Fig 1.
Potential epizootic areas of Rift Valley fever in Africa and Madagascar are shown in green [4].
Four areas in Saudi Arabia and Yemen are shown in the insert where significant numbers of people were infected in the 2000–2001 outbreak were noted by the red triangles. While Rift Valley fever has largely been an African disease, there were no documented Rift Valley fever outbreaks in Arabia prior to 2000–2001 and there have been none since that time.
Fig 2.
Mosquito numbers after mosquito habitats were flooded in East Africa as determined from collecting and identifying mosquito species.
Vector specimens collected from the Kamiti dambo, Kenya from November 28—December 27, 1982 [6].
Fig 3.
The Landsat-7 NDVI difference between May/June 2000 and September 2000 shows the increase in green vegetation density from increased rainfall by September 2000 in the Sarawat Mountains for Southwest Arabia.
This in turn, resulted in more runoff to the coastal plain or Tihama that provided ideal conditions for the emergence of Rift Valley fever mosquito vectors. Specific outbreak locations occurred from Al Qunfuda, Saudi Arabia in the north to Wadi Mawr, Yemen in the south and are noted by red triangles where they were reported. This figure is from Anyamba et al. [5].
Fig 4.
(A). The AVHRR NDVI 8 km anomalies from July 1981 to December 2016 from the area in (4c). (B). The MODIS 250 m NDVI anomalies for the same area from 2000 to 2019 in (4c) from Al Qunfunda, Saudi Arabia to Wadi Mawr, Yemen, from the coast to the foothills of the Sarawat mountains, an area of 100,000 km2 in Southwestern Arabia bordering the Red Sea in the image of (C). Positive NDVI values are a consequence of above-average rainfall and are color-coded in blue in both 4a and 4b [27]. Dryer periods are color-coded in red. It is possible the introduction of Rift Valley fever virus into Southwest Arabia occurred in 1997–1998, while the East Africa 1997–1998 Rift Valley fever outbreak was underway. Note the very similar NDVI trends from 2000 to 2016 derived from AVHRR NDVI and from MODIS NDVI data. The MODIS NDVI data in Fig 4b show favorable conditions for Rift Valley fever outbreaks in 2016–2019 but none have occurred in Arabia during this time.
Fig 5.
(A) WorldView-1 panchromatic 2 m resolution image from November 7, 2017 from the Wadi Mawr village area of Northwest Yemen; and (B) a stereo digital elevation hillshaded image and elevation profile produced from a stereo pair of WorldView-1 panchromatic images acquired on November 7, 2017 from the same area. The high-resolution elevation data shows potential inundated areas along the terrian. Mapping inundated areas to identify potential mosquito-breeding habitats is a new tool for infectious disease study.