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| Sunday, 15 August 2004 |
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Features |  |
| News Business Features Editorial
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Controlling dengue with biological agents
Apart from dengue, other mosquitoes also convey various deadly diseases like Malaria (caused by the Anopheles Culcifacies), Filariasis (conveyed by the Culex Quinquefasciatus) and Japanese Encephalitis (caused by the Culex Spp), which have their peak season at different times of the year. The failure of chemical agents now in use, and increased public concern of the potential adverse environmental effects associated with the extensive use of chemical insecticides, has prompted a search for alternative methods of mosquito control: One of the most promising of such alternatives, is the use of biocontrol agents such as Entomopathogenic Bacterium, Bacillus Thuringiensis (Bt), a technique which has been used with success in Cuba. Observer staffer Carol Aloysius speaks to Dr Radhika Samarasekera, Senior Research Officer of ITI, who is currently leading a project using Bt in a local setting for mosquito control in Sri Lanka. The project, if successful, will bring new hope to victims of all mosquito borne diseases including Dengue. Q: Tell us about this project. For how long has it been in operation?
Upto now we have sprayed around 203 soil and water samples from different habitats islandwide and found 12 active Bt strains in areas like Hambantota, Gampaha and the dry zone. Most of the habitats were abandoned lakes and marshy lands. Q: Who ise involved in this research? A: An entomological team from the MRI did the collection of samples. The ITI's job was to isolate the bacteria and test it at lab level against all three vector mosquitoes - dengue, filaria and malaria. When we found that 12 were active, we did a wetable powder formulation which is tested at lab level. At present we are conducting field studies of the formulation. We are doing this in collaboration with the CMC and MRI and are still only half way in our studies. Q: What have been the results so far? A: We could see that after 24 hours of applying this formula, hundred per cent of the mosquito larvae was destroyed. I'm also monitoring the new larvael breeding on the sites applied. So far I have found zero larvael breeding upto 21 days following spraying. Q: Are you targeting only the dengue vector or other mosquitoes as well? A: At lab level we have found it effective against all mosquitoes including the dengue vector. But we're still continuing our field studies. Q: What has been the popular method of eliminating these mosquitoes upto now? A: So far we have been using mostly chemical agents to control our mosquito population islandwide. They include Malathion. Temephose, Fenethion etc. Q: How effective are these chemical agents? A: The most important factor is that the mosquito has developed a resistance to these chemicals which have thus become ineffective in the field. Apart from this, these artificial chemicals are causing adverse effects on humans, animals, plant life and the environment as a whole. They are toxic to many beneficial flora and fauna and the residual effects last for a longer period in food and water. chemical agents are also very expensive to develop and take a long time to be registered before they are marketed. Q: Is this why your organisation has started experimenting with biological agents as an alternative for mosquito control? A: Yes. We believe that bacillus thuringiensis (Bt)t is much safer than chemical agents both for man and the environment. Bt is also the most widely used microbial pesticide in the world, accounting for 95 per cent of the world market of microbial pesticides. Compared with the growth rate of chemicals annually, which is only 2 per cent, the growth rate of bio pesticides per year is now between 10 to 15 per cent. Q: What is bacillus thuringensis? A: Bacillus thuringensis is a germ positive, rod shape, aerobic and spore forming bacterium closely related to the omnipresent soil bacterial called bacillus cereus. The vegetative cells are 1 cm in width, 5 cm long and have short hair lie flagellae. Q: How does this bacteria function? A: Bt produces crystal protein (gamma endotoxin) during sporulation. These crystal proteins can cause lysis of midgut epitheilal cells of mosquito larvae which leads to gut paralysis and death of the larvae. Q: What are the advantages of using Bt? A: It is target specific, ecologically safe and non toxic to mammals and non target organisms. It also has the distinct advantage as a non resistant development agent. Bt also has consistent performance in various habitats and has been found to survive for long periods of time. Q: For how long can it persist in the environment? A: For upto 7 to 28 days. Q: This means that you need less frequent spraying? A: Yes. Q: Can Bt survive in any kind of soil? A: Bt endospores can survive in most types of soils, which is another advantage. The fate of the Bt in soil is likely to depend on microbial competitions. Q: What about water bodies? A: Bt can be found in water for 8-12 days after spraying. It has been observed for a longer time in natural water bodies due to the presence of higher amounts of nutrients. Q: What are the effects of Bt on the environment in general? A: So far we have found no change in productivity and fertility of soil because of Bt's natural occurrence in soil, lack of accumulation and relatively short persistence. Water quality is also not directly affected by Bt. Hence the presence of Bt on water is not considered to cause any adverse effects on human health as it is not a human pathogen. In the case of plant life, phytotoxicity from Bt has never been observed in our studies. Terrestrial and aquatic plants cannot be affected as there is no mechanism for ingesting the bacteria and for processing the crystal proteins. Q: Any adverse effects on amphibians, reptiles, birds and mammals? A: None. Q: What about human beings? A: No evidence of any adverse effects from Bt on humans through dermal, oral and inhalation has been found, apart from minor ailments like nausea and itching in spray workers. Q: Who can use this technique? A: Only authorised persons will be allowed to use the larvae sites for mosquito control in Sri Lanka. So spraying will only be by government bodies like the CMC, anti filaria campaign and anti malaria campaign etc who have the necessary equipment. Q: When does the Project end? What happens afterwards? A: We still have to cover more scientific data like identifying sub species of Bt bacteria. Once we complete our field studies and we see positive results we can recommend this method to be used for mosquito control. Q: If this technique should work, will dengue, filariais, malaria and Japanese encephalitis be diseases of the past? A: I certainly hope so. |
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News | Business | Features
| Editorial | Security Produced by Lake House |
The dengue epidemic is at its peak. Despite efforts to eliminate the
dengue carrying vector, it is still at large transmitting its deadly
disease to young and old alike. The mosquitoes that transmit this deadly
disease are the Aedes Egyti. and the Aedes Albopictis, also known as Tiger
mosquitoes.
A: We began our project in 2002 August. It was initially fully funded
by the Sri Lanka Insurance Corporation administered by the Sri Lanka
Association for the Advancement of Science (SLAS). Although the funding
was withdrawn last year, our project is still continuing.
