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Verster AM, Liang JE, Rostal MK, Kemp A, Brand RF, Anyamba A, Cordel C, Schall R, Zwiegers H, Paweska JT, Karesh WB, van Huyssteen CW. Selected wetland soil properties correlate to Rift Valley fever livestock mortalities reported in 2009-10 in central South Africa. PLoS One 2020; 15:e0232481. [PMID: 32421747 PMCID: PMC7233588 DOI: 10.1371/journal.pone.0232481] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2019] [Accepted: 04/15/2020] [Indexed: 11/18/2022] Open
Abstract
Outbreaks of Rift Valley fever have devastating impacts on ruminants, humans, as well as on regional and national economies. Although numerous studies on the impact and outbreak of Rift Valley fever exist, relatively little is known about the role of environmental factors, especially soil, on the aestivation of the virus. This study thus selected 22 sites for study in central South Africa, known to be the recurrent epicenter of widespread Rift Valley fever outbreaks in Southern Africa. Soils were described, sampled and analyzed in detail at each site. Of all the soil variables analyzed for, only eight (cation exchange capacity, exchangeable Ca2+, exchangeable K+, exchangeable Mg2+, soluble Ca2+, medium sand, As, and Br) were statistically identified to be potential indicators of sites with reported Rift Valley fever mortalities, as reported for the 2009–2010 Rift Valley fever outbreak. Four soil characteristics (exchangeable K+, exchangeable Mg2+, medium sand, and Br) were subsequently included in a discriminant function that could potentially be used to predict sites that had reported Rift Valley fever-associated mortalities in livestock. This study therefore constitutes an initial attempt to predict sites prone to Rift Valley fever livestock mortality from soil properties and thus serves as a basis for broader research on the interaction between soil, mosquitoes and Rift Valley fever virus. Future research should include other environmental components such as vegetation, climate, and water properties as well as correlating soil properties with floodwater Aedes spp. abundance and Rift Valley fever virus prevalence.
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Affiliation(s)
- Anna M. Verster
- Department of Soil, Crop and Climate Sciences, University of the Free State, Bloemfontein, Republic of South Africa
| | - Janice E. Liang
- EcoHealth Alliance, New York City, New York, United States of America
| | - Melinda K. Rostal
- EcoHealth Alliance, New York City, New York, United States of America
| | - Alan Kemp
- National Institute for Communicable Diseases, Johannesburg, Republic of South Africa
| | - Robert F. Brand
- Department of Soil, Crop and Climate Sciences, University of the Free State, Bloemfontein, Republic of South Africa
| | - Assaf Anyamba
- NASA Goddard Space Flight Center, Greenbelt, Maryland, United States of America
- Universities Space Research Association, Columbia, Maryland, United States of America
| | - Claudia Cordel
- ExecuVet Veterinary Clinical and Scientific Consulting, Bloemfontein, Republic of South Africa
| | - Robert Schall
- Department of Mathematical Statistics and Actuarial Sciences, University of the Free State, Bloemfontein, Republic of South Africa
| | - Herman Zwiegers
- Department of Soil, Crop and Climate Sciences, University of the Free State, Bloemfontein, Republic of South Africa
| | - Janusz T. Paweska
- National Institute for Communicable Diseases, Johannesburg, Republic of South Africa
| | - William B. Karesh
- EcoHealth Alliance, New York City, New York, United States of America
| | - Cornie W. van Huyssteen
- Department of Soil, Crop and Climate Sciences, University of the Free State, Bloemfontein, Republic of South Africa
- * E-mail:
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Brand RF, Rostal MK, Kemp A, Anyamba A, Zwiegers H, Van Huyssteen CW, Karesh WB, Paweska JT. A phytosociological analysis and description of wetland vegetation and ecological factors associated with locations of high mortality for the 2010-11 Rift Valley fever outbreak in South Africa. PLoS One 2018; 13:e0191585. [PMID: 29462214 PMCID: PMC5819772 DOI: 10.1371/journal.pone.0191585] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2017] [Accepted: 01/08/2018] [Indexed: 11/23/2022] Open
Abstract
Rift Valley fever (RVF) is endemic in Africa and parts of the Middle East. It is an emerging zoonotic disease threat to veterinary and public health. Outbreaks of the disease have severe socio-economic impacts. RVF virus emergence is closely associated with specific endorheic wetlands that are utilized by the virus' mosquito vectors. Limited botanical vegetation surveys had been published with regard to RVF virus (RVFV) ecology. We report on a phytosociological classification, analysis and description of wetland vegetation and related abiotic parameters to elucidate factors possibly associated with the 2010-2011 RVFV disease outbreak in South Africa. The study sites were located in the western Free State and adjacent Northern Cape covering an area of ~40,000 km2 with wetlands associated with high RVF mortality rates in livestock. Other study sites included areas where no RVF activity was reported during the 2010-11 RVF outbreak. A total of 129 plots (30 m2) were selected where a visible difference could be seen in the wetland and upland vegetation. The Braun-Blanquet method was used for plant sampling. Classification was done using modified Two-Way Indicator Species Analysis. The vegetation analysis resulted in the identification of eight plant communities, seven sub-communities and two variants. Indirect ordination was carried out using CANOCO to investigate the relationship between species and wetland ecology. The study also identified 5 categories of wetlands including anthropogenic wetlands. Locations of reported RVF cases overlapped sites characterized by high clay-content soils and specific wetland vegetation. These findings indicate ecological and environmental parameters that represent preferred breeding habitat for RVFV competent mosquito vectors.
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Affiliation(s)
- Robert F. Brand
- Cuyahoga County Board of Health, Parma, Cuyahoga County, Ohio, United States of America
- Department of Botany, University of the Free State, Republic of South Africa
| | | | - Alan Kemp
- Centre for Emerging, Zoonotic and Parasitic Diseases, National Institute for Communicable Diseases, Sandringham, South Africa
| | - Assaf Anyamba
- NASA Goddard Space Flight Center, Biospheric Science Laboratory & Universities Space Research Association, Greenbelt, MD, United States of America
| | | | - Cornelius W. Van Huyssteen
- Soil- and Crop- and Climate Sciences Department, University of the Free State, Free State, Republic of South Africa
| | | | - Janusz T. Paweska
- Centre for Emerging, Zoonotic and Parasitic Diseases, National Institute for Communicable Diseases, Sandringham, South Africa
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