Why mosquitoes are scaring Europe this year – What is happening in Greece
Reduced positivity for West Nile virus so far in Macedonia. The protocols for Zika, dengue, chikungunya. Explains to iatronet.gr Dr. biology Sp. Mourelatos.
With recent announcements the ECDC and the World Health Organization have sounded the bell for the spread of the mosquito “Asian tiger” (Aedes albopictus) in Europe and the risk of transmitting to humans dangerous infectious viruses such as Chikungunya, Dengue, Yellow fever, Zika and West Nile virus. Epidemiologists in Greece also warn that it is only a matter of time before we have to deal with mosquito-borne diseases, the number of which is increasing on the old continent.
One of the most international experts on mosquito control issues, biologist Dr Spyros Mourelatos, head of Ecodevelopment and former president of the European Mosquito Control Association (EMCA), maps for iatronet.gr the current situation, which currently does not seem worrying for Greece. He explains that Central and Western Europe were worried because of heat and early mosquito nuisance, which is not the case for our country, which seems to have gained a month this year due to low temperatures, despite the many rainfalls of the past period.
Sampling so far, as part of the West Nile virus surveillance network in Central Macedonia – where the vast majority of cases are recorded nationwide -, shows low seropositivity compared to last year, which was the third worst historically, with 32 deaths.
What the first blood samples show
The process of blood sampling and analysis of samples has started again this year in the framework of the entomological and surveillance networks for West Nile virus circulation established and operated by Ecodevelopment since 2010. Every month, blood sampling cycles are carried out on young chickens, while the analysis of seropositivity is carried out by the collaborating laboratories of the Aristotle University of Thessaloniki, the Foundation for Research and Technology-Hellas (FORTH) and the newly established molecular and biochemical laboratory of the company.
In the Region of Central Macedonia for the period 16/05 to 25/06, a positivity of 1.6% was recorded in 2023 from a total number of 182 adult mosquito samples, compared to a positivity of 4% from a number of 299 samples for 2022. Similarly, in sentinel chickens less than 6 months old in 2023 a seropositivity of 2% was recorded in 45 settlements, compared to a seropositivity of 11% in 53 settlements for 2022. In terms of nuisance, mosquito populations are varying without outbreaks and recessions and close to the average of the last five years.
“Despite the rainfall in the previous period, we had lower temperatures. Now that the temperature is rising, it will obviously ‘load’ the system, but we have already gained a month,” says Mourelatos, adding that the indications so far suggest a reduced virus circulation in the coming months, but without prejudging the evolution.
He explains that in the temperate zone, where Greece belongs, active transmission is mainly in July, August and September. This is the epizootic phase, during which infected mosquitoes that have picked up the pathogen from birds will bite humans. This is preceded by the endozoan phase (the pathogen is transferred between birds and mosquitoes) in spring, which, depending mainly on the temperature, may or may not increase the concentration.
Why Europe is concerned
Unlike Greece, where the tiger mosquito has been endemic for years and where there are anyway favourable conditions for mosquito development, in Central and Western Europe such conditions have been created this year due to the heat. “They had high temperatures, early nuisance mosquitoes, this increased the levels of concern and rang a bell,” says the biologist, who was in London in the past few days and experienced the unseasonal phenomenon of mosquito nuisance himself. On the contrary, he reiterates, Greece had lower temperatures and a lower level of risk.
“There may be a concern, but it’s not a concern for us at the moment. In the future things may change,” he notes, adding that the development of the next season will largely depend on the weather conditions in autumn. “Last year the phenomenon started early, went into the summer and was prolonged in the autumn due to high temperatures until October. That’s why we had a lot of human cases and cases of encephalitis,” he explains.
The protocols for Zika, Chikungunya, Dengue
These data apply to West Nile virus. The other viruses, for which ECDC and WHO warn, are potential threats for which intervention protocols apply. “We have a vector, the ‘tiger mosquito’, which is quite capable, particularly for chikungunya and for dengue – not so much for Zika and yellow fever – but we don’t have the virus. There is no reservoir of it in animals, but in humans,” Murelatos explains, adding: “So, the potential threat is that someone from India, Pakistan, South America or the Caribbean, who is a carrier of the virus, will be bitten by tiger mosquitoes and then they will bite their neighbour.” Such cases were recorded last year in France, with local outbreaks of dengue fever.
In these cases, the protocols provide for aggressive mosquito control (adulticiding and larviciding) at the place of residence of the carrier/patient or even in hospital if hospitalised, and traps are set.
Read the greek article here.