Dengue Outbreaks on the Rise: The Role of Climate Change
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Dengue fever, a mosquito-borne viral disease, is surging globally, and Bangladesh is facing its worst outbreak yet. In 2023, nearly 227,801 confirmed cases were reported by November, marking the most severe outbreak since record-keeping began in 2000. This alarming rise in dengue cases is closely linked to the changing climate. A World Bank report from October 2021 highlights that over the past 44 years, Bangladesh has experienced a 0.5°C temperature increase. Summers are growing hotter and longer, winters are warmer, and by 2050, the country's temperatures are expected to rise by another 1.4°C. Additionally, Bangladesh is experiencing shifts in precipitation patterns, with earlier and more intense monsoon seasons. These changes result in prolonged periods of standing water, creating ideal breeding grounds for Aedes mosquitoes, the primary vectors of dengue. These climatic shifts significantly contribute to the current outbreak, underscoring the need to understand the climate-dengue connection for developing effective public health strategies.
The Climate Connection
Climate change significantly influences the environmental conditions that allow Aedes mosquitoes, the primary vectors of dengue, to thrive. These mosquitoes depend on a combination of temperature, humidity, and rainfall to reproduce and survive. Even during drier weather following the monsoon seasons in Bangladesh, less rainfall does not always reduce the spread of dengue.
The Role of Rainfall
Monsoon rains in Bangladesh create ideal breeding grounds for Aedes mosquitoes. Every downpour leaves multiple breeding spots, such as discarded tires, flowerpots, and standing water in puddles and waterlogged areas. El Ni?o events have historically been linked to major dengue epidemics due to the warm and humid environments that follow heavy rainfall, ideal for mosquito breeding.
Densely populated urban areas with inadequate drainage systems worsen the impact of increased rainfall. Water pools in areas where people live and work, creating more breeding sites for mosquitoes. A pre-monsoon survey conducted by the health directorate in 2022 found a higher density of Aedes mosquitoes in Dhaka compared to the previous year. By September, the Communicable Diseases Control (CDC) unit of the Directorate General of Health Services (DGHS) found that mosquito density was twice as high in Dhaka city as in its pre-monsoon survey. These findings underscore the impact of changing weather patterns on mosquito proliferation and dengue risk.(https://www.acaps.org/fileadmin/Data_Product/Main_media/20230926_ACAPS_briefing_note_Bangladesh_2023_dengue_outbreak.pdf)
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The Role of Temperature
Temperature plays a crucial role in the biology and behavior of Aedes mosquitoes. Studies have shown that a 1°C rise in higher temperatures is associated with a 13% increase in the risk of dengue. Optimal temperatures for dengue transmission range between 27-31°C. In June 2023, the onset of El Ni?o, which is associated with increased temperatures in Southeast Asia, further exacerbated the situation. Within this range, mosquito biting rates and carrying capacity are at their peak, increasing the likelihood of disease spread. However, as temperatures rise beyond 31°C, the determinants of dengue risk shift. Higher temperatures decrease mosquito survival probabilities and alter the duration of the human infectious period, affecting the efficacy of control measures. (Dengue fever: the impact of increasing temperatures and heatwaves - eBioMedicine (thelancet.com))
Temperature changes also affect biological rates and processes related to disease transmission, including contact and infection rates. For instance, increased temperatures can speed up vector development rates at lower temperatures, while high temperatures can decrease mosquito survival probabilities. These temperature-dependent dynamics underscore the complexity of dengue transmission in the context of climate change.?(Changing temperature profiles and the risk of dengue outbreaks | PLOS Climate)
In conclusion, climate change is driving the rise in dengue outbreaks. Fluctuations in temperature, humidity, and rainfall create ideal conditions for Aedes mosquitoes. To combat this threat, we must improve water and sanitation management, enhance mosquito control measures, and research climate change's impact on mosquito behavior. Addressing these factors can protect vulnerable populations and mitigate dengue's impact in Bangladesh and beyond.
Author:
Research Assistant