Oropouche virus is an arbovirus (transmitted by insect vectors) that is endemic to parts of South America. Oropouche is commonly known as ‘sloth fever’ and symptoms include a sudden fever, vomiting, severe headaches and muscle pain.
The virus is transmitted primarily by biting midges (small flies), but the virus has been detected in mosquito species as well -in fact it was first isolated from a Culex species.
In 2024, there was a major outbreak of Oropouche in the Americas (beyond the endemic regions) with the WHO reporting 8087 confirmed cases by July 2024. Whilst there wasn’t an outbreak in Europe, there were 30 confirmed cases of travel-related Oropouche across Spain, Italy and Germany.
One of the questions raised by the outbreak is whether European mosquito species can get infected and transmit Oropouche virus after biting an infected individual returning from an endemic area. Such a scenario would represent a significant threat of Oropouche virus becoming endemic in Europe, especially as no official vaccine exists yet against the virus.
Rafael Gutiérrez-López and colleagues tested out the competence of three mosquitoes that are present in Spain (and several parts of Europe) to act as vectors for this virus. They tested Aedes albopictus (Asian tiger mosquito) from Spain, Culex pipiens biotype molestus from Spain and Aedes aegypti (although not present on the mainland it has been found on the Canary Islands) to see whether they could be vectors for the Oropouche virus strain from the 2024 outbreak.
Female mosquitoes were fed blood containing the virus and kept at ambient laboratory conditions (27 degrees Celsius). Measurements were taken 7, 14 and 21 days after infection. The researchers looked at:
- infection of the mosquito midgut
- dissemination of the virus to other tissues
- transmission potential (which was measured by presence of virus in saliva)
- survival of infected mosquitoes and transmission to offspring
They also gave a second blood meal that was virus free to investigate whether this impacted viral transmission rates.
The findings were reassuring as all three species showed limited or poor vector competencies for the virus. Aedes albopictus showed limited competency as some mosquitoes became infected and there was occasional dissemination of the virus beyond the gut and rare transmission events.
Aedes aegypti and Culex pipiens were considered poor vectors. Whilst both species could become infected by the virus, and some dissemination was seen, no evidence of transmission was observed under experimental conditions.
For all three species, viral replication within the mosquito body was low, and there was no evidence of vertical transmission to offspring. The second blood meal (without virus) did not increase the infection, dissemination or transmission rates.
Overall, these findings are reassuring that the existing mosquito population in Spain do not currently have competency to spread the virus. However, as we all know, viruses evolve quickly and so continued monitoring is needed.
Cover image credit:Image by Mohamed Nuzrath from Pixabay