DHAKA IS MORE VULNERABLE TO DENGUE OUTBREAKS CLIMATE CHANGE AND DENGUE DENGUE OUTBREAK IN 2019 Bangladesh is one of the countries most vulnerable to the effects Bangladesh experienced its largest ever dengue outbreak in 2019 of climate change. Through complex pathway, climate change with the number of people who were hospitalized due to dengue adversely affects human health (figure 1). was ten times higher than the previous such outbreak (figure 2). Of the total dengue cases and related deaths in 2019, Dhaka city Figure 1. Effects of climate change on human health accounted for over 50 percent of the cases and 77 percent of Injuries, fatali�es, Asthma, total deaths (figure 3). mental health impacts cardiovascular disease Severe Air Malaria, dengue, Heat-related Weather Pollu�on encephali�s, Figure 3. Distribution of Dengue Cases in 2019 illness hantavirus, and deaths, ri� valley fever, cardiovascular lyme disease, Chattogram 8% Khulna 12% failure chikungunya, Extreme Changes in west nila virus Rangpur 2% Heat Vector Ecology Dhaka 12% Rajshahi 5% (Excluding Dhaka City) Increasing Barisal 7% Environmental Allergens % of Total Degrada�on Mymensingh 2% Forced Dengue Cases Sylhet 1% migra�on Respiratory civil conflict, Water and Food Water allergies, by Division mental health Supply Impacts Quality Impacts asthma impacts Dhaka City 51% Cholera, Malnutri�on, cryptosporidiosis, diarrheal disease campylobacter, leptospirosis, harmful algal blooms Globally, climatic conditions are becoming more suitable for dengue outbreaks. The urban hubs of Bangladesh, primarily Dhaka and This outbreak can be partially explained by weather patterns – Chattogram, are more susceptible to these effects. Evolving uncharacteristically heavy rain in February 2019, followed by climatic conditions such as excessive and erratic rainfall, water temperature and humidity levels conducive to mosquito breeding logging, flooding, and heat and cold waves coupled with rising in the subsequent months of March to July 2019. Dhaka recorded temperatures and congestion have increased the likelihood of the highest rainfall ever in February with 115mm of rain, more than vector borne diseases such as dengue to alarming levels. three times the average rain for the month (figure 4). BOX 1: WHAT IS CLIMATE CHANGE? Figure 4. February rainfall (mm), Dhaka 1976-2020 115 Climate change refers to changes in average metrological conditions and seasonal patterns over a long period, often spanning years. Climate change, as currently understood, is leading to a rise in global temperature and number of extreme weather events. 66 61 54 56 52 47 48 42 44 44 36 Figure 2. Dengue cases and related deaths, 2000-2020 32 32 31 30 25 100 180 20 21 20 Cases (in thousand) 15 17 160 13 12 13 Deaths Cases (in thousand) 7 8 7 8 80 140 1 1 0 0 4 4 3 1 2 0 1 0 0 01 1 120 60 Deaths 2000 2004 2008 2006 100 2002 2020 2010 2014 2018 2016 1994 1998 1996 2012 1984 1980 1988 1990 1986 1982 1992 1978 1976 40 80 60 20 40 20 0 0 2004 2000 2008 2006 2009 2002 2020 2007 2003 2005 2014 2001 2010 2018 2016 2019 2012 2017 2013 2015 2011 BRIEF | 2021 THE RECIPE FOR DENGUE Figure 5. Weather station locations in Bangladesh Lower levels of humidity at higher temperatures are more conducive for mosquitoes spreading dengue to breed and reproduce (box 2). BOX 2: WHERE DOES DENGUE THRIVE? • Temperatures between 25°C and 35°C • Humidity between 60 and 80 percent • Rainfall between 200 and 800 millimeters • Risk of a dengue outbreak increases at the onset of rainfall, lasting up to three months. Dhaka is becoming warmer with average maximum temperature increasing by 0.5°C between 1976 and 2019. Climatic conditions are suitable for mosquito breeding: • Summers are becoming longer: maximum temperatures averaging more than 30°C between March and October. • Minimum temperature rising: average monthly minimum temperatures from November to February are close to or above 18°C; • Rainfall increasing particularly between April and August; more importantly, average monthly rainfall is within the range of 200 to 800 millimeters; • Average monthly humidity declining but well within the BOX 3: WHAT IS SURVEILLANCE? range of 60 and 80 percent. Public health surveillance can be used to monitor emerging With falling humidity levels, rising temperatures, and increasing health issues and identify solutions in a timely manner. rainfall in the summer months, the risk of dengue spread in the These systems include information on when and where future may be higher in Dhaka. Associated factors like urbanization, health problems are occurring and who are being affected. travel, and demographic change that affect the spread of dengue Source: World Health Organization are all relevant for Dhaka city. KEY RECOMMENDATIONS Gather more accurate and localized weather data between the MoHFW and the Bangladesh Meteorological Department. • Increase the number of weather stations, currently there are 43 and are not spread-out uniformly (figure 5). Promote Collaboration • Collect and analyze more precise weather data, which is • Work with each other and include sectors beyond health like more location specific. This would help in building dengue water and sanitation, education, transportation. mapping and prediction models. • Begin at home through community engagement to find Increase surveillance of diseases and set-up a dengue solutions in dealing with mosquito habitats. early warning system • Talk to each other and disseminate information regarding • The Ministry of Health and Family Welfare (MoHFW) needs dengue transmission and risk factors. to strengthen its routine surveillance mechanisms to track • Hit when the iron is hot: efforts to controlling mosquitoes incidence and prevalence of diseases. should be done during high temperature seasons to • The MoHFW should set up a climate-based dengue early maximize the effects of the interventions. Examples include warning system, which will use climate data to track spraying insecticides, clearing drainage, and other commu- potential disease outbreaks. This requires close cooperation nity-based interventions. This brief is part of a series titled “Climate Afflictions,” which comprises a book, three synthesis reports and multiple briefs. The series aims to explore the link between the effects of climate change and health. The series, with full citation, is available at: www.worldbank.org. BRIEF | 2021