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Edinburgh: Mosquitoes in hot and sensual parts of the world have been agents of great misery for thousands of years, carrying within them microscopic parasites that are responsible for around 5 lakh of deaths per year.
These parasites belong to the Plasmodium gender and causes malaria, a disease that is one of the leading causes of death in children under the age of five. Concerted efforts over the past decade have led to a decrease in cases. However, progress seems to be stagnant again.
This is particularly worrying for a country like India, which Reportedly has the fourth highest incidence of malaria in the world.
Multiple factors contribute to this worrying trend. An important one is the emergence of drug resistance in the parasite, rendering the current line of antimalarials ineffective against the disease. Another is the development of insecticide resistance in mosquitoes.
Also read: Malaria cases decreased in India by 51% in 2018, but it is still among the most affected countries
The role of mosquitoes.
The parasite needs two hosts for its survival: humans and mosquitoes. Although the multiplication of the parasite in human blood is responsible for the symptoms of the disease, the mosquito acts as a transmission vehicle.
When a female Anopheles mosquito feeds on an infected person, it ingests parasites from their blood and provides an ideal environment for them to develop into infectious forms called sporozoites.
These are stored in the mosquito’s salivary glands, about to infect another human through their next blood meal.
Mosquitoes are therefore instrumental in the spread of the disease. Their vital role in transmission was recognized from the start, and insecticides have since been used to kill mosquitoes and break this vicious chain of transmission.
Over the past decade, 40 percent of the decline in cases it has been attributed to the class of “pyrethroid” insecticides used in mosquito nets in endemic areas.
The idea behind this form of disease intervention is believed to be exactly what malaria-endemic countries need, as it is simple and cost-effective.
Encourage people to sleep under insecticide-treated mosquito nets, a kind of mesh curtain that can cover the bed on all sides, a common sight in Indian homes – It has been shown to dramatically reduce the spread of the disease.
This happens in two ways: While nets offer protection from mosquitoes that harbor the parasite, exposure to the insecticidal coating kills mosquitoes. With the disappearance of the carriers of the disease, the chances of spread in the community decrease.
Also read: Indians to become infected with malaria, cholera and influenza as part of new vaccination trials
A cyclical battle
However, reports of insecticide resistance have emerged from 73 countries, including India, sounding the alarms that the positive effects of insecticide-treated mosquito nets may be fading.
This strategy seems to follow the same pattern that was observed with DDT in the 1950s.
The indiscriminate spraying of DDT at that time had led to a large decrease in the incidence of malaria, but over the years, mosquitoes developed immunity.
In the 1970s, the wasteful use of the insecticide had already caused rampant ecological damage, damaging many birds, amphibians, and fish.
And now, we know that certain strains of mosquitoes no longer succumb to the insecticides currently used in mosquito nets.
Scientists have taken a closer look at the mosquito’s inner workings to identify the mechanisms through which they are acquiring resistance. The most common among these is a certain detoxifying protein belonging to the class “cytochrome P450”, which is present in mosquitoes And it can break down the drug and flush it out of the system. In humans, similar proteins detoxify artificial chemicals like medications, food preservatives, etc. of the body. However, this is not the only strategy used by mosquitoes to combat insecticides.
Laboratory studies have also confirmed that some lethal insecticide resistant mosquitoes produce higher amounts of a certain “chemosensory” protein. that allows them to feel different smells.
Experiments show that these proteins bind strongly to insecticides, perhaps hijacking them and protecting the insect from its toxic effects.
By understanding why mosquitoes do not respond to the current line of insecticides, new strategies can be devised to attack the resistance problem.
Cytochrome P450-mediated resistance is already being addressed by the development of a new compound that, when administered in combination with insecticides, counteracts resistance. These studies are relevant to sub-Saharan Africa and India, accounting for 85 percent of the global burden of malaria.
Regardless of resistance, the use of mosquito nets still offers a degree of protection to people and is therefore highly recommended by the World Health Organization in endemic areas. However, it is worrying that the beneficial effect for the community of these insecticides may be eroding.
The results of these studies are important to help design new strategies and solutions: millions of lives are at stake.
Neelakshi Varma is a science writer and research student working in malaria at the University of Edinburgh Faculty of Biological Sciences.
Also read: Chinese study says hydroxychloroquine is no better than regular coronavirus treatment
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