The mere knowledge that mosquitoes are the carriers ofa number of Diseases like malaria, filariasis and dengue is not enough to check the spread of vector-borne diseases. P K Dits, director of the Pondicherry-based Vector Control Research Centre (VCRC) was at the Centrefor Science and Environment recently and spoke to SONIA KAPOOR and PRITI KUMAR about the problem
On the status of vector borne diseases in India - whether these have been on the rise over the years:
Using large ancounts of DDT has not helped in lowering the number of malaria cases caused by ILasmodium falciparum The number of malaria cases are about two million and have remained so for several years. Incidence of all the other vector-borne diseases is on the rise and some of the diseases which were not a problem earlier, like Japanese encephalitis and dengue, have now become a matter of serious concern.
On the various factors responsible for this rise:
The first major factor is the rise in population. The lower is the population of the area where a vector-borne disease strikes, the less are the chances of its becoming an epidemic. The spread of the disease is directly proportional to the population. Secondly, we have converted a complex ecosystem into a very simple one where mosquitoes can breed much more easily. For instance, earlier there was a seasonality in the vector, that is, each vector was present in a particular season. Now, because of developmental activities, we have made favourable Conditions for the vectors to breed throughout the year. Also, normally during extreme climatic conditions, vectors do not breed. But now we have coolers and aftconditioners which create ideal breeding grounds for mosquitoes. our developmental activities are mainly in the direction of providing food to everyone. For this purpose, we have dug bore-wells in order to do paddy cultivatio.. As a result, Japanese encephalitis, which was earlier prevalent only in the rainy season, is now seen all the year round.
Mosquito" causing dengue often breed in moist and dirty sites. Rainwater accumulates in waste cans and containers lying around in the open- These and garbage are excellent sites fordengue mosquitoes to breed- Ifive have better recycling and garbage disposal systems, the problem will be solved to a great extent.
I am not being optimistic or pessimistic, but I'm being realistic when I say that unless there is a revolution, these diseases will not go.
On how correct the statistics are about these diseases:
Data is collected in India by the organisationt that is responsible for controlling the disease So this data is as good as no data. I would like to share my personal experience with everyone.
In a village consisting of 200 people, there were 64 deaths due to malaria. However, a survey which was based on a questionnaire did not reveal malaria. Instead, it concluded that all 64 deaths were due to meningitis. The results seemed to be manipulated and the matter became the health department's responsibility, which sent another team with a strong description of malaria. But malaria could not be confirmed. Finally, the case went to the revenue department and they concluded that the deaths were due to starvation. When the final report came out, all the in outbreak areas 64 deaths were shown to be due to a combination of old age, diarrhoea, meningitis and malaria, and all these were below epidemic levels. So do not ask me about statistics; I can tell you that statistics are used and misused in many ways.
On what is VCRC's overall approach towards the control of vector-borne diseases:
At VCRC, we believe that if our country has better recycling of waste and proper water management, then only can vector-borne diseases be controlled, otherwise we are fighting a losing battle. For example in Tamil Nadu, a state where people are much more receptive, VCRC is conducting training prog;rammes in nine zones to keep vector-borne diseases under control. A major filariasis control programme is being carried out in many rural areas, which involves the use of insecticideimpregnated bed-nets.
On VCRC's approach to environmental management of vectors:
In the past, VCRc has demonstrated in a number of places that vectors can be controlled by environmental management. But its experience has been that after a successfully demonstrated project is handed over to the state government, it fails. VCRc has decided that, in future, it is not going to conduct demonstration projects on environmental management. Instead, we will train the state government in such a way that they can do the work right from the beginning.
on the role of the state:
Public health is a state subject. But the state does not have enough power and resources. For example, the Centre decides whether chloroquine should be sent to the state. The state is involved only in executing the plans made by the Centre. What business does the Centre have to decide? The Centre should only have surveillance and monitoring units.
On the current strategy for the control of malaria, which involves giving chloroquine and spraying insecticides in the outbreak areas
It is stupid to implement this strategy. In fact, I strongly objected to this strategy and now I am not called to most meetings. But now it is being realised that this method is only going to make a cheap drug like chloroquine ineffective. Resistance to this drug develops very fast; therefore, its careless and casual distribution will only create problems. In future, new and costly drugs will have to be bought, which our country wfll not be able to afford.
On the alternative methods of vector control:
Remember that any insecticide is a poison. If it can kill a mosquito, it can definitely affect at least one or two cells of your liver. Synthetic pyrethroids are an alternative to DDT. These are used in mosquito coils and mosquito-repellent mats. By using coils and mats, you may not die immediately but in the long run, you may end up having liver cancer. Another effective way of vector control is to screen houses. Usage of hed-nets and insecticideimpregnated bed-nets are alternative methods for disease prevention.
On natural pyrethroids as alternative methods of vector control:
There are certain drawbacks in natural pyrethroids. Firstly, how do you produce so much natural pyrethroids? Secondly, in biological products there is no standardisation. Two common examples of natural pyrethroids are Deem and citronella. Although, natural pyrethroids may seem to be a good alternative, their long-term safety is not yet known.
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