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Volume 17, Number 8–August 2011
Fatal Neurologic Disease and Abortion in Mare Infected with Lineage 1 West Nile Virus, South Africa
Marietjie Venter, Comments to Author Stacey Human, Stephanie van Niekerk, June Williams, Charmaine van Eeden, and Frank Freeman
Author affiliations: University of Pretoria, Pretoria, South Africa (M. Venter, S. Human, C. van Eeden, S. van Niekerk, J. Williams); National Institute for Communicable Diseases, Sandringham, Johannesburg, South Africa (M. Venter); and Ceres Veterinary Hospital, Western Cape, South Africa (F. Freeman)
Suggested citation for this article
In 2010, lineage 1 West Nile virus was detected in South Africa in the brain of a pregnant mare that succumbed to neurologic disease and in her aborted fetus, suggesting an association with abortion in horses. All West Nile virus strains previously detected in horses and humans in South Africa were lineage 2.
West Nile virus (WNV), a mosquito-borne flavivirus, may cause outbreaks of febrile disease and encephalitis in humans and horses. Although <1% of human patients experience severe disease (1), up to 90% of symptomatic cases in horses result in neurologic disease with case-fatality rates of 30%–40% (2). In sheep, WNV infection may result in abortion, stillbirth, and neonatal death (3). In humans, transmission by transplacental route and breastfeeding has been described. Congenital WNV infection has been accompanied by bilateral chorioretinitis and severe malformation of the fetal central nervous system (4). We report a case of WNV with fatal neurologic disease and abortion in a horse.
Five genetic lineages of WNV exist, the major 2 being lineages 1 and 2 (5,6). Lineage 1 is distributed widely in North and South America, Europe, parts of Asia, North Africa, and Australia. Lineage 2 strains have been identified in humans and horses with febrile and neurologic disease in southern Africa and Madagascar (7) and recently emerged in central Europe causing encephalitis in birds, humans, and horses (7,8). WNV has become recognized as an important horse pathogen in South Africa with all cases positive by nucleic acid detection or virus isolation belonging to lineage 2 (6,7).
Bird deaths due to WNV are rare in South Africa, probably because of the long-term endemic nature of the virus, which limits their use in sentinel surveillance (9). A positive correlation exists between occurrence of symptomatic equine and human cases, which suggests equine outbreaks might predict disease risk for humans (3).
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Suggested Citation for this Article
Venter M, Human S, van Niekerk S, Williams J, van Eeden C, Freeman F. Fatal neurologic disease and abortion in mare infected with lineage 1 West Nile virus, South Africa. Emerg Infect Dis [serial on the Internet]. 2011 Aug [date cited]. http://www.cdc.gov/EID/content/17/8/101794.htm
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Marietjie Venter, Respiratory and Zoonosis Programmes, Department of Medical Virology, Faculty of Health Sciences, PO Box 2034, Pretoria 0001, South Africa; email: firstname.lastname@example.org