Population Density, Poor
Sanitation, and Waste Disposal
Rapid
urbanization and extreme population density in Bangladesh are creating ideal
conditions for intensified dengue transmission. In overcrowded cities with
inadequate sanitation, stagnant water accumulates easily, offering abundant
breeding sites for Aedes mosquitoes. Dhaka-home to more than 75,000
people per square mile [49] is now the world’s second most densely populated
city [50], and its tightly packed, human-built landscape accelerates Aedes aegypti
growth, reproduction, and survival far more than suburban or rural settings
[51]. Monsoon-season spikes in heat, humidity, and rainfall further amplify
this risk, with 2019 data showing that nearly 90% of dengue cases erupted
between June and October, overwhelmingly concentrated in the city’s hottest, most
densely built neighborhoods [52]. Dengue hotspots consistently emerge where
population density is highest, particularly in Thanas such as Badda, Jatrabari,
Kadam Tali, Mirpur, Mohammadpur, Sobujbagh, Shyampur, Tejgaon, Dhanmondi, and
Uttara, where close human–mosquito contact further amplifies transmission [53].
In Bangladesh, roughly 40% of the population lives in urban areas, with over
half residing in densely packed slums [54]. Communities without adequate
sanitation especially in these overcrowded settlements are highly vulnerable to
mosquito-borne diseases such as dengue and chikungunya [55]. Dhaka’s congested
neighborhoods, compounded by poor sanitation, provide abundant stagnant water,
creating ideal breeding grounds for mosquitoes. More than one-third of the
population still lacks access to safely managed sanitation, and UNICEF
estimates that about 230 tons of fecal waste enter Dhaka’s 4,500-kilometer
drainage network every day. The system is already 70% clogged with trash and
debris because of poor infrastructure and longstanding neglect, according to
the Institute of Water Modelling [56,57]. As a result, even moderate rainfall
creates stagnant, mosquito-infested pools-a problem further intensified by
flooding and extreme weather across both urban and rural areas [58].
Additionally, in many dense urban neighborhoods, inconsistent water supply
forces residents to store water in containers, a practice well documented in
neighboring India, further increasing the risk of mosquito-borne diseases [59].
Poor waste management is a critical driver of dengue risk among both children
and adults and in urban Bangladesh this threat looms large. Shockingly, 55% of
solid waste in urban areas remains uncollected, creating ideal breeding grounds
for the mosquitoes that spread the disease [60]. Evidence from urban
Thiruvananthapuram, South India, indicates that inadequate waste management
infrastructure can be associated with a 40% higher incidence of dengue and
chikungunya cases [61]. Likewise, studies in informal urban settlements in
Indonesia and Fiji reported that by age 4–5, over half of children had already
been infected, highlighting how insufficient waste disposal accelerates early
exposure to dengue [62].
Pollution as a Trigger
for viral resistance and mosquito dynamics
The
WHO estimates that nearly a quarter of human diseases and deaths stem from
long-term exposure to pollution [63]. While research on environmental impacts
on dengue in Bangladesh remains limited, international studies underscore their
significance. Recent findings from cities in Taiwan [64], Singapore [65],
Guangzhou [66], Upper Northern Thailand [67], Melaka, Malaysia [68], and
Greater São Paulo [69] demonstrate that air pollutants-such as particulate
matter PM2.5, SO?, O?, CO, and Nox-interact with climate factors to influence
mosquito populations, viral activity, and human immunity to the virus. These
impacts, however, vary depending on pollutant type, concentration, and region,
often producing complex, non-linear effects on mosquito dynamics. Interestingly,
a study covering 76 provinces in Thailand from 2003 to 2021 found that higher
surface concentrations of SO? and PM2.5 were generally associated with lower
incidences of dengue, malaria, chikungunya, and Japanese encephalitis, likely
due to adverse effects on mosquito survival and behavior [70]. These findings
highlight the need for further research. A Lancet study reported that
improperly discarded plastics accumulate stagnant water, creating ideal
breeding sites for Aedes mosquitoes that transmit dengue, Zika,
chikungunya, and yellow fever, thereby directly increasing vector populations.
Indirectly, plastic debris also clogs drainage systems, producing large
stagnant pools that promote mosquito proliferation and elevate the risk of
diseases such as malaria [71]. Bangladesh is now experiencing an alarming rise
in micro plastic pollution. Just three rivers--Meghna, Karnaphuli, and Rupsha
discharge nearly one million metric tons of mismanaged plastic each year [72].
In total, 36 rivers in Bangladesh are among the 1,656 waterways worldwide
responsible for 80% of global riverine plastic emissions [73]. Per-capita
plastic consumption has tripled—from 9 kg in 2005 to 2020-while COVID-19
contributed an additional 78,000 tons in a single year, according to a 2021
report by the Environment and Social Development Organization (ESDO) [74]. In
Dhaka, per-capita use reaches 24 kg, and nearly one-eighth of all plastic waste
ends up in canals and rivers. An estimated 23,000 to 36,000 tons of plastic
waste accumulate annually across 1,212 dumping hotspots surrounding the
Buriganga, Turag, Balu, and Shitalakhsya rivers, a trend highlighted by a
former World Bank country director during a program in Dhaka [75]. Beyond
environmental degradation, this rising plastic burden may intensify
mosquito-borne disease risks: researchers from the Beijing Institute of
Microbiology and Epidemiology show that mosquitoes exposed to micro plastics
can transfer them to mammals, develop altered gut microbiomes, experience
delayed development, and exhibit reduced insecticide susceptibility-factors
that could heighten disease transmission. Also, micro plastics can adsorb
pyrethroid insecticides such as deltamethrin, reducing the concentration
available to act on mosquitoes. However, because the findings rely on a single
study and other research shows conflicting results, more evidence is needed to
clarify how micro plastic exposure influences mosquito dynamics and dengue
transmission.