In Bangladesh, regular cycles of heat and rain have long cultivated dense populations of insects, and, by extension, the diseases they carry. Dengue fever was first confirmed in Bangladesh 60 years ago, but the disease, carried by Aedes aegypti mosquitoes, caused unforeseen devastation in 2023. By the end of the year, the death toll reached more than 1,700, making it the worst outbreak of dengue fever in Bangladesh’s recorded history.
One scientific study linked the unprecedented rash of disease to climatic changes that fostered especially ideal breeding conditions for mosquitoes and warned that future epidemics would likely arise as Bangladesh experiences changes to seasonal rain patterns and temperature spikes. Failures of common prevention techniques, due to gained genetic resistance and changes in the disease itself, intensify the threat of future dengue fever outbreaks, as well as other mosquito-borne diseases like chikungunya and malaria.
Afsana Al Latif, a graduate student and research assistant at the Insect Rearing and Experimental Station (IRES) at Jahangirnagar University, is one of the many people looking for ways to better control mosquito populations.
“There are a lot of problems with mosquitoes, but people are not interested in this. It’s a small insect, but many people are dying because of just this mosquito,” Al Latif said.
IRES is the only research facility in the country that breeds captive mosquitoes for research. Nestled in a dense grove of trees far removed from more populous parts of campus, the lab is surrounded by a variety of traps for capturing wild mosquitoes. Inside the building, broods of mosquitoes coat the insides of mesh cages.
Because of their short life cycles and prolific breeding patterns, mosquitoes are known to evolve quickly, and regional populations often develop traits that make prevention strategies less effective. Under the direction of Kabirul Bashar, research assistants like Al Latif expose the captive mosquitoes to common prevention mechanisms to test whether resistance has formed.
Most recently, the lab tested their lab-bred mosquitoes against eight chemicals commonly used as insecticides. Researchers placed mosquitoes in plastic tubes with insecticide-soaked papers for 24 hours and counted the resulting numbers of dead and live mosquitoes. According to the World Health Organization, if less than 98% of the mosquitoes died, there is “possible resistance” to the insecticide. Once mosquito mortality dips below 90%, resistance is considered “confirmed.”
IRES has determined there is “possible resistance” to seven out of eight commonly used insecticides in Bangladesh, as well as in common types of insecticide-treated bed nets.
“Mainly these resistors occur because people are using a higher dose than the recommended one,” said Al Latif. “They think that if I use higher, [the mosquitoes] will die quickly.”
Using insecticides in large quantities can accelerate the process by which regional populations gain resistance. One of the main goals of IRES is to slow the development of resistance by providing data that Dhaka City Corporation can use to make informed decisions on how and when to spray insecticides in public areas.
However, with chemical resistance already taking root, other strategies are needed. Mosquitoes lay eggs in water. Eliminating breeding sources like puddles and open drains is one of the most efficient ways to reduce mosquito populations and prevent mosquito-borne diseases.
Many of Bangladesh’s largest cities have drainage systems for stormwater runoff and flood prevention. These systems also prevent disease by reducing sources of standing water that mosquitoes could breed in and improving overall sanitation. However, influxes of climate migrants are straining city infrastructure.
Selina Begum’s family is one of about 255 households that make up Notun Bazar, a squatter settlement, or slum, neighborhood in the southern city of Khulna. Every day, Begum walked the concrete alleyways to a public pump to get water for cooking, bathing and other household chores. Despite the often-oppressive heat, standing water lingered around the old water pump for hours, attracting swarms of mosquitoes and other insects.
In December 2023, Begum fell ill with debilitating fatigue and soaring fevers. At the hospital, she was diagnosed with dengue fever and given medicine, but the disease had already taken a toll. Six months after first becoming ill, Begum said that she still feels tired. Her two daughters and mother-in-law have taken on extra household chores, like drawing water from the nearby pump.
However, the household task is now safer for the Begum family and their neighbors. In early 2024, the Bangladesh Rural Advancement Committee (BRAC) replaced the water pump with one that reached deeper underground and incorporated a drainage system for excess water.
“We believe that if we make the construction on the ground, people will know about the diseases and there will be less diseases,” said Ashik Rubai, deputy manager at BRAC.
However, while things may be improving in Notun Bazar, others are not so lucky. Brishti Mondol lives in the small village of Dhangmari, about 50 kilometers (30 miles) downstream of Notun Bazar. There is no city corporation to spray insecticides along Dhangmari’s dirt roads and no NGOs to install drains and sanitary water pumps.
Mondol said she worries about the health of her 2-year-old daughter, Prapti. The young mother said she does not know much about the diseases carried by mosquitoes, but she does know that young children are especially vulnerable to many illnesses. There are no health services in Dhangmari, which is situated on a sand bar in an inlet of the Pashur River, making any childhood disease all the more dangerous.
Mondol’s husband purchased a mosquito net with the household’s personal funds. The family sleeps under it every night, even during the dry season when mosquitoes are scarcer.
Mondol’s instincts mirror the concerns of Mohammad Shafiul, a scientist at the International Centre for Diarrheal Disease Research, Bangladesh (icddr,b) which focuses on leishmaniasis, dengue fever and malaria. While the 2023 dengue epidemic centered in the city of Dhaka, more cases of dengue fever are occurring in rural villages like Dhangmari.
“Many people think this is a disease for cities,” Shafiul said. “We have thousands of villages, and in those villages, we don’t have anything, and now [dengue fever] is spreading to the rural areas.”
Shafiul estimated that the country is now seeing more cases of dengue fever in rural areas than in cities, a particularly disturbing trend considering the minimal health services available in such remote places. Shafiul is also concerned about how insecticide resistance could manifest differently in rural areas, where many of the same chemicals sprayed to prevent mosquitoes are used for agriculture.
However, without more research and monitoring in rural areas, it is impossible to confirm Shafiul’s suspicions. At this point, there is little government support for such an initiative.
“Our response will be maybe reactive,” Shafiul said. “Maybe when we’ll see a lot of cases in the [rural areas], then maybe our policymakers will take some actions, but at this point, we don’t see it.”
Meanwhile, IRES, icddr,b and international researchers continue to proactively look for solutions, and people like Begum and Mondol use the resources they have to protect themselves and their loved ones.
(This article was republished from Mongabay under Creative Commons License)
Hailey Smalley is a journalist based out of western Montana who enjoys writing about human-wildlife interactions and ecological perceptions in the ever-changing landscape of the Anthropocene.
