Unattended Canals Provide Dengue Breeding Grounds

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By Dinouk Colombage
The newly dredged canals and lakes are providing the perfect breeding grounds for the dengue mosquito, according to microbiologist Sohan Fernando. Fernando explained that in and around Colombo the lakes and canals that have been dredged needs constant monitoring by the authorities to ensure the dengue carrying virus does not breed in the waterways. “While most of the waterways in Colombo have live fish and bird life, there are areas which are being overgrown. These are the areas that are providing ample breeding grounds for the Aedesaegypti mosquito (dengue carrying mosquito),” he said.
Fernando went on to explain that the mosquito does not need a large area of water to breed in, “even a small puddle of water will be enough for this mosquito. With that in mind the canals are providing a perfect area. There are spots in many of the canals in Colombo which are being overgrown with water-hyacinth or water-lilies.”
He said that the surface of the water in these areas is cut off from sunlight repelling both the fish and birds. “We will often find the mosquito has laid its eggs amongst the water-hyacinth, in the space of eight days the eggs will have hatched and transformed into a fully formed adult mosquito,” Fernando said.
He said that while the waterways in Colombo have added a new dimension to the city they cannot be left unattended. “Most of these canals that have been cut were pre-existing ones. They were simply overgrown due to negligence on the path of the authorities. If this happens again we will be faced with a serve dengue outbreak,” he explained.
Dr. Chamara Perera, contributing micro-biologist lecturer at the University of Moratuwa, voiced his support for Fernando’s theory regarding the spread of dengue. “The canals are large and mosquito free, however, there are pockets which are providing ample breeding grounds for the virus carrying insect,” he explained.
Perera went on to say that it is not only the canals which are being overgrown with vegetation that are helping the spread of the virus, but also those that are not being cleaned by the municipal councils.
“In Wellawatta and even on Lake Drive the canals are not being cleaned by the council, they are full of garbage and the top layer of water is covered with a thick layer of oil,” he explained. In 2010 Perera was part of a team consisting international scientists who were studying the spread of dengue around the world. “The most common feature in the spread of dengue around the world was the presence of canals in urban areas. This is not to say that the canals are the root cause. In Europe many cities have canals but there is no dengue. It is a case of where the canals have been poorly monitored allowing the dengue mosquito to breed,” he said.
In Lake Drive near the canal residents have complained that the pollution in the canal is affecting them greatly. “We have had several cases of dengue in the neighbourhood, while there have been other countless illnesses that we know are being caused by the polluted waterway,” Sajan Pushpakumara, a local resident, said.
Pushpakumara said that they had been complaining to the local council but the authorities are not doing anything. “They are more concerned about building roads than worrying about the health concerns in the city. By now they should have cleaned up this canal,” he said.
However, CMC Public Health Inspector, M. Karunatilaka, explained that despite their efforts the local residents continued to pollute the waterways. “We have sent teams there to clean the waterways but it is very difficult to keep them clean without the assistance of the residents in the area. If you look in the water it is polluted with plastic bottles, bags and garbage. That is all coming from the neighbouring houses,” he said.
Karunatilaka added that the UDA along with the relevant municipal councils are systematically cleaning up the canals to ensure they are not overgrown. “We know the danger that could result if these canals are not tended for. We doing everything possible to make sure that does not happen,” he said.
However, Pushpakumara countered these allegations, “If you look at the canal the CMC has allowed a major drain to lead right into the canal. When it rains heavily, garbage is washed into the canal. They need to re-design their canals rather than blame the residents.”
While the blame game continues to be played between the public and the authorities, the number of dengue cases continues to rise in the country. Nearly 16,000 cases of dengue have been reported around Sri Lanka in 2012 alone.