie, Laura
                Poma, Roberto

                  MeSH Terms

                  • Animals
                  • Diagnosis, Differential
                  • Disease Outbreaks / veterinary
                  • Encephalomyelitis / diagnosis
                  • Encephalomyelitis / epidemiology
                  • Encephalomyelitis / veterinary
                  • Female
                  • Horse Diseases / diagnosis
                  • Horse Diseases / epidemiology
                  • Horse Diseases / virology
                  • Horses
                  • Male
                  • Ontario / epidemiology
                  • West Nile Fever / diagnosis
                  • West Nile Fever / epidemiology
                  • West Nile Fever / veterinary
                  • West Nile virus / pathogenicity


                  This article includes 29 references
                  1. Ostlund EN, Andresen JE, Andresen M. West Nile encephalitis.. Vet Clin North Am Equine Pract 2000 Dec;16(3):427-41.
                    pubmed: 11219341doi: 10.1016/s0749-0739(17)30087-1google scholar: lookup
                  2. Smithburn KC, Hughes TP, Burke AW. A neurotropic virus isolated from blood of a native in Uganda. Am J Trop Med 1940; 20:471.
                  3. Le Guenno B, Bougermouh A, Azzam T, Bouakaz R. West Nile: a deadly virus?. Lancet 1996 Nov 9;348(9037):1315.
                    pubmed: 8909403doi: 10.1016/s0140-6736(05)65799-6google scholar: lookup
                  4. Hubu00e1lek Z, Savage HM, Halouzka J, Juricovu00e1 Z, Sanogo YO, Lusk S. West Nile virus investigations in South Moravia, Czechland.. Viral Immunol 2000;13(4):427-33.
                    pubmed: 11192289doi: 10.1089/vim.2000.13.427google scholar: lookup
                  5. Lvov DK, Butenko AM, Gromashevsky VL, Larichev VP, Gaidamovich SY, Vyshemirsky OI, Zhukov AN, Lazorenko VV, Salko VN, Kovtunov AI, Galimzyanov KM, Platonov AE, Morozova TN, Khutoretskaya NV, Shishkina EO, Skvortsova TM. Isolation of two strains of West Nile virus during an outbreak in southern Russia, 1999.. Emerg Infect Dis 2000 Jul-Aug;6(4):373-6.
                    pmc: PMC2640908pubmed: 10905970doi: 10.3201/eid0604.000408google scholar: lookup
                  6. Weinberger M, Pitlik SD, Gandacu D, Lang R, Nassar F, Ben David D, Rubinstein E, Izthaki A, Mishal J, Kitzes R, Siegman-Igra Y, Giladi M, Pick N, Mendelson E, Bin H, Shohat T. West Nile fever outbreak, Israel, 2000: epidemiologic aspects.. Emerg Infect Dis 2001 Jul-Aug;7(4):686-91.
                    pmc: PMC2631774pubmed: 11585533doi: 10.3201/eid0704.010416google scholar: lookup
                  7. Tsai TF, Popovici F, Cernescu C, Campbell GL, Nedelcu NI. West Nile encephalitis epidemic in southeastern Romania.. Lancet 1998 Sep 5;352(9130):767-71.
                    pubmed: 9737281doi: 10.1016/s0140-6736(98)03538-7google scholar: lookup
                  8. Weiss D, Carr D, Kellachan J, Tan C, Phillips M, Bresnitz E, Layton M. Clinical findings of West Nile virus infection in hospitalized patients, New York and New Jersey, 2000.. Emerg Infect Dis 2001 Jul-Aug;7(4):654-8.
                    pmc: PMC2631758pubmed: 11589170doi: 10.3201/eid0704.010409google scholar: lookup
                  9. Durand B, Chevalier V, Pouillot R, Labie J, Marendat I, Murgue B, Zeller H, Zientara S. West Nile virus outbreak in horses, southern France, 2000: results of a serosurvey.. Emerg Infect Dis 2002 Aug;8(8):777-82.
