Sindbis Virus Detected in Southwestern Spain for the First Time

A new study reported that the seldom-discussed mosquito-transmitted Sindbis virus (SINV) has been confirmed for the first time in southwestern Spain.

Published on December 13, 2024, this One Health early release (Volume 20, June 2025, 100947) showed that five mosquito species, including Cx. perexiguus, may be important vectors for transmitting this enveloped RNA virus to humans.

The Spanish SINV isolates, which belong to Genotype I, are in a different clade and are more related to sequences from Northern-Central African countries, such as Argelia or Kenya. This indicates a possible African origin for Spanish SINV. 

Previous studies indicate that the virus's origin in Northern Europe was a single introduction into Sweden that later spread to Finland and Germany.

The presence of other mosquito-borne viruses with ecology and life cycles similar to SINV include West Nile virus, which causes severe diseases in people. Given the high circulation in 2022, these researchers propose that the Spanish National Health System consider including it in the differential diagnosis of arboviral diseases in 2025.

SINV was first recognized in 1952 from a pool of mosquitoes collected from the Nile River delta in Egypt. Despite the wide distribution of SINV, symptomatic infections in humans have been reported in only a few geographically restricted areas, such as northern Europe, Africa, Australia, and China. 

Mosquitoborne viruses such as chikungunya and SINV are members of the genus Alphavirus (Togaviridae) and cause human arthritic diseases, with symptoms such as rash, arthritis, and mild fever.

According to the U.S. CDC, most patients recover within weeks or months, but arthralgia and myalgia can persist for years following infection, suggesting an inflammatory response or a persistent infection.

As of December 15, 2024, no preventive vaccine or medication is available for SINV infection. The CDC recommends using mosquito bed nets as a personal protective measure to reduce the risk of mosquito bites.