The health emergency and limitations of the past year and a half had temporarily removed them from our worries. And so, now that the vaccination campaign is proceeding quickly and the summer allows us to spend more time outdoors, we end up being almost surprised by mosquito bites. Annoying, especially in large numbers, these insects rarely pose a health threat. However, in some cases, mosquitoes can act as vectors and spread viral diseases with serious consequences such as dengue – news of a case in Bologna these days – and above all West Nile fever, the so-called West Nile, which has now become endemic to Northern Italy.
The health risk
“In Italy there are more than sixty of the 3,500 existing mosquito species. However, there are few that create concern for human health“, the entomologist said. Marco Pombi, researcher in Parasitology of the Department of Public Health and Infectious Diseases of the Sapienza University of Rome. The list of special observations includes, in addition to homegrown mosquitoes such as the common one (Culex pipiens) and that of the rice fields (Aedes caspius), also exotic species now established in our country such as the tiger mosquito (A. albopictus), the Japanese one (A. japonicus) or the Korean one (A. koreicus).
West Nile is particularly widespread in Emilia-Romagna and Veneto and is mainly transmitted by the common mosquito: mostly asymptomatic, in about a fifth of cases the infection causes fever, with flu-like symptoms that disappear after a few days. However, in about one in two hundred cases, West Nile can manifest itself in a neuroinvasive form with potentially fatal consequences, especially among the elderly.
In our country, dengue can instead be transmitted by the tiger mosquito and is known as “bone splitting fever” due to the intense bone and muscle pain it can cause when it is symptomatic. The chance of getting sick is low, but not as remote as exotic names would suggest.
Strategy against dengue: “infected” the mosquitoes that transmit it
by Noemi Penna
“Despite travel limitations, even last summer we recorded a small outbreak of dengue in the province of Treviso, triggered by a person who had contracted the virus abroad” resumes the entomologist, underlining how in our country the contagion is so far always started from people and not from infected mosquitoes. Vector surveillance is complex and articulated: entomologists, infectious disease specialists and veterinarians work side by side to promptly identify possible outbreaks and prevent the risk of transmission.
Containment strategies
Attempts to contain mosquito populations vary according to the context – urban or rural – and the approach used. “The most common one is of a chemical type and involves the periodic sprinkling of larvicides in spring with the aim of reducing the density of adults in the following months. If this strategy is not successful, towards the end of the summer, insecticides such as pyrethroids to eliminate adults “continues Pombi.
However, this is an extreme move: first of all, as happens with antibiotics with bacteria, exposure to pyrethroids triggers resistance phenomena among mosquitoes and therefore in the long run reduce the effectiveness of the treatment. Secondly, as they are broad-spectrum insecticides, pyrethroids are also lethal to valuable insects such as bees and bumblebees. For this reason, whenever possible, we try to prefer biological remedies such as the introduction of fish, such as gambusia, which feed on mosquito larvae in ponds and lakes.
More refined strategies, but which so far lack persistence or speed, involve the dispersion of certain bacteria (Bacillus thuringiensis) which produce specific toxins for mosquitoes or of fungal spores that feed on them. The last path is through genetic modification, as demonstrated by the large-scale project launched last month in the United States to contain the yellow fever mosquito (Aedes aegypti).
Florida, genetically modified killer mosquitoes released into the environment
Bacterial infection
Even in Italy, however, something is moving: in recent weeks the Experimental Zooprophylactic Institute of the Venezie has launched a pilot project to control the tiger mosquito by releasing sterilized males. The project was developed by the research company Biovecblok, a spin-off of the University of Camerino, which started testing in the municipalities of Arzignano (Vicenza) and Occhiobello (Rovigo).
The protocol involves the release of male individuals of common mosquito rendered sterile by infection with the Wolbachia bacterium. The European Food Safety Authority (EFSA) considers it a non-GMO technique that meets the safety criteria. Male mosquitoes do not bite, therefore they do not cause any discomfort and pose no threat to humans. Furthermore, Wolbachia is a harmless bacterium for humans and other vertebrates and is already present in nature in over 60% of known insect species. “This is a species-specific approach that has already been successfully tested against dengue.
In the case of the Italian experimentation, the bacterium is used to modify the physiology of males: their mating with uninfected females produces sterile progeny “sums up Pombi. If the pilot project respects expectations, this technique could represent an alternative in integrated pest management. and environmentally friendly to mosquitoes.
Exterminating them is not a good idea
Yes, because the complete annihilation of mosquitoes is not only a mission doomed to failure but would end up turning against us. “The species that harm humans are a very small percentage of the total and moreover our blood represents an exception in their diet, based for a large part of the life cycle on sugars of vegetable origin”, the entomologist recalls, clarifying that “beyond to act as small pollinators, both the adults and the mosquito larvae represent the nourishment for a large number of animals, from birds to fish.
Their complete disappearance would have serious ecological repercussions. “Are we therefore destined to suffer their summer bites forever? Probably yes, even if each of us can do something to limit them. How to empty saucers and other stagnant water deposits where the larvae.
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