Ecological factors associated with abundance and distribution of mosquito vectors of Rift Valley fever virus during an epidemic period in Isiolo, Kenya

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Poster by Max Korir, Joel Lutomiah and Bernard Bett presented the 8th All Africa Conference on Animal Agriculture, Gaborone, Botswana, 26–29 September 2023.

Ecological factors associated with abundance and distribution of mosquito
vectors of Rift Valley fever virus during an epidemic period in Isiolo, Kenya
Max Korir1, Joel Lutomiah2, Bernard Bett1
1.International Livestock Research Institute, P. O. Box 30709-00100, Nairobi
2.Kenya Medical Research Institute, P. O. Box 54840-00200, Nairobi
Introduction
o Rift Valley fever (RVF) is a zoonotic disease caused by the Rift Valley
fever virus (RVFV), impacting both animals and humans. The
disease is prevalent in Sub-Saharan Africa and the Middle East,
often emerging after periods of intense rainfall and subsequent
flooding.
o These climatic conditions create a conducive environment for the
transmission of the virus. RVF epidemics can have severe economic
repercussions, particularly for rural communities that depend on
livestock for their livelihoods. Mosquito vectors thrive in areas that
have been flooded, facilitating the spread of RVFV among animals
and humans.
Pictures
Conclusion
o Geospatial and machine learning technologies are valuable for
predicting RVF heterogeneity.
o Understanding ecological factors aids in predicting and
managing RVF outbreaks.
o Study contributes to the development of effective early
warning and mitigation strategies.
Max Korir
International Livestock Research Institute
m.korir@cgiar.org ● Box 30709 Nairobi Kenya
Objective
o To identify the ecological factors that are associated with the
abundance and distribution of mosquito vectors of Rift Valley fever
virus during an epidemic period in Isiolo, Kenya.
Methods
o Entomological survey during RVF outbreak in Isiolo, Kenya, in 2020-
2021.
o Mosquitoes trapped using CDC light traps over 48 hours.
o Generalized Additive Model (GAM) used for analysis, considering
factors like land cover, vegetation indices (NDVI), elevation,
curvature, soil type, soil texture, slope, land surface temperature
(LST), and modified normalized difference water index (MNDWI)
Discussion
o Forest-to-cropland conversion observed over time, affecting
mosquito habitats.
o The analysis showed the possible cause of RVF being floods
rather than rainfall. The model developed would be useful for
predicting the spatial distribution of potential RVFV vector
breeding sites in the region
Results
o 5,307 mosquitoes of 22 species were trapped during the study.
o Significant factors influencing mosquito abundance: Standard
deviation of NDVI, mean MNDWI, curvature, elevation, and land
cover.
o Negative correlation between mean NDVI and rainfall quantity,
suggesting floods trigger RVF more than rainfall.
o Negative correlation between NDVI and rainfall quantity,
suggesting floods trigger RVF more than rainfall.

Vector borne diseases like malaria and Rift Valley fever pose significant risks to human and animal health in Africa. One Health approaches that consider the environmental, animal, and human factors are needed to develop early warning systems. The document discusses developing tools to detect climate sensitive disease outbreaks and assessing environmental and vector characteristics. It also presents models of Rift Valley fever transmission dynamics and the importance of vertical transmission between outbreaks. Spatial distribution models of Rift Valley fever vectors in Kenya were developed using climatic and ecological variables. The results can help target surveillance and control in high-risk areas.

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