Dengue prevention is everyone's responsibility

Dengue is once again making headlines every day. For Dhaka dwellers, who have been living with mosquitoes for centuries, mosquito-borne diseases will forever be a part of their lives, likely worsening over time because of climate change. 

From 1908 to 2016, more than 120 mosquito species were recorded in Bangladesh. Each of Aedes, Anopheles and Culex spp has several species, many of which are found in Dhaka. And due to the geographical location of Bangladesh, warm temperature and significant rainfall, mosquitoes are able to breed throughout the year, making eliminating mosquitoes and mosquito-borne pathogens an impossible task. 

However, mosquito control is possible with the use of science-based methods that, unfortunately, have never been followed religiously in Bangladesh. 

The key is three 'C's: coordination, consistency, and continuity.

Covid-19 has taken away a lot from us, but it has also taught us one thing in particular — to work together. To keep the mosquitoes at bay too, everyone has to work together. For the prevention of mosquito-borne diseases, there should be year-round programs involving educators, entomologists, microbiologists, epidemiologists, physicians and other healthcare professionals.

Due to the pandemic, the laboratory infrastructure in Bangladesh has developed significantly and many laboratories are now able to collect mosquitoes for surveillance and detect dengue or other mosquito-borne viruses through RT-PCR tests. Laboratory data can easily measure the rate and distribution of infected mosquitoes and information can be disseminated through daily news, TV and other social media platforms, just like weather forecasts. 

Every year, the authorities in Dhaka city often ignore scientific methods and rather try to kill adult mosquitoes by spraying insecticide. This aggravates mosquitoes rather than controlling them. 

According to experts, killing adult mosquitoes should be the last resort. Adulticide strategy with huge budget provision may show a good picture for a few days, but it is not a long-term solution. Dhaka or any other municipality must play their role in the fight against dengue by adopting up-to-date scientific approaches to mosquito prevention and control. 

Most of the scientific study suggests source reduction works best. So, the number one task should be to reduce the sources of mosquito breeding, i.e., minimising the number of larval habitat areas available to mosquitoes. Regular inspections by house owners or flat dwellers are one of the most important methods to eliminate mosquitoes around houses and drains in residential areas. 

Using structural barriers can also be very helpful. Both of Dhaka's city corporations should have bylaws to have window and door screens installed if they are not already in place to prevent mosquitoes entering houses. People should practise using bed nets while sleeping.

The next most important step is larval mosquito control, a method which targets immature mosquitoes living in water before they become biting adults. In many countries, a naturally-occurring soil bacteria, Bacillus thuringiensis israelensis, Saccharopolyspora spinosa, or  Lysinibacillus sphaericus are applied directly to water using backpack sprayers and truck or aircraft-mounted sprayers. 

This bacterium was extensively studied and found to have no bad effects on non-target organisms when it is applied properly. There are also other naturally-occurring products that can be used safely as well. Many larvicides have the highest ratings for safety and environmental compatibility in western countries. 

Spraying adulticide should be the last resort if all else fails and adult mosquitoes are still hungry for blood. It is better to have an ongoing adult mosquito surveillance programme using local experts for effective results. Adult mosquito surveillance can be programmed in many ways, depending on the budget and human resources. Similar to larvicidal application, crop dusters should be used for adulticide spray as well. 

Meanwhile, a new approach using engineered mosquitoes is gaining momentum in many countries. Dhaka's city corporations must study this approach and utilise it if suitable. Oxitec, a UK-based biotech firm, started developing genetically engineered mosquitoes as an alternative to insecticides in early 2000. Mosquitoes have a unique sexual mating pattern: female mosquitoes need to mate only once with their male partners, and then they store the sperm inside a sac and release it from time to time when they need to reproduce. 

So, Oxitec created non-biting male mosquitoes engineered to only produce viable male offspring. These genetically engineered males carry a gene that passes to their offspring and kills female progeny in early larval stages. Male offspring will not die, but instead become carriers of the gene and pass it to future generations. As more females die, the mosquito population should diminish gradually. This technology will have no impact on human health since no pesticide or radiation will be used. 

Oxitec did many trials over time and recently in 2021, it released 2.4 billion genetically modified mosquitoes in California and Florida. Dhaka should keep a close eye on its development and embrace this new technology. But monitoring is needed to see what would be the long-term ecological impact on genetically modified mosquitoes. 

It has been proven that clearly traditional ways of controlling mosquitoes are not working in Dhaka city and other parts of the country. A well coordinated and an integrated approach is essential.

Dr Muhammad Morshed is a clinical microbiologist, programme head of Zoonotic Diseases and Emerging Pathogens at BC Centre for Disease Control and a clinical professor at the Department of Pathology and Laboratory Medicine, University of British Columbia. He is also an expatriate fellow at the Bangladesh Academy of Sciences.