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Equine Encephalosis Virus. Animals (Basel) 2022; 12:ani12030337. [PMID: 35158658 PMCID: PMC8833465 DOI: 10.3390/ani12030337] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/10/2022] [Revised: 01/24/2022] [Accepted: 01/26/2022] [Indexed: 11/17/2022] Open
Abstract
Simple Summary Equine encephalosis (EE) is a febrile disease of horses caused by EE virus (EEV) and transmitted by Culicoides midges. This virus was first isolated from a horse in South Africa in 1967 and until 2008 was believed to be restricted to southern Africa. In 2008–2009, isolation of EEV in an outbreak reported from Israel demonstrated the emergence of this pathogen into new niches. Indeed, further testing revealed that EEV had already spread outside of South Africa since 2001. Although EEV normally does not cause severe clinical disease, it should be considered important since it may indicate the possible spread of other related, much more pathogenic viruses, such as African horse sickness virus (AHSV). The spread of EEV from South Africa to central Africa, the Middle East, and India is an example of the possible emergence of new pathogens in new niches and should be a reminder not to limit the differential diagnoses list when facing a possible outbreak or a cluster of undiagnosed clinical cases. This review summarizes current knowledge regarding EEV structure, pathogenesis, clinical significance, and epidemiology. Abstract Equine encephalosis (EE) is an arthropod-borne, noncontagious, febrile disease of horses. It is caused by EE virus (EEV), an Orbivirus of the Reoviridae family transmitted by Culicoides. Within the EEV serogroup, seven serotypes (EEV-1–7) have been identified to date. This virus was first isolated from a horse in South Africa in 1967 and until 2008 was believed to be restricted to southern Africa. In 2008–2009, isolation of EEV in an outbreak reported from Israel demonstrated the emergence of this pathogen into new niches. Indeed, testing in retrospect sera samples revealed that EEV had already been circulating outside of South Africa since 2001. Although EEV normally does not cause severe clinical disease, it should be considered important since it may indicate the possible spread of other related, much more pathogenic viruses, such as African horse sickness virus (AHSV). The spread of EEV from South Africa to central Africa, the Middle East and India is an example of the possible emergence of new pathogens in new niches, as was seen in the case of West Nile virus, and should be a reminder not to limit the differential list when facing a possible outbreak or a cluster of clinical cases. This review summarizes current knowledge regarding EEV structure, pathogenesis, clinical significance, and epidemiology.
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Bunpapong N, Charoenkul K, Nasamran C, Chamsai E, Udom K, Boonyapisitsopa S, Tantilertcharoen R, Kesdangsakonwut S, Techakriengkrai N, Suradhat S, Thanawongnuwech R, Amonsin A. African Horse Sickness Virus Serotype 1 on Horse Farm, Thailand, 2020. Emerg Infect Dis 2021; 27:2208-2211. [PMID: 34287126 PMCID: PMC8314833 DOI: 10.3201/eid2708.210004] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
To investigate an outbreak of African horse sickness (AHS) on a horse farm in northeastern Thailand, we used whole-genome sequencing to detect and characterize the virus. The viruses belonged to serotype 1 and contained unique amino acids (95V,166S, 660I in virus capsid protein 2), suggesting a single virus introduction to Thailand.
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Calvo-Pinilla E, Marín-López A, Utrilla-Trigo S, Jiménez-Cabello L, Ortego J. Reverse genetics approaches: a novel strategy for African horse sickness virus vaccine design. Curr Opin Virol 2020; 44:49-56. [PMID: 32659516 PMCID: PMC7351391 DOI: 10.1016/j.coviro.2020.06.003] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/22/2020] [Revised: 06/05/2020] [Accepted: 06/10/2020] [Indexed: 01/26/2023]
Abstract
African horse sickness (AHS) is a devastating disease caused by African horse sickness virus (AHSV) and transmitted by arthropods between its equine hosts. AHSV is endemic in sub-Saharan Africa, where polyvalent live attenuated vaccine is in use even though it is associated with safety risks. This review article summarizes and compares new strategies to generate safe and effective AHSV vaccines based on protein, virus like particles, viral vectors and reverse genetics technology. Manipulating the AHSV genome to generate synthetic viruses by means of reverse genetic systems has led to the generation of potential safe vaccine candidates that are under investigation.
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Affiliation(s)
- Eva Calvo-Pinilla
- Centro de Investigación en Sanidad Animal (CISA), Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), Valdeolmos, Madrid, Spain
| | - Alejandro Marín-López
- Section of Infectious Diseases, Department of Internal Medicine, Yale University School of Medicine, New Haven, CT, USA
| | - Sergio Utrilla-Trigo
- Centro de Investigación en Sanidad Animal (CISA), Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), Valdeolmos, Madrid, Spain
| | - Luís Jiménez-Cabello
- Centro de Investigación en Sanidad Animal (CISA), Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), Valdeolmos, Madrid, Spain
| | - Javier Ortego
- Centro de Investigación en Sanidad Animal (CISA), Instituto Nacional de Investigación y Tecnología Agraria y Alimentaria (INIA), Valdeolmos, Madrid, Spain.
