Dengue situation: Drives fail to curb mosquito population

Dhaka South City Corporation conducted a 'combing operation' last July to control mosquitoes. The North also followed suit, engaging in an all-out action titled as a 'crash programme.' However, it is needless to say what the result of such activity has been.

This year, the country has experienced the highest number of dengue-related deaths in its history. Even with three and a half months remaining in the year, the number of affected individuals is at its highest. Public health experts express concerns about the future.

A month after initiating a special operation to control mosquitoes, in August, the Directorate General of Health Services (DGHS) conducted a 'monsoon survey of mosquitoes.' It revealed that, in the last five years, the highest number of Aedes mosquito larvae were found during this period. The density of larvae is also higher than in any previous year. The results of this mosquito survey clearly indicate that combing operations or crash programmes have proven largely ineffective.

During the special anti-dengue drive, 204 people died of dengue in July and 342 people died in the following month in the country. And 159 people died in the first 12 days of the current month, September. In total, 752 people have died of dengue this year. Among them, 531 people died in different hospitals of Dhaka. Since last January, 154, 228 people have been admitted to hospital due to dengue in the country.

Entomologists say that adult mosquitos grow from larvae within seven days. To observe this situation, the disease control wing of the DGHS conducts mosquito surveys in the capital three times a year. They also provide the results of these surveys to the city corporation. The survey is conducted during pre-monsoon, monsoon and post-monsoon periods. Notably, Aedes is the vector mosquito of dengue.

The monsoon survey was conducted in the last week of August in two cities of Dhaka. The survey was done in 1,335 houses in 40 wards of Dhaka North and 1,815 houses in 59 wards of Dhaka South. It can be seen that aedes mosquito larvae were found in 23 per cent houses of Dhaka North and 19 per cent of Dhaka South.

Before this, the pre-monsoon survey was conducted June. Larvae were found in 20 per cent houses of Dhaka North and 15 per cent of Dhaka South. Compared to that, more mosquito larvae were found in the monsoon survey this time. Usually in full monsoon, there are more mosquito larvae.

MD Jahirul Islam, an associate professor in the Public Health Department at North South University, shared with Prothom Alo, "The survey conducted in the two city corporations indicates that the sources of mosquitoes are increasing in these areas. The number of breeding grounds is on the rise, and the environmental conditions are favorable for them. However, the initiatives taken by the two city corporations are proving to be ineffective."

According to the survey of the DGHS, larvae were found in 10 per cent and seven per cent more houses respectively in Dhaka North and Dhaka South compared to the survey of last year in the same period.

The recognised method of measuring the density of larvae of aedes mosquitoes is Breteau Index (BI). If the density of larvae is more than 20 per cent in this scale that means the outbreak of dengue will surely increase.
DGHS survey revealed that 75 per cent of the Dhaka North area has a mosquito density of more than 20 per cent for Aedes mosquitoes. The highest density, at 60 per cent, was found in ward number 24 (Tejgaon Industrial Area-Begunbari-Kunipara). Ward number six (comprising parts of Pallavi and Mirpur) had a density of 49 per cent. In Dhaka South, 19 per cent of areas has a Breteau Index (BI) of more than 20. The highest BI recorded was 73 per cent in ward number 19 (Kakrail-Siddheshwari-West Malibagh), and 70 per cent in ward number 20 (Segunbagicha-Gulistan-Press Club-Dhaka Medical Area).

The former chief entomologist of the disease control wing of the DGHS, Khalilur Rahman was associated with the monsoon survey. He told Prothom Alo, "I have never seen the presence of larvae like this before."

According to the survey, the number and percentage of houses with larvae is greater in Dhaka North than in South.  For the first time, a type of bacteria called 'Bacillus thuringiensis israelensis (BTI)' has been used to control larvae in Dhaka North. Dhaka North City Corporation commissioned Marshall Agrovet Chemical Industries Limited to bring BTI.

