Entomologists say half-hearted measures are why mosquito control programmes are failing
Before 2018, no dengue patient would be found in the country in February. However, in February last year, there were 18 reported patients.
This month, the number of reported cases has jumped to about 250.
Dr Ayesha Akter, assistant director of the Health Emergency Operation Centre and Control Room at the Directorate General of Health Services, told The Business Standard the spread of dengue was limited to Dhaka in the past.
"Cases reported in Chattogram and Sylhet were below 100. Even a few years back, there would only be a few dengue patients in April."
Figures now show, dengue fever – once a seasonal disease – has become a chronic one and has spread across the country, and experts are saying that lack of proper and timely steps to eliminate mosquitoes have led to this situation.
Failure at many levels
According to experts, not applying scientific methods to destroy mosquito, absence of entomologists in the city corporations, lack of civic engagement, manpower shortage in the city corporations, and programmes aimed at controlling only Culex mosquitoes are behind the failure in containing the Aedes genus.
In the last 20 years, more than 1.5 lakh people were affected by dengue and 450 of them died. The numbers are higher, according to unofficial data. The health directorate prepares dengue statistics after analysing information from 41 government and private hospitals in Dhaka and other divisional levels.
Dengue situation likely to deteriorate this year
Based on available evidence, researchers fear that the number of dengue cases have the potential to be even higher this year. Data collected so far showed the presence of Aedes mosquitoes was at a risky level in some areas even in January.
"We have also found more Aedes larvae in some areas than last year. If effective steps are not taken by March, the incidence of dengue may be higher than last year," said Dr Kabirul Bashar, entomologist and zoology professor at Jahangirnagar University, lead of a research project being conducted by the zoology department at the university.
The research, being done on the presence of mosquitoes in different areas of the capital under the "Dengue Surveillance and Prediction Project" has been financed by the education ministry.
Dr Bashar said the number of dengue patients in January and February this year is more than that of last year from the same period. The researchers have divided the city into six zones for their study and the presence of mosquitoes is being monitored since January 1. The survey will continue for two years.
First massive outbreak
The first massive outbreak of dengue in the country was recorded in 2000, infecting 5,500 people and killing 93.
The dengue outbreak was reined in to some extent by the Dhaka City Corporation when it took a project to control Aedes aegypti mosquito – the carrier of dengue. In 2001, the number of dengue patients dropped to 200-400, and the death rate also decreased.
Aedes aegypti can also spread chikungunya and cases have been reported as early as 2011. A major outbreak of which was seen in 2017 in Dhaka.
The project, however, was closed after a year, and the subsequent authorities did not take any serious measures to control the Aedes mosquito.
Entomologists say there are four important methods for controlling Aedes mosquitoes. Those are environmental management, biological control, use of insecticides and involving the citizens in the mosquito control programmes.
"However, until now, attempts have been made in Dhaka to destroy mosquitoes only with insecticides. The other methods have not been included in the city corporations' budget and planning," said Dr Bashar, of Jahangirnagar University.
He said controlling Aedes mosquito is not possible if the four methods are not employed simultaneously.
"Also, insecticides are sprayed in drains, ditches and on roadsides but those are the habitats of Culex mosquitoes. Aedes mosquitoes grow in water deposited in pots inside the house," said Bashar.
In a research report, the Transparency International Bangladesh said the mosquito control programmes of the two city corporations are mostly adulticide-dependent. Its report said adulticide is 30 percent effective and larvicide is 80 percent effective in controlling mosquitoes.
But the city corporations' programmes are always adulticide-centric because the scope for corruption is higher there, the report said.
Another reason is that using adulticide for mosquito control has more publicity value for the city officials as it is more visible to the city dwellers.
Professor Dr Meerjady Sabrina Flora, director of the Institute of Epidemiology, Disease Control and Research, adds that dengue control programmes are failing due to climate change and ineffective measures.
