How effective is fogging against Aedes mosquitioes?

Jakia Ahmed
Published : 07:30, Aug 09, 2019 | Updated : 08:59, Aug 09, 2019

Mosquito repellents being sprayed with a fogger machine in a bid to controll the dengue outbreak. PHOTO: BANGLA TRIBUNE/Sazzad HossainThe hospitals are nearly folding under the sheer pressure of dengue patients everyday, leaving the entire country in a state of panic. Even thought the government refuses to acknowledge the massive breakout as an epidemic, the number of deaths is increasing with the alarming number of patients being admitted into hospitals.
Dhaka being the worst-hit region of the mosquito menace, the two city corporations are up to their neck tackling the situation and their workers spraying mosquito repellents with fogger machines across the city.
However, the World Health Organisation Southeast Asia regional chief etymologist Dr Bhupendra Nagpal says, “Aedes mosquitoes are smart, fogging is ineffective against them.”
Aedes is the vector or carrier of the dengue virus and they generally breed in stagnant water and dark, humid corners such as behind the curtains or under tables or chairs.
His remarks came amidst the shower of criticism on the two city corporation for the ineffectiveness of their mosquito repellents.
“It’s only a myth that spraying repellents in open spaces through fogger machines kills Aedes mosquitoes,” he said.
Instead, he recommended keeping the houses clean and spraying aerosol twice a day. He observed that failure to spray the correct repellent in the correct amount will render the drive against Aedes larvae completely futile.
Saying that the repellents sprayed through fogging are 95 percent diesel or kerosene he added, “We are inhaling those medicines which cause respiratory and coronary complications. That’s why the WHO does not recommend it.”
He recommended focusing more on destroying the larvae. “Aedes mosquitoes lay eggs on the surface level of water and they stay alive all year.”
“It’s a misconception that Aedes mosquitoes lay eggs only during monsoon. In reality they lay eggs 356 days of the year and nothing happens to those eggs even if they lie around for one year,” he said.
“Hence there is no way to control the disease without vector control,” he added.
“A mixture of one gram of Temephos in 10 litres of water is very effective to destroy Aedes larvae,” he said and added that if it can be used then the mosquitoes won’t be able to breed for at least three weeks.
The WHO official said that around 40 percent of the outbreak can be brought under control by keeping the breeding grounds in the under-construction buildings clean.
He said that spraying diesel and kerosene in those breeding spaces once a week will be quite effective.
Although she refused to comment on the effectiveness of fogging, Institute of Epidemiology Disease Control and Research (IEDCR) chief Dr Meerjady Sabrina Flora emphasised on the destruction of breeding grounds of dengue carriers.
“If the source reduction can be carried out mosquitoes can be controlled. If not, it’ll go on till September,” she said and added that September is the peak time and source reduction is the only way to control the menace.
Vehemently disagreeing with Dr Nagpal, etymologist Manzur A Chowdhury said “There is an epidemic situation in the country.”
“Emergency measures have to be taken to destroy the adult mosquitoes,” he told Bangla Tribune.
He said that a mosquito that has already become a vector can spread the virus further and hence destroying adult mosquitoes are a must.
On the destruction of breeding ground, he said that it’s not completely possible and already a large number of mosquitoes have become carriers.
“If fogging is done right then at least some mosquitoes will die,” he said.
The Directorate General of Health Services (DGHS) dengue program chief Dr MM Akhtaruzzaman said that Aedes mosquito eggs remain fertile for around a year even in dry environment.
Agreeing with WHO’s Dr Nagpal, blood disorder specialist Dr Gulzar Hossain Ujjal said that fogger machines are indeed ineffective against Aedes mosquitoes.
Citing Singapore’s dengue control team chief he said that the process is counterproductive as fogging kills those insects that are capable of destroying those mosquitoes.
“Dengue never left the country it once entered,” he said and added that the Singaporean team chief has termed it as an “endless war.”
An IEDCR employee wishing to remain anonymous disagreed with Dr Nagpal and said that fogging is effective against Aedes.
Contrary to his comments, former IEDCR chief Dr Mahmudur Rahman agreed that it is ineffective.
“When fogging is done, the mosquitoes fly someplace else. That’s the failure of fogging. In fact it harms the environment,” he said.
Meanwhile, Jahangirnagar University professor and etymologist, Dr Kabirul Bashar said that environmental initiatives, biological control, use of insecticides and community involvement are imperative to control the ongoing mosquito menace.
He, however, said that spraying of repellents and fogging cannot be stopped as it’s crucial that the infected mosquitoes [carriers] are killed.
Urging community engagement, he agreed with the IEDCR chief that source reduction is a must.