Eid-ul-Adha typically draws homebound travellers, busy cattle markets and a festive atmosphere to Dhaka. This year, a quieter danger has surfaced amid the celebrations: dengue.

Heavy rainfall at the start of the holiday left large areas of the capital waterlogged, just as millions began heading to their villages from May 25. Public focus fell on traffic congestion and the strains of the mass exodus. Public health experts warn, however, that weak official preparedness has meanwhile created ideal conditions for Aedes mosquitoes to thrive in a largely deserted city. They expect infections to climb sharply as early as this week.

Meteorologists define heavy rain as 44 to 88 millimetres. Downpours over the three days before Eid flooded roads, alleys and low-lying areas, heightening fears of dengue transmission.

Sacrificial animal markets officially opened five days before Eid. The two city corporations turned their attention to managing those markets, maintaining cleanliness and clearing slaughter waste. Routine mosquito-control work slowed as a result, critics say.

Rainwater offers perfect breeding grounds for Aedes mosquitoes. Discarded coconut shells, plastic cups, snack packets, polythene bags and crevices in construction materials quickly fill with stagnant water.

The Eid exodus compounds the risk. With countless homes left empty, water gathers on balconies, in plant pots, bathrooms and air-conditioner trays — favoured sites for Aedes mosquitoes, which breed in clean, still water.

If water sits for more than three days, larvae develop. By the time the long holiday ends and residents return, many may already carry the virus without knowing it.

Dengue cases remain modest for now, according to Directorate General of Health Services data. Hospitals reported 20 to 50 confirmed infections daily throughout May.

Public health specialists note that this year’s weather conditions have sharpened the threat. Repeated rainfall interspersed with warmer spells has sped up mosquito breeding. Weak urban management, inadequate drainage and lapses at construction sites have made containment harder.

Hospitals are already reporting rising numbers of fever patients across the city. Not every fever signals dengue however, they stress, urging anyone with symptoms to seek testing quickly. They advise particular caution for children, older people and those with underlying conditions.

On-site visits at several neighbourhoods found stagnant rainwater in alleyways, around drains, between construction materials, in rooftop flower pots and discarded tyres. With many homes vacant, nobody remains to clear them.

Dr Kabirul Bashar, an entomologist and professor of zoology at Jahangirnagar University, told Bonik Barta that dengue cases would begin climbing steadily this week.

“Cases will double within the next 15 days,” he said. “Mosquito-control operations have slowed and continuous rainfall has created breeding grounds. Schools, colleges, offices and homes now stand largely empty. Water collects in flower pots, around refrigerators, in kitchens, bathrooms and many other places. Aedes mosquitoes will breed there and dengue cases will rise rapidly.”

Dr Bashar warned that this year’s outbreak could surpass previous ones.

“Dengue won’t increase only in Dhaka; it will rise across the country,” he said. “We’re conducting surveys nationwide and finding high mosquito densities outside Dhaka as well. Where we previously found five, we are now finding 15 to 20. The dengue situation has consequently become a cause for concern.”

The Eid holiday has also disrupted mosquito-control drives by the two city corporations. Residents in many areas say routine spraying has become less visible. Visits at Palashi, Lalbagh, Dhanmondi, Science Lab, Karwan Bazar, Wari, Gendaria, Jatrabari, Jurain, Postogola and Shyampur found no fogging during the holiday period.

Amir Hossain, a Jurain resident, said dengue had lingered in his neighbourhood all year, yet mosquito-control teams rarely appeared. “We hardly ever see mosquito-control staff in our area. During the Eid holidays, we see them even less,” he said. Wasim Khan, from Jatrabari, voiced similar complaints.

Arman Hossain, of Azimpur, described mosquitoes as unbearable after dusk, making it difficult to stay indoors or out. He said the city corporation had taken no visibly effective action.

The Dhaka South City Corporation denies any slowdown. It insists its health department has continued routine activities, including larvicide application and fogging according to standard procedures.

Mohammad Zahirul Islam, the DSCC chief executive officer, told Bonik Barta that waste management naturally took priority during the Eid sacrifice period, but public health work continued in parallel. “We haven’t neglected mosquito-control activities in any way,” he said.

He acknowledged that the extended holiday and heavy rain could heighten risks. “Rain creates breeding grounds for Aedes mosquitoes, while homes, offices and other premises often remain empty during extended holidays, allowing water to accumulate,” he said. “We’ve carried out awareness campaigns and placed advertisements urging residents to empty open containers before leaving home and ensure that no water remains stagnant. We hope the situation won’t deteriorate significantly.”