Simulation models of dengue transmission in Funchal, Madeira Island: influence of seasonality
Authors: Salami Donald , Capinha César , Sousa Carla Alexandra , Martins Maria do Rosário Oliveira , Lord Cynthia 
Published: October 2019

The recent emergence and established presence of Aedes aegypti in the Autonomous Region of Madeira, Portugal, was responsible for the first autochthonous outbreak of dengue in Europe. The island has not reported any dengue cases since the outbreak in 2012. However, there is a high risk that an introduction of the virus would result in another autochthonous outbreak given the presence of the vector and permissive environmental conditions. Understanding the dynamics of a potential epidemic is critical for targeted local control strategies.

Here, we adopt a deterministic model for the transmission of dengue in Aedes aegypti mosquitoes. The model integrates empirical and mechanistic parameters for virus transmission, under seasonally varying temperatures for Funchal, Madeira Island. We examine the epidemic dynamics as triggered by the arrival date of an infectious individual; the influence of seasonal temperature mean and variation on the epidemic dynamics; and performed a sensitivity analysis on the following quantities of interest: the epidemic peak size, time to peak and the final epidemic size.

Our results demonstrate the potential for summer to early winter transmission of dengue, with the arrival date significantly affecting the distribution of the timing and peak size of the epidemic. Mid-summer to early autumn arrivals are more likely to produce larger epidemics within a short peak time. Epidemics within this favorable period had an average of 18% of the susceptible population infected at the peak, at an average peak time of 70 days. We also demonstrated that seasonal temperature variation dramatically affects the epidemic dynamics, with warmer starting temperatures producing peaks more quickly after an introduction and larger epidemics. Overall, our quantities of interest were most sensitive to variance in the date of arrival, seasonal temperature, biting rate, transmission rates, and the mosquito population; the magnitude of sensitivity differs across quantities.

Our model could serve as a useful guide in the development of effective local control and mitigation strategies for dengue fever in Madeira Island.

Author Summary

The presence of Aedes aegypti mosquitoes in Madeira Island had recently caused the first local outbreak of dengue in Europe. The island is at risk of another local transmission if triggered by the introduction of the dengue virus by an infected person. Using a mathematical model for the transmission of dengue, we examine the dynamics of a potential epidemic triggered by the arrival of an infected person on the island. We also examine the impact of seasonal temperature variation on the epidemic dynamics. Our results show the potential for summer to early winter transmission of dengue on the island, and that the arrival date of an infectious person affects the distribution of the timing and peak size of the epidemic. Arrival dates during mid-summer to early autumn were more likely to produce larger epidemic peak size within a short time. We also show that seasonal temperature variation dramatically affects the epidemic dynamics. With warmer starting temperatures, epidemics peak more rapidly and produce a larger epidemic size. Our model could be useful to estimate the risk of an epidemic outbreak and as a guide for local control and mitigation strategies for dengue on the island.