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Pathology of fatal lineage 1 and 2 West Nile virus infections in horses in South Africa.
Abstract: Since 2007, West Nile virus (WNV) has been reported in South African horses, causing severe neurological signs. All cases were of lineage 2, except for one case that clustered with lineage 1 viruses. In the present study, gross and microscopic lesions of six South African lineage 2-infected horses and the one lineage 1 case are described. Diagnoses were confirmed by real-time reverse-transcriptase polymerase chain reaction (RT-PCR) of central nervous system (CNS) tissue and one by RT-PCR of a brain virus isolate. The CNS of all cases was negative by RT-PCR or immunohistochemistry (IHC) for African horse sickness (AHS), equine encephalosis virus, equine herpes viruses 1 and 4, other zoonotic flaviviruses, alphaviruses, and shunivirus, and either by immunofluorescence or IHC for rabies. Gross visceral lesions were nonspecific but often mimicked those of AHS. The CNS histopathology of WNV lineage 2 cases resembled the nonsuppurative polioencephalomyelitis reported in the Northern Hemisphere lineage 1 and recent Hungarian lineage 2 cases. Occasional meningitis, focal spinal ventral horn poliomalacia, dorsal and lateral horn poliomyelitis, leucomyelitis, asymmetrical ventral motor spinal neuritis and frequent olfactory region involvement were also seen. Lineage 2 cases displayed marked variations in CNS lesion severity, type and distribution, and suggested various viral entry routes into the CNS, based on findings in experimental mice and hamsters. Lineage 1 lesions were comparable to the milder lineage 2 cases. West Nile virus IHC on CNS sections with marked lesions from all cases elicited only two antigen-positive cells in the olfactory cortex of one case. The presence in the CNS of T-lymphocytes, B-lymphocytes, plasma cells and macrophage-monocytes was confirmed by cluster of differentiation (CD) 3, CD20, multiple myeloma oncogene 1 (MUM1) and macrophage (MAC) 387 IHC.
Publication Date: 2014-09-01 PubMed ID: 25686260DOI: 10.4102/jsava.v85i1.1105Google Scholar: Lookup 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.
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Summary
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This study examines the impact and symptoms of two strains of West Nile virus (WNV) in horses in South Africa, with significant focus on how the disease appears and affects the central nervous system (CNS) of the animal.
Overview of the Study
- The research focuses on the pathological effects of West Nile virus lineage 1 and lineage 2 in horses, a subject which has gained importance since the virus was reported in South African horses in 2007.
- These cases show severe neurological signs and the researchers aimed to describe the physical and microscopic characteristics of the diseases in several horses.
- The diagnosis of WNV was confirmed by real-time reverse-transcriptase polymerase chain reaction (RT-PCR) testing of CNS tissue in the horses.
Pathologies Observed
- The research describes significant variation in the types, severity, and distribution of lesions in the CNS across the infected horses. These variations could indicate possible multiple routes of viral entry into the CNS.
- The gross physical lesions observed were non-specific, often resembling those caused by African Horse Sickness (AHS).
- Lineage 2-infected horses showed similar histopathology to the polioencephalomyelitis observed in Northern Hemisphere lineage 1 and recent Hungarian lineage 2 cases.
- Lineage 1 lesions were comparable to the milder lineage 2 cases.
Immunity Response and Presence of Virus in CNS
- The central nervous systems of all studied horses were tested and found to be negative for various other pathogens, ensuring that the observed effects were due to WNV.
- Immunohistochemistry (IHC) on sections of the CNS with notable lesions was performed and resulted in finding only two antigen-positive cells in the olfactory cortex of one case.
- The presence of different types of immune cells – T-lymphocytes, B-lymphocytes, plasma cells, and macrophage-monocytes – was also confirmed in the CNS, implying an active immune response to the infection.
Cite This Article
APA
Williams JH, van Niekerk S, Human S, van Wilpe E, Venter M.
(2014).
Pathology of fatal lineage 1 and 2 West Nile virus infections in horses in South Africa.
J S Afr Vet Assoc, 85(1), 1105.
https://doi.org/10.4102/jsava.v85i1.1105 Publication
Researcher Affiliations
- Department of Paraclinical Sciences, University of Pretoria, South Africa; Department of Medical Virology, University of Pretoria, South Africa. june.williams@up.ac.za.
MeSH Terms
- Animals
- Fatal Outcome
- Female
- Horse Diseases / pathology
- Horse Diseases / virology
- Horses
- Male
- Reverse Transcriptase Polymerase Chain Reaction / veterinary
- West Nile Fever / epidemiology
- West Nile Fever / veterinary
- West Nile Fever / virology
- West Nile virus / classification
Citations
This article has been cited 9 times.- Moir M, Sitharam N, Hofstra LM, Dor G, Mwanyika G, Ramphal Y, Reichmuth ML, San JE, Gifford R, Wilkinson E, Tshiabuila D, Preiser W, Konou AA, Bitew M, Onoja AB, Paganotti GM, Abera A, Maror JA, Kayiwa J, Abuelmaali S, Lusamaki EK, Venter M, Burt F, Baxter C, Lessells R, de Oliveira T, Tegally H. Identifying genomic surveillance gaps in Africa for the global public health response to West Nile virus: a systematic review. Lancet Microbe 2025 Oct;6(10):101176.
- Naveed A, Eertink LG, Wang D, Li F. Lessons Learned from West Nile Virus Infection:Vaccinations in Equines and Their Implications for One Health Approaches. Viruses 2024 May 14;16(5).
- Hungwe FTT, Laycock KM, Ntereke TD, Mabaka R, Paganotti GM. A historical perspective on arboviruses of public health interest in Southern Africa. Pathog Glob Health 2024 Mar;118(2):131-159.
- Schwarz ER, Long MT. Comparison of West Nile Virus Disease in Humans and Horses: Exploiting Similarities for Enhancing Syndromic Surveillance. Viruses 2023 May 24;15(6).
- Agliani G, Giglia G, Marshall EM, Gröne A, Rockx BHG, van den Brand JMA. Pathological features of West Nile and Usutu virus natural infections in wild and domestic animals and in humans: A comparative review. One Health 2023 Jun;16:100525.
- Woodburn DB, Steyl J, Du Plessis EC, Last RD, Reininghaus B, Mitchell EP. Pathological findings in African buffaloes (Syncerus caffer) in South Africa. J S Afr Vet Assoc 2021 Aug 17;92(0):e1-e11.
- Bertram FM, Thompson PN, Venter M. Epidemiology and Clinical Presentation of West Nile Virus Infection in Horses in South Africa, 2016-2017. Pathogens 2020 Dec 30;10(1).
- Mentoor JL, Lubisi AB, Gerdes T, Human S, Williams JH, Venter M. Full-Genome Sequence of a Neuroinvasive West Nile Virus Lineage 2 Strain from a Fatal Horse Infection in South Africa. Genome Announc 2016 Jul 28;4(4).
- van Niekerk S, Human S, Williams J, van Wilpe E, Pretorius M, Swanepoel R, Venter M. Sindbis and Middelburg Old World Alphaviruses Associated with Neurologic Disease in Horses, South Africa. Emerg Infect Dis 2015 Dec;21(12):2225-9.
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