Interview conducted by April Cashin-Garbutt, BA Hons (Cantab)
Please can you give a brief introduction to dengue fever and explain how it is transmitted?
Dengue is a mosquito-transmitted viral infection. The disease is widespread in tropical and sub-tropical climates and most commonly found in urban areas. Around half of the world's population are now estimated to live in dengue endemic regions.
Transmission occurs through a mosquito-human cycle. The principal dengue mosquito is the Aedes aegypti. Infected Aedes mosquitoes can transmit the virus by biting human hosts.
Dengue epidemics depend on large numbers of mosquitoes, a susceptible human population, and high rate of contact between mosquitoes and humans.
How many cases of dengue fever have been recorded in Brazil in recent years?
So far this century, Brazil has recorded more cases of dengue fever than anywhere else in the world, with more than 7 million cases reported between 2000 and 2013.
Why have the number of cases recorded in Brazil been so high compared to other countries in the world?
According to the latest census in 2010, the population of Brazil is estimated to be 190.8 million. The majority of the population live in large, densely populated cities in the Southeast and Northeast regions.
Many of these cities have tropical and sub-tropical climate conditions that allow the dengue mosquito to thrive, particularly during warmer, wetter and more humid months.
Could you please outline the early warning system that has recently been developed to predict the risk of dengue infections in Brazil during the football World Cup?
We developed a statistical model, conditioned on past monthly data from 2000-2013, to make probabilistic dengue predictions for the 553 microregions of Brazil.
The model is driven by multiple risk factors, including seasonal climate forecasts and the dengue epidemiological situation several months ahead.
How does this system work and what evidence is used to make the predictions?
We used severity thresholds that the Ministry of Health use in their decision making, to work out the chance of dengue cases exceeding medium and high levels.
By assessing the performance of the early warning system on past data, we devised optimum trigger thresholds to indicate whether low, medium or high warnings should be issued for the 12 host venues.
How much of an impact does climate have on dengue transmission?
Mosquito biology is dependent on temperature and rainfall can influence mosquito breeding sites. However, many other factors influence dengue transmission, such as urbanisation and herd immunity.
When devising predictive models for dengue fever, the interplay of different environmental and social factors with transmission dynamics should be considered.
How high do you estimate the risk of dengue outbreaks will be during the forthcoming World Cup?
The probability of dengue cases exceeding the “high” threshold of 300 cases per 100,000 inhabitants is 48% in Natal, 46% in Fortaleza and 19% in Recife.
Although the most likely scenario for all twelve cities is for low risk, these microregions deserve more attention when planning vector control measures.
Which cities have the highest and lowest risks and why?
The model results showed a low probability of dengue outbreaks for cities located in the south and central regions (Brasília, Cuiabá, Curitiba, Porto Alegre and São Paulo), moderate risk in Rio de Janeiro, Belo Horizonte, Salvador and Manaus, and a higher risk for Fortaleza, Natal and Recife.
This is based on a combination of drivers including the forecast climate conditions in the preceding months and the epidemiological situation at the time of forecast.
How accurate do you think these predictions are?
Along with the forecast we provided an assessment of past performance of the model. We found that over the last 14 years (2000-2013) the early warning system performed better than the long-term average distribution in all twelve World Cup host venues, particularly in the northeast region.
Will the early warning system give local authorities adequate opportunity to reduce or contain any potential epidemics?
The early warnings can be issued three months in advance. This allows health authorities enough time to prepare preventive actions in those areas most at risk.
Since there is no vaccine against dengue, these actions are focussed on mosquito control and health care assistance (reducing the risk of severe dengue cases). This may be useful, not only ahead of major global events, but also before the peak dengue season each year, to control or contain potentially explosive dengue epidemics.
Where can readers find more information?
For full article see: http://www.thelancet.com/journals/laninf/article/PIIS1473-3099%2814%2970781-9/fulltext
Title: Dengue outlook for the World Cup in Brazil: an early warning model framework driven by real-time seasonal climate forecasts
Authors: Rachel Lowe, Christovam Barcellos, Caio A S Coelho, Trevor C Bailey, Giovanini Evelim Coelho, Richard Graham, Tim Jupp, Walter Massa Ramalho, Marilia Sá Carvalho, David B Stephenson and Xavier Rodó
Publisher: The Lancet Infectious Diseases
About Dr. Rachel Lowe
Dr Rachel Lowe is the Head of Climate Services for Health at the Catalan Institute of Climate Sciences, Barcelona. Her research involves modelling climate-sensitive disease risk and finding novel ways to communicate probabilistic forecasts to public health decision makers.
Rachel graduated from the University of East Anglia in 2004 with a First Class Honours BSc in Meteorology and Oceanography with a year in Europe. She spent one year at the University of Granada in Spain reading Environmental Science.
In 2007 she completed an MSc with distinction in Geophysical Hazards at University College London where she received a Graduate Masters Award. She then went on to obtain her PhD in Mathematics at the College of Engineering, Mathematics and Physical Sciences, University of Exeter (PhD Thesis: Spatio-temporal modelling of climate-sensitive disease risk: towards an early warning system for dengue in Brazil).
Alongside her PhD, Rachel was Network Facilitator for the Leverhulme Trust funded project EUROBRISA. As part of the project she collaborated with climate scientists and public health experts at CPTEC/INPE and the Oswaldo Cruz Foundation (Fiocruz) during long-term visits to Brazil, which resulted in her ongoing participation in the innovative Brazilian Observatory for Climate and Health.
Rachel was also a Visiting Scientist at the International Centre for Theoretical Physics, Italy, where she worked closely with the Ministry of Health in Malawi towards the development of predictive models for malaria and a platform to integrate climate information and rural telemedicine.