Thomas C ErrenI,1; Michael ErrenII
IInstitute and Policlinic for Occupational and Social Medicine, School of Medicine and Dentistry, University of Cologne, Kerpener Straße 62, D-50937 Köln, Lindenthal, Germany
IIInstitute of Clinical Chemistry and Laboratory Medicine, Westphalian Wilhelms-University of Münster, Münster, Germany
In a news item in the Bulletin, Orozco outlines some of the history and extent of dengue transmission in tropical countries since the 1970s.1 According to experts, a major reason for the disease's re-emergence in Latin America during the past two decades is the widespread presence of the mosquito vector, the female Aedes aegypti mosquito, which transmits dengue among humans. The balanced call for a combination of measures, including vector control, dengue prevention and, preferably, developing a vaccine, is to be commended. Overemphasis of, and too much reliance on, any single approach should be avoided.
To illustrate, Chadee et al.2 see much promise in the recent release of the genome sequence of Aedes aegypti3 which comes four years after the genome sequence of Anopheles gambiae, the key mosquito vector of malaria in Africa.4 Even while acknowledging that there are challenges ahead in using the genetic code to better control dengue and yellow fever, the authors title their report in Science "A breakthrough for global public health", suggesting that tangible results could be just around the corner.
But from the experience with Anopheles gambiae which transmits malaria to some 400 million people globally per year, of whom up to 3 million die of the disease, we know that mosquito-associated diseases are enormously complex. Malaria is caused by parasites of the genus Plasmodium and, according to the United States Centers for Disease Control and Prevention,5 some 3040 different Anopheles species may serve as vectors. This did not prevent the claim being made in the course of the Malaria Genome Project that a solution to malaria might be only five years away. But despite the deciphering of the genome of Plasmodium falciparum in 20026 and the release of the Anopheles gambiae genome in the same year,4 the director of WHO's Global Malaria Programme, Arata Kochi, recently urged not high-tech genome-based measures but the old-fashioned and "politically unpopular" indoor spraying with DDT to effectively prevent malaria.7
Mapping the genome of the second mosquito species in full is an important achievement, but there is no reason to expect that issues surrounding Ae. Aegypti will be less complex than those concerning Anopheles gambiae. In fact, the vectorvirusdisease relationships may be even more complex to unravel (the Ae. aegypti genome is about five times the size of the genome of the malaria mosquito),3 and it is likely to be a long time before genome sequence information can be translated into "new approaches for vector-targeted control of disase".3 A real breakthrough in global public health is likely to take even longer.
Comprehensive prevention plans, as suggested by Orozco's article, seem a must to fulfil the difficult tasks of defeating dengue.
1. Orozco J. Defeating dengue: a difficult task 1. ahead. Bull World Health Organ 2007;85:737-8. PMID:18038050
2. Chadee. DD, Kittayapong P, Morrison AC, Tabachnick WJ. Genetics. A breakthrough for global public health. Science 2007;316:1703-4. PMID:17588917 doi:10.1126/science.1138904
3. Nene V, Wortman JR, Lawson D, Haas B, Kodira C, Tu ZJ, et al. Genome sequence of Aedes aegypti, a major arbovirus vector. Science 2007;316:1718-23. PMID:17510324 doi:10.1126/science.1138878
4. Holt RA, Subramanian GM, Halpern A, Sutton GG, Charlab R, Nusskern DR, et al. The genome sequence of the malaria mosquito Anopheles gambiae. Science 2002;298:129-49. PMID:12364791 doi:10.1126/science.1076181
5. Malaria. Anopheles mosquitoes. Centers for Disease Control and Prevention. Available from: http://www.cdc.gov/Malaria/biology/mosquito/ [accessed on 6 February 2008].
6. Gardner MJ, Hall N, Fung E, White O, Berriman M, Hyman RW, et al. Genome sequence of the human malaria parasite Plasmodium falciparum. Nature 2002;419:498-511. PMID:12368864 doi:10.1038/nature01097
7. Kochi, A. WHO malaria head to environmentalists: 7. "help save African babies as you are helping to save the environment". Press statement, National Press Club, Washington DC. 15 September 2006. Available from: http://malaria.who.int/docs/KochiIRSSpeech15Sep06.pdf [accessed on 6 February 2008].