                    pmc: PMC2732513pubmed: 12141961doi: 10.3201/eid0808.010486google scholar: lookup
                  10. Komar N, Langevin S, Hinten S, Nemeth N, Edwards E, Hettler D, Davis B, Bowen R, Bunning M. Experimental infection of North American birds with the New York 1999 strain of West Nile virus.. Emerg Infect Dis 2003 Mar;9(3):311-22.
                    pmc: PMC2958552pubmed: 12643825doi: 10.3201/eid0903.020628google scholar: lookup
                  11. Murgue B, Murri S, Zientara S, Durand B, Durand JP, Zeller H. West Nile outbreak in horses in southern France, 2000: the return after 35 years.. Emerg Infect Dis 2001 Jul-Aug;7(4):692-6.
                    pmc: PMC2631744pubmed: 11585534doi: 10.3201/eid0704.010417google scholar: lookup
                  12. Nasci RS, Savage HM, White DJ, Miller JR, Cropp BC, Godsey MS, Kerst AJ, Bennett P, Gottfried K, Lanciotti RS. West Nile virus in overwintering Culex mosquitoes, New York City, 2000.. Emerg Infect Dis 2001 Jul-Aug;7(4):742-4.
                    pmc: PMC2631767pubmed: 11585542doi: 10.3201/eid0704.010426google scholar: lookup
                  13. Kulasekera VL, Kramer L, Nasci RS, Mostashari F, Cherry B, Trock SC, Glaser C, Miller JR. West Nile virus infection in mosquitoes, birds, horses, and humans, Staten Island, New York, 2000.. Emerg Infect Dis 2001 Jul-Aug;7(4):722-5.
                    pmc: PMC2631749pubmed: 11589172doi: 10.3201/eid0704.010421google scholar: lookup
                  14. Malkinson M, Banet C, Weisman Y, Pokamunski S, King R, Drouet MT, Deubel V. Introduction of West Nile virus in the Middle East by migrating white storks.. Emerg Infect Dis 2002 Apr;8(4):392-7.
                    pmc: PMC2730252pubmed: 11971773doi: 10.3201/eid0804.010217google scholar: lookup
                  15. Cantile C, Di Guardo G, Eleni C, Arispici M. Clinical and neuropathological features of West Nile virus equine encephalomyelitis in Italy.. Equine Vet J 2000 Jan;32(1):31-5.
                    pubmed: 10661382doi: 10.2746/042516400777612080google scholar: lookup
                  16. Tber A. West Nile fever in horses in Morocco. Bull Off Int Epizoot 1996;11:867u2013869.
                  18. Anderson JF, Andreadis TG, Vossbrinck CR, Tirrell S, Wakem EM, French RA, Garmendia AE, Van Kruiningen HJ. Isolation of West Nile virus from mosquitoes, crows, and a Cooper's hawk in Connecticut.. Science 1999 Dec 17;286(5448):2331-3.
                    pubmed: 10600741doi: 10.1126/science.286.5448.2331google scholar: lookup
                  19. Lanciotti RS, Roehrig JT, Deubel V, Smith J, Parker M, Steele K, Crise B, Volpe KE, Crabtree MB, Scherret JH, Hall RA, MacKenzie JS, Cropp CB, Panigrahy B, Ostlund E, Schmitt B, Malkinson M, Banet C, Weissman J, Komar N, Savage HM, Stone W, McNamara T, Gubler DJ. Origin of the West Nile virus responsible for an outbreak of encephalitis in the northeastern United States.. Science 1999 Dec 17;286(5448):2333-7.
                    pubmed: 10600742doi: 10.1126/science.286.5448.2333google scholar: lookup
                  20. Trock SC, Meade BJ, Glaser AL, Ostlund EN, Lanciotti RS, Cropp BC, Kulasekera V, Kramer LD, Komar N. West Nile virus outbreak among horses in New York State, 1999 and 2000.. Emerg Infect Dis 2001 Jul-Aug;7(4):745-7.