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Dennis SJ, Meyers AE, Hitzeroth II, Rybicki EP. African Horse Sickness: A Review of Current Understanding and Vaccine Development. Viruses 2019; 11:E844. [PMID: 31514299 PMCID: PMC6783979 DOI: 10.3390/v11090844] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2019] [Revised: 08/30/2019] [Accepted: 09/04/2019] [Indexed: 01/05/2023] Open
Abstract
African horse sickness is a devastating disease that causes great suffering and many fatalities amongst horses in sub-Saharan Africa. It is caused by nine different serotypes of the orbivirus African horse sickness virus (AHSV) and it is spread by Culicoid midges. The disease has significant economic consequences for the equine industry both in southern Africa and increasingly further afield as the geographic distribution of the midge vector broadens with global warming and climate change. Live attenuated vaccines (LAV) have been used with relative success for many decades but carry the risk of reversion to virulence and/or genetic re-assortment between outbreak and vaccine strains. Furthermore, the vaccines lack DIVA capacity, the ability to distinguish between vaccine-induced immunity and that induced by natural infection. These concerns have motivated interest in the development of new, more favourable recombinant vaccines that utilize viral vectors or are based on reverse genetics or virus-like particle technologies. This review summarizes the current understanding of AHSV structure and the viral replication cycle and also evaluates existing and potential vaccine strategies that may be applied to prevent or control the disease.
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Affiliation(s)
- Susan J Dennis
- Biopharming Research Unit, Department of Molecular and Cell Biology, University of Cape Town, Rondebosch 7701, Cape Town, South Africa.
| | - Ann E Meyers
- Biopharming Research Unit, Department of Molecular and Cell Biology, University of Cape Town, Rondebosch 7701, Cape Town, South Africa.
| | - Inga I Hitzeroth
- Biopharming Research Unit, Department of Molecular and Cell Biology, University of Cape Town, Rondebosch 7701, Cape Town, South Africa.
| | - Edward P Rybicki
- Biopharming Research Unit, Department of Molecular and Cell Biology, University of Cape Town, Rondebosch 7701, Cape Town, South Africa.
- Institute of Infectious Disease and Molecular Medicine, Faculty of Health Sciences, University of Cape Town, Observatory 7925, Cape Town, South Africa.
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Evidence of Intragenic Recombination in African Horse Sickness Virus. Viruses 2019; 11:v11070654. [PMID: 31323749 PMCID: PMC6669442 DOI: 10.3390/v11070654] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2019] [Revised: 05/06/2019] [Accepted: 05/07/2019] [Indexed: 12/24/2022] Open
Abstract
Intragenic recombination has been described in various RNA viruses as a mechanism to increase genetic diversity, resulting in increased virulence, expanded host range, or adaptability to a changing environment. Orbiviruses are no exception to this, with intragenic recombination previously detected in the type species, bluetongue virus (BTV). African horse sickness virus (AHSV) is a double-stranded RNA virus belonging to the Oribivirus genus in the family Reoviridae. Genetic recombination through reassortment has been described in AHSV, but not through homologous intragenic recombination. The influence of the latter on the evolution of AHSV was investigated by analyzing the complete genomes of more than 100 viruses to identify evidence of recombination. Segment-1, segment-6, segment-7, and segment-10 showed evidence of intragenic recombination, yet only one (Segment-10) of these events was manifested in subsequent lineages. The other three hybrid segments were as a result of recombination between field isolates and the vaccine derived live attenuated viruses (ALVs).
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Quantitative RT-PCR assays for identification and typing of the Equine encephalosis virus. Braz J Microbiol 2019; 50:287-296. [PMID: 30637652 DOI: 10.1007/s42770-018-0034-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/06/2018] [Accepted: 09/17/2018] [Indexed: 10/27/2022] Open
Abstract
Equine encephalosis (EE) is an acute, arthropod-borne, noncontagious, febrile disease of equids. The clinical signs of EE are similar to milder forms of African horse sickness (AHS) and the two diseases can be easily confused. The Equine encephalosis virus (EEV) is a distinct virus species within the genus Orbivirus, family Reoviridae, with ten linear segments of dsRNA genome. Seven distinct serotypes of EEV have been recognised on the basis of sequence analyses of Seg-2. The need for differential diagnosis of similar forms of EE and AHS warranted the development of molecular diagnostic methods for specific detection and identification of EEV. We report the development of quantitative real-time RT-PCR assay for detection of any member of the EEV species targeting the highly conserved EEV Seg-9. Similar serotype-specific qRT-PCR assays were designed for each of the seven EEV serotypes targeting genome Seg-2, encoding the serotype determining VP2 protein. These assays were evaluated using different EEV serotypes and other closely related orbiviruses. They were shown to be EEV virus species-specific, or EEV type-specific capable of detecting 1 to 13 copies of viral RNA in clinical samples. The assays failed to detect RNA from closely related orbiviruses, including AHSV and Peruvian horse sickness virus (PHSV) isolates.
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Grewar JD, Weyer CT, Venter GJ, van Helden LS, Burger P, Guthrie AJ, Coetzee P, Labuschagne K, Bührmann G, Parker BJ, Thompson PN. A field investigation of an African horse sickness outbreak in the controlled area of South Africa in 2016. Transbound Emerg Dis 2018; 66:743-751. [PMID: 30449073 DOI: 10.1111/tbed.13077] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2018] [Revised: 07/01/2018] [Accepted: 11/08/2018] [Indexed: 11/30/2022]
Abstract
An outbreak of African horse sickness (AHS) caused by AHS virus type 1 occurred within the South African AHS surveillance zone during April and May 2016. The index case was detected by a private veterinarian through passive surveillance. There were 21 cases in total, which is relatively low compared to case totals during prior AHS outbreaks in the same region (and of the same AHS virus type) in 2004, 2011 and 2014. The affected proportion of horses on affected properties was 0.07 (95% CI 0.04, 0.11). Weather conditions were conducive to high midge activity immediately prior to the outbreak but midge numbers decreased rapidly with the advent of winter. The outbreak was localized, with 18 of the 21 cases occurring within 8 km of the index property and the three remaining cases on two properties within 21 km of the index property, with direction of spread consistent with wind-borne dispersion of infected midges. Control measures included implementation of a containment zone with movement restrictions on equids. The outbreak was attributed to a reversion to virulence of a live attenuated vaccine used extensively in South Africa. Outbreaks in the AHS control zones have a major detrimental impact on the direct export of horses from South Africa, notably to the European Union.
