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

• Published in: Emerging infectious diseases Vol. 15; no. 6; pp. 877 - 884
• Main Authors: Venter, Marietjie, 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
• Format: Journal Article
• Language: English
• Published: United States U.S. National Center for Infectious Diseases 01.06.2009; Centers for Disease Control and Prevention
• Subjects: Africa; Animals; Antibodies, Viral - blood; Brain - virology; Control; Disease Outbreaks; Distribution; Drug therapy; encephalitis; Enzyme-linked immunosorbent assay; Health aspects; Horse Diseases - epidemiology; Horse Diseases - mortality; Horse Diseases - virology; Horses; Immunoglobulin M - blood; Nervous system diseases; Phylogeny; Reverse Transcriptase Polymerase Chain Reaction; Risk factors; RNA, Viral - blood; Sequence Analysis, DNA; South Africa - epidemiology; viruses; West Nile Fever - epidemiology; West Nile Fever - mortality; West Nile Fever - veterinary; West Nile Fever - virology; West Nile Virus; West Nile virus - classification; West Nile virus - genetics; West Nile virus - immunology; West Nile virus - pathogenicity; Zoonoses; South Africa
• ISSN: 1080-6040; 1080-6059
• DOI: 10.3201/eid1506.081515

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.