The complicated global epidemiological situation, with large ongoing outbreaks of potentially serious infectious diseases such as chikungunya and dengue fever in various countries in Latin America, Africa and Southeast Asia, has resulted in a significant increase in cases identified in Spain in travelers from these areas. . The most striking case is that of chikungunya, a disease that Spanish hospitals have practically not seen since 2015 —the year in which the American continent suffered another epidemic— and for which Madrid, Andalusia and Catalonia have already detected a hundred patients since January.
The growth of imported cases of dengue, for its part, already began to be observed in the summer of 2022 and has accelerated in recent months, doubling in these three communities. A trend that has put experts on alert since only half of the summer has elapsed and the bulk of diagnoses usually occur in Spain at the end of August and in September, at the end of the holidays.
“These are diseases that can be mild or even asymptomatic, but that often also cause serious and fatal conditions. People traveling to destinations with outbreaks should take steps to avoid being bitten by mosquitoes, which is the form of transmission. It is important to wear clothes that cover most of the body, use repellents and sleep with mosquito nets”, explains Manuel Linares, president of the iO Foundation, specialized in Tropical and Traveler Medicine.
The presence of the tiger mosquito on practically the entire Mediterranean coast and several areas in the interior of Spain adds another cause for concern, since if an infected traveler is bitten upon returning, when they are in the viraemia phase —when the virus is most present in the blood -, after a few days the mosquito will transmit the disease to other people. This would give rise to local outbreaks of both diseases.
The European Center for Disease Control and Prevention (ECDC) has described as “very high” the probability that this will occur in areas of the continent with the presence of the tiger mosquito “in the coming weeks, as temperatures continue to rise.”
The Community of Madrid has detected 47 cases of chikungunya since January, 38 of them (81%) in people from Paraguay and the rest from Brazil, Cuba, Guatemala, the Dominican Republic, Tanzania, Uganda, the Ivory Coast, Guinea Conakry and Cambodia, with one case from each country. In 2022, the Madrid Ministry of Health did not detect any cases.
The Carlos III-La Paz Hospital, located in this community and a benchmark in international health —which is why it cares for some travelers from the rest of Spain who arrive at the Barajas Airport with symptoms— has raised the number of diagnoses since January to 59 ( four by this time of the year in 2022). “It is a disease that usually produces severe pain in the joints that can become very disabling. We have had patients who were in a wheelchair because they could not walk. The problem is that these pains can extend over time and last for several months. In general, we have seen more intense symptoms than those described in other places”, explains Marta Díaz, head of the Imported Pathology and International Health Unit at Hospital Carlos III (Madrid).
Hospitals in Andalusia have detected 35 imported cases of chikungunya this year, for only two in 2022, although the place of origin of the patients has not been made public. Catalonia, for its part, has reported five cases, although the data for this community refer only to people diagnosed as of June 5 who are in the viremia phase. These cases are subjected to special surveillance —to see if there is a presence of the tiger mosquito in their place of residence, recommendation to take extreme measures to avoid being bitten…— with the aim of preventing the onset of local outbreaks of the disease.
Of dengue, the Community of Madrid has detected 39 cases this year (18 at this time last year), Catalonia 28 (since June 5 and in the viraemia phase) and Andalusia 21 (five in 2022). On this occasion, and unlike last year —in which most of the cases came from Cuba—, the countries of origin are widely distributed among Latin America, Africa and Asia. “Travellers are a kind of thermometer that shows us what is happening in the world. And this year we are noticing the increase in international travel and the existence of large outbreaks in many countries,” says Marta Díaz.
Dengue and chikungunya are two infectious diseases caused by viruses transmitted by mosquitoes of the aedes genus. The first is characterized by symptoms such as fever, muscle aches and headaches, and a skin rash, although it is often asymptomatic or very mild, so it can be confused with other ailments. Chikungunya has more characteristic symptoms, such as severe joint pain and the sudden onset of high fever. In addition, asymptomatic infection is less frequent (more than 75% of cases produce clear symptoms).
