Poor urban planning, government mismanagement and resilience of some viral strands lead to the worst-ever outbreak.

Dhaka, Bangladesh – With hospitals packed with patients and an increasing tally of deaths and infections, Bangladesh is grappling with its worst dengue fever outbreak on record, according to official data.

The disease is endemic in the South Asian country, where heavy rains during the monsoon season have created the perfect breeding ground for the mosquito-borne virus.

However, this year’s outbreak is unprecedented, with hospitals registering hundreds of new patients every day, according to a daily updated released by the Directorate of General Health Services (DGHS).

On Wednesday, DGHS revealed that a record 2,428 new patients had been admitted over the past 24 hours, exceeding the previous record set only a day earlier at 2,348.

According to the DGHS data, nearly 30,000 people have been infected with the dengue virus so far this year in the country of 170 million.

While the disease returns every year in the country, the death rate has gradually declined since 2003, with some years seeing no recorded fatalities.

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There is a dispute over how many lives it has claimed so far this year, with leading newspaper Prothom Alo saying 85 people had died, while the DGHS put the figure much lower at 23 deaths.

Confirming dengue as a cause of death is notoriously difficult unless the government collects blood samples and other information from the deceased, Meerjady Sabrina Flora, director of the Institute of Epidemiology, Disease Control and Research (IEDCR) told Al Jazeera.

Flora, who heads the DGHS’s death review committee, said the group believes that of the 23 deaths they have confirmed, 60 percent were second-time dengue patients.

She said most of the deaths were caused by what is known as the dengue shock syndrome – a dangerous complication often caused by a secondary infection.

Bangladesh is not the only country suffering from a dengue outbreak this year. The Philippines, Honduras and Sri Lanka are also grappling with the mosquito-borne menace.

Changing symptoms and dengue patterns

Renowned Bangladeshi physician Dr ABM Abdullah told Al Jazeera that in the earlier years, symptoms during a dengue outbreak included high fever, headache, muscle and joint pain, nausea, swollen glands and rashes.

The more severe symptoms – abdominal pains, bleeding gums and rapid breathing – appeared three to seven days after a patient was infected with the virus.

This year, however, some of the early signs were apparently absent from patients and more severe symptoms were seen much earlier than normally expected, Abdullah told Al Jazeera.

Overcrowded hospitals have become a regular sight, with new dengue patients admitted each day [Mahmud Hossain Opu/Al Jazeera]

According to the World Health Organization (WHO), dengue is caused by a virus with four distinct strands.

Recovery from infection by one provides lifelong immunity against that particular strand, but subsequent infection by other strands increases the risk of developing severe dengue.

“When the patients are getting infected with dengue for the second or third time, the new patterns are found and they suffer shock syndrome or severe dengue,” Dr Khan Abul Kalam Azad, principal of the Dhaka Medical College told Al Jazeera.

In previous years, Bangladesh witnessed outbreaks of the DEN-1 and DEN-2 strand, but this year DEN-3 and DEN-4 are more prevalent, Azad said.

The DEN-3 and DEN-4 strands are considered deadly and cause plasma leakage, respiratory distress and organ impairment in patients.

Increasing mosquito population

The carrier of dengue, the Aedes mosquito, breeds in clear water and prefers a subtropical climate and urban or semi-urban landscapes. Dhaka – Bangladesh’s sprawling capital, home to about 17 million people – fits the bill.

The city has thousands of building sites, which turn into pools of stagnant water during monsoon season, becoming a breeding ground for mosquitoes.

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Dengue has spread to all of Bangladesh’s country’s 64 districts, but DGHS records show more than 86 percent of cases in the country are concentrated in the capital.

“Cities like Dhaka, where development is taking place in an unplanned manner, the grounds are ripe for mosquitoes to breed and procreate,” Bangladeshi urban planner Dr Sarwar Jahan told Al Jazeera.

“Our city corporations also are not doing their jobs properly in controlling the mosquito population,” he said.

An investigation by Prothom Alo unearthed how the two city corporations – Dhaka South City Corporation (DSCC) and Dhaka North City Corporation (DNCC) – used “ineffective” insecticides and mosquito repellents, because of which the mosquito population has increased.

A study by the International Centre for Diarrhoeal Disease Research, Bangladesh had previously shown that permethrin, the main insecticide used by the two city corporations in Dhaka, was ineffective against mosquitoes.

Dengue symptoms include: fever, vomiting, fatigue, joint pain and severe headaches [Mahmud Hossain Opu/Al Jazeera]

On top of this, fogging – almost always taken as an immediate step by authorities during a dengue outbreak – has been dismissed by experts as nothing more than an “eyewash”.

Dr BN Nagpal, WHO’s senior entomologist for Southeast Asia, told reporters it was a myth that fogging streets and open areas killed mosquitoes.

DNCC mayor Atiqul Islam told Al Jazeera that the council had consulted with neighbouring India’s Kolkata Municipal Corporation and taken their advice in controlling the outbreak.

Kolkata, the capital of India’s West Bengal state, had a severe dengue outbreak seven years ago, but the corporation has since had considerable success in controlling the disease.

“In Bangladesh, this year’s dengue outbreak is unprecedented. But we have to understand that there is no alternative but to raise awareness in destroying the breeding grounds for mosquitoes to bring the dengue menace to an end. We all have to work together to end this,” Islam said.