livestock and environmental variables to identify possible...
TRANSCRIPT
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