Climate change making dengue an annual affair in Bangladesh: Experts

Dengue, a mosquito-borne tropical infectious disease, is gradually becoming an annual affair in Bangladesh as an endemic due to the adverse impacts of climate change, say experts.

They also said Bangladesh's climate conditions are becoming more suitable for dengue and other vector-borne diseases like malaria and chikungunya due to excessive and erratic rainfall, waterlogging, flooding, and rise in temperature and abnormal shifts in the country's traditional seasons.

The analysts think the government should focus on rigorous scientific research to understand the Aedes mosquitoes' reproductive and behavioural changes due to climate change and thus find out effective measures to contain it.

Bangladesh saw the first dengue fever cases in 2000 and the country reported a few hundred cases each year until 2017.

The country experienced a massive dengue outbreak in 2019, claiming the lives of 164 people and infecting 101,354 others.

After the hiatus of a year, dengue cases surged again in the country this year.

According to the Directorate General of Health Services (DGHS), 82 people died of dengue this year as of Wednesday while 20,729 were admitted to different hospitals with the disease since January.

Correlation with climate change  

A World Bank (WB) study report released last week finds a wider link between the shifting climatic conditions and the increase in dengue and some other diseases in Bangladesh.

It says with falling humidity levels, rising temperatures, and increasing rainfall caused by climate change, the risk of dengue spread can be higher in the country, mainly in Dhaka and Chattogram cities, in the future.

The report says Bangladesh has experienced a 0.5 degrees Celsius increase in average temperature between 1976 and 2019 and is slowly losing the variations between seasons.

It also said summers are becoming hotter and longer while winters are warmer, and the monsoon seasons are being extended from February to October.

The report also predicted that average temperatures across Bangladesh will rise by 1.4 degrees Celsius by 2050 while annual rainfall is likely to increase by 74 millimeters by 2040-2059.

Conducive climate condition

Prof Kabirul Bashar, an entomologist of Jahangirnagar University, said some factors like erratic rainfall, growing temperature and shift in seasons are helping dengue and other mosquito-borne diseases like Chikungunya, malaria to spread and stay for a longer period in Bangladesh due to suitable climate conditions.

He said dengue is gradually becoming endemic in Bangladesh as lower levels of humidity at higher temperatures are more conducive for dengue virus-carrying blood-sucking insects to breed and reproduce in almost every season.

Kabirul said the country is experiencing moderate rainfall during October this year and this is unusual. "Due to the untimely rainfall and favourable climate conditions, the density of the Aedes mosquito population is increasing. "It's happening due to the impact of climate change."

He said whenever the Aedes mosquitos get conducive climate conditions, they will spread, the entomologist observed.

No longer a seasonal disease

Kabirul said dengue will not be limited to any season in Bangladesh. "The prevalence of this disease may remain low or high at different times, but it's certain that the disease will continue to affect people all over the year."

He said 25-35 degrees temperature is suitable for the breeding of the Aedes mosquitos. "You will see this temperature remain in our country even during winter at day time."

As people keep water in different places and buckets, pots in their houses imprudently, the JU Professor said, Aedes mosquitos will be able to breed there without rainfall. "The breeding will be at a minimum level without rain, but the mosquito will remain with low intensity."

 He said the mosquitos are also changing their reproductive nature and will be able to breed without rainfall. "So, the dengue will remain all-round the year and dengue patients won't come down to a zero level in any season."

Public health expert MH Chowdhury (Lenin), chairman of the medicine department at the Health and Hope Hospital, said dengue was a seasonal disease in the past and it used to remain during the rainy season.

"But we've been observing since 2019 that dengue is no longer a seasonal disease and we're now getting dengue patients all through the year at different levels. When any disease is found sporadically all over the year it then becomes endemic. So, dengue is now an endemic character in Bangladesh."

Aedes mosquito reaching rural areas

Dr Lenin said the presence of Aedes mosquitoes was there in major cities several years back. "But the dengue virus-carrying mosquitoes have already spread to almost all cities and district towns through the outbreak of the disease in 2019.

He warned that these mosquitos will now gradually reach the rural areas. "We got dengue patients from different upazilas this year. So, the city-based character of dengue has also been changing."

What should be done?

Prof Kabirul said mosquitoes are changing their reproductive and behavioural changes due to climate change. "So, we've to carry out extensive studies to know this change and take effective steps accordingly."

"We've to form a research cell keeping in mind the adaptation of the climate change regarding the vector-borne disease. As per the recommendations of this cell, effective control measures must be established to control dengue and other diseases.

As Dengue is becoming endemic in Bangladesh, Dr Lenin said the government now needs to conduct a coordinated anti-dengue drive across the country instead of only in cities.

Besides, he said, the awareness campaign should be conducted all over the country to motivate people to destroy the possible breeding grounds of the Aedes mosquitos and to remove stagnant water inside and outside of their houses.

The WB report put forwarded a set of recommendations to deal with the dengue problem, including increasing the number of weather stations to get accurate and localised weather data for building dengue mapping and prediction models, setting up climate-based dengue early warning system, enhancing the government's routine surveillance capacity, increasing community engagement to eliminate breeding grounds for mosquitos and making people aware of dengue transmission and risk factors.