But this organisation was not registered. The company bought BTI from China when it said it would import it from Singapore's Best Chemical Limited. But that BTI was later learnt to be effective.

Regarding the issue of finding more larvae in the North than in the South, entomologist Professor Kabirul Bashar told Prothom Alo that residential houses are densely packed in many areas of the southern city, leaving less space between one house and another. Consequently, less water can accumulate in these areas. On the other hand, houses in the northern areas are relatively less dense. However, there is no doubt that mosquito control is not being carried out effectively in both cities.

Two cities spent Tk 4.21 billion in five years

Dhaka North, where the presence of mosquito larvae is higher, has spent the most on mosquito control over the past five years. Its amount is Tk 2.85 billion. And Tk 1.36 billion have been spent on South in the last five years. However, the salaries of the Dhaka South labourers have not been included in this calculation.

As the dengue situation did not improve, Dhaka South mayor Sheikh Fazle Noor Taposh in the first week of the current month of September declared, if more than 10 dengue patients are found in a ward that ward would be marked ‘red zone’ and combing operation will be conducted in that ward. So far six wards are marked as red zone. These are five (Sabujbagh), 22 (Hazaribag), 53 (East Jurain), 60 (South Jurain and adjacent area), 14 (zigatola and adjacent area) and 56 (kamrangirchar Rasulpur area).

A Prothom Alo correspondent and a photographer visited 16 wards during the combing operation in Dhaka South July. In a special operation, 14 mosquito extermination workers are supposed to spray medicine together in one ward. But never more than seven workers were seen spraying the repellant. The mosquito repellent workers told Prothom Alo at that time that due to the shortage of equipment, they were all unable to work simultaneously.

When asked why mosquitos are not under control despite spending Tk 1.36 billion in five years, the chief health officer of Dhaka South City Corporation Fazle Shamsul Kabir told Prothom Alo, the number of patients in Dhaka South is completely under control now.

Regarding the increase of mosquito larvae growth in the South this time, Shamsul Kabir told the Prothom Alo, “here the number of wards is much higher as is the density of people. It has been raining frequently. So, there may be larvae. But we have objections about the way the DGHS conducts its survey."

Tk 2.31 billion have been spent in various sectors in Dhaka North in five years including purchase of mosquito killers, salaries of mosquito exterminators (mosquito exterminators employed through contractors). And Tk 460.5 million has been spent to buy mosquito repellent spray machines (foggers and spray machines). Apart from this, another 73.4 million have been spent on dengue control, cleaning activities and campaigns.

When asked why the situation is not improving despite significant spending on mosquito control, Dhaka City Corporation Chief Health Officer Brigadier General AKM Shafiqur Rahman told Prothom Alo that the locations where larvae were previously found in old surveys have changed, as evidenced in the new survey. If the repellent was ineffective, then the mosquito larvae should still be found in the previous locations. However, mosquitoes are changing their breeding places in order to survive. He further explained that mosquito larvae are being discovered in areas where city corporation staff cannot access for control measures. Therefore, city dwellers have no choice but to be more vigilant and aware in these areas.

Professor Nazrul Islam, the director of disease control wing of the DGHS told Prothom Alo, "during the survey I found the larvae of aedes mosquitos in all three houses I visited in Gulshan."

The disease control wing helps two city corporations by providing the information of larvae survey. In the beginning of the year, they said the outbreak of dengue may increase. In the surveys of June and August it was seen that the outbreak of aedes is continuously increasing.

Former Director of the Disease Control Wing, Be-Nazir Ahmed, told Prothom Alo that finding such a significant number of larvae in Dhaka suggests that the dengue season is expected to be more extensive this time. The upcoming days may pose a higher risk, and it is crucial for city corporations to prioritize mosquito control. Any complacency in regard to dengue control could escalate the hazard.

(Mohammad Mustafa and Drinza Chambugang helped preparing the article)

*This report originally published in Prothom Alo print edition, has been rewritten in English by Syed Faiz Ahmed