For thousands of years, mosquito-borne diseases have been a burden on mankind. The University of Oxford, the Serum Institute of India, and other researchers have conducted clinical trials of an effective malarial vaccine in Burkina Faso in West Africa. The former President of the Indian Academy of Sciences, D. Balasubramanian, has described that more tools are available to prevent mosquito-borne diseases.
About 700 million people get infected with mosquito-borne diseases while over a million people die each year. There are three most common mosquito-borne diseases: (Malaria) Plasmodium falciparum, dengue, and West Nile virus. Malaria is a mosquito-borne protozoan disease, and is a major public health concern, the world over.
New Vaccine for Malaria
Mosquitoes breed and throng in huge numbers during the rainy season after the hot summer in Burkina Faso, West Africa. The new malarial vaccine, R21 created by the university of Oxford, has shown an efficacy of 77 per cent in the clinical trials. It targets the circumsporozoite protein (CSP) of the malarial parasite, Plasmodium falciparum. The sporozoite stage of this parasite involves secretion of CSP. Mosquito bites transfer the CSP and sporozoites into the human bloodstream. The CSP pushes the parasite towards the liver, and from there it enters the liver cells, matures, and proliferates. The onset of the symptoms of malaria is marked by the release of mature merozoites.
Some Other Efficient Vaccines
The pharmaceutical company, GlaxoSmithKline, has tested its new vaccine, Mosquirix (RTS,s). This vaccine has been tested by the company on over 8,00,000 children in Ghana, Kenya, and Malawi with a joint effort with the London School of Hygiene and Tropical Medicine. It has been approved by the WHO. It has an efficacy of over 50 per cent in the first year; however, the efficacy drops as time progresses. The Global Vaccine Alliance (GAVI) is planning to purchase the vaccine for countries that request for it. Indian drug manufacturer, Bharat Biotech (based in Hyderabad) also has entered into a deal with GSK to develop Mosquirix vaccine in India, with a dedicated facility in Bhubaneshwar.
Dengue
Dengue is another mosquito-borne disease spreading rapidly due to Aedes aegypti mosquitoes. The main breeding place for these mosquitoes are tiny stagnant pools of fresh water, such as water stagnated in discarded tyres, etc. There are four serotypes (strains) of dengue viruses: DEN-1, DEN-2, DEN-3, and DEN-4 which share about 65 per cent of their genomes. This makes it difficult to develop a single vaccine as against each serotype a different vaccine is required. Dengvaxia, a vaccine developed by Sanofi Pasteur (the largest vaccine-devoted company), France, has been approved in several countries for dengue. It has shown efficacies ranging between 42 and 78 per cent against all the four serotypes of the dengue virus.
In India, Zydus Cadilla has been developing a DNA vaccine against dengue. Scientist, Easwaran Sreekumar of the Rajiv Gandhi Centre for Biotechnology, Thiruvananthapuram, has modelled a consensus of the four serotypes of dengue virus. It has served as the basis for Zydus Cadilla DNA vaccine for COVID-19 vaccine.
There are many other innovative methods in pipeline to fight dengue. One among them is by using a bacterium Wolbachia pipients. It is an intracellular parasite that has been commonly found in many insects but not in the dengue-carrying mosquitoes. When this bacterium is introduced into mosquito’s cells, it fights against other parasites, such as the viruses that cause dengue, chikungunya, yellow fever, and Zika.
Aedes mosquitoes doped with Wolbachia in a laboratory, are released in localities where the disease is prevalent. Wolbachia quickly spreads the bacterium into Aedes mosquitoes and the incidence of new dengue cases starts to decline. This way, mosquito-borne diseases are fought with mosquitoes.
In December 2017, in Jakarta, researchers from the Gadjah Mada University (Indonesia) had placed clusters of mosquito eggs infected with Wolbachia in 12 localities. The study proved that those 12 localities had registered 77 per cent fewer cases of dengue fever compared to other localities. Also, the intensity of the fever was less. There was an 86 per cent drop in the hospitalisation due to dengue.
West Nile virus (WNV) is a major cause of mosquito-borne disease in the continental US. Presently, there is no vaccine available for the treatment of the WNV-affected people. About 1 in 5 infected people develop a fever, whereas 1 in 150 develop a serious, sometimes fatal disease. As a prevention, wearing long-sleeved shirts and long pants are recommended.
Prevention Mechanism for Mosquito-Borne Diseases
Accurately predicting the next outbreak and focusing on health care and mosquito-control machinery accordingly is another way of preventing mosquito-borne diseases, rather than curing. Warm and moist weather are favourable for mosquitoes and the Plasmodium parasite to multiply. The NOAA-19 (an environmental satellite) and scientists at the Indian Council of Medical Research (ICMR)’s National Institute of Malaria Research have built elaborate models that correlate monthly rainfall data. It also provides data on annual state-wise incidence of dengue and malaria with El-Nino Southern Oscillation (an irregular periodic variation in winds and sea surface temperature over the tropical Eastern Pacific Ocean.), that influences the global atmospheric circulation. It gives an early warning tool that forecasts the start of an outbreak and the dynamics of its progression. It also gives an estimate of the likely number of cases. To minimise the impact of an outbreak, the health authorities could take precautionary actions. This information is presently available in Indian states; however, it has to be elevated to district levels as well to make precautionary measures effective.
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