Mosquito-borne infectious diseases like malaria, dengue fever, Zika fever and chikungunya, for which there is no vaccine as yet, pose a great threat to human health. It is estimated that they cause more than 700,000 deaths a year.
There are around 3,500 species of mosquitoes in the world. Of these, just a few transmit pathogens and parasites to humans and animals. Nevertheless, it is estimated that more than half of the human population is exposed to the risk of contracting a mosquito-borne disease.
In Europe, some of the mosquitoes that transmit infectious diseases are invasive species - species not native to the region - but have great capacity to adapt and thrive in urban and suburban environments. These are species of enormous epidemiological importance, as they can transmit severe exotic diseases when their pathogens are introduced into Europe.
In a context of globalisation and climate change, everything points to the phenomenon of disease transmission by mosquitoes increasing in the coming years. Two research projects supported by the ”la Caixa” Foundation aim to help prevent this problem in our country.
Doctor Frederic Bartumeus leads a project whose goal is to study, monitor and combat the spread of Aedes invasive species capable of transmitting diseases caused by viruses such as dengue, Zika and chikungunya. His team has developed an innovative real-time monitoring and data collection system based on new technologies and citizen science methods. Aedes albopictus (the Asian tiger mosquito), Aedes aegypti (the yellow fever mosquito), Aedes japonicus (the Asian bush mosquito), Aedes koreicus (the Korean bush mosquito) and Culex pipiens (the common house mosquito) are among the species monitored under the project.
Diseases like dengue, chikungunya and Zika can cause fever and joint and muscle pain, among other symptoms, at times requiring the hospitalisation of patients. The virus is transmitted when one of these mosquitoes of the Aedes genus bites a person after being infected by previously biting another person who has the virus. These diseases are not endemic in Spain: until recently, all cases detected were infected people arriving from other countries. However, in 2018 there were six local cases of dengue in people infected in Spain. The spread of the tiger mosquito throughout the Iberian Peninsula and recurring attempts at colonisation by the yellow fever mosquito in the Canary Islands all increase the risk of outbreaks. Travel to countries where mosquito-transmitted diseases are endemic has also led to an rise in imported cases. In view of all this, there is a danger that these diseases could become a public health problem.
Monitoring is conducted via the Mosquito Alert app, which enables anybody to report, by means of a photo, the possible discovery of one of the mosquitoes studied, as well as collecting information about activity (bites) and breeding sites. Along with the photo, the location of the observation and other necessary information to help identify the species is collected. A team of expert entomologists is responsible for validating the photos received, and the results are published on a public online map. The information obtained in this way complements scientific work in the surveillance of invasive species and makes it possible to generate real-time risk models and maps with greater predictive capacity that can be used by public health managers to monitor and control these mosquitoes.
The project led by Jordi Figuerola focuses on preventing possible outbreaks of West Nile virus in Spain, where the disease is endemic. The virus can be transmitted by some of the more than 60 indigenous mosquito species present in the country. Although Europe has been practically free of this type of pathology over the last half century, the West Nile virus has re-emerged in the last decade, and its incidence and geographical distribution have increased. In Spain, it caused 77 severe cases and 8 deaths in 2020, most of them in Andalusia.
In most cases, the infection does not produce significant symptoms. Around 80 % of human infections are asymptomatic, while there may be a slight fever in 19 % of cases. In just under 1 % of cases, however, it can cause a severe illness known as West Nile virus fever, which can lead to encephalitis and sometimes even death.
Until now, the strategies for managing this disease have been based on attempting to control the spread of the virus using biocides against mosquitoes once the first human cases of infection are detected. However, rather than reacting to their appearance, the goal of this project is to prevent the appearance of cases of infection in order to reduce the risk of transmission of this and other arboviruses among the population. The aim is to establish an early warning mechanism so that, several weeks before an outbreak occurs, mosquito control can be reinforced, reducing the possible circulation of the virus and preventing it from spreading to humans. To this end, maps are made that show the distribution of the different mosquito species, breeding areas are identified, and strategies are proposed to control the population of these insects using methods compatible with environmental conservation.
Every week, Jordi Figuerola and his team take samples of mosquitoes to test whether they carry the virus. They determine which species the mosquitoes belong to and correlate the circulation of the pathogen to meteorological parameters such as average temperature and rainfall, as well as infectivity in humans. In this way, they hope to be able to predict the risk of transmission according to weather conditions and numbers of mosquitoes.
Frederic Bartumeus Ferré, principal investigator and ICREA research professor at the Centre for Advanced Studies of Blanes, National Research Council (CEAB-CSIC).
Jordi Figuerola Borrás, research professor at the Doñana Biological Station, National Research Council (EBD-CSIC).
Eva Rodríguez, journalist with the SINC agency specialising in science, environment and society
Projects supported by CaixaResearch: