V Environmental applications of microbial symbionts of insects

Use and release of mosquitoes for the control of dengue transmission: A world-first trial in Australia

Inaki Iturbe-Ormaetxe and Scott L. O’Neill School of Biological Sciences, Monash University, Clayton, Victoria 3800, Australia

Mosquito-borne diseases such as malaria or dengue fever cause a huge health burden to people living in tropical and subtropical countries. Current control efforts are not always effective and many of these diseases have increased in prevalence, geographic distribution and severity. The transinfection of Aedes aegypti mosquitoes with the endosymbiotic bacterium Wolbachia pipientis is a promising biocontrol approach for those diseases. Naturally occurring Wolbachia strains have been stably introduced from fruit flies into mosquitoes and shown that these strains can invade and sustain themselves in mosquito populations while blocking the replication of dengue viruses and other pathogens inside the insects. This chapter discusses the release of Wolbachia-infected A. aegypti mosquitoes in North Queensland, Australia. The regulatory process for this kind of release had no precedent in Australia and was authorised after a thorough community engagement process and an independent risk assessment. At the time of writing (April 2012), a second release trial was currently underway in Queensland and the technology will soon be deployed in dengue-endemic areas of Southeast Asia and in Brazil, once appropriate approvals are in place.

Introduction

Mosquito-bome diseases are one of the major threats to human health. The malaria parasite transmitted by anopheline mosquitoes in particular causes an enormous health burden mainly among African children, and kills about 1 million people every year (World Health Organization, 2008). The second most deadly mosquito-borne disease, dengue fever, is caused by an RNA virus transmitted primarily by the bite of female Aedes aegypti (yellow fever mosquitoes). Causing about 50 000 deaths every year and affecting between 50-100 million people, this disease has increased in severity and distribution, and is now affecting more than 100 countries in tropical and subtropical regions of the world (Kyle and Harris, 2008; World Health Organization, 2009). A. aegypti mosquitoes are highly anthropophilic and breed in water containers around houses (old tyres, vases, fallen palm tree fronds, discarded items, etc.), therefore rapid urbanisation in developing countries has contributed to increasing mosquito populations and the concomitant spread of dengue. There are currently no effective vaccines or specific treatments for dengue fever nor the most severe form of the disease dengue haemorrhagic fever (Wilder-Smith et al., 2010), therefore disease monitoring and mosquito control programmes are the only preventive methods currently available. Traditional control approaches for dengue have targeted the mosquito by spraying insecticides, reducing breeding sites or using predatory copepods and fish to eliminate larvae (Kay and Vu, 2005), but these approaches can be very costly and they have not proven as effective as desired, in particular due to the rise of insecticide resistance (Kyle and Harris, 2008; Morrison et al., 2008). More recently, there has been a clear increase in activities related to the development and release of genetically modified (GM) mosquitoes, particularly to control the dengue and malarial vectors. The first generation of transgenic mosquitoes designed to suppress A. aegypti populations by effectively using a method similar to the sterile insect technique were released in the Cayman Islands in November 2009 (Reeves et al., 2012), while another release took place in Pahang, in Malaysia, between 2009 and 2012. These releases have been somewhat controversial and have not always been preceded by publication of the associated hazards and their regulatory approval processes (reviewed by Reeves et al., 2012).

 
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