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Affiliation(s)
- John Duncan Grewar
- Epidemiology Section, Department of Production Animal Studies, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa.,Equine Health Fund, Wits Health Consortium, Parktown, South Africa
| | - Camilla Theresa Weyer
- Equine Research Centre, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa
| | - Gert Johannes Venter
- Epidemiology, Parasites and Vectors, Agricultural Research Council- Onderstepoort Veterinary Research, Onderstepoort, South Africa
| | | | - Phillippa Burger
- Equine Health Fund, Wits Health Consortium, Parktown, South Africa
| | - Alan John Guthrie
- Equine Research Centre, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa
| | - Peter Coetzee
- Equine Research Centre, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa
| | - Karien Labuschagne
- Epidemiology, Parasites and Vectors, Agricultural Research Council- Onderstepoort Veterinary Research, Onderstepoort, South Africa
| | - Gary Bührmann
- Western Cape Veterinary Services, Elsenburg, South Africa
| | | | - Peter Neil Thompson
- Epidemiology Section, Department of Production Animal Studies, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa
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van Rijn PA, Maris-Veldhuis MA, Boonstra J, van Gennip RGP. Diagnostic DIVA tests accompanying the Disabled Infectious Single Animal (DISA) vaccine platform for African horse sickness. Vaccine 2018; 36:3584-3592. [PMID: 29759377 DOI: 10.1016/j.vaccine.2018.05.044] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/19/2018] [Revised: 05/03/2018] [Accepted: 05/07/2018] [Indexed: 01/09/2023]
Abstract
African Horse Sickness Virus (AHSV) (Orbivirus genus, Reoviridae family) causes high mortality in naïve domestic horses with enormous economic and socio-emotional impact. There are nine AHSV serotypes showing limited cross neutralization. AHSV is transmitted by competent species of Culicoides biting midges. AHS is a serious threat beyond the African continent as endemic Culicoides species in moderate climates transmit the closely related prototype bluetongue virus. There is a desperate need for safe and efficacious vaccines, while DIVA (Differentiating Infected from Vaccinated) vaccines would accelerate control of AHS. Previously, we have shown that highly virulent AHSV with an in-frame deletion of 77 amino acids (aa) in NS3/NS3a is completely safe, does not cause viremia and shows protective capacity. This deletion mutant is a promising DISA (Disabled Infectious Single Animal) vaccine platform, since exchange of serotype specific virus proteins has been shown for all nine serotypes. Here, we show that a prototype NS3 competitive ELISA is DIVA compliant to AHS DISA vaccine platforms. Epitope mapping of NS3/NS3a shows that more research is needed to evaluate this prototype serological DIVA assay regarding sensitivity and specificity, in particular for AHSVs expressing antigenically different NS3/NS3a proteins. Further, an experimental panAHSV PCR test targeting genome segment 10 is developed that detects reference AHSV strains, whereas AHS DISA vaccine platforms were not detected. This DIVA PCR test completely guarantees genetic DIVA based on in silico and in vitro validation, although test validation regarding diagnostic sensitivity and specificity has not been performed yet. In conclusion, the prototype NS3 cELISA and the PCR test described here enable serological and genetic DIVA accompanying AHS DISA vaccine platforms.
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Affiliation(s)
- Piet A van Rijn
- Department of Virology, Wageningen Bioveterinary Research (WBVR), Lelystad, The Netherlands; Department of Biochemistry, Centre for Human Metabolomics, North-West University, Potchefstroom, South Africa.
| | - Mieke A Maris-Veldhuis
- Department of Virology, Wageningen Bioveterinary Research (WBVR), Lelystad, The Netherlands
| | - Jan Boonstra
- Department of Virology, Wageningen Bioveterinary Research (WBVR), Lelystad, The Netherlands
| | - René G P van Gennip
- Department of Virology, Wageningen Bioveterinary Research (WBVR), Lelystad, The Netherlands
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Weyer CT, Grewar JD, Burger P, Rossouw E, Lourens C, Joone C, le Grange M, Coetzee P, Venter E, Martin DP, MacLachlan NJ, Guthrie AJ. African Horse Sickness Caused by Genome Reassortment and Reversion to Virulence of Live, Attenuated Vaccine Viruses, South Africa, 2004-2014. Emerg Infect Dis 2016; 22:2087-2096. [PMID: 27442883 PMCID: PMC5189153 DOI: 10.3201/eid2212.160718] [Citation(s) in RCA: 51] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
Epidemiologic and phylogenetic analyses show repeated outbreaks derived from
vaccine viruses. African horse sickness (AHS) is a hemorrhagic viral fever of horses. It is the
only equine disease for which the World Organization for Animal Health has
introduced specific guidelines for member countries seeking official recognition
of disease-free status. Since 1997, South Africa has maintained an AHS
controlled area; however, sporadic outbreaks of AHS have occurred in this area.
