An outbreak of West Nile virus, which is spread by mosquitoes, has claimed the lives of two people in southern Spain and left 23 others in hospital, local health authorities said Friday.

An 85-year-old woman died on Friday from the disease at a Seville hospital, a day after a 77-year-old man became the first victim of the outbreak, a spokeswoman for the health department of the regional government of Andalusia said.

Of the 23 other people who are in hospital with the disease, seven are in intensive care units, she added. West Nile virus can cause symptoms similar to those of the flu, but in extreme cases, it can result in tremors, fever, comas and a lethal swelling of the brain tissue known as encephalitis. It can also cause meningitis.

First discovered in Uganda in 1937, the virus is carried by birds and spread to humans by mosquitoes. It is indigenous to Africa, Asia, Europe and Australia. The Spanish outbreak has occurred in the towns of Coria del Rio and La Puebla del Rio, both located next to the Guadalquivir marshes.

The regional government of Andalusia has sprayed several wetland areas with pesticides to kill mosquitos and lower the risk of West Nile Virus transmission, and has urged people to install mosquito nets and screens in their homes.

The outbreak comes as Spain battles one of the severest COVID-19 epidemics in Europe with close to 378,000 diagnosed cases and nearly 29,000 deaths.