Scientific news
El Niño brings fears of dengue fever outbreaks
October 2015
No. 487
Health Centre in Laos (© IRD / M. Choisy)
The dengue virus affects 390 million people globally every year, and fears are
that early 2016 will see an epidemic, particularly in South-East Asia, due to the
predicted extreme intensity of El Niño. A new study published in the
Proceedings of the National Academy of Sciences has revealed the significant
role that this monster climatic phenomenon plays in the outbreak of
haemorrhagic fevers.
Reviewing health reports from eight South-East Asian countries, spanning a
period of 18 years, the research group in question developed models for
dengue fever transmission across the entire region and highlighted the
correlation between the most serious epidemic waves and the abnormally high
atmospheric temperatures associated with intense El Niño events.
A few facts
Transmitted to humans by mosquitoes, namely Aedes aegyti and Aedes albopictus – the famous
tiger mosquito, the dengue virus has a presence in more than 100 countries, largely in Asia and
Latin America. It affects some 390 million people each year, causing symptoms of varying severity,
such as fever, muscular pain, headaches, digestive problems and even haemorrhaging, resulting
in a global annual death rate of 100,000. No vaccine or specific treatment has been identified to
date.
Contact / Subscribe – [email protected]
Department of Scientific Information and Culture for the South – Research Institute for Development (IRD)
The number of cases of dengue fever throughout the world is rising rapidly, propelling it to
the status of a 're-emerging disease'. Many countries in the intertropical zone see the
number of cases of haemorrhagic fever peak during the rainy season each year. But when
and why do these annual peaks turn into real outbreaks, spreading beyond borders, like the
viruses rife in Latin America and the Caribbean in 2010 and 2013? Up to now, it has been
difficult to understand and predict these major epidemic waves.
Eighteen years of epidemiological data scrutinised
To lift the veil on this question, an international research group collected and analysed
18 years of monthly dengue fever monitoring reports from eight countries in South-East Asia.
This enabled them to identify very pronounced trends in the transmission of the virus across
the entire region.
Monster El Niño phenomenon to blame
Of particular note, the researchers observed a period of high incidence throughout SouthEast Asia from 1997 to 1998. This coincided with the most intense El Niño event of the 20th
century. For them, the link was unmistakeable: this climatic phenomenon, originating from
the Pacific Ocean around every five years, plays a key role in the development of major
dengue fever epidemics, as it brings abnormally high atmospheric temperatures. These
temperatures allow the vector mosquitoes to reproduce more quickly and proliferate,
increasing the spread of the virus.
Higher risk in built-up areas
This study also retraced the spread of the main epidemic waves to hit South-East Asia over a
period of almost 20 years. These waves had successively emerged from western Thailand,
central Laos and the southern Philippines. Finally, the findings from this work highlighted the
increased risk of an epidemic in large urban areas, such as Bangkok, Singapore, Phnom
Penh or Kuala Lumpur, due to the constant influx of new residents never previously exposed
to the virus, making them particularly vulnerable to infection.
Now that climatologists have announced the most intense El Niño since 1997-98, these
findings have led to fears of a major new dengue fever epidemic in Asia in early 2016.
However, by sounding the warning bell in advance, this work will enable the introduction of
immediate health measures.
Partners
The international team was made up of scientists from 18 institutions across the world, including
health ministries from each country in the study and the University of Pittsburgh.
This work was funded by the Bill & Melinda Gates Foundation, the National Institutes of Health and the
National Institute of General Medical Sciences.
References
W. G. van Panhuis, Marc Choisy, X. Xiong, N. S. Chok, P. Akarasewi, S. Iamsirithaworn, S. K. Lam,
C. K. Chong, F. C. Lam, B. Phommasak, P. Vongphrachanh, K. Bouaphanh, H. Rekol, N. Tran Hien,
P. Q. Thai, T. N. Duong, J.-H. Chuang, Y.-L. Liu, L.-C. Ng, Y. Shi, E. A. Tayag, V. G. Roque, L. L. Lee
Suy, R. G. Jarman, R. V. Gibbons, J. M. S. Velasco, I. Yoon, D. S. Burke, D. A. T. Cummings.
Region-wide synchrony and traveling waves of dengue across eight countries in Southeast
Asia. Proceedings of the National Academy of Sciences, 2015; 201501375.
DOI:10.1073/pnas.1501375112
Scientific contact
Marc Choisy, IRD researcher
Tel. +84(0) 1638997896
[email protected]
Joint Research Unit Infectious diseases and vectors: ecology, genetics, evolution and control –
MIVEGEC (IRD / CNRS / University of Montpellier)
Contact / Subscribe – [email protected]
Department of Scientific Information and Culture for the South – Research Institute for Development (IRD)