We compared the whole genome sequences of 39 AHS viruses (AHSVs) from field AHS
cases to determine the source of 3 such outbreaks. Our analysis confirmed that
individual outbreaks were caused by virulent revertants of AHSV type 1 live,
attenuated vaccine (LAV) and reassortants with genome segments derived from AHSV
types 1, 3, and 4 from a LAV used in South Africa. These findings show that
despite effective protection of vaccinated horses, polyvalent LAV may,
paradoxically, place susceptible horses at risk for AHS.
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Pullinger GD, Guimerà Busquets M, Nomikou K, Boyce M, Attoui H, Mertens PP. Identification of the Genome Segments of Bluetongue Virus Serotype 26 (Isolate KUW2010/02) that Restrict Replication in a Culicoides sonorensis Cell Line (KC Cells). PLoS One 2016; 11:e0149709. [PMID: 26890863 PMCID: PMC4758653 DOI: 10.1371/journal.pone.0149709] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2015] [Accepted: 02/04/2016] [Indexed: 11/18/2022] Open
Abstract
Bluetongue virus (BTV) can infect most ruminant species and is usually transmitted by adult, vector-competent biting midges (Culicoides spp.). Infection with BTV can cause severe clinical signs and can be fatal, particularly in naïve sheep and some deer species. Although 24 distinct BTV serotypes were recognized for several decades, additional 'types' have recently been identified, including BTV-25 (from Switzerland), BTV-26 (from Kuwait) and BTV-27 from France (Corsica). Although BTV-25 has failed to grow in either insect or mammalian cell cultures, BTV-26 (isolate KUW2010/02), which can be transmitted horizontally between goats in the absence of vector insects, does not replicate in a Culicoides sonorensis cell line (KC cells) but can be propagated in mammalian cells (BSR cells). The BTV genome consists of ten segments of linear dsRNA. Mono-reassortant viruses were generated by reverse-genetics, each one containing a single BTV-26 genome segment in a BTV-1 genetic-background. However, attempts to recover a mono-reassortant containing genome-segment 2 (Seg-2) of BTV-26 (encoding VP2), were unsuccessful but a triple-reassortant was successfully generated containing Seg-2, Seg-6 and Seg-7 (encoding VP5 and VP7 respectively) of BTV-26. Reassortants were recovered and most replicated well in mammalian cells (BSR cells). However, mono-reassortants containing Seg-1 or Seg-3 of BTV-26 (encoding VP1, or VP3 respectively) and the triple reassortant failed to replicate, while a mono-reassortant containing Seg-7 of BTV-26 only replicated slowly in KC cells.
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Affiliation(s)
- Gillian D. Pullinger
- Vector-borne Viral Diseases Programme, The Pirbright Institute, Pirbright, Woking, Surrey, United Kingdom, GU24 0NF
- * E-mail: ;
| | - Marc Guimerà Busquets
- Vector-borne Viral Diseases Programme, The Pirbright Institute, Pirbright, Woking, Surrey, United Kingdom, GU24 0NF
| | - Kyriaki Nomikou
- Vector-borne Viral Diseases Programme, The Pirbright Institute, Pirbright, Woking, Surrey, United Kingdom, GU24 0NF
| | - Mark Boyce
- Vector-borne Viral Diseases Programme, The Pirbright Institute, Pirbright, Woking, Surrey, United Kingdom, GU24 0NF
| | - Houssam Attoui
- Vector-borne Viral Diseases Programme, The Pirbright Institute, Pirbright, Woking, Surrey, United Kingdom, GU24 0NF
| | - Peter P. Mertens
- Vector-borne Viral Diseases Programme, The Pirbright Institute, Pirbright, Woking, Surrey, United Kingdom, GU24 0NF
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Weyer CT, Joone C, Lourens CW, Monyai MS, Koekemoer O, Grewar JD, van Schalkwyk A, Majiwa PO, MacLachlan NJ, Guthrie AJ. Development of three triplex real-time reverse transcription PCR assays for the qualitative molecular typing of the nine serotypes of African horse sickness virus. J Virol Methods 2015; 223:69-74. [DOI: 10.1016/j.jviromet.2015.07.015] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/26/2014] [Revised: 07/14/2015] [Accepted: 07/27/2015] [Indexed: 11/25/2022]
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Grewar JD, Thompson PN, Lourens CW, Guthrie AJ. Equine encephalosis in Thoroughbred foals on a South African stud farm. ACTA ACUST UNITED AC 2015; 82:966. [PMID: 26842364 PMCID: PMC6238798 DOI: 10.4102/ojvr.v82i1.966] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2015] [Revised: 08/11/2015] [Accepted: 08/18/2015] [Indexed: 11/01/2022]
Abstract
Thoroughbred foal body temperature data were collected from shortly after birth until shortly after weaning during the 2007/2008 season on a stud farm in the Western Cape Province of South Africa. Equine encephalosis (EE) caused by EE virus (EEV) serotype 4 (EEV-4) occurred in the foal group during the first autumn after their birth (March and April 2008). A descriptive study was undertaken to provide data on the EEV maternal antibody status, the association between pyrexia and EEV infection, and the incidence of infection amongst the foals prior to and during the episode. This included the frequent capturing of foal body temperature data and regular collection of serum and whole blood during pyretic episodes. Infection by EEV was determined using both virological and serological methods. A high EE incidence of at least 94% occurred amongst the foal cohort, despite the fact that 37% of foals had previously shown maternal antibody to EEV-4. Pyrexia in foals was not directly associated with EE infection and 41% of infected foals showed no detectable pyretic episode. Information obtained from this EE episode showed the high incidence of EEV infection in foals during the first autumn after their birth. Monitoring foal body temperature can alert farmers to outbreaks of infectious disease, such as EE. These results are relevant to the epidemiology of EE and facilitate greater understanding of it as a differential diagnosis of African horse sickness (AHS), given that EE and AHS have similar epidemiologic profiles.
