Another kind of Aedes spreading dengue outside Dhaka?

The number of dengue infected patients outside Dhaka has seen a sharp rise this year, and in many cases the disease was transmitted locally -- becoming a matter of serious concern.

Though Aedes aegypti has been primarily associated with dengue fever, experts think that another type of Aedes mosquito might be a reason for the spread of dengue outside Dhaka.

A survey of Institute of Epidemiology, Disease Control and Research (IEDCR) -- on since last month -- has found the presence of Aedes albopictus outside Dhaka.

Aedes albopictus -- also called the Asian tiger mosquito -- is a small, dark mosquito with a white dorsal stripe and banded legs. It can transmit the virus that causes dengue fever. It lays eggs on the inner sides of water-holding containers in urban, suburban, and rural areas as well as the edges of forested areas, and is closely associated with vegetated areas. Larvae can also be found in natural habitats such as tree holes and hollow bamboo stumps.

The IEDCR survey was conducted in areas of Barishal, Meherpur and Kushtia. The preliminary report found seven Aedes albopictus out of 755 adult mosquitoes in Barishal, 78 Aedes albopictus out of 116 adult mosquitoes in Meherpur and 14 out of 21 adult mosquitoes in Kushtia.

As there is presence of Aedes albopictus in these places and prevalence of dengue, there is a probability of it being a vector in the areas, said Prof Meerjady Sabrina Flora, director of IEDCR.

Transmission of dengue through Aedes albopictus is comparatively slower than Aedes aegypti, she said.

In an “epidemic condition” with mosquito-borne diseases like dengue and chikungunya, a secondary vector (carrier) becomes active alongside the primary one, experts say.

Of the two varieties, Aedes aegypti is the primary and albopictus is the secondary vector of dengue fever.

Experts say reports of a growing number of dengue cases outside Dhaka indicate that their suspicion regarding the secondary vector is likely true. They recommended carrying out an extensive survey on the matter and taking action accordingly.

Prof Flora said they will complete the survey as early as possible and submit their final report to Communicable Disease Control of Directorate General of Health Services (DGHS) and Local Government Division to take necessary steps.

According to DGHS, a total of 79,367 dengue cases have been reported so far, of which 34,929 were outside Dhaka.

“We have to focus on destroying the breeding sources [of the mosquitoes] across the country and it will have to be done in a sustainable manner,” Prof Flora said.

It is not a one-off issue and Aedes in our country is now endemic -- for which, yearlong efforts will have to be undertaken, she said.

Prevalence of Aedes albopictus is higher in rural areas, though both aegypti and albopictus breed in clean water.

“So, we have to identify that places and apply insecticide accordingly to kill the mosquitoes and larvae,” she added.

Prof Sanya Tahmina, line director of Communicable Disease Control of DGHS, said they would conduct a survey to learn about the density and pattern distribution of Aedes mosquitoes outside the capital.

“We will start from Chattogram shortly,” she said.

Prof Kabirul Bashar, an entomologist at Jahangirnagar University, said dengue might be transmitted locally as a huge number of infected people went to rural areas.

Prof Bashar said if Aedes albopictus has indeed become a vector in rural areas, it is a matter of concern as its management method is different.

Local administration, under the leadership of DCs, will have to be proactive, and necessary training will also have to be provided, he said.

Md Mahbub Hossain, additional secretary of Local Government Division, said as the trend of dengue is new in the country, city corporations are reorganising their working approach.

He said they have sought master plans from every city corporation regarding mosquito control activities and will take final decision on it afterwards.

Earlier, city corporations would not conduct anti-Aedes drives round the year, but now they will have to do it, Mahbub said.

About Aedes albopictus, he said they need necessary information from DGHS based on their research and will work accordingly.

Apart from city corporations across the country, people will also have to play a major role to destroy Aedes mosquitoes at source, he added.