Battle against dengue

Lt Col Nazmul Huda Khan, MBBS, MPhil, MPH :

Bangladesh is experiencing a large dengue outbreak that is unusual in its scale and seasonality. DGHS has already recorded more than 40,000 dengue cases this year. The fatalities are rising 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.
It is noteworthy that, 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. Climate changes, such as rainfall, humidity and temperature were principal factors since recorded outbreak in 2000. Afterward, rapid unplanned urbanization has become the strong predictor that has led to increase in dengue cases. The WHO said, Bangladesh’s climate conditions are becoming more favorable to the transmission of dengue.
Seasonality of dengue outbreak in changing climate is 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.
The evolution 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, DENV-3 has been the most prevalent circulating serotype. Three genotypes (I, II, II) of DEN-3 and the cosmopolitan genotype of DEN-2 are currently circulating in Bangladesh. The emergence of the DENV-4 serotypes, which has been missing for more than 20 years, may pose a significant public health threat to Bangladesh because of secondary infection. Data regarding a fifth serotype (DENV-5) were also published.
Clinical spectrum and severity of dengue has 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, mainly melena and bleeding gums. Less than 1 per cent of patients presented with dengue shock syndrome (DSS).
In 2019, so far, the largest outbreak in Bangladesh, the most predominant presentation was GI symptoms apart from fever, especially abdominal pain and vomiting. 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. Therefore, it is discernible that, dengue is possibly going through an epidemiological shift towards more severe disease in Bangladesh.
In spite of limited resources, insufficient healthcare facilities and infrastructure, inadequate outbreak preparedness; all concerned bodies, authorities and machineries are taking all out efforts to combat the situation. Dedicated hospitals in Dhaka city for dengue case management are functioning. Establishment of distinct 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.
To prevent 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.
Chemical control is also effective to kill the mosquitoes in addition to fogging and spraying. This can also be applied directly to mosquito breeding sites or resting areas to kill the larvae and adults respectively. Mosquitoes may develop resistance to insecticides. 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 have 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 typically 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.
Biological 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; though not much realistic in Bangladesh context of view. However, 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 too.
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.
A 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.
Nationwide sustainable 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.
The battle against dengue disaster is not belonged to a certain authority; it’s indeed a multisectoral 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. These initiatives can encourage people to take an active role in participating in source reduction. Communities need to make behavioral changes in controlling dengue. Mass media can impart more active and effective role by disseminating information to the people to perceive the holistic dengue control programme and to contain the burden of this epidemic.

(The writer is Public Health Specialist, now deputed to Kuwait).