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Affiliation(s)
- John D Grewar
- Western Cape Department of Agriculture: Veterinary Services, Elsenburg, South Africa; Department of Production Animal Studies, University of Pretoria, South Africa.
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Aharonson-Raz K, Steinman A, Kavkovsky A, Bumbarov V, Berlin D, Lichter-Peled A, Berke O, Klement E. Analysis of the Association of Climate, Weather and Herd Immunity with the Spread of Equine Encephalosis Virus in Horses in Israel. Transbound Emerg Dis 2015; 64:593-602. [DOI: 10.1111/tbed.12424] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2015] [Indexed: 11/28/2022]
Affiliation(s)
- K. Aharonson-Raz
- Koret School of Veterinary Medicine; The Robert H. Smith Faculty of Agriculture, Food and Environment; The Hebrew University of Jerusalem; Rehovot Israel
| | - A. Steinman
- Koret School of Veterinary Medicine; The Robert H. Smith Faculty of Agriculture, Food and Environment; The Hebrew University of Jerusalem; Rehovot Israel
| | - A. Kavkovsky
- Koret School of Veterinary Medicine; The Robert H. Smith Faculty of Agriculture, Food and Environment; The Hebrew University of Jerusalem; Rehovot Israel
| | - V. Bumbarov
- Department of Virology; Kimron Veterinary Institute; Bet Dagan Israel
| | - D. Berlin
- Koret School of Veterinary Medicine; The Robert H. Smith Faculty of Agriculture, Food and Environment; The Hebrew University of Jerusalem; Rehovot Israel
| | - A. Lichter-Peled
- Koret School of Veterinary Medicine; The Robert H. Smith Faculty of Agriculture, Food and Environment; The Hebrew University of Jerusalem; Rehovot Israel
| | - O. Berke
- Department of Population Medicine; Ontario Veterinary College; University of Guelph; Guelph Ontario Canada
| | - E. Klement
- Koret School of Veterinary Medicine; The Robert H. Smith Faculty of Agriculture, Food and Environment; The Hebrew University of Jerusalem; Rehovot Israel
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Dhama K, Pawaiya R, Karthik K, Chakrabort S, Tiwari R, Verma A. Equine encephalosis virus (EEV): A Review. ACTA ACUST UNITED AC 2014. [DOI: 10.3923/ajava.2014.123.133] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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Grewar JD, Weyer CT, Guthrie AJ, Koen P, Davey S, Quan M, Visser D, Russouw E, Bührmann G. The 2011 outbreak of African horse sickness in the African horse sickness controlled area in South Africa. J S Afr Vet Assoc 2013. [DOI: 10.4102/jsava.v84i1.973] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
African horse sickness (AHS) is a controlled animal disease in South Africa, and as a result of the high mortality rates experienced, outbreaks in the AHS controlled area in the Western Cape Province have a significant impact on affected properties as well as on the exportation of live horses from the AHS free zone in metropolitan Cape Town. An outbreak of AHS serotype 1 occurred in the surveillance zone of the AHS controlled area of the Western Cape during the summer of 2011. The epicentre of the outbreak was the town of Mamre in the magisterial district of Malmesbury and the outbreak was confined to a defined containment zone within this area by movement control of all equids and a blanket vaccination campaign. A total of 73 cases of AHS were confirmed during this outbreak, which included four confirmed subclinical cases. The morbidity rate for the outbreak was 16%with a mortality rate of 14%and a case fatality rate of 88%. Outbreak disease surveillance relied on agent identification using polymerase chain reaction (PCR)-based assays, which is novel for an AHS outbreak in South Africa. The source of this outbreak was never confirmed although it is believed to be associated with the illegal movement of an infected animal into the Mamre area. This detailed description of the outbreak provides a sound scientific basis to assist decision making in future AHS outbreaks in the AHS controlled area of South Africa and in countries where AHS is an exotic or emerging disease.
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Rathogwa NM, Quan M, Smit JQ, Lourens C, Guthrie AJ, van Vuuren M. Development of a real time polymerase chain reaction assay for equine encephalosis virus. J Virol Methods 2013; 195:205-10. [PMID: 24161811 DOI: 10.1016/j.jviromet.2013.10.018] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2013] [Revised: 10/06/2013] [Accepted: 10/08/2013] [Indexed: 11/24/2022]
Abstract
Equine encephalosis virus (EEV) is the cause of equine encephalosis. The disease is similar to mild forms of African horse sickness (AHS) and the two diseases are easily confused. Laboratory identification and serotyping of EEV is based on viral isolation in BHK-21 cells and a viral plaque inhibition neutralisation test. These procedures are time-consuming and therefore a more rapid diagnostic assay for EEV that can distinguish EEV from African horse sickness virus (AHSV) infections was developed. The S7 (VP7) gene from 38 EEV isolates representing all seven serotypes was amplified and sequenced. A conserved region at the 5' end of the gene was identified and used to design group-specific EEV primers and a TaqMan(®) MGB™ hydrolysis probe. The efficiency of the EEV real-time RT-PCR assay was 81%. The assay was specific, as it did not detect any of the nine serotypes of AHSV, nor 24 serotypes of bluetongue virus (BTV) and sensitive, with a 95% limit of detection of 10(2.9) TCID50/ml blood (95% confidence interval: 10(2.7) to 10(3.3)). The real-time format was selected because of its convenience, sensitivity and ability to produce results rapidly.
