Asymptomatic individuals and dengue transmission – insights from mathematical modeling

Abstract

Introduction Dengue is one of the most important vector-borne viral diseases. During the last few decades a geographic expansion has been observed and the first dengue outbreak in modern history of Europe occurred in Madeira, 2012. Dengue clinical presentation varies, with the majority of infections being asymptomatic. Despite its worldwide importance the role of asymptomatic in dengue transmission and spread is not well understood. This work aims at understanding the role of asymptomatic in transmission of dengue through mathematical modelling-both deterministic and stochastic. Methods Two models were built that consists of both humans and vector-Aedes aegypti mosquito. In Model 1, the humans were divided into four compartments: Sh (susceptible), Eh (exposed), Ih (infectious), Rh (recovered), where the Ih was further divided into 2 classes: symptomatic and asymptomatic. Different recovery period were assumed for these classes. The vector was divided into three compartments: Sv, Ev, Iv. In Model 2, Iv was further divided into 2 classes with different transmission probabilities per bite coming from asymptomatic and symptomatic individuals. Vector and human parameters were collected from the literature, considering Madeira setting. Basic reproduction number (R0) was calculated for each model. Results When varying the recovery period for asymptomatic humans from 6 days to 1 day (R0 changes from 2.4 to 1.4), sustained dengue transmission was observed for the first model. As the recovery period decreases for asymptomatics, the outbreak delays with decreasing peaks. In model 2, no outbreak was observed where R0 is less or near 1. Shorter recovery period and smaller transmission probability for asymptomatics than the symptomatics eliminated the outbreak. Conclusions Based on Madeira's population and assumed vector population , our results suggest that asymptomatic individuals are able to transmit the disease and have an important role on dengue transmission. Future research should include more study in this area as well as vector survey. Key messages Asymptomatic individuals seem to contribute to dengue outbreak. Research on asymptomatic individuals should be conducted to understand dengue transmission and outbreak better, allowing the development of more accurate models.