Lt Col Nazmul Huda Khan, MBBS, MPhil, MPH :
Bangladesh is grappling with the largest dengue outbreak that is unusual in its scale and seasonality. DGHS has already recorded close to 2.25 lakh dengue cases this year. The death toll from dengue infection has crossed the 1000-mark up to outset of October 2023. The fatalities are raising every day. The World Health Organization classifies dengue as one of the top ten threats to public health.In the world, more than 4 billion people are at risk of dengue infection, endemic in 129 countries with 70 per cent of cases in Asia. From 1990 to 2019 cases have been increased by 85 per cent. As per their prediction, 60 per cent of the world’s population predicted to be at risk by 2080.
Dengue was first detected in Bangladesh in 1965, referred to as Dhaka fever during that time. Since first recorded outbreak of dengue in Bangladesh in the year 2000; there have been significant changes in the trends and epidemiological spectrum of this disease. The WHO said, Bangladesh’s climate conditions are becoming more favorable to the transmission of dengue. It is one of the frequent and continuously affected countries. Given the fact that, proper preventative strategies, strengthening healthcare infrastructure, adequate outbreak preparedness and community-level awareness are the armaments to win the warfare against dengue infection.
Pattern of dengue outbreak in changing climate are varying. Dengue cases are mostly recorded during the monsoon (June-September) in Bangladesh and post-monsoon (October-November) seasons, with a peak in September. However, during the 2019 outbreak, the incidence peak was observed in August when more than 50 per cent of all cases were reported in this month. It is now projected that; dengue transmission may be extended all year round at the end of 21 century under the consistently changing climate of Bangladesh.
Inconsistency in the behaviour of Aedes mosquitoes is a newer challenge. Studies reveal that Ades female mosquito used to lay eggs in clean water, now it is laying eggs in dirty water too. Larvae can now survive and adapt in sewerage, seawater, brackish and drain water also. These mosquitoes were known to bite during the early hours of the day and in the evening. Recent research indicates that they remain active in biting during the night though in a lower frequency.
This disease, once considered as an urban disease, is now extending its reach into rural areas. This year, dengue infection held in all 64 districts of the country. The breeding grounds of Aedes mosquitoes have also increased due to massive constructionsin the whole country. The growing consumption of packaged food and bottled beverages in both urban and rural areas is generating huge wasteleading to the accumulation of rainwater during the rainy season, creating suitable environments for Aedes mosquito breeding.
The transformation and genetic diversity of dengue virus is sparse in Bangladesh. In early outbreaks (2000-2002), DENV-3 was the prevalent serotype. DENV-1 and DENV-2 were the prevalent circulating serotypes between 2013 and 2016. Since the largest outbreak in 2019, dengue infected cases are experiencing a heightened impact from DENV-3, which is the most pernicious strain so far. The emergence of the DENV-4 serotypes, which had been missing for more than 20 years, has beendetectedin this year and imposing significant public health threat. Data regarding a fifth serotype (DENV-5) are also being published.
Natural chronicle and spectrum of denguehas manifested variations in different outbreaks. During the first outbreak in 2000, the predominant symptoms were fever (100 per cent), headache (91 per cent) and joint pain (85 per cent), which are typical of dengue fever. About half of the patients had bleeding manifestations; less than 1 per cent of patients presented with dengue shock syndrome (DSS). In 2019, the most predominant presentation was GI symptoms apart from fever. Joint pain/arthralgia was reported by only few, while this was a common presentation in previous outbreaks. The incidence of bleeding manifestations was low in the 2019 outbreak. It was significant that, DSS was reported in up to 10 per cent of cases compared to only fraction in the first outbreak.