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Affiliation(s)
- N M Rathogwa
- Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, University of Pretoria, Private Bag X04, Onderstepoort 0110, South Africa.
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Urban forests as hubs for novel zoonosis: blood meal analysis, seasonal variation in Culicoides (Diptera: Ceratopogonidae) vectors, and avian haemosporidians. Parasitology 2013; 140:1799-810. [PMID: 23981661 DOI: 10.1017/s0031182013001285] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
Abstract
Culicoides vectors can transmit a diverse array of parasites and are globally distributed. We studied feeding preferences and seasonal variation of Culicoides (Diptera: Ceratopogonidae) vectors in an urban forest of Germany to determine whether humans living nearby are readily exposed to vector-borne parasites from wild animals. We used a fragment of the mtDNA COI gene to identify hosts from blood meals. We amplified a fragment of the mtDNA cyt b to detect haemosporidian infections in Culicoides abdomens and thoraxes. We detected a total of 22 Culicoides species. Fifty-eight blood meals (84%) were from humans, 10 from birds, and one from livestock. We found Culicoides kibunensis (considered ornithophilic) with 29 human blood meals. Host generalist Culicoides festivipennis and Culicoides obsoletus had 14 human blood meals. Culicoides clastrieri and Culicoides semimaculatus fed on birds; previously humans were their only known host. Six thoraxes and three abdomens were infected with either Haemoproteus pallidulus or Haemoproteus parabelopolskyi. There were changes in Culicoides community structure across months. Culicoides pictipennis was the dominant species during spring, C. kibunensis and C. clastrieri were dominant during summer, and C. obsoletus was dominant by early autumn. All dominant species were generalists feeding on birds, livestock and humans. Our results indicate that humans can serve as a blood source for dominant Culicoides species instead of the normal wild animal hosts in urban areas.
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18
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Guthrie AJ, MacLachlan NJ, Joone C, Lourens CW, Weyer CT, Quan M, Monyai MS, Gardner IA. Diagnostic accuracy of a duplex real-time reverse transcription quantitative PCR assay for detection of African horse sickness virus. J Virol Methods 2013; 189:30-5. [DOI: 10.1016/j.jviromet.2012.12.014] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2012] [Accepted: 12/10/2012] [Indexed: 10/27/2022]
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19
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Weyer CT, Quan M, Joone C, Lourens CW, MacLachlan NJ, Guthrie AJ. African horse sickness in naturally infected, immunised horses. Equine Vet J 2012; 45:117-9. [PMID: 22612775 DOI: 10.1111/j.2042-3306.2012.00590.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
To determine whether subclinical cases, together with clinical cases, of African horse sickness (AHS) occur in immunised horses in field conditions, whole blood samples were collected and rectal temperatures recorded weekly from 50 Nooitgedacht ponies resident in open camps at the Faculty of Veterinary Science, University of Pretoria, Onderstepoort, during 2008-2010. The samples were tested for the presence of African horse sickness virus (AHSV) RNA by a recently developed real-time RT-PCR. It was shown that 16% of immunised horses in an AHS endemic area were infected with AHSV over a 2 year period, with half of these (8%) being subclinically infected. The potential impact of such cases on the epidemiology of AHS warrants further investigation.
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Affiliation(s)
- C T Weyer
- Equine Research Centre, Faculty of Veterinary Science, University of Pretoria, Onderstepoort, South Africa
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20
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Santiago-Alarcon D, Havelka P, Schaefer HM, Segelbacher G. Bloodmeal analysis reveals avian Plasmodium infections and broad host preferences of Culicoides (Diptera: Ceratopogonidae) vectors. PLoS One 2012; 7:e31098. [PMID: 22363557 PMCID: PMC3282704 DOI: 10.1371/journal.pone.0031098] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2011] [Accepted: 01/02/2012] [Indexed: 11/19/2022] Open
Abstract
Changing environmental conditions and human encroachment on natural habitats bring human populations closer to novel sources of parasites, which might then develop into new emerging diseases. Diseases transmitted by host generalist vectors are of special interest due to their capacity to move pathogens into novel hosts. We hypothesize that humans using forests for recreation are exposed to a broad range of parasites from wild animals and their vectors. A corollary of this is that new vector-host, parasite-host, and vector-parasite associations could eventually develop. Thus, we expect to observe atypical vector-host associations. Using molecular bloodmeal analysis via amplification of the mtDNA COI gene we identified the vertebrate hosts of Culicoides (Diptera: Ceratopogonidae) species in a sub-urban forest of Southwestern Germany. Bloodmeals were also checked for haemosporidian infections by amplifying a fragment of the mtDNA cyt b gene. We identified a total of 20 Culicoides species, thirteen of which fed on humans. From 105 screened bloodmeals we obtained high quality sequences for 77 samples, 73 (94.8%) originated from humans, two from livestock (Bos taurus and Equus caballus), and two from wild birds (Sylvia atricapilla and Turdus merula). We found that four Culicoides species previously assumed to feed exclusively on either birds (C. kibunensis) or domestic mammals (C. chiopterus, C. deltus, C. scoticus) fed also on humans. A total of six Culicoides abdomens were infected with avian haemosporidian parasites (Plasmodium or Haemoproteus), four of those abdomens contained blood derived from humans. Our results suggest that parasites of wild animals may be transferred to humans through infectious bites of Culicoides vectors. Further, we show that Culicoides vectors believed to be a specialist on specific vertebrate groups can have plastic feeding preferences, and that Culicoides are susceptible to infection by Plasmodium parasites, though vector viability must still be experimentally demonstrated.
