1. Mosquito-borne diseases: a global problem

Excluding malaria, there are five main diseases transmitted by mosquitoes: dengue, yellow fever, chikungunya, West Nile virus, and Zika virus. They differ in terms of their severity and geographical extension, but all are spread by the Aedes mosquito. There are two types of Aedes mosquito: Aedes aegypti and Aedes albopictus, the latter also known as the “tiger mosquito” (already present in European regions such as Italy, the French Riviera, and the Spanish Mediterranean coast). These are the so-called ‘necessary vectors’.

As stated by Collen Acosta, epidemiologist at the World Health Organization (WHO), “dengue affects between 70 and 500 million people each year, around two million of whom will develop a serious illness.” And up to 4,000 million people are exposed to contracting the disease.

Chikungunya fever was for a long time considered a mild disease, but doubts started to arise and it is now believed to be serious in some cases. Yellow fever is more dangerous, and is the only one of these diseases for which there is an effective vaccine. Despite this, “there have been three major outbreaks between 2015 and 2017 in Angola, the Democratic Republic of the Congo, and Brazil”, says Acosta.

Western Nile virus. Despite its name, this virus has a wide, global distribution. “Its impact is unknown”, admits Acosta, but in 2006 in the United States alone “more than 4,000 cases were reported, of which 3 and 15% resulted in death.”

The latest of these infections to gain notoriety is the Zika virus. Although its existence has been known since 1947, it was not until 2014 that it began to spread, reaching the American continent. Today, evidence has been found of its transmission in more than 80 countries, with over 200,000 confirmed patients and at least 3,000 cases of babies with microcephaly born of mothers infected with the virus during pregnancy.

The virus has not reached Europe, or has at least not reached the mosquitoes that could carry and transmit it (the virus has only been found in infected people returning from areas where it is already endemic). However, it cannot be ruled out that it will not arrive in the future. Globalization and climate change “are changing the frequency and distribution of many infectious diseases”, says Acosta. Although the Zika virus has not been transmitted in Europe, there have been “recent outbreaks of dengue, chikungunya, yellow fever and Western Nile virus in regions that were previously free of these diseases, including the European Union.”

In fact, as mentioned by Laurence Marrama, an expert in vector-transmitted diseases at the European Centre for Disease Prevention and Control in Stockholm, what we are seeing now may just be the tip of the iceberg, as these diseases are often not properly diagnosed or pass as asymptomatic infections. Therefore, we need to be prepared, especially in countries where some of these mosquitoes are present. This involves research into how to control the disease and its vectors, in addition to surveillance and effective communication strategies.

According to Pablo Martínez de Salazar, leader of this B·Debate and coordinator of arbovirus research and the response to the Zika virus at the ISGlobal Institute, this meeting serves to “identify the challenges, capacities and existing gaps, and to explore new ways in which to collaborate”.