MOSCOW, November 3, Tatyana Pichugina. More than a hundred people in Italy, France and Spain have become infected with dengue fever. It is carried by Asian tiger mosquitoes, which have managed to adapt to local conditions. Scientists fear that a permanent outbreak of infection will emerge in the region.
The largest dengue outbreak in Europe
At the end of October, 105 cases of local infection with the dengue virus were confirmed in Europe, of which 66 were in Italy, 36 in France and three in Spain. This is reported by Nature with reference to the European Center for Disease Prevention and Control.
Dengue fever is caused by an RNA virus of the same name from the flavivirus genus. There are four known serotypes that infect humans. The most dangerous are the first and third, which during primary infection cause a more severe form of fever up to hemorrhagic shock.
The virus is spread by mosquitoes. After a bite, the incubation period lasts from three days to two weeks. In some, the disease is asymptomatic, so people do not see a doctor. Others experience fever, headaches, chills, nausea, and rash.
Doctors who have not encountered dengue before confuse these symptoms with ARVI and do not prescribe tests, so the real scale of the outbreak is difficult to assess. There is no specific treatment. Repeated infection increases the risk of a more severe course, in which the patient is treated in a hospital.
According to WHO statistics, over the past two decades, the number of dengue cases in the world has increased by an order of magnitude — from half a million to five. The infection occurs in one hundred countries.
Successful conquest of the world by mosquitoes
Dengue originates from Southeast Asia, where it is mainly transmitted by mosquitoes of the Aedes aegypti, or yellow fever, species. In the current century, these insects have spread throughout the world, populations have established themselves in places where the temperature does not drop below ten degrees Celsius in cold weather. Their relatives — Asian tiger mosquitoes (species Aedes albopictus) — turned out to be more successful.
Aedes albopictus was first discovered outside its original range in 1979 — in the center of Europe, in Albania. In 1990, the mosquito reached Italy, after 2000 it was noticed in other Mediterranean countries, and very soon it appeared in Europe, the USA, Latin America and Africa.
«Aedes albopictus is one of the most successful invasive species. In just a few decades, it has spread from Southeast Asia throughout the world — mainly due to the movement of its frost-resistant larvae in used tires,» write scientists from Italy and the United States in the journal PLOS Neglected Tropical Diseases.
The blood-sucking animal has perfectly adapted to urban environments and suburbs, where there is a high population density, which means there is enough blood and there are suitable places for reproduction. The female lays eggs in water collectors, containers, and flower pots. It reminds her of tree hollows and bamboo stumps where she lives in the tropics. Asian tiger mosquito eggs are able to survive frost and other adverse conditions due to the ability to remain in a long state of diapause — a period of rest before hatching.
Mosquitoes of this species are extremely aggressive, active even during the day, and among all invasive species of blood-sucking mosquitoes, they are the most dangerous for Europe. Over the past ten years, they have caused several outbreaks: in 2010 in France, in 2018 in Spain, in 2020 in Italy. In addition to dengue, insects carry Zika viruses, chikungunya, and larvae of threadworms of the genus Dirofilaria, which cause dirofilariasis in humans and animals.
The largest European populations of Aedes albopictus have developed in Italy. This year, most dengue cases were detected in the provinces of Lombardy and Lazio, as well as in Rome.
In France, there are fewer local infections than last year, but the outbreak has spread to two new regions: Auvergne-Rhône-Alpes and Ile-de-France. In addition, the country recorded 1,414 imported cases, mostly among those returning from Martinique and Guadeloupe. This is seven times more than in 2022.
In addition to yellow fever and tiger, two more invasive species have settled in Europe — Aedes japonicus and Aedes koreicus. Aedes atropalpus was also found there, although its population has not yet become established in this part of the world.
All dengue
By 2050, half the world's population will be forced to coexist with yellow fever and Asian tiger mosquitoes. These are the results of modeling by an international team of scientists published in Nature Microbiology.
The authors took the rate of spread of insects across the planet as a basis. Calculations have shown that in the United States, Aedes aegypti is moving north at a speed of approximately 250 kilometers per year and will reach Chicago by 2050. Aedes atropalpus invades America more slowly — about 60 kilometers per year.
In Europe, the opposite is true. The yellow fever mosquito will only establish itself in a few isolated areas in southern Italy and Turkey. And its relative will spread throughout almost the entire region. Nothing will stop it from establishing itself in the highlands of South America and East Africa over the next 30 years.
By 2080, 197 countries will be at risk for infections carried by this species of bloodsucking.