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Affiliation(s)
- Diego Santiago-Alarcon
- Biología y Conservación de Vertebrados, Instituto de Ecología A.C., Xalapa, Veracruz, México.
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21
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Maan S, Maan NS, Nomikou K, Veronesi E, Bachanek-Bankowska K, Belaganahalli MN, Attoui H, Mertens PPC. Complete genome characterisation of a novel 26th bluetongue virus serotype from Kuwait. PLoS One 2011; 6:e26147. [PMID: 22031822 PMCID: PMC3198726 DOI: 10.1371/journal.pone.0026147] [Citation(s) in RCA: 140] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2011] [Accepted: 09/20/2011] [Indexed: 11/18/2022] Open
Abstract
Bluetongue virus is the "type" species of the genus Orbivirus, family Reoviridae. Twenty four distinct bluetongue virus (BTV) serotypes have been recognized for decades, any of which is thought to be capable of causing "bluetongue" (BT), an insect-borne disease of ruminants. However, two further BTV serotypes, BTV-25 (Toggenburg orbivirus, from Switzerland) and BTV-26 (from Kuwait) have recently been identified in goats and sheep, respectively. The BTV genome is composed of ten segments of linear dsRNA, encoding 7 virus-structural proteins (VP1 to VP7) and four distinct non-structural (NS) proteins (NS1 to NS4). We report the entire BTV-26 genome sequence (isolate KUW2010/02) and comparisons to other orbiviruses. Highest identity levels were consistently detected with other BTV strains, identifying KUW2010/02 as BTV. The outer-core protein and major BTV serogroup-specific antigen "VP7" showed 98% aa sequence identity with BTV-25, indicating a common ancestry. However, higher level of variation in the nucleotide sequence of Seg-7 (81.2% identity) suggests strong conservation pressures on the protein of these two strains, and that they diverged a long time ago. Comparisons of Seg-2, encoding major outer-capsid component and cell-attachment protein "VP2" identified KUW2010/02 as 26th BTV, within a 12th Seg-2 nucleotype [nucleotype L]. Comparisons of Seg-6, encoding the smaller outer capsid protein VP5, also showed levels of nt/aa variation consistent with identification of KUW2010/02 as BTV-26 (within a 9th Seg-6 nucleotype - nucleotype I). Sequence data for Seg-2 of KUW2010/02 were used to design four sets of oligonucleotide primers for use in BTV-26, type-specific RT-PCR assays. Analyses of other more conserved genome segments placed KUW2010/02 and BTV-25/SWI2008/01 closer to each other than to other "eastern" or "western" BTV strains, but as representatives of two novel and distinct geographic groups (topotypes). Our analyses indicate that all of the BTV genome segments have evolved under strong purifying selection.
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Affiliation(s)
- Sushila Maan
- Vector-Borne Diseases Programme, Institute for Animal Health, Pirbright, Woking Surrey, United Kingdom
| | - Narender S. Maan
- Vector-Borne Diseases Programme, Institute for Animal Health, Pirbright, Woking Surrey, United Kingdom
| | - Kyriaki Nomikou
- Vector-Borne Diseases Programme, Institute for Animal Health, Pirbright, Woking Surrey, United Kingdom
| | - Eva Veronesi
- Vector-Borne Diseases Programme, Institute for Animal Health, Pirbright, Woking Surrey, United Kingdom
| | | | | | - Houssam Attoui
- Vector-Borne Diseases Programme, Institute for Animal Health, Pirbright, Woking Surrey, United Kingdom
| | - Peter P. C. Mertens
- Vector-Borne Diseases Programme, Institute for Animal Health, Pirbright, Woking Surrey, United Kingdom
- * E-mail:
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22
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Quan M, Lourens CW, MacLachlan NJ, Gardner IA, Guthrie AJ. Development and optimisation of a duplex real-time reverse transcription quantitative PCR assay targeting the VP7 and NS2 genes of African horse sickness virus. J Virol Methods 2010; 167:45-52. [PMID: 20304015 DOI: 10.1016/j.jviromet.2010.03.009] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2009] [Revised: 03/01/2010] [Accepted: 03/08/2010] [Indexed: 10/19/2022]
Abstract
Nucleotide sequences of 52 South African isolates of African horse sickness virus (AHSV) collected during 2004-2005 and including viruses of all nine AHSV serotypes, were used to design and develop a duplex real-time reverse transcription quantitative PCR (RT-PCR) assay targeting the VP7 (S8) and NS2 (S9) genes of AHSV. The assay was optimized for detection of AHSV in fresh and frozen blood of naturally infected horses. Assay performance was enhanced using random hexamers rather than gene-specific primers for RT, and with denaturation of double-stranded RNA in the presence of random hexamers. The assay was efficient with a linear range of at least five orders of magnitude. The analytical sensitivity of the assay was 132 copies of the target genes (4125 copies per ml of blood), and the assay was at least 10-fold more sensitive than virus isolation on BHK-21 cells. The assay was also highly specific because it did not detect related orbiviruses, such as bluetongue and equine encephalosis viruses.
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Affiliation(s)
- M Quan
- Equine Research Centre, Faculty of Veterinary Science, University of Pretoria, Private Bag X04, Onderstepoort 0110, South Africa.
