The Hindu 25.11.2009
Density of mosquitoes goes up in urban areas
Ramya Kannan
| Good news is that they are unlikely to cause major diseases |
CHENNAI: The bad news is that the density of mosquitoes, primarily in urban and peri-urban areas in the State, has gone up, in a comparative analysis over the last six months. According to the classic 10 man hour density test, there has been a steady build-up over the last six months in Tamil Nadu.
However, the good news is that these mosquitoes are mostly ‘nuisance’ mosquitoes, unlikely to cause major vector-borne diseases like malaria, dengue, and chikungunya. In fact, the disease load has come down drastically throughout the State, especially in the Chennai region otherwise endemic to malaria. “This is because when we say the density of adult mosquitoes is up, we mean the Culex variety. In fact, the density of the malaria-causing Anopheles mosquito is actually less than normal for the season,” S. Elango, Director of Public Health, told The Hindu.
The Culex variety causes filariasis or Elephantiasis, but can transmit the disease only if the Micro Filaria (or filarial parasites in the human blood) rate in the community reaches a critical point. “We are well below the transmission rate, so practically the Culex mosquito can only cause nuisance, buzzing around and biting,” he said.
Some of the Chennai Corporation wards, the areas under the Corporation of Coimbatore, Erode, Tiruvannamalai, Madurai Corporation zones, Theni and the municipal corporation area of Tuticorin are areas where the 10 man hours test has shown an increase. “It is by no means an alarming increase, but a gradual build-up over a period of six months,” Dr. Elango said.
Chennai Corporation Commissioner Rajesh Lakhoni said the rise was consistent with the post-monsoon season. “We are trying to get rid of the malarial parasite in the community. But apart from that, we are into source reduction, the focus now being larvicides, rather than fogging,” he said.
The practical thing to do is to focus on the larval mosquito; it takes a week to mature into an adult. Using bio-larvicides along larval breeding grounds daily will nip the problem in the bud and prove to be more effective than the regular dawn and dusk fogging that is anyway being carried out everyday. However, post rains, water stagnation in open grounds, small containers and pools are rendered breeding grounds for freshwater mosquitoes.
Corporation Health Officer P. Kuganantham said the campaign is on with residents’ associations to take action and get rid of breeding grounds inside apartment complexes and clean the overhead tankers periodically. These efforts will have to be carried out throughout the State.
“We cannot achieve low mosquito density without the involvement of the public. Freeing their homes of breeding areas and clearing overhead water tanks is essential. Otherwise, even if we manage to reduce external breeding there will be no effect whatsoever.”
Public health officials, however, caution that members of the public should take adequate precautions to avoid mosquito infestation and go for blood tests if they have persistent fever.
