With entire Bangladesh grappling with the worsening dengue situation, a WHO expert has shared some important and new information about the fever, including the reason behind its rapid spread, and its carrier Aedes mosquito.

He said a single female Aedes mosquito, which sucks blood in every alternative day, bites 5-17 people a day during the daytime to meet its need for blood, and as it can survive for upto 30 days in ideal conditions, it can, therefore, infect over 75 people in its entire lifecycle.

Another reason behind so many infections by a mosquito is that when one person feels its biting and reacts accordingly, it to flies to another person, said Dr BN Nagpal, Senior Entomologist of WHO Southeast Asia region.

Attending a media briefing arranged by the Directorate General of Health Services (DGHS) in the city on Monday, he elaborated the reasons behind the growing dengue cases and the ineffective attempt to eliminate the threat of Aedes mosquito.

An adult Aedes mosquito never rests on open spaces as it requires hot and humid conditions away from light, Dr Nagpal said. "They rest under the sofa, under the bed...because they need darkness and humidity," he said, adding that due to such unusual biology, Aedes mosquito cannot be killed by applying insecticides through fogging machines on streets.

"WHO has totally stopped the recommendation of fog," he said, adding that as it rests inside the house, the mosquito does not come in contact with the chemical. "The spray can work in semi-urban or rural areas, but fails in urban areas."

Shedding light on the breeding habit of Aedes aegypti species, the carrier of dengue virus, Dr Nagpal who has worked on mosquito-borne diseases for 40 years termed the notion that it lays eggs on water as a myth. "This mosquito is a smart one. A female Aedes mosquito lays eggs on the brims of containers. In ideal conditions, eggs can survive for upto one year."

"When there's flood or when the container is full to the brim, eggs hatch rapidly. As little as two millilitres of water is sufficient for the hatching of larvae," he said.

The WHO expert shared another important fact that a single female Aedes mosquito lays eggs, 60-100 in total, on the brims of every container within its vicinity.

Dr Nagpal warned that these eggs can be transported a long distance in dry conditions.

According to WHO, the outbreak of dengue is a common phenomenon in all regions across the globe in recent times compared to the past when dengue was only known to a fewer countries.

"Before 1970, only nine countries were affected with dengue. At present, 126 countries are infected with it," said the WHO expert.

Although data suggests that the cases of dengue disease have skyrocketed, its dissection shows decreased mortality among patients. "From 2011, the dengue diseases are increasing everywhere but the fatality rate is decreasing...because the management has improved," he added.

Dr Nagpal put emphasis on cleanliness over the use of insecticides on the street to prevent dengue infection. "It's necessary that you keep your houses clean to avoid the dengue infection," he said.

He also underscored the need for disposal of unused containers and advised for properly cleaning the empty containers and even placing them upside down to prevent the mosquito from hatching.

The WHO expert emphasised detecting the sources of mosquitoes to eliminate them, saying it is the best method during this time of distress.

He also recommended the use of aerosol instead of fogging method as it can easily reach places where the Aedes mosquito rests.

Dr Nagpal urged everyone to convey the message of cleanliness to arrest the dengue outbreak.

He advised all the government agencies, including transport, police, airport authorities, horticulture department and the civil department, to work collaboratively to this end.

The WHO expert said keeping the different institutions such as schools, hospitals, urban households, construction sites and offices clean can reduce the dengue outbreak to a significant level.

According to the DGHS, total of 2,065 people were infected with dengue in 124 hours till Monday morning.

Of them, 1159 were infected in the capital alone and nine of them were suffering from dengue hemorrhagic while two others from dengue shock syndrome.

A total of 27,437 people were hospitalised with dengue since 1 January.

At least 7,658 patients, including children, are undergoing treatment at hospitals now, while the rest were discharged after treatment. Currently, a total of 4,962 patients were undergoing treatment in different hospitals in Dhaka, it said.

During the period, 18 dengue patients died, all in the capital, the DGHS said although the unofficial estimates suggest the death toll is much higher.