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.
| Original language | English |
|---|---|
| Article number | e0191585 |
| Journal | PLoS ONE |
| Volume | 13 |
| Issue number | 2 |
| DOIs | |
| State | Published - Feb 2018 |
| Externally published | Yes |
Funding
This work was supported by the Defense Threat Reduction Agency, Grant Number: HDTRA1-14-1-0029, DTRA URL: http://www.dtra. mil/. The only funding that was used or contributed to this study was provided via a grant by DTRA. The funding agency, DTRA, did not play a role in the study design, data collection and analysis, decision to publish, or preparation of the manuscript and only provided financial support in the form of authors’ salaries and/or research materials. The specific roles of authors are articulated in the ‘author contributions’ section. The author would like to express his thanks to Nacelle Collins (Free State Department of Environmental Affairs) for his design of and permission to use VegCap, and for his invaluable assistance with the vegetation analysis using Juice, in which the primary synoptic table and ordination diagrams were produced. Claudia Cordell of ExecuVet for all her help with logistics, contacts with scientists and farmers, communications and local in-country project management and administration. All the farmers for their kind and generous help, time and ongoing access to their farms. The staff at Geo Potts Herbarium at the University of the Free State, in particular the Curator, Liza Joubert and Professor Johan Venter for his encyclopaedic knowledge and help with identification of problematic plants. The National Herbarium Pretoria, South African National Biodiversity Institute (SANBI) Pretoria for access to the collection, and the following staff for their assistance with identification of plant material; P. P. J. Herman and M. Welgemoud for help with Asteraceae, Lin Fish for Poaceae, Clare Archer for Cyperaceae, Pieter Bester for Fabaceae and Peter Manning at Kirstenbosch, with 2 geophytes. Thanks also to SANParks, for permission to work at Holpan/Graspan National Park; in particular Hugo Bezuidenhout and Herman Odendaal, Senior Ranger at Holpan/Graspan. The Defense Threat Reduction Agency, U.S. Department of Defense, for sponsorship. The content of the information does not necessarily reflect the position or the policy of the federal government, and no official endorsement should be inferred. Fig 1. Courtesy of Professor van Huyssteen and Mariet Verster, University of the Free State. Fig 2. Ettienne Theron for his time and effort in producing this excellent figure. Fig 3A and 3B. Courtesy of Dr. Assaf Anyamba, Universities Space Research Association (USRA) Figs 5, 6 and 7 photographs taken by H Zwiegers and courtesy of Excue Vet and EcoHealth Alliance.
| Funders | Funder number |
|---|---|
| Defense Threat Reduction Agency | HDTRA1-14-1-0029 |
