The 2012 Madeira Dengue Outbreak: Epidemiological Determinants and Future Epidemic Potential

Abstract

Dengue, a vector-borne viral disease of increasing global importance, is classically associated with tropical and sub-tropical regions around the world. Urbanisation, globalisation and climate trends, however, are facilitating the geographic spread of its mosquito vectors, thereby increasing the risk of the virus establishing itself in previously unaffected areas and causing large-scale epidemics. On 3 October 2012, two autochthonous dengue infections were reported within the Autonomous Region of Madeira, Portugal. During the following seven months, this first ‘European’ dengue outbreak caused more than 2000 local cases and 81 exported cases to mainland Europe. Here, using an ento-epidemiological mathematical framework, we estimate that the introduction of dengue to Madeira occurred around a month before the first official cases, during the period of maximum influx of airline travel, and that the naturally declining temperatures of autumn were the determining factor for the outbreak's demise in early December 2012. Using key estimates, together with local climate data, we further propose that there is little support for dengue endemicity on this island, but a high potential for future epidemic outbreaks when seeded between May and August—a period when detection of imported cases is crucial for Madeira's public health planning.

Determinants and Drivers of Infectious Disease Threat Events in Europe

“…The natural environment driver was present in all WNV infection events; in half of those events, it was present with the climate driver, and in 6 events, it was present with the surveillance and reporting failure driver (Figure 2, panel B). This finding is consistent with other findings that show environmental and climatic determinants play contributing roles in WNV infection outbreaks (17). Of 7 malaria threat events, 5 included autochthonous cases (in Spain, Greece, and Belgium).…”

Impact of human mobility on the emergence of dengue epidemics in Pakistan

“…To model dengue dynamics, we used an ordinary differential equation model based on a model by Lourenco and Recker to describe a dengue outbreak in Madeira, Portugal (10). This model captures the dynamics of dengue between human and mosquito hosts where the mosquito dynamics are dependent on temperature and relative humidity (SI Text and Fig.…”

“…We next modeled the number of infected individuals traveling from the endemic areas in southern Pakistan to all other tehsils, using different approaches to characterize mobility: direct observations from the mobile phone data and various modified gravity models of travel (Materials and Methods) (10,19). To compare the performance of the mobile phone data against the next best alternative, we used a parameter-free gravity model (referred to as the diffusion model) that is equivalent to a population-weighted spatial diffusion model (Materials and Methods) based on the travel time distance between the origin and the destination.…”

“…The introduction of dengue into new populations is mediated by travel of infected individuals to areas that can support transmission, because mosquito vectors move only short distances during their lifespans (3,(7)(8)(9)(10)(11)(12). International travel to endemic countries has resulted in imported cases and outbreaks in Europe and the Americas (2,8,10,13).…”

“…International travel to endemic countries has resulted in imported cases and outbreaks in Europe and the Americas (2,8,10,13). Local variation in transmission, within a single city for example, is also driven by mobility patterns of individuals on short timescales (7).…”