Tiger mosquito season begins soon

As is the case every year, warmer temperatures in Spain bring back the tiger mosquito season. While the COVID-19 pandemic rages on, diseases carried by the tiger mosquito herald a different but not unthreatening public health issue. 

While the tiger mosquito otherwise known as Aedes albopictus is an invasive species from Southeast Asia that was first observed in Spain in 2004, it has been seen in different localities every summer. The tiger mosquito is a vector for diseases including zika, dengue, and chikungunya—2018 saw six local cases of dengue.

Can COVID-19 spread through a mosquito bite?

With COVID-19 on our minds, many wonder whether mosquitoes can transmit SARS-CoV-2, the virus that causes COVID-19. At the moment, these fears remain unfounded. Experts say that tiger mosquitoes can spread 22 viruses but not SARS-CoV-2.

SARS-CoV-2 spreads through droplets from infected individuals and not through a mosquito vector, according to the World Health Organization. “At this time there is no evidence to suggest that pests such as mosquitoes and ticks may be involved in the transmission of COVID-19,” says Jim Fredericks, an entomologist with the National Pest Management Association, United States, in a statement. "However, you have to remember that they can transmit other serious diseases like West Nile virus and Lyme disease."

What might the 2020 tiger mosquito season be like?

The fall in tourism due to COVID-19 might lower transmission of diseases spread by the tiger mosquito. “Although the nuisance caused by mosquitoes will not decrease, in 2020 we can expect less probability of autochthonous cases of these diseases than those detected in recent years in Andalusia, Murcia and Catalonia,” says Frederic Bartumeus, ICREA researcher at CEAB-CSIC and CREAF, and director of the Mosquito Alert project.

But, experts say that the African-origin Aedes aegypti, which causes yellow fever among other diseases and has been seen in the Canary Islands in 2017, and the Asian-origin Aedes japonicus may also arrive in Spain this summer. The former, at least, may be decimated with local management. 

Mosquito Alert: Citizen science tracking vectors of disease

The citizen science project, Mosquito Alert run by multiple research outfits helps track and control disease-spreading mosquitoes. Using a mobile application, people can click a photo and record the presence of a tiger or yellow fever mosquito in public areas. Entomologists review these photos—such information helps public health workers in their efforts to control mosquito populations in urban areas.

“At the moment, the application allows giving warnings of the tiger mosquito and the yellow fever mosquito,” says Alex Richter Boix, a biologist and communication technician at CREAF and member of the Mosquito Alert team. “Users who wish to participate only have to upload a photo of the mosquito, unless they can see the thorax, which is what allows them to identify the species, and then mark where they have found it. The app has a GPS so you can automatically use the location, or manually mark it on a map.”

Identifying a tiger mosquito is quite easy—citizen scientists can spot the white-striped black mosquitoes. “It is easily identified by the white band on its head and chest,” says the expert. “The yellow fever mosquito, on the other hand, is dark brown, with white stripes too, but on the thorax, it has four lines that draw a lyre."

Millions of people at risk of exposure to disease-spreading mosquitoes

Data from the Mosquito Alert platform revealed that in 2019 tiger mosquitoes were seen in 251 municipalities, which are occupied by 13 million residents. If the numbers of tourists who frequent these areas are added into the mix, the total jumps even higher—more than 70 million people may have been exposed to tiger mosquitoes and any diseases they carry. 

What does climate change have to do with this?

With global warming, species that favour warm climes are able to spread even further. “All studies predict that the habitable territory for both the tiger mosquito and the yellow fever mosquito will increase in the coming years,” says Richter Boix. “The increase in temperature will allow, especially the yellow fever species, to complete its cycle in areas outside the tropics and subtropics. Many of these models suggest that in 20 or 30 years, the south of the peninsula and other Mediterranean regions will have favourable conditions for the yellow fever mosquito to settle. The tiger mosquito, in turn, will continue to spread to northern Europe.”