Mosquitoes from Senegal have become resistant to chemicals impregnated with mosquito nets used in Africa, reports the Lancet Infectious Diseases.
In recent years, insecticide-containing mosquito nets have become the leading method of malaria prevention, especially in Africa, due to their excellent cost-effectiveness ratio. However, according to research carried out in Senegal, mosquitoes have become resistant to them. Moreover, according to the authors of the study, the massive use of impregnated mosquito nets may have reduced the resistance of older children and adults to malaria – although not everyone agrees.
In recent years, mosquito nets have been imported into Africa to reduce the number of cases by as much as half in recent years, according to research by the World Health Organization (WHO). About six million mosquito nets were delivered to Senegal alone.
In a small village observed by the researchers, the number of cases of mosquito-borne malaria initially decreased by 13 times, but between 2007 and 210, the percentage of insects resistant to insecticide contained in mosquito nets increased from 8 to 48 percent. By the end of the study, the incidence of malaria had increased again, and among older children and adults, the disease was even more common than before the introduction of mosquito nets. However, it is not clear to what extent this phenomenon is present in other regions of Africa.
Mosquitoes are found all over the globe – from the tropics to beyond the Arctic Circle, in cities, in the steppes and high in the mountains. About 3200 species have been described, of which at least 47 live in Poland. Until the 60s, outbreaks of malaria transmitted by mosquitoes also occurred in our country, as Dr. Aleksandra Gliniewicz from the National Institute of Hygiene recalled when asked about mosquitoes. Anyone who does not believe should remember Dr. Judym from Żeromski’s Homeless People, who fights against malaria.
Mosquitoes, or actually female mosquitoes, need to drink blood – without the protein contained in it, they will not lay eggs capable of developing. Although they attack the host mainly in the evening and early morning, in high humidity, sheltered from the wind and little sunlight, they can be aggressive even around noon. They are attracted by the lactic acid and ammonia contained in sweat and the carbon dioxide we exhale. When a female sucks blood, she secretes a pheromone that attracts more females. Although different species of mosquitoes specialize in suckling different animals or humans, in the absence of a suitable prey, they pounce on anything that is warm, sweats and breathes.
The skin is pierced with a proboscis; the victim does not always feel this as the end of the proboscis can bypass the nerve endings. Saliva is introduced into the wound which contains substances that prevent blood from clotting. At this point, the sting is felt by the victim, but it’s better not to chase the mosquito away as it may leave some traces of proboscis in the wound. If a female mosquito sucks, it is no longer looking for a new victim – when sucking blood was not enough, it looks for another option.
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The secretion of salivary glands in sensitive people causes an allergic reaction – swelling and itching, but much worse diseases are transmitted by these insects in countries with hot climates, including malaria or dengue fever.
When the female is satisfied, she looks for a water reservoir where the offspring could develop. If the water dries up, the eggs can survive in the ground for several years. A single female can lay up to 1000 eggs. Several generations of mosquitoes appear in one season.
Natural substances have been used for centuries to repel mosquitoes – camphor, pyrethrins, anise, bergamot, cinnamon, clove, coconut, eucalyptus, geranium, lavender, lemon, nutmeg, orange flower, mint, pine, thyme, citronella oils. Oils are effective, but often don’t last long, and high concentrations may not be well tolerated. They have largely been replaced by synthetic compounds – especially N, N-diethyl-m-toluamide (DEET), dimethyl phthalate (DMP), 3- (Nn-butyl-N-acetyl) aminopropionic acid ethyl ester, 2-ethylhexadienol or icaridine . The best protection against blood-drinking insects is the simultaneous use of repellants – repellants and other personal protection, such as appropriate clothing, headgear and mosquito nets (PAP).