Fig 1.
Reported deaths of livestock due to Rift Valley Fever, during the 2010 outbreak, centred in the Free State, South Africa.
The diagonally lined box indicates the 200km x 200km study area. Rift Valley Fever deaths of livestock were reported in eight of the nine South African provinces. The study area was centred in the region of highest mortality in the western Free State. Mortality data derived from the RSA, OIE Report 17.
Fig 2.
Location of study sites and nearest towns, with endorheic pans, upland depressions and palustrine wetlands shown in blue.
Study sites are situated in the areas of highest Rift Valley Fever mortalities coinciding with the most dense concentration of wetlands in the western Free State.
Fig 3.
Rainfall data for the study sites.
Fig 3a. Annual total rainfall map for the study region showing a gradient on decreasing rainfall from East to West/Southwest. Also shown are locations of weather stations (that are coincident with vector sampling sites) and other vector sampling sites at farm locations with high mortality during the 2010/2011 epizootic outbreak. Fig 3b. Cumulative daily rainfall profiles for Graspan/Holpan and Brakput monitoring locations. Graspan and Brakput locations showing rainfall trajectories for different years including the RVF epizootic year 2010/2011 (above normal rainfall shown in green) and the record drier-than-normal year 2015/2016.
Fig 4.
Ordination: The ordination diagram illustrates the gradients of ecological and microclimatic conditions.
Community 8 to Community 1, horizontal axis represents an east to west gradient of geology, solid, species diversity. Vertical axis shows plant height, wetland status and degree of wetness.
Fig 5.
Categorization of five, freshwater wetland depressions-types with descriptions of vegetation and ecology. A. Deelpan, a typical saline endorheic pan, with narrow, the dense vegetated pan-margin, providing ideal breeding habitat for Aedes. Aa. Holpan, a non-saline pan, covered with Eragrostis bicolor the low, caespitose, specialist arid-region grass. B. De Dam, shallow depression wetland with clay soil and emerging sedge Fuirena coerulescens, grass Echinochloa colona and fern, Marisela capensis. Bb. Petrusburg wetland with large-tufted Scirpoides dioecious, emerging Cyperus laevigatus sedges, and the spreading, prostrate forb Hypertelis salsoloides. C. Mature ox-bow cut-off, 100cm deep, with wetland vegetation, sedges, grasses, on the margins. Cc. Inundated ox-bow wetland-type at Bougainvillea, a site of high sheep mortality during the 2010 outbreak. D. Riet River in flood, near Mokala National Park, with dense, monotypic stands of Phragmites australis. Dd. Seven Dams had no RVF mortalities. The most species-rich wetlands with extensive stands of Phragmites australis (foreground) and Typha capensis. E. Sedge and Juncus dominated wetland. The deep grove is created by the wheel of the pivot irrigator. Ee, Extensive, spill-over wetland created at Rooibokpan near Jacobsdal, dominated sedges, Juncus and OBL forbs in the <50 cm deep water.
Table 1.
Five wetland category types, location, the association with mosquitoes, dominant vegetation, geology, soils and site identification number.
Table 2.
Relationship between named plant communities, vegetation characteristics and reported RVF mortalities.
Table 3.
Animal cases and deaths during the 2010 Rift Valley fever outbreak.
Fig 6.
Culex pupae and larvae (known RVF virus amplifying-vectors), found at Oppermansgronde. Sheep trough full of Culex, capable of 2 km flight from wetlands, a known amplifying Aedes RVF vector. a. Culex pupae and larvae, more than 400m from any pan or wetlands, at a confirmed high mortality site during the 2010 RFV outbreak.
Fig 7.
Annual comparison over 3 years of numbers of Culex and Aedes collected.
The columns show the clear relationship between rainfall and mosquito numbers. The annual comparison of mosquito samples from 2014 to 2017 is derived from the Rift Valley fever virus vector surveillance work package.
Fig 8.
Palustrine wetland vegetation matrix, clay soils and sandstone habitat for Aedes.
Wetland vegetation matrix of sedges; Scirpoides dioecious, Cyperus laevigatus, and the grass Miscanthus junceus, on high clay-content soils from Ecca series sandstone and shales found at most sites.