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12.42% of city locations visited are potential dengue mosquito breeding grounds: CMC
The results of a survey on dengue breeding grounds conducted in Colombo on Tuesday (16), Wednesday (17) and Thursday (18) have given the Colombo Municipal Council (CMC) cause for concern the Sunday Times learns.
A total of 7,883 premises comprising houses, state owned institutions, private institutions, bare lands, schools and religious places were visited. The report submitted by the municipality stated that of the places visited, 979 premises (12.42 per cent) contained possible dengue breeding grounds. Of these it was the private institutions and state owned institutions that had the most number of potential dengue mosquito breeding places with 51 and 18 such places respectively.
CMC’s Chief Medical Officer of Health (MOH), Dr. Ruwan Wijayamuni, told The Sunday Times “the 12.42 percent of the premises which contained possible breeding places for mosquito larvae is my main worry. The various breeding places found on these premises have the potential to collect water during the rainy season. Following this, a week of dry weather could show an increase in the mosquito population”.
He added “past dengue eradication programmes were very effective and we are pleased with the work being carried out. This is the peak dengue season, yet the dengue case-load is very low in comparison to figures from last year.”
Dr. Wijayamuni added “we have had 1,279 cases reported from within Colombo city limits up to June this year. This is a remarkable reduction in comparison with the 1,435 cases reported in the corresponding period last year.
“This reduction is due to the strategy that we adopted. We targeted several dengue prone areas such as Mutwal, Aluthmawatha, New Bazaar, Fort, Suduwella, Kollupitiya, Pamankada, Wellawatte and Cinnamon Gardens. The programmes we carried out in these areas have proven effective”, he said.
Dr. Wijayamuni added that “ten years earlier the reporting of cases of dengue began in Colombo West and Colombo East and later shifted to Colombo North and Colombo Central from these areas. However these patterns changed and in 2013 and 2014 the outbreaks started occurring first in Colombo North and Colombo Central and shifted to Colombo West and Colombo East from there.
“This year patterns have changed once again and it was observed the pattern which was observed ten years ago is repeating itself. We have changed our strategy accordingly. “We have an effective cadre of workers and I have reorganised the pest control unit that was established two months ago,” Dr Wijayamuni said.
The MOH said the recently formed pest control unit comprised an Entomological Unit which is now in place and had full-filled a long-felt need. He noted the entomologist in place conducted several forms of research on mosquito density and carried out surveys and calculates a house index and container index etc.
As a result of the studies undertaken by the entomologist, the CMC has been able conduct research into identifying mosquito types and the efficacy of several biological methods used to kill the larvae, he said. “For example we breed mosquitoes at the laboratory and subject them to control methods such as fogging etc. When it comes to fogging we conduct two tests known as the knocking time and the lethal dose. The knocking time decides how long it takes for the mosquitoes to die and the lethal dose decides on the dosage necessary to kill the mosquitoes.”
“We have never had this facility before and it has helped us significantly since we received it. We will be using this facility for health education as well, Dr. Wijayamuni said.
“We are aware that some people say these programmes aren’t effective, but we have faith in the programmes and they have helped reduce the number of cases. The technical difficulty in controlling the disease has to be attributed to the female mosquito laying eggs that already contain the dengue virus. The offspring developing from those eggs are already infected and can spread the disease,” he said.