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Published : 05 Aug 2019, 03:31 PM
Municipality authorities are struggling to bring in new insecticides as they depend on fogging to kill Aedes mosquitoes.
But Dr B N Nagpal, senior entomologist of WHO Southeast Asia region, dismissed fogging as a “myth” while talking to journalists in Dhaka.
“Fogging on the street and open areas is a myth. Clean your own house and spray aerosol in the morning and evening because Aedes rest inside the house,” he said in a special briefing organised by the health department, DGHS.
Dengue fever cases are rising in the region with hundreds of thousands of people are being affected, he said.
But he said the “source detection” of the dengue mosquito breeding is the key. “It can breed even in 2ml water,” he said, showing a cap of a water bottle.
He said dengue mosquitoes lay eggs not directly inside the water. “They lay eggs on the brim where those eggs can survive as long as one year and when flooded or when the container is fully poured, eggs hatch rapidly”.
“It’s a smart mosquito. It does not rest on walls. It rests under the tables, beds, sofas, curtains, hanging clothes and dark places,” he said, suggested spraying in those places.
“But source detection is the key. We should give a plain message to the people that clean your house once in a week for one hour,” he said, adding that Sri Lanka could control the spread of this mosquito with this message involving people.
“We need to give proper message to the community because without community mobilisaiton this disease cannot be controlled,” he said, adding that if people act on the message, in 10 days the disease can come under control.
. Clean your house once a week for one hour · Dengue mosquito breeds inside homes, even in 2 ml water or in a small water bottle-cap · Dengue mosquito does not sit on walls · It rests under the bed, sofa, chair, table, or behind the curtain or hanging clothes. Spray aerosol in those places · Aerosol spray inside homes is more effective after sunrise and before sunset · For larvicide, WHO suggests the use of Temephos 1 gram in 10 litres of water |
His information has opened a new avenue in mosquito control, but come on the contrary to the common perception. This also exposes the depth of Aedes mosquito control knowledge of the policymakers, and a journalist asked him whether such disaster could be prevented if the government knew the right information even six months ago.
“This is also the right time,” he said, adding that now the government can act before rising the number of cases to 100,000, 200,000 or 300,000 as seen in many countries this year.
“We’re still not losing the time. Up to September, this transmission will be there. So we’ve to cut all the breeding places,” he said.
“Each mosquito has its own way of breeding and surviving, thus control is different.”
On another question why WHO did not intervene when the outbreak began couple of months back since Bangladesh is a very active member of the Southeast Asia region, the expert did not give any answer.
Director General for Health Services Prof Abul Kalam Azad who invited him to come to Dhaka intercepted and said “it’s a question to WHO administration, not for him”.
He also urged the media to act as a bridge between the government and people so that the right message can be conveyed to all.
The WHO expert also urged the media to reach public with the right message. “We can give the technical input and output. But you can give the right message to the people”.
He also said that the larvicide would not be effective “unless you put right medicine in right dose and in right way. You will be only polluting the environment”.
“This is very important for Aedes mosquito,” he said, adding that WHO suggests use of Temephos 1 gram for 10 litre water for larvicide.
He said in fogging ingredients over 95 percent is diesel or kerosene. “We all are inhaling those and getting respiratory diseases and heart problems,” he said, “WHO totally stopped recommending fogging”.
He said this mosquito never breeds in drains, ponds, lakes, rivers, pits, and garbage. “Those are Culex mosquito.”
He said in searching of resting places adult mosquitos frequent a wide range of places. “Mosquitos are generally found in areas where the air is relatively static and the humidity is high.”
“They can disperse maximum three to four hundred meters,” he said. “Eggs can be transported long distances in dry conditions, he said, suggesting scribing the brim of water pots, glasses.
He said male Aedes mosquito survives 7 to 10 days while the female that sucks blood survives four to six weeks. They bite every alternate day. Each oviposition (laying of eggs) is followed by another blood meal”.
“They need blood for laying eggs. To get that required blood, one female mosquito can bite from five to 17 people because since they bite in daytime when one person feels the pain of piercing the blood vessel, they react and the mosquito flies away, and sits to another person. In this way it goes person to person to complete its blood need.
“We don’t have cattle in urban setting, so they depend on human,” he said, adding that massive construction sites in Bangladesh also a contributor of the dengue mosquito breeding.
Transport department, police, airport authorities, horticulture department, civil department and all government offices have role to play. He said police dump stolen cars outside where this Aedes mosquito also breeds.
He also suggested cleaning the outer side of the overhead water tanks.
Even the drop of rain water accumulates in steel gates outside the home can be the breeding ground of Aedes mosquito.
He said aerosol spray inside the home is more effective after sunrise and before sunset.
He said Bombay controlled dengue through some legislations for construction sites and tyre repairing shops. “They cannot keep tyres open outside like elsewhere. Instead they display tubes as a sign of their shop”.
As the dengue spreads outside Dhaka, people fear the presence of Aedes albopictus can aggravate the situation.
But the WHO expert said Aedes aegypti is the main vector for dengue. “The albopictus, which is common in rural settings, is less virulent when it comes to spreading dengue. It’s not a strong vector. Albopictus can play a 0.5 percent to 1 percent role when a large number of cases are there [in rural settings]. Then only few cases can be generated by the albopictus.”