                    pmc: PMC2631776pubmed: 11585543doi: 10.3201/eid0704.010427google scholar: lookup
                  21. Ostlund EN, Crom RL, Pedersen DD, Johnson DJ, Williams WO, Schmitt BJ. Equine West Nile encephalitis, United States.. Emerg Infect Dis 2001 Jul-Aug;7(4):665-9.
                    pmc: PMC2631754pubmed: 11589171doi: 10.3201/eid0704.010412google scholar: lookup
                  22. Anonymous. West Nile virus: Historical summary. 2002; http://www.cfe/cornell.edu/erap/WNV/Summary.cfm#year
                  23. Anonymous. Update on the current status of West Nile Virus. 2002; http://www.aphis.usda.gov/oa/wnv/wnvstats.html
                  24. Centers for Disease Control and Prevention. 2002; http://www.cdc.gov/od/media/wnvcount/html
                  25. Anonymous. West Nile virus confirmed Windsor area. 2001; http://www.wechealthunit.org/pages/hottopics/westnileresult.html
                  26. Health Canada. West Nile virus: Canada. 2002; http://www.hc-sc.gc.ca/pphb-dgspsp/wnv-vwn/pdf_sr-rs/2002/situation_report/110102_db.pdf
                  27. Snook CS, Hyman SS, Del Piero F, Palmer JE, Ostlund EN, Barr BS, Desrochers AM, Reilly LK. West Nile virus encephalomyelitis in eight horses.. J Am Vet Med Assoc 2001 May 15;218(10):1576-9.
                    pubmed: 11393367doi: 10.2460/javma.2001.218.1576google scholar: lookup
                  28. Steinman A, Banet C, Sutton GA, Yadin H, Hadar S, Brill A. Clinical signs of West Nile virus encephalomyelitis in horses during the outbreak in Israel in 2000.. Vet Rec 2002 Jul 13;151(2):47-9.
                    pubmed: 12148602doi: 10.1136/vr.151.2.47google scholar: lookup
                  29. Bunning ML, Bowen RA, Cropp CB, Sullivan KG, Davis BS, Komar N, Godsey MS, Baker D, Hettler DL, Holmes DA, Biggerstaff BJ, Mitchell CJ. Experimental infection of horses with West Nile virus.. Emerg Infect Dis 2002 Apr;8(4):380-6.
                    pmc: PMC3393377pubmed: 11971771doi: 10.3201/eid0804.010239google scholar: lookup


                  This article has been cited 10 times.
                  1. Fehu00e9r OE, Fehu00e9rvu00e1ri P, Tolnai CH, Forgu00e1ch P, Malik P, Jerzsele u00c1, Wagenhoffer Z, Szenci O, Korbacska-Kutasi O. Epidemiology and Clinical Manifestation of West Nile Virus Infections of Equines in Hungary, 2007-2020.. Viruses 2022 Nov 18;14(11).
                    doi: 10.3390/v14112551pubmed: 36423160google scholar: lookup
                  2. Cavalleri JV, Korbacska-Kutasi O, Leblond A, Paillot R, Pusterla N, Steinmann E, Tomlinson J. European College of Equine Internal Medicine consensus statement on equine flaviviridae infections in Europe.. J Vet Intern Med 2022 Nov;36(6):1858-1871.
                    doi: 10.1111/jvim.16581pubmed: 36367340google scholar: lookup
                  3. More S, Bicout D, Bu00f8tner A, Butterworth A, Calistri P, De Koeijer A, Depner K, Edwards S, Garin-Bastuji B, Good M, Gortazar Schmidt C, Michel V, Miranda MA, Nielsen SS, Raj M, Sihvonen L, Spoolder H, Thulke HH, Velarde A, Willeberg P, Winckler C, Bau A, Beltran-Beck B, Carnesecchi E, Casier P, Czwienczek E, Dhollander S, Georgiadis M, Gogin A, Pasinato L, Richardson J, Riolo F, Rossi G, Watts M, Lima E, Stegeman JA. Vector-borne diseases.. EFSA J 2017 May;15(5):e04793.
