Why are there more mosquitoes in Badajoz than in Cáceres?

Currently there are numerous arthropods, that is, culicid mosquitoes, sandflies, bedbugs, blackflies, ticks, flies, mites, lice, etc., that are capable of transmitting diseases, which cause more than 700,000 deaths worldwide each year according to WHO data. In recent times, an increase in these vector-borne diseases has been observed due, among other causes, to climate change, the modification of urban centers, as well as the exponential increase in passenger, animal and merchandise traffic.

As Extremadura is no stranger to these challenges, the Badajoz Veterinary College, in collaboration with researchers from the Faculty of Veterinary Medicine of the University of Extremadura, has launched a research project that sought to determine both the presence, abundance and distribution of these vectors in the cities of Cáceres and Badajoz, in addition to determining the existence of some important viruses and parasites in them.

To do this, between May 2021 and April 2022 they have placed numerous traps at 31 points in urban and peri-urban areas of both cities, (important gardens and parks, as well as in various urbanizations). A total of 8,298 mosquitoes, 1,190 simuliids (black flies) and 1,354 sandflies were captured. One of the most important results has been the identification, for the first time, of the tiger mosquito in the city of Cáceres, captured in the month of September 2021. This mosquito had been found sporadically in some parts of the region in the years 2018 and 2019 in Badajoz, Aldea del Cano, Monesterio, Navalmoral de la Mata and Almaraz, but it had never before been captured in the city of Cáceres. After the identification of this important vector of diseases such as dengue, zika or chikungunya, the health authorities of the region were immediately notified, in order to implement measures to control and eradicate this mosquito in the area where He was captured.

Another of the most important findings has been the presence, in various sampled areas, of the main transmitting species of the West Nile virus, the virus responsible for the outbreak that occurred in Andalusia and Extremadura in the summer of 2020, which caused 8 deaths and almost 80 affected serious. Specifically, a total of 18 specimens of mosquitoes belonging to the Univittatus subgroup, which includes the Culex univittatus and Culex perexiguus species, have been captured and identified. However, another of the main vectors of West Nile virus, the common mosquito (Culex pipiens), was the most frequently captured insect, accounting for 86% of the total number of specimens identified throughout the study year.

For the researchers, “the greater number of mosquitoes captured in the capital of Badajoz compared to the city of Cáceres is striking, possibly due to the presence of the Guadiana River in the urban and peri-urban areas of this city,” they indicate. Of the points sampled in the city of Badajoz, the Rivillas area especially concentrates a high number of these insects throughout the year, having been captured even on the coldest days of the year, in January 2022. For its part, in Cáceres, the traps located along the banks of the Marco River, as in some points of the La Mejostilla neighborhood or the University area, have offered the largest catches.

Regarding the simulidae or black flies, it must be remembered that “some species of these small insects cause bites and skin lesions that can become very annoying and painful”, although the researchers have yet to determine if the species found in the areas of the Guadiana and Rivillas dams in Badajoz and Ribera del Marco (Cáceres) show human or animal tropism.

Las Vaguadas and Parque del Principe

Finally, this project has made it possible to observe the presence of sandflies only between the months of May and September, with a special concentration in the area of ​​Las Vaguadas (Badajoz) and in the areas of Parque del Príncipe and Olivar Chico (Cáceres). The main species identified have been Phlebotomus perniciosus and Phlebotomus ariasi, both considered the main transmitters of Leishmania infantum, the parasite that causes leishmaniasis in Spain. This is an endemic disease in Extremadura that seriously affects dogs and can also cause cutaneous and visceral leishmaniasis in humans, so these results call for greater prevention, early diagnosis, control of the vector and reservoirs and , of course, to improve public awareness.

Power supply

Once the trapping period of all these vector insects has ended and their identification at the species level has been carried out, now the UEx researchers are working hard to determine, through the well-known PCR technique, which has been the food source of the captured mosquitoes, and if they are infected by some of the viruses and parasites with importance in Public Health. “It is not an easy task, but these types of studies are the key to determining the real risk of transmission of diseases such as West Nile fever, leishmaniasis, Toscana virus, etc. to the human population, and thus be able to prevent possible outbreaks of unknown consequences.