Objective: Annually Rift Valley Fever, a phelbovirus from the family of Bunyaviridae, causes billions of economic damages and loss of productive human days through illness and death in Africa. Humans exhibit flu-like symptoms such as chills and fever or may persist to hemorrhagic fever. In pastoral

animals, spontaneous abortions or death occurs, especially in sheep and cattle (Linthicum, and Peters 125). This impact alone advises further investigation of this disease, but an increase in epizootic outbreaks since the introduction of Rift Valley Fever in Kenya in 1912 warrants a

comprehensive look on disease amplification variables in this already vulnerable region (Murith, et al., 139). Geographic informational System was the chosen technology to aid in this investigation because of its ability to present and analyze multiple disease and ecological factors. The

chosen disease variables in this study include: human population, livestock herds, and flooding plains of oxbow along the Tana River.

Disease Background

The known vectors of Rift Valley

Fever are species within the Culex

and Aedes families of floodwater

mosquitoes. After rainy seasons in

Kenya, mosquitoes lay their eggs in

the flood plains or pond that were

created. After maturation, vectors

choose to feed on pastoral animals,

especially cattle and sheep, which

acts as an amplification host

(Linthicum, and Peters 125). An

amplification host serves as a place

where a virus can replicate. Pastoral

animals tend to graze near water

sources and humans tend to settle

within distance to water sources,

which causes a dependency on water

sources. The relationship between

these variables creates an optimum

situation for outbreaks.

Study Site Due to population growth, size of freshwater

source, and source breeding habitat, the

study area of choice is along the Tana River

(Kenya) which runs 1050 km from the

Aberdares range and drains in the Indian

Ocean (“Kenya National Water

Development Report” 46). Seasonal

flooding along the Tana River creates

flooding zones along oxbows, and ponds

that are fertile grounds for mosquito

oviposition and hatching of eggs (Tourre, et

al. 70). This poses an increase in possible

transmission because of the pastoral

system around Tana River. The land

surrounding the Tana River’s flood plains is

categorized as semi-arid which means

animals are classified at pastoral. Pastoral

animals graze over large areas of land in

search of food and water, which increases

the chance of transmission if animal is

virulent (Otte 17; Zaal).

Map 7: In the

comprehensive map,

regions of vulnerability are

indicated by circles based

on density of livestock and

human population as well

as proximity to floodplains

and oxbow buffers.

Map 3:. Using Google

Earth, oxbow were pin

marked and outlined

using a polygon tool. In

ArcMap, the oxbows

were digitalized using

the conversional tool

from KML file to layers.

Results

Analysis of maps with multiple variables: oxbow buffers, livestock density

and grazing buffers, floodplains, and population’s densities shows there are

three vulnerable regions within the Tana River and Garissa Districts. The

northwest portion of the map and near the town of Garissa shows vulnerable

regions due to high the population and livestock density as well as the

livestock’s close proximity to the oxbow buffers. The high density of livestock

near the floodplain poses a risk of substantial amplification after heavy

rainfall. Also, if livestock are brought to the town of Garissa for trading and

buy purposes a risk of transmission could be exposed to the urban

population.

Study Limitations:

• Inconsistent and inaccurate sampling of data collection

• Livestock data did not contain subgroups specifically for sheep and cattle

• Outdated population data; no updated data since 1999

• Data could not be statistical analyzed easily because of parameters of

how the attribute table was set up

Conclusions:

Instead of focusing on limitations within the data, improvement of collection

and dissemination of transmission variables of Rift Valley Fever would

greatly improvement identification of vulnerable districts. This would allow for

implementation of serovsurveillance programs and potential vaccines sites to

prevent in outbreaks. Further resources and efforts should be invested into

obtaining and analyzing transmission variables for Rift Valley Fever along the

Tana River. Map 6:Livestock densities of 20 or more animals per

kilometer square were selected by attribute and a

proximity analysis was run to create multiple ring

buffers, which represent grazing areas. The densest

areas are centered around the river floodplains as well

floodplains to the west.

Discussion

Map 4: Overlay of highest density livestock

and their buffer zones were compared

against the population density. Near the town

of Garissa and to the northwest have the

greatest correlation between high livestock

and population density.

Map 5: Proximity analysis of oxbows was

performed to created multiple rings buffers and

compared to livestock over 20 density per

kilometer square. Overlap and highest proximity

areas are located in the northwest and by the town

of Garissa.

Map 2: Tana River study site

Map 1: Kenya, location of Tana River

References:

Kenya National Water Development Report. Rep. no. 2. World WaterAssessment Programme, United Nations, Dec. 2006. Web. 2 Dec. 2012.

Linthicum , K.J., and C.J. Peters. "Rift Valley Fever." Trans. Array Handbook of Zoonoses. George W. Beran. 2nd ed.CRC Press, 1994. 125. Web. 3 Dec. 2012.

Murithi, R. M., et al. "Rift Valley fever in Kenya: history of epizootics and identification of vulnerable districts." Epidemiology and infection 139.3 (2011): 372-380.

Otte, M. J., and P. Chilonda. "Cattle And Small Ruminant Production Systems In Sub-Saharan Africa: A Systematic Review." Food and Agriculture Organization. United Nations, 2002. Web. 3 Dec. 2012.

Tourre, Yves M., et al. "Mapping of zones potentially occupied by Aedes vexans and Culex poicilipes mosquitoes, the main vectors of Rift Valley Fever in Senegal." Geospatial health 3.1 (2008): 69-79.

Zaal, Fred. Pastoralism in a global age: livestock marketing and pastoralcommercial activities in Kenya and Burkina Faso. Thela Publishers, 1999.

Livestock and Environmental Variables to Identify Possible Vulnerabilities for Rift Valley Fever along the Tanya River, Kenya Emily Schwartz, MSPH Candidate

GIS DATA World Resource Institute, http://www.wri.org/publication/content/9291#landcover, Accessed December 3ed- 7th 2012 International Livestock Research Institute , http://192.156.137.110/gis/search.asp?id=280, Accessed December 3rd-7th 2012