Aedes aegypti y Aedes albopictus These are two names that, just a few months ago, would surely have been completely unknown to the general population of the Canary Islands. However, in a short period of time, they have become strangely present in the media, as they are the scientific names of two species of mosquitoes of African and Asian origin, respectively, some specimens of which have arrived this year in various towns on the islands, triggering the corresponding health alerts and the implementation of the appropriate control protocols.
These mosquitoes belong to the group of organisms known in health terminology as "vectors," meaning they transmit diseases that can affect humans. Specifically, these mosquitoes can be the entry point for diseases such as dengue, chikungunya, yellow fever, and Zika, among others. These are arboviruses (viruses transmitted by arthropods) that can have very serious consequences for human health, including death.
These mosquitoes, and therefore the diseases they transmit, were usually found in other latitudes, but the combination of factors such as rising temperatures (which make areas that were previously too cold for these vectors habitable), trade and tourism (which facilitates the transport of these insects or their larvae in luggage and goods) has made it easier for them to reach areas where they are not native, such as the European continent and also the Canary Islands.
Carolina Fernández
Coordinated surveillance system
While global warming and the movement of people and goods have exacerbated the problem, it is not new, and in fact, many countries and autonomous communities have been carrying out invasive species control activities for several years. In the case of the Canary Islands, a Canary Islands Entomological Surveillance Plan has been in place since 2013, coordinated by the General Directorate of Public Health of the regional government. The Medical Entomology Laboratory plays a very important role in this strategy. Institute of Tropical Diseases and Public Health of the Canary Islands (IUETSPC), attached to the University of La Laguna.
At the end of November 2023, the University of La Laguna hosted a workshop on surveillance and control of invasive vectors which featured the participation of the most prestigious panel of experts in this field in Spain and was opened by the representative of Center for Coordination of Health Alerts and Emergencies María José Sierra Moro, from the Ministry of Health, participated in the meeting, both as speakers and as tutors for the practical part. Several members of the vector-based laboratory, whose principal investigator is the institute's director, were also present., Jacob Lorenzo Morales and also has the support of the tenured professor of the Parasitology area Antonio del Castillo Remiro and the emeritus professor Basilio Valladares Hernández. Therefore, a few days later we met with them so they could explain in more detail what their work entails within this control system to address this problem. They are the biologists Carolina Fernández Serafín, Irene Serafín Pérez and Sara Rodríguez Camacho.
As the first of these explains, the Medical Entomology Laboratory of the IUETSPC is responsible for surveillance in areas where goods are opened and passengers pass through, including airport terminals and their baggage carousels (the labyrinth of conveyor belts), the port, the container unloading terminal, the border inspection point where goods are opened, and passenger terminals, especially those associated with cruise ship traffic, "which is one of the main entry points for these mosquitoes into the archipelago." Currently, control efforts focus almost exclusively on invasive mosquitoes, although they are now beginning to introduce control of invasive ticks, which are responsible for transmitting other diseases and require different protocols.
Trap for adult specimens
A network of traps across all the islands
The task at their laboratory begins with placing traps at all passenger and cargo entry points to the islands. There are basically two types, depending on their intended use. For adult mosquitoes, a rather bulky, cylindrical device is used, with an opening at the top through which the insects, attracted by a scented lure, enter. This opening is actually the entrance to a fine mesh that traps these vectors and prevents their escape thanks to an internal fan that creates a suction effect.
Ovitrap.
To trap the immature stages of the vector (eggs and larvae), ovitraps are used. These are less sophisticated in design but equally effective: a plastic container, about the size and shape of a soda glass, filled with water, into which a flat piece of wood is inserted. They are installed on the outskirts of port areas, especially in landscaped areas that serve as refuge for these insects. The humidity attracts them to lay their eggs, which will remain both in the water and on the surface of the wood. In areas with higher evaporation rates, due to warmer temperatures or greater sun exposure, larger containers are used, but their function remains the same.
Fernández explains that the traps are checked and emptied of samples every ten days, which is the time it takes for the vector to complete its life cycle, taking into account the climatic conditions of the Canary Islands. Within this timeframe, the researchers would be able to detect any of the immature or adult stages of these organisms. “When there is an alert in effect, this ten-day period is reduced to seven, to ensure that none of these mosquitoes escape detection.”.
The University of La Laguna's laboratory coordinates monitoring and surveillance efforts throughout the Canary Islands. In Tenerife, it is also responsible for traveling to areas of interest to place and collect traps. This constant back-and-forth movement across the island is managed by three researchers, supported by two other colleagues from the laboratory, Beatriz Yanes Manrique and Víctor González Alonso. On the other islands, the system employs freelance technicians to set and remove traps. "We train them, install the traps with them for the first time, and supervise if any installations need to be modified or new traps placed. However, they are the ones who collect the samples periodically and send them to the laboratory.".
It is difficult to calculate how many traps of both types are installed at any given time on all the islands, as it will depend largely on whether it is the months of higher or lower breeding risk and also if an alert has been issued, but it ranges between 600 and 800. This number varies, "but it very rarely goes down," adds Sara Rodríguez.
Laboratory work
The next step in the surveillance protocol is processing the samples in the university institute's laboratory. For adult specimens, the vector species is identified by observing a series of morphological characteristics that the specimens must possess, while for ovitraps, the wooden supports are examined for the presence of eggs, a process that must be carried out under a magnifying glass or microscope because identification is not possible with the naked eye.
