Globally, dengue is one of the most important vector-borne viral diseases that is transmitted to humans by mosquitoes. Stagnant water, particularly when it is associated with inadequate drainage provisions, is the prime cause for dengue outbreaks, but the spread and intensity is greatly influenced by a range of other climatic factors which drive mosquito behaviour. Studies have shown that weather and climate variables, mainly temperature and humidity, influence vectors, viruses, and human biology, and consequently the intensity and distribution of dengue (and vector-borne diseases). Studies indicate that warmer temperatures, due to climate change, will influence the dengue transmission.
This month, our cover story highlights the emergence of dengue as a major public health problem in India in recent years, with frequent outbreaks, encompassing the length and breadth of the country, responsible for hundreds of thousands of deaths and life-debilitating impacts; statistics collated from the National Vector-Borne Disease Control Programme (NVBDCP) show that there has been a steady progress in the intensity and extent of the disease nationwide ever since 2010. Our cover story also discusses that this worsening situation corresponds to delayed monsoons, unseasonal rain, and shorter winters, especially in the last few years. The rapid spread of the disease can be easily linked to vagaries in the climate over the last few years. In 2017, India saw a delayed southwest monsoon, particularly in western India, followed by widespread floods in many parts of the country. The monsoon retreated from all parts of India as late as October 25, 2017, which is nearly a month later than normal. There were above normal day and night temperatures over major parts of the country in late October, 2017 along with high humidity levels. Thus, the conditions were right for the creation of stagnant water pools, and ideal for the breeding of disease vectors during the post-monsoon period, leading to an epidemic in urban and peri-urban centres. This has occurred due to misplanned urbanization and uncontrolled construction activity which blocks drainage, and gives rise to accumulated water at sites. The climatic conditions of 2017 are likely to become more frequent with increasing climate change—consequently, source reduction of vector breeding sites—drainage of stagnant water pools—becomes an evermore urgent task for today—as not doing it today will lead to increased incidence of dengue tomorrow.
We can now be sure that each new dengue case and death in our own family and community is because of the non-enforcement of municipal rules leading to pools of collected, stagnant water in which the dengue-causing mosquitoes thrive.
This is a call to action—insist that there are adequate drainage facilities, and that they work; ensure attention is drawn to collected and stagnant water pools, and drain them if possible; call for municipal bodies to urgently revise municipal master plans to enhance drainage facilities.