Biological method of bringing aedes under control

The news pours honey into people's ears, particularly the inhabitants of the capital city and other urban centres grappling with a vicious zoonotic disease called dengue. Aedes aegypti serves as the vector of dengue virus in spreading the disease, at times in an epidemic form. Now the news is that wolbachia, a bacteria found in butterflies and some species of mosquitoes but not in aedes has the potential to render dengue virus biologically inactive. But it does not happen naturally. Scientists have had to intervene. An international team of scientists from the QIMR Berghofer Medical Research Institute, the University of Queensland, the International Centre for Diarrhoeal Disease Research (ICDDR), Bangladesh and the US Centre for Disease Control and Prevention has developed a wolbachia-infected strain of aedes called 'good mosquito' that can adapt to the tropical condition prevailing in the capital or perhaps Bangladesh.

Now the wolbachia-infected mosquito loses the capacity to transmit not only the dengue virus but also the viruses of chikungunia and zika. While it acts as an antidote against dengue, chikungunia and zika viruses, it is safe for human beings and the environment. It is like, as a conventional Bangla adage can be translated, 'one thorn drives away another'. This heat-tolerant strain of Wolbachia was developed through cross-breeding with several generations of local aedes varieties.

The research team proposes to do the trick by employing two methods. First, the suppression method that envisages release of wolbachia-infected males developed in laboratory, which when mate with wild females, the eggs will become unviable. In the process, the mosquito population will decline on its own. The other is replacement method which approves release of both male and female infected with wolbachia bacterium. Here the objective is to see that the successive generations of mosquito offspring carry the bacterium and gradually replace the virus-carrying females which alone cause dengue and other diseases.

This biological containment of the aedes, however, is not unique to Bangladesh. Quite a few countries have successfully applied this by this time. In northern Queensland, the success rate of containment has been 96 per cent. The control rate of this sub-species of mosquitoes is 95 per cent in Indonesia, Brazil, Colombia, Malaysia, Singapore and the United States of America. The heat-tolerant variety suitable for release in conditions and climes like those of Dhaka has shown 92.7 per cent reduction in transmission of dengue virus. The rate is a little lower than in the countries mentioned above but still it is good enough to bring the aedes population under control provided that the outcome in the open condition corresponds to the laboratory test results.

Fumigation and other methods applied so far to fight dengue has proved mostly futile. This biological system of control is preferable because it is unlikely to have any adverse impact on the environment. Scientists claim that infecting mosquito with Wolbachia is no genetic medication because the natural bacterium is present in butterflies and other varieties of mosquitoes. If this is no genetic transformation, the scientific tinkering with the vector's capacity to transmit the dengue virus does not pose the threat of evolution of dangerous strains of mosquitoes. However, if the population of aedes aegypti is drastically limited or, in extreme cases, eliminated, will there be another strain of mosquitoes to replace it?  Researchers may spare a thought for any such possibility.

Presently, though, local etymologists have expressed their scepticism about the success of the drive. Some of them think that the strain of aedes developed in laboratory will be weaker and fail to compete with their wild counterparts. In a highly crowded city, aedes mosquitoes have their breeding ground in the most congested spots of residential accommodations where the laboratory-bred type will fail to reach. Considering this argument substantive, however, there is no reason to abandon the project. After all, mosquitoes have to come to people at some point to bite and infect the latter. The laboratory type will have a meeting point there and avail of the chance to neutralise the wild variety's infection capability. There is no harm in considering release of wolbachia-infected aedes a vital part of an integrated strategy for controlling mosquitoes that act as vectors of dengue and other related diseases.

nilratanhalder2000@yahoo.com