Mortality in both cases is close to one death per 1,000 cases, although this rate depends a lot on the number of infections detected in asymptomatic patients or with mild symptoms. Neither of the two diseases has specific treatment, although the prognosis of those affected improves a lot with life support measures and symptomatic treatment. Against dengue there is a new vaccine that the international health services have begun to recommend this year to people traveling to the countries at greatest risk. There is no approved against chikungunya.
According to the latest ECDC alert bulletin, published last Friday, 300,000 cases and more than 300 deaths from chikungunya have been reported worldwide between January 1 and July 27, most of them in South American countries such as Brazil. (193,000 cases and 60 deaths) and Paraguay (102,000 and 256, respectively). Although with lower incidences, the disease is also present in most of the American countries south of Mexico, on the west coast of Africa, and in southern Asia.
Identified cases of dengue this year exceed three million in the world, with more than 1,500 deaths and especially extensive outbreaks in Brazil and Peru (which is suffering the worst epidemic in its history). In these countries, the most important vector of virus transmission is the Aedes aegypti mosquito, which is even more efficient at transmitting these viruses than the tiger mosquito (Aedes albopictus). Aedes aegypti is not present in Spain and has only been occasionally detected in the Canary Islands, where control efforts have managed to eradicate it.
“Large outbreaks in some countries are being favored by changes in weather conditions that increase the proliferation of mosquitoes. In Paraguay, for example, it seems that the seasonality is breaking. Although less than six months ago (summer in the southern hemisphere), there is still a significant number of cases. And now the rainy season arrives, with favorable conditions that can cause a snowball effect”, explains Manuel Linares.
The World Health Organization (WHO) has recently warned of these changes. “The climate crisis is already here and the public health crisis associated with it has also arrived. Dengue is spreading to South America. If the climatic conditions change and the viruses can find more areas with favorable conditions, many more people are exposed to them and the incidence and mortality increase,” said the executive director of the agency’s Health Emergencies Program on July 5, Michael J. Ryan.
The increase in temperatures is one of the factors to which many experts attribute the great expansion that the tiger mosquito has experienced in recent decades in southern Europe, where it arrived three decades ago —it was identified in Spain for the first time in Sant Cugat del Vallès (Barcelona) in 2004—from Asia. The heat not only allows this insect to colonize new areas, but also to develop its life cycle for more days a year in those it already inhabits.
With the tiger mosquito established on the continent, autochthonous outbreaks of dengue and chikungunya on European soil did not take long to occur with the arrival of infected travelers from endemic areas. Of the first disease, the most serious have occurred in Italy in 2007 and 2017, with more than 800 affected and two deaths.
Dengue has also been reported in recent years by dozens of smaller outbreaks in France, Italy, Croatia and Spain. France, for example, registered half a dozen last year with a total of 65 affected. According to a risk report published on July 5 by the Health Alerts and Emergencies Coordination Center (CCAES) of the Ministry of Health, the first autochthonous outbreak registered in Spain occurred in 2018 in the Region of Murcia with five cases. Subsequently, two isolated cases have been detected in Barcelona that same year and in 2019.
The experts, however, consider that the surveillance systems in Spain are not being able to detect other autochthonous cases of dengue. “France notified 65 cases last year, many of them in areas close to Spain, while none here. It is something that is favored by the few symptoms that it sometimes produces, which make an accurate diagnosis difficult. It would be important to improve the sensitivity of the system”, defends Marta Díaz.
These suspicions were confirmed last year, when six German tourists were diagnosed with dengue in their country after returning from spending a few days on vacation in Ibiza in different groups and on different dates, while the island had not reported any autochthonous cases throughout the year.
In any case, all the experts rule out that epidemic outbreaks of the dimensions suffered by the most affected countries in the world can occur in Europe. Although local infections may continue to occur, the work to control tiger mosquito populations and the most developed health systems should limit the circulation of the virus.
The CCAES, unlike the ECDC, considers in its risk report that “the probability of associated autochthonous cases appearing is low” in Spain, while “the risk to public health is considered low for dengue” and “very low”. for chikungunya.
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