In our country; despite the limited resources, insufficient healthcare facilities and infrastructure, inadequate outbreak preparedness; all concerned authorities and machineries are taking all outefforts to combat the situation. Dedicated hospitals in Dhaka city for dengue case management are functioning. Establishment ofdistinct dengue wards/dengue corners in medical college hospitals are in vogue. Conducting capacity-building activity on clinical case management by the inhouse trained facilitators on clinical case management is an ongoing process. Diagnostic kits are being provided to all the health care facilities. Provisioning all required supportive medications for immediate response to health facilities. Blood banks are being geared towards making platelets available for hemorrhagic dengue patients. Public health awareness campaigns are being strengthened. The City Corporations are carrying out awareness programme and alerting building owners; fines have been imposed on buildings where the Aedes larvae have been found. The local government engineering department (LGED) is leading vector control activities including the elimination of breeding sites and larvicidal and adult mosquito control using different insecticides. But state of dengue infection yet to curb up to contentment.
To restrain outbreak progression, nationwide actions must be strengthened. There are several ways dengue mosquitoes can be controlled or eliminated. At the outset, source reduction should be the priority. Key mosquito breeding areas must be destroyed by removing all indoor and outdoor containers where water can be collected and mosquitoes can lay their eggs and suspected areas should be sprayed with insecticides. Measures to address waterlogging and cleaning of canals, water tanks, rainwater collection tanks, sump pits, downpipes and gutters should be put in place. Communities must be esteemed responsive and more resilient in these regards.
Chemical control also effective to kill the mosquitoes, by fogging and spraying. This can also be applied directly to mosquito breeding sites or resting areas to kill the larvae and adults respectively. But it is revealed that, mosquito populations from different countries had undergone a series of mutations that made them virtually impervious to some chemicals. In addition, insecticides are expensive and high doses can be toxic to humans and other species. Therefore, it is best to be cautious about applying these chemicals.
Personal protection measures are playing significant role, whereby a person can be protected from mosquito bites using repellent, mosquito coil, mat, clothing and mosquito net.
The risk of mosquitoes entering their homes may be reduced by using window and door screens where feasible. Aedes aegypti largely bite people during the day, so wearing long pants and long-sleeved shirts can reduce mosquito bites when spending time at outdoors; special focus should be given to school children regarding their school uniform.
Organic or biologic control approaches have the advantages of safety to the environment and other non-target organisms, and there is much less risk of mosquito resistance developing. Effective use of parasites, predators, pathogens and symbionts of mosquitoes, has fruitful outcomes. The most successful biocontrol agents to date are fish and the bacteria known as Bacillus thuringiensis israelensis and Bacillus sphaericus. The use of Wolbachia falls into this category. The groundbreaking Wolbachia solution for protecting communities from mosquito-borne diseases has been proved to be a self-sustaining, safe and cost-effective method, which has been deployed in many countries over the past decade.
Genetic control is another technique which uses genetically modified mosquitoes to result in early death of larvae or eggs that do not hatch. Genetically engineered mosquitoes could be used to control mosquito populations and reduce dengue transmission.
Specific types of sticky trap that attracts female mosquitoes are useful to some extent to reduce the number of vectors.
Safe and effective vaccine should soon be in planning process to vaccinate children and vulnerable groups, as it has been shown to reduce severity and hospital admissions by 80-90 per cent in many countries in Asia against varieties of dengue virus serotypes 1, 2, 3 and 4.
Singapore dengue control programme has been succeeded in reducing the dengue infection 10-fold within 30 years and has maintained it at low levels ever since. Key to this success is strong focus on source reduction as the dominant vector control strategy. In India, Kolkata dengue control model is a tale of success. Put aside the vision to break up the dengue nests throughout the year, efforts are made to reduce dengue breeding grounds with a sharp focus on cleanliness.
In our country, sustainable nationwide actions are essential to control future outbreaks, which include evidence-based dengue surveillance; development of risk mapping for scoping vulnerable zones; research on the trend and virus evolution over the geographical time period and the implementation of inexpensive and accessible bioassay systems for early detection of dengue countrywide.
Dengue has become endemic in Bangladesh with recurrent outbreaks. The warfare against dengue outbreaks is not belonged to a certain authority; it’s indeed a concerted approach. Community participation must go hand in hand with educational initiatives that teach people about mosquito vectors and the risks of having mosquito-breeding habitats near their homes. Mass media can impart more active and effective role by disseminating information to the people to perceive the holistic dengue control programme and to comprehend the burden of this epidemic.
(The writer is a public health specialist, now deputed to Kuwait).