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Rainfall and epizootic Rift Valley fever.
Bulletin of the World Health Organization
|January 1, 1985
Summary
Rift Valley fever (RVF) outbreaks in Kenya are linked to heavy, persistent rainfall. This rainfall floods mosquito habitats, leading to increased mosquito populations and subsequent RVF epizootics.
Area of Science:
- Veterinary Epidemiology
- Environmental Science
- Arbovirology
Background:
- Rift Valley fever (RVF) is an epizootic disease that has occurred in Kenya four times in the last 30 years.
- Previous epizootics were characterized by widespread, frequent, and persistent rainfall patterns.
Purpose of the Study:
- To investigate the correlation between rainfall characteristics and the occurrence of epizootic Rift Valley fever in Kenya.
- To understand the ecological factors contributing to RVF outbreaks.
Main Methods:
- A composite statistic was developed based on measurements of rainfall characteristics (widespread, frequent, persistent).
- This statistic was analyzed in relation to historical RVF epizootic periods in Kenya.
Main Results:
- The composite rainfall statistic was positive during periods of epizootic Rift Valley fever.
- Heavy rainfall elevates water tables, flooding dambos and creating habitats for Aedes mosquito larvae.
- Transovarial transmission of RVF virus in Aedes mosquitoes likely contributes to large vector populations under these conditions.
Conclusions:
- Widespread, frequent, and persistent rainfall is a key predictor of Rift Valley fever epizootics in Kenya.
- Flooding of dambos and subsequent emergence of Aedes mosquitoes play a critical role in RVF transmission cycles.