"In case of Aedes mosquito, we always recommend starting the programmes earlier before the mosquito population becomes critical," says Dr Flora.
"The mosquito control programmes are taken when the mosquito population increases and the infection rate is going higher. "We know mosquitoes will increase in the monsoon. We recommend destroying mosquitoes when their number is still small during the pre-monsoon period. However, timely steps are not taken," she explained.
The researcher said authorities should also consider using biological solutions like Wolbachia, a parasitic bacteria that can reduce mosquito population, rather than chemicals for controlling mosquitoes.
"This way, the mosquitoes will not become resistant to chemicals and biological solutions are also good for the environment," she added.
At present, there is no entomologist in the city corporations for collecting mosquito samples and measuring their density. Those who work to eliminate mosquitoes do not have any solid information of the insect's density so their work is more hit or miss in nature.
At present, there are only five inadequately trained mosquito control workers in each ward of the city corporations
Dr Flora said lack of entomological surveillance is another reason why Aedes mosquito control measures are failing.
"Disease, viral and entomological surveillance is necessary for prediction of dengue outbreak. We collect entomological surveillance data from the mosquito survey data of the health directorate. It would have been better if we could arrange entomological surveillance ourselves.
"Neither we nor the city corporations have the capacity required for arranging entomological surveillance.
There were good days
In the wake of the 2000 dengue outbreak, the ICDDR,B and the then Dhaka City Corporation jointly took an Aedes mosquito control project funded by the Japanese government. Under the project, entomologists collected mosquitoes and also helped the city corporation in its eradication programmes.
When the project ended after four months, the city corporation appointed 14 entomologists who would go door to door to collect samples of larvae as well as adult and pupa populations of Aedes mosquito and later test those in the lab.
The mosquito eradication workers would be given the information of mosquito density to work on. Mosquito control programmes would then be conducted based on the data.
Dr Bashar said this brought the situation somewhat under control.
However, when the new mayor took office in 2002, the city corporation stopped paying the entomologists for four months and as a result, they quit. The project was also shut down.
The city corporation at the time said two of the 14 entomologists would be appointed permanently. However, the result of the oral exam of the entomologists held at that time in 2002 has not yet been published.
Depicting the dire state of dengue control measures, prestigious British medical journal Lancet wrote on December 14 last year, "We cannot underscore the seriousness of the current epidemic, which is unfortunately being handled with great laxity by the country's authorities, as shown not only by the marked under-reporting, but also by the absence of health awareness campaigns targeting both the general public and health professionals.
"Such campaigns that aim for earlier and more consistent recognition and supportive clinical management of dengue cases are a major factor underlying reduced mortality for this highly contagious disease, and are urgently needed."
Risk of more diseases from Aedes
Aedes-borne disease chikungunya broke out in the country in 2017. The number of deaths from the disease was lower than that of the number of patients.
The Institute of Epidemiology Disease Control and Research conducted a survey on the number of people affected by chikungunya but the report was not published.
The institute's director, Dr Flora, said the number of patients was not low.
She said new diseases would continue to emerge as long as Aedes mosquitoes remained uncontrolled.
"People affected with all types of mosquito-borne diseases – dengue, chikungunya, zika and yellow fever – are found in the country. So, controlling mosquitoes is urgent."
Mosquito control budget increasing
The city corporations' budgets for mosquito eradication measures have been increasing every year.
In the last six years, the city corporations spent a total of Tk262.7 crore to eradicate mosquitoes.
Mosquito: World's deadliest animal
Across the world, 7,25,000 people die of mosquito-borne diseases every year. This little insect has been the world's deadliest animal for years.
According to the World Health Organisation, some 20,000 people die of dengue fever throughout the world every year.
The health directorate said 1,01,354 people were hospitalised with dengue fever across the country last year. Of them, 1,01,037 patients recovered.
In Bangladesh, the Institute of Epidemiology, Disease Control and Research confirmed 156 dengue deaths last year.