Study shows paradoxical relationship between dengue hemorrhagic fever and its carrier mosquitoes

A study by researchers in Thailand, Japan, and the UK has shown a negative correlation between dengue hemorrhagic fever (DHF) and the density of the Aedes mosquitoes that transmit the virus. The study, published July 16th in the open-access journal PLoS Neglected Tropical Diseases, explains how current efforts to reduce the mosquitoes may actually increase the incidence of the potentially fatal viral disease.

At least tens of millions of people are infected by dengue virus every year. Therefore, health authorities in tropical countries and the World Health Organization, have organized tremendous efforts towards the reduction of Aedes mosquitoes. However, the number of DHF patients continues to increase. To find an answer to this paradox, the researchers tested the hypothesis that more people with a mosquito-borne illness exist where there are more mosquitoes.

The researchers organized community volunteers who visited one million houses in Thailand and surveyed local densities of Aedes mosquitoes. They then compared this data to the number of people with DHF from each of 1,000 districts visited. The researchers found the incidence of DHF in areas of moderate mosquito density to be 40% higher than in areas of the highest mosquito density.

The researchers hypothesized that this paradoxical relationship is due to the peculiar fact that DHF develops most frequently when the patient is infected with dengue a second time. The results of this study imply that the current strategy of dengue control — reducing Aedes mosquitoes — may not necessarily be beneficial.

Additionally, the researchers developed computer simulation software based upon their hypothesis. The simulation predicted that epidemiological studies should be continued for a very long duration, preferably over a decade, to clearly detect such a paradoxical relationship between Aedes abundance and incidence of DHF. Such long-term studies are necessary, especially because tremendous efforts and resources have been (and perhaps will be) spent on combating Aedes.

PLEASE ADD THIS LINK TO THE PUBLISHED ARTICLE IN ONLINE VERSIONS OF YOUR REPORT: http://www.plosntds.org/doi/pntd.0000263 (link will go live on Wednesday, July 16)

CITATION: Thammapalo S, Nagao Y, Sakamoto W, Saengtharatip S, Tsujitani M, et al. (2008) Relationship between Transmission Intensity and Incidence of Dengue Hemorrhagic Fever in Thailand. PLoS Negl Trop Dis 2(7): e263. doi:10.1371/journal.pntd.0000263

Dr. Yoshiro Nagao
Osaka University Graduate School of Medicine
2-2 Yamadaoka, Suita, 565-0871, Japan
Email: nagaoy@anes.med.osaka-u.ac.jp

This press release refers to an upcoming article in PLoS Neglected Tropical Diseases. The release is provided by the article authors. Any opinions expressed in these releases or articles are the personal views of the journal staff and/or article contributors, and do not necessarily represent the views or policies of PLoS. PLoS expressly disclaims any and all warranties and liability in connection with the information found in the releases and articles and your use of such information.

PLoS Neglected Tropical Diseases (http://www.plosntds.org/) is a peer-reviewed, open-access journal devoted to the pathology, epidemiology, prevention, treatment, and control of the neglected tropical diseases, as well as public policy relevant to this group of diseases. All works published in PLoS Neglected Tropical Diseases are open access, which means that everything is immediately and freely available subject only to the condition that the original authorship and source are properly attributed. The Public Library of Science uses the Creative Commons Attribution License, and copyright is retained by the authors.

The Public Library of Science (PLoS) is a non-profit organization of scientists and physicians committed to making the world's scientific and medical literature a freely available public resource. For more information, visit http://www.plos.org.