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Predicting Rift Valley Fever Inter-epidemic Activities and Outbreak Patterns: Insights from a Stochastic Host-Vector
Sansao A Pedro1,2,3, Shirley Abelman1, Henri E Z Tonnang4
1School of Computer Science and Applied Mathematics, University of the Witwatersrand, Johannesburg, South Africa.
Plos Neglected Tropical Diseases
|December 22, 2016
Summary
Rift Valley fever outbreaks in East Africa are irregular. Vertical transmission in mosquitoes, combined with nonlinearity and stochasticity, explains the disease
Area of Science:
- Epidemiology
- Mathematical Biology
- Vector-borne Diseases
Background:
- Rift Valley fever (RVF) outbreaks in East Africa occur irregularly, with inter-epidemic periods maintained by vertical transmission in Aedes mcintoshi mosquitoes.
- Previous models have not fully explained the irregular oscillatory behavior of RVF outbreaks, despite considering climate and mosquito presence.
Purpose of the Study:
- To formulate and analyze a stochastic host-vector model for RVF transmission incorporating both vertical and horizontal routes.
- To investigate the role of vertical transmission in the irregular periodicity of RVF outbreaks.
Main Methods:
- Development of a full stochastic host-vector model.
- Application of branching process theory to establish relationships between R0, vertical transmission, and invasion/extinction probabilities.
- Utilizing van Kampen system-size expansion techniques to derive an analytical expression for stochastic fluctuation spectra.
Main Results:
- Novel relationships were found between the basic reproduction number (R0), vertical transmission, and invasion/extinction probabilities.
- The model predicts complex fluctuations with a dominant periodicity of 1-10 years, dependent on vertical transmission efficiency.
- Model predictions align with temporal patterns of RVF outbreaks in Tanzania, Kenya, and South Africa.
Conclusions:
- The interaction of nonlinearity, stochasticity, and vertical transmission provides a plausible explanation for the irregular oscillations of RVF outbreaks.
- While rainfall influences outbreak onset and cessation, vertical transmission efficiency contributes to outbreak build-up and occurrence.
