The 2012 Madeira dengue outbreak: epidemiological determinants and future epidemic potential - PubMed (original) (raw)
The 2012 Madeira dengue outbreak: epidemiological determinants and future epidemic potential
José Lourenço et al. PLoS Negl Trop Dis. 2014.
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.
Conflict of interest statement
The authors have declared that no competing interests exist.
Figures
Figure 1. Tourism and temperature data for the island of Madeira.
(A) Mean of minimum (green), average (blue) and maximum (red) temperatures per day between 2002 and 2012. Coloured areas are the standard deviation. (B) Number of airline passengers entering Madeira per year (dashed, black) and local investment in tourism per year (solid, grey). (C) Relative weight (bubbles) of each country in the total number of passengers arriving at Madeira per year (columns). Data compiled from the 30 most frequent cities of origin for airline passengers per year. Portuguese cities were excluded - Oporto, Lisbon, Porto Santo (Madeira) and Ponta Delgada (Azores). (D) Map representation of (C), including Portugal. Colours match the weight of each country with the 4 highest highlighted in green.
Figure 2. Climate and dengue outbreak data for the island of Madeira.
Mean of minimum temperatures per week (solid, green), precipitation (solid, cyan) and dengue reported cases per week (dotted, black) for August-2012 to March-2013.
Figure 3. Model fitting to Madeira's dengue outbreak data.
(A,B) Reported cases (incidence and cumulative) per week (dotted, black) and example of model fitting (solid, purple). Coloured area (purple) is the standard deviation of all accepted steps in the MCMC chain. The dashed vertical line represents the date of the first reported clinical cases. The red dashed line represents the epidemic progression ignoring the first week in November, when a new surveillance method was introduced. (C) Stationary distributions of the estimated timepoint of first case for 30 independent MCMC runs with random initial conditions and 1 million steps.
Figure 4. Model-derived epidemiological and entomological parameter estimates for 2012.
(A) Example of estimated [Image: see text] values for 2012 (solid, red) together with the weekly minimum temperatures for 2012 (solid, blue) and long-term average of minimum temperatures (2001–2011, dashed green). The dashed red line marks the epidemic threshold [Image: see text]. (B) Example of estimated number of mosquitoes per human (solid, black), incubation period (solid, cyan) and adult life-span (solid, orange) for 2012.
Figure 5. Model-derived epidemic potential for the island of Madeira.
(A) Temperatures for the year of 2012 (red, solid line) and average temperatures for the past 10 years (2001–2011; blue, solid line). The points mark the mean outbreak size (number of cases) for 100 stochastic introductions at different timepoints using temperature data from 2012 (red) and the average over the past 10 years (blue). (B) Derived real-time [Image: see text] (red, solid line) for 2012, with an annual mean of [Image: see text] (dashed line). (C) Derived real-time [Image: see text] (blue, solid line) for the past 10 year, with an annual mean of [Image: see text] (dashed line). (B,C) Grey shaded areas are the frequency of simulations (in 100) achieving either more than 3 (light grey) or 1000 (dark grey) cases.
References
- Kyle JL, Harris E (2008) Global spread and persistence of dengue. Annual review of microbiology 62: 71–92. -PubMed
- Almeida APG, Gonçalves YM, Novo MT, Sousa CA, Melim M, et al. (2007) Vector monitoring of Aedes aegypti in the Autonomous Region of Madeira, Portugal. Euro surveillance 12: E071115.6. -PubMed
Publication types
MeSH terms
LinkOut - more resources
Full Text Sources
Other Literature Sources
Medical