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23
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Maclachlan NJ, Guthrie AJ. Re-emergence of bluetongue, African horse sickness, and other orbivirus diseases. Vet Res 2010; 41:35. [PMID: 20167199 PMCID: PMC2826768 DOI: 10.1051/vetres/2010007] [Citation(s) in RCA: 167] [Impact Index Per Article: 11.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2009] [Accepted: 01/25/2010] [Indexed: 11/14/2022] Open
Abstract
Arthropod-transmitted viruses (Arboviruses) are important causes of disease in humans and animals, and it is proposed that climate change will increase the distribution and severity of arboviral diseases. Orbiviruses are the cause of important and apparently emerging arboviral diseases of livestock, including bluetongue virus (BTV), African horse sickness virus (AHSV), equine encephalosis virus (EEV), and epizootic hemorrhagic disease virus (EHDV) that are all transmitted by haematophagous Culicoides insects. Recent changes in the global distribution and nature of BTV infection have been especially dramatic, with spread of multiple serotypes of the virus throughout extensive portions of Europe and invasion of the south-eastern USA with previously exotic virus serotypes. Although climate change has been incriminated in the emergence of BTV infection of ungulates, the precise role of anthropogenic factors and the like is less certain. Similarly, although there have been somewhat less dramatic recent alterations in the distribution of EHDV, AHSV, and EEV, it is not yet clear what the future holds in terms of these diseases, nor of other potentially important but poorly characterized Orbiviruses such as Peruvian horse sickness virus.
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Affiliation(s)
- N James Maclachlan
- Department of Pathology, Microbiology and Immunology, University of California, Davis, CA 95616, USA.
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24
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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. Lineage 2 west nile virus as cause of fatal neurologic disease in horses, South Africa. Emerg Infect Dis 2009; 15:877-84. [PMID: 19523285 PMCID: PMC2727306 DOI: 10.3201/eid1506.081515] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
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.
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Guthrie AJ, Quan M, Lourens CW, Audonnet JC, Minke JM, Yao J, He L, Nordgren R, Gardner IA, Maclachlan NJ. Protective immunization of horses with a recombinant canarypox virus vectored vaccine co-expressing genes encoding the outer capsid proteins of African horse sickness virus. Vaccine 2009; 27:4434-8. [PMID: 19490959 DOI: 10.1016/j.vaccine.2009.05.044] [Citation(s) in RCA: 54] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2009] [Revised: 04/27/2009] [Accepted: 05/11/2009] [Indexed: 11/25/2022]
Abstract
We describe the development and preliminary characterization of a recombinant canarypox virus vectored (ALVAC) vaccine for protective immunization of equids against African horse sickness virus (AHSV) infection. Horses (n=8) immunized with either of two concentrations of recombinant canarypox virus vector (ALVAC-AHSV) co-expressing synthetic genes encoding the outer capsid proteins (VP2 and VP5) of AHSV serotype 4 (AHSV-4) developed variable titres (<10-80) of virus-specific neutralizing antibodies and were completely resistant to challenge infection with a virulent strain of AHSV-4. In contrast, a horse immunized with a commercial recombinant canarypox virus vectored vaccine expressing the haemagglutinin genes of two equine influenza H3N8 viruses was seronegative to AHSV and following infection with virulent AHSV-4 developed pyrexia, thrombocytopenia and marked oedema of the supraorbital fossae typical of the "dikkop" or cardiac form of African horse sickness. AHSV was detected by virus isolation and quantitative reverse transcriptase polymerase chain reaction in the blood of the control horse from 8 days onwards after challenge infection whereas AHSV was not detected at any time in the blood of the ALVAC-AHSV vaccinated horses. The control horse seroconverted to AHSV by 2 weeks after challenge infection as determined by both virus neutralization and ELISA assays, whereas six of eight of the ALVAC-AHSV vaccinated horses did not seroconvert by either assay following challenge infection with virulent AHSV-4. These data confirm that the ALVAC-AHSV vaccine will be useful for the protective immunization of equids against African horse sickness, and avoids many of the problems inherent to live-attenuated AHSV vaccines.
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Affiliation(s)
- Alan J Guthrie
- Equine Research Centre, University of Pretoria, Private Bag X04, Onderstepoort 0110, South Africa.
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26
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Genome segment reassortment identifies non-structural protein NS3 as a key protein in African horsesickness virus release and alteration of membrane permeability. Arch Virol 2009; 154:263-71. [DOI: 10.1007/s00705-008-0302-8] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/14/2008] [Accepted: 12/09/2008] [Indexed: 10/21/2022]
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27
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Wilson A, Mellor PS, Szmaragd C, Mertens PPC. Adaptive strategies of African horse sickness virus to facilitate vector transmission. Vet Res 2008; 40:16. [PMID: 19094921 PMCID: PMC2695022 DOI: 10.1051/vetres:2008054] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2008] [Accepted: 12/16/2008] [Indexed: 11/14/2022] Open
Abstract
African horse sickness virus (AHSV) is an orbivirus that is usually transmitted between its equid hosts by adult Culicoides midges. In this article, we review the ways in which AHSV may have adapted to this mode of transmission. The AHSV particle can be modified by the pH or proteolytic enzymes of its immediate environment, altering its ability to infect different cell types. The degree of pathogenesis in the host and vector may also represent adaptations maximising the likelihood of successful vectorial transmission. However, speculation upon several adaptations for vectorial transmission is based upon research on related viruses such as bluetongue virus (BTV), and further direct studies of AHSV are required in order to improve our understanding of this important virus.
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Affiliation(s)
- Anthony Wilson
- Vector-Borne Disease Programme, Institute for Animal Health, Ash Road, Pirbright, Woking, Surrey, GU24 0NF, United Kingdom
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