- by Roxana

Why I fight mosquito-borne disease

I grew up in Scotland and studied zoology at Edinburgh University. A lecture there on mosquito-transmitted disease inspired me to become a medical entomologist and I followed up my first degree with a Ph.D. from the University of Florida. My doctoral research involved fieldwork in Colombia and I moved there after graduating to work with the Fundacion CIDEIM in Cali.
I loved being able to work outdoors and interact with local people, talking with them about their problems with insect-transmitted disease and trying to devise solutions that could involve their active participation. I moved to Brazil in 1996 and while my field sites were now largely urban rather than rural, the disease I worked on (leishmaniasis) was invading cities all over the country. I found the interactions between the local people, their environment and the sand flies that transmitted leishmaniasis to be a fascinating field of study. Once again I had the chance to talk to ordinary people and learn what they felt about the problems they faced and how they might be resolved.

Bruce Alexander giving a talk to public health workers in Montes Claros, Brazil

The first cases of dengue appeared while I was living in Belo Horizonte and meant that residents of poor neighbourhoods now faced two very different insect-borne diseases. I was asked to form part of an expert committee to advise on dengue control measures in Belo Horizonte shortly before I left Brazil in 2002, but in the intervening 12 years dengue has become established there as a serious public health problem.
Returning to the UK after 20 years’ absence was a challenge. A research position at the Liverpool School of Tropical Medicine allowed me to continue working on leishmaniasis but a friend had convinced me that my ideas for vector control would best be exploited by forming my own company. I thus set up Xeroshield in 2005 to develop a pesticide-free technology for use in mosquito nets. This received an award from the Bill & Melinda Gates Foundation and is still under development.

Impression of WaterWasp™ unit in 208L oil drum used to store water

WaterWasp™ was my second idea and was born out of my previous experience with dengue control. I had seen first-hand how millions of people obtain all their water for household use from water barrels, oil drums and similar containers which are used as breeding sites by Aedes mosquitoes. I was struck by the realisation that people who already faced the threat of dengue also had to accept the contamination of their air and water by chemical pesticides as the only effective control measures against the disease. While the doses used are well within accepted safety levels, there’s no information on the possible long-term effects of ingesting these chemicals on a daily basis for months or even years on end. Furthermore, it shouldn’t be necessary – knowledge of mosquito biology reveals that there are alternative methods of killing the larvae.
Mosquito larvae are air-breathers and although they feed underwater they return to the surface every few minutes to replenish their oxygen supply. If prevented from doing so, they sink to the bottom of the container as the air bubble they use for buoyancy is exhausted. They then depend on the oxygen reserves in the system of tubes or “tracheae” that permeate all their tissues. This principle is already used in additives such as surfactants or layers of oil – our solution is a small, floating, autonomously powered device that prevents dengue mosquito larvae from reaching the surface, without tainting the water. WaterWasp™ has a robust, distinctive design and requires no regular maintenance, remaining in place over a period of 6 months before being replaced by a new unit. Each unit could be recharged and reused several times, reducing the cost to the public health authorities, construction companies and hotel chains whom we envision as being the main clients for the technology.

Larva of Aedes aegypti replenishing its oxygen supply at water surface (photo: Ray Wilson)

WaterWasp™ could also form part of an integrated control strategy, involving the destruction or removal of other receptacles, recycling programmes for trash and reduced pesticide application if necessary. The device therefore follows Xeroshield’s basic ethos of developing control methods that are environmentally friendly and can be used by as many people in as many situations as possible. Given the need to have blanket coverage in any dengue control measure, we see WaterWasp™ as being supplied to public health authorities and distributed by their personnel rather than sold off the shelf to the general public. However, local people could participate by ensuring that devices in their yards remain in place and functioning.
Our hope is therefore to license the patented technology to manufacturers in several dengue-endemic countries, including of course India, which reports over 30% of all cases worldwide. Because the technology involves no pesticides or genetically modified organisms we believe it could receive widespread approval from entities involved with dengue control worldwide and be implemented in a relatively short time.
Dengue is likely to remain as one of the world’s major public health problems for years to come and a safe, sustainable alternative to conventional pesticide use is badly needed. I firmly believe that in WaterWasp™ we already have such an alternative.