If adults cannot be identified even under close examination using existing taxonomic standards, and only their genus can be determined, samples are analyzed to detect molecular markers widely used to identify animal species. When invasive mosquitoes are detected, Public Health requests analysis of adults, especially females because they are the ones that bite, to determine if they carry any pathogens. They also request a study of insecticide resistance, which is important for deciding which insecticides are most suitable for treating each type of mosquito.
Irene Serafín.
Action in the event of an alert
What happens when one of these invasive vectors is detected? Irene Serafín explains that, in addition to the aforementioned increase in the frequency of trap checks from ten to seven days, the number of traps is increased around the detection site, within a radius that will vary depending on the species' dispersal and flight range, but which can be estimated at around 200 meters on average. If no specimens are found within this new area, it is sometimes expanded again to ensure that the mosquitoes have not escaped or reproduced.
Even so, the absence of detection does not imply the lifting of the state of alert, which will not occur until eighteen months have passed from the initial detection of the vector. Only then can it be stated with certainty that it has been eradicated or that its arrival was an isolated incident that came to nothing. "We have to wait that period; it has been observed that they can survive that time in dry conditions, and if they were to come into contact with water again, the larvae could emerge." Therefore, if a mosquito were to reappear during those months of waiting, the count would restart from zero.
The IUETSPC is responsible for implementing the Canary Islands entomological surveillance project in coordination with the regional Directorate General of Public Health (which, in turn, has an agreement with the Ministry of Health). The Directorate General is responsible for epidemiological surveillance through measures such as surveys on the presence of mosquito bites in the population, in which the institute also participates. “If bites appear in an area of the port, it's not so alarming, but if they appear in a residential area, as has been the case with the recent appearances of the tiger mosquito in Santa Cruz de Tenerife, it's necessary to conduct this entomological survey in all homes to see where the vector may have moved based on the bites.”.
In case of an outbreak, this epidemiological protocol is also activated in pharmacies and health centers. Anyone complaining of a possible mosquito bite must complete an entomological and epidemiological survey, which asks for specific information that can provide clues about the vector's movements. Based on this collected data, Public Health conducts fumigation campaigns both in homes where the vector has been located and in outdoor areas, as well as in water accumulation points where mosquitoes may be breeding. The most effective control method is to target the immature stages of the mosquito, as treating adults involves using treatments that are more harmful to the environment.
All these actions, such as setting traps, are part of active surveillance. But passive surveillance is also important in this system, and citizen collaboration is essential, since it relies on information about specific cases that reaches the surveillance systems through designated communication channels. Therefore, Carolina Fernández emphasizes the importance of taking photos if someone sees a mosquito that seems unusual or receives an uncommon bite, and sending them to the email address provided. vectores.scs@gobiernodecanarias.org. “Sometimes they send you a picture of a fly or a bird, but I prefer that to receiving nothing at all. It’s the fastest way for us to get information, and in fact, it was how we detected the tiger mosquito in Santa Cruz de Tenerife in 2023.”.
Sara Rodriguez
Development cooperation
Although monitoring invasive vectors occupies a large part of the laboratory's work, its members have also participated in other types of development cooperation projects. A good example is the project carried out thanks to a grant from the Government of the Canary Islands through the Vice-Ministry of Foreign Action, in which insecticidal paint, provided by a collaborating company, was used in selected homes in two disadvantaged neighborhoods of Praia (the capital of the Republic of Cape Verde, located on the island of Santiago). Inesfly, whose effectiveness had already been proven in Latin America with bed bugs and in several areas of Africa with various types of mosquitoes.
In addition to the work on the buildings, the project included training provided by IUETSPC technicians to residents of both neighborhoods. The training aimed to raise awareness about the seriousness of the problem and teach them how to reduce mosquito populations through their daily cleaning, trash removal, and elimination of standing water, as well as by applying the paints. Two youth associations collaborated with the residents themselves to apply the paints. The project was extremely successful, and other municipalities have already expressed interest in joining similar initiatives. A new project with European funding has been requested.
The fact is that, whether in Cape Verde, the Canary Islands, or the rest of Spain and Europe, invasive mosquitoes are becoming a growing problem. Just look at the evolution of their influx in the Canary Islands: the surveillance system has existed since 2013, but it wasn't until 2017 that the first alarm was raised in a private residential area in Puerto del Rosario. “In 2019, the species was declared eradicated (Aedes aegypti"In Fuerteventura, and we hadn't had any more warnings since then until March 2022 in Santa Cruz de La Palma, the first alarm of the last wave and, from then on, one after another," recalls Irene Serafín.
Since mosquitoes thrive at temperatures above 14 degrees Celsius, the conditions in the Canary Islands have long been conducive to their arrival. Therefore, the factor explaining this increase in the islands is not so much the climate as mobility. “We’ve noticed differences in the movement of people, the flow of goods, and especially tourism, which has increased. After the pandemic, it seems that people have become much more inclined to travel, and we have a high volume of cruise ships and flights,” explains Carolina Fernández. In other regions, however, rising temperatures have been the main cause of cases of mosquito-borne diseases, as seen in France, Italy, and even Russia.
The University of Zaragoza, on behalf of the Ministry, is responsible for monitoring the situation in the other autonomous communities. “We are in contact with them, and they praise us, telling us that the work being done in the Canary Islands is quite thorough. But it's becoming increasingly difficult. (…) The outlook for the future is that we will have to increase monitoring. In 2023, we already have several active alerts, and we see that global change is real in our archipelago. We will receive more and more alerts; that's just how it is.”.
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