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Climate variability contributes to inconsistent transmission of yellow fever in Africa
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Annual variations in climate across West and East Africa, including temperature suitability and rainfall, contribute to the differences in yellow fever transmission, according to findings published in PLoS Neglected Tropical Diseases.
“Not only have static variables, such as annual temperature and rainfall, been shown to have substantial predictive availability, but the importance of seasonality has also been highlighted, suggesting that taking into account seasonality in disease control and prevention interventions could translate to substantial public health gains,” Arran Hamlet, MSc, from the MRC Center for Outbreak Analysis and Modeling, and colleagues wrote.
“Characterizing the relationship between yellow fever occurrence and environmental factors, in combination with future predictions of these factors, could allow for forecasting of periods of ‘heightened risk,’” the researchers continued. “These predictions would then allow proactive intensification of surveillance to detect initial cases and respond with appropriate measures such as vaccination or vector-control.”
To examine whether changes in climate throughout seasons affected the seasonality of yellow fever reports, Hamlet and colleagues created a temperature suitability index related to virus transmission. This index gathered information on how temperature affected mosquito behavior and viral replication within the mosquito.
The researchers then used several multilevel logistic regression models to assess data from yellow fever reports in Africa. When using these models, Hamlet and colleagues accounted for location and seasonality of disease, and they compared these factors with the temperature suitability index, rainfall and the Enhanced Vegetation Index, among other demographic factors. The fit of the model was evaluated through the area under the curve (AUC), and the researchers ranked all models using Akaike’s information criterion.
The researchers observed that the model created correctly gathered the diverse geographic and temporal characteristics associated with yellow fever transmission (AUC = 0.81; 95% CI, 0.79-0.84). When compared with a model that collects information on only geographic distribution, the new model did not perform significantly worse.
Using the model, Hamlet and colleagues observed that the combination of temperature suitability and rainfall was responsible for the majority of yellow fever reports. According to the researchers, this factor explains the spatiotemporal inconsistency of yellow fever transmission.
“While research into the seasonality of vector-borne diseases has previously been undertaken, it had not been applied to yellow fever, and these findings represent an important first step in quantifying and understanding the seasonality of yellow fever,” Hamlet and colleagues wrote.
“This study has significant and far reaching consequences,” the researchers continued. “The presence of both temporal and spatial aspects to transmission opens up the possibility of seasonally timed vector-borne disease control and the potential for the development of ‘early-warning’ systems, which evaluate current or future climatic variables in order to predict periods of heightened transmission potential for yellow fever virus.” – by Katherine Bortz
Disclosures: The authors report no relevant financial disclosures.
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