                    doi: 10.2903/j.efsa.2017.4793pubmed: 32625493google scholar: lookup
                  4. Paru00e9 J, Moore A. West Nile virus in horses - What do you need to know to diagnose the disease?. Can Vet J 2018 Oct;59(10):1119-1120.
                    pubmed: 30510321
                  5. Humblet MF, Vandeputte S, Fecher-Bourgeois F, Lu00e9onard P, Gosset C, Balenghien T, Durand B, Saegerman C. Estimating the economic impact of a possible equine and human epidemic of West Nile virus infection in Belgium.. Euro Surveill 2016 Aug 4;21(31).
                  6. Chaintoutis SC, Diakakis N, Papanastassopoulou M, Banos G, Dovas CI. Evaluation of Cross-Protection of a Lineage 1 West Nile Virus Inactivated Vaccine against Natural Infections from a Virulent Lineage 2 Strain in Horses, under Field Conditions.. Clin Vaccine Immunol 2015 Sep;22(9):1040-9.
                    doi: 10.1128/CVI.00302-15pubmed: 26178384google scholar: lookup
                  7. Marka A, Diamantidis A, Papa A, Valiakos G, Chaintoutis SC, Doukas D, Tserkezou P, Giannakopoulos A, Papaspyropoulos K, Patsoula E, Badieritakis E, Baka A, Tseroni M, Pervanidou D, Papadopoulos NT, Koliopoulos G, Tontis D, Dovas CI, Billinis C, Tsakris A, Kremastinou J, Hadjichristodoulou C, Vakalis N, Vassalou E, Zarzani S, Zounos A, Komata K, Balatsos G, Beleri S, Mpimpa A, Papavasilopoulos V, Rodis I, Spanakos G, Tegos N, Spyrou V, Dalabiras Z, Birtsas P, Athanasiou L, Papanastassopoulou M, Ioannou C, Athanasiou C, Gerofotis C, Papadopoulou E, Testa T, Tsakalidou O, Rachiotis G, Bitsolas N, Mamouris Z, Moutou K, Sarafidou T, Stamatis K, Sarri K, Tsiodras S, Georgakopoulou T, Detsis M, Mavrouli M, Stavropoulou A, Politi L, Mageira G, Christopoulou V, Diamantopoulou G, Spanakis N, Vrioni G, Piperaki ET, Mitsopoulou K, Kioulos I, Michaelakis A, Stathis I, Tselentis I, Psaroulaki A, Keramarou M, Chochlakis D, Photis Y, Konstantinou M, Manetos P, Tsobanoglou S, Mourelatos S, Antalis V, Pergantas P, Eleftheriou G. West Nile virus state of the art report of MALWEST Project.. Int J Environ Res Public Health 2013 Dec 2;10(12):6534-610.
                    doi: 10.3390/ijerph10126534pubmed: 24317379google scholar: lookup
                  8. Cargnelutti JF, Brum MC, Weiblen R, Flores EF. Stable expression and potential use of west nile virus envelope glycoproteins preM/E as antigen in diagnostic tests.. Braz J Microbiol 2011 Jul;42(3):1161-6.
                  9. Epp T, Waldner C, West K, Townsend H. Factors associated with West Nile virus disease fatalities in horses.. Can Vet J 2007 Nov;48(11):1137-45.
                    pubmed: 18050794
                  10. Epp T, Waldner C, Leighton FA, Berke O, Townsend HG. Seroprevalence and risk factors for infection with West Nile virus in Saskatchewan horses, 2003.. Can J Vet Res 2007 Oct;71(4):256-63.
                    pubmed: 17955899