Emerging infectious diseases2009; 15(6); 877-884; doi: 10.3201/eid1506.081515

Lineage 2 west nile virus as cause of fatal neurologic disease in horses, South Africa.

Abstract: Serologic evidence suggests that West Nile virus (WNV) is widely distributed in horses in southern Africa. However, because few neurologic cases have been reported, endemic lineage 2 strains were postulated to be nonpathogenic in horses. Recent evidence suggests that highly neuroinvasive lineage 2 strains exist in humans and mice. To determine whether neurologic cases are being missed in South Africa, we tested 80 serum or brain specimens from horses with unexplained fever (n = 48) and/or neurologic signs (n = 32) for WNV. From March 2007 through June 2008, using reverse transcription-PCR (RT-PCR) and immunoglobulin (Ig) M ELISA, we found WNV RNA or IgM in 7/32 horses with acute neurologic disease; 5 horses died or were euthanized. In 5/7 horses, no other pathogen was detected. DNA sequencing for all 5 RT-PCR-positive cases showed the virus belonged to lineage 2. WNV lineage 2 may cause neurologic disease in horses in South Africa.
Publication Date: 2009-06-16 PubMed ID: 19523285PubMed Central: PMC2727306DOI: 10.3201/eid1506.081515Google Scholar: Lookup
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  • Journal Article
  • Research Support
  • Non-U.S. Gov't

Summary

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This research discusses the study carried out in South Africa to test the hypothesis that a lineage 2 strain of West Nile Virus (WNV) could be responsible for fatal neurologic diseases in horses. The study uncovered that such strains could indeed pose neurologic threats to horses, challenging previous beliefs that these strains were nonpathogenic to horses.

Introduction and Background

  • The study originates from the serological evidence (based on or involving the examination of blood serum) indicating the widespread distribution of West Nile Virus (WNV) in horses across southern Africa.
  • Linking neurologic cases amongst horses to WNV was previously limited as endemic lineage 2 strains were assumed to be nonpathogenic (not causing disease) in horses.
  • However, recent studies have pointed towards highly neuroinvasive lineage 2 strains having severe effects on humans and mice.

Methodology and Results

  • To explore whether South Africa was missing neurologic cases in horses caused by WNV, researchers conducted tests including reverse transcription-PCR (RT-PCR) and Immunoglobulin (Ig) M ELISA on 80 serum or brain specimens from horses showing unexplained fevers and/or neurologic symptoms.
  • Of the 32 horses with acute neurologic disease, WNV RNA or IgM was found in seven horses; five of these horses either passed away or were euthanized.
  • In five out of seven horses, no other pathogens were detected, hinting that WNV could be the sole cause of their symptoms.

Conclusion and Implication

  • DNA sequencing of the five RT-PCR-positive cases revealed the presence of lineage 2 WNV strains, directly countering the previously held conjecture that they were non-pathogenic for horses.
  • This research advocates that the lineage 2 strain of the West Nile Virus may be causing neurologic diseases that lead to fatality in horses in South Africa.

Cite This Article

APA
Venter M, Human S, Zaayman D, Gerdes GH, Williams J, Steyl J, Leman PA, Paweska JT, Setzkorn H, Rous G, Murray S, Parker R, Donnellan C, Swanepoel R. (2009). Lineage 2 west nile virus as cause of fatal neurologic disease in horses, South Africa. Emerg Infect Dis, 15(6), 877-884. https://doi.org/10.3201/eid1506.081515

Publication

ISSN: 1080-6059
NlmUniqueID: 9508155
Country: United States
Language: English
Volume: 15
Issue: 6
Pages: 877-884

Researcher Affiliations

Venter, Marietjie
  • University of Pretoria, Pretoria, South Africa. marietjie.venter@up.ac.za
Human, Stacey
    Zaayman, Dewald
      Gerdes, Gertruida H
        Williams, June
          Steyl, Johan
            Leman, Patricia A
              Paweska, Janusz Tadeusz
                Setzkorn, Hildegard
                  Rous, Gavin
                    Murray, Sue
                      Parker, Rissa
                        Donnellan, Cynthia
                          Swanepoel, Robert

                            MeSH Terms

                            • Animals
                            • Antibodies, Viral / blood
                            • Brain / virology
                            • Disease Outbreaks
                            • Horse Diseases / epidemiology
                            • Horse Diseases / mortality
                            • Horse Diseases / virology
                            • Horses
                            • Immunoglobulin M / blood
                            • Phylogeny
                            • RNA, Viral / blood
                            • Reverse Transcriptase Polymerase Chain Reaction
                            • Sequence Analysis, DNA
                            • South Africa / epidemiology
                            • West Nile Fever / epidemiology
                            • West Nile Fever / mortality
                            • West Nile Fever / veterinary
                            • West Nile Fever / virology
                            • West Nile virus / classification
                            • West Nile virus / genetics
                            • West Nile virus / immunology
                            • West Nile virus / pathogenicity

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