Better water-storage practices can control mosquitoes, dengue
Various factors including unplanned urbanisation have led to more frequent dengue outbreaks recorded between 1997 and 2010 in T&T. Studies conducted in T&T at the University of the West Indies and Carec reveal the incidence of dengue has not been controlled adequately because of a lack of resources, poor management practice in the dengue and vector control programmes and resistance to insecticides in mosquitoes. There are no vaccines available for dengue so only the control of the mosquito can lead to the control of dengue transmission and spread.
The dengue viruses (Den 1-4) are transmitted by the bite of infected Aedes aegypti and Aedes albopictus mosquitoes. The female mosquito acquires the virus while feeding on the blood of infected humans. Infected humans are the source of the virus for uninfected mosquitoes. The mosquito lives in close association with humans in the urban and suburban environments. Therefore, dengue is generally considered a disease of urban areas, and its epidemiology is highly related to the biology of the mosquito vector, the environment and human behaviour.
In Trinidad and Tobago the main breeding sites of the Aedes aegypti mosquito are water drums or water barrels which account for over 70 per cent of the mosquito breeding, followed by tubs and basins (16 per cent) and buckets (9 per cent), with small containers like, bottles, vases, cans in and around the home accounting for less than 5 per cent of the mosquito population. Clean-up campaigns such as removal of garbage, small containers and large household items are good for the environment and aesthetics but have little or no impact on the mosquito population and on dengue transmission as these containers are not major producers of adult mosquitoes.
What is required is a source reduction programme targeting water storage containers such as drums, buckets and basins and, in the long term, a more efficient water supply to prevent householders from storing potable water. Unfortunately, new approaches have not been adopted by vector control programmes to meet with these new challenges. For example, the school spraying programme was designed to kill mosquitoes which alight on wall surfaces of the school building but this approach is treating the symptoms and not the root cause.
Why not attack the source of the mosquito breeding population by treating all water storage containers in and around houses in close proximity to the schools as well as the water storage tanks which are the main Aedes aegypti breeding sites and the primary water supply for schools? This approach would be treating the source of the mosquito breeding problem. The effect of heavy rainfall on insecticide treated containers is that as the water overflows it causes the dilution of the chemicals or insecticides applied and these sub lethal doses can lead to mosquitoes acquiring resistance to these agents. In addition, heavy rainfall does not wash out the Aedes aegypti immature stages from water drums and other primary breeding sites since immature stages swim to the bottom of the container.
Based on the Caribbean approach, it seems evident that many specialists feel that it is easy to control mosquitoes and their associated disease because you simply destroy the breeding sites of the mosquitoes by clean-up campaigns and by applying insecticides, and like magic, “abracadabra” the problem disappears. Clearly, it is more complicated than that and until a vaccine becomes available (unlikely in the near future) a thorough understanding of the mosquito, the dengue virus aetiology and human behaviour, are essential for control of dengue fever transmission.”