THE potentially fatal West Nile Virus is surging among mosquito populations in southern Spain, it has emerged.

In its annual surveillance campaign, the Andalucian government detected a total of 49,629 mosquitoes carrying the pathogen at 26 different sites throughout the region between June 14 and November 2023.

The government uses a graded system to gauge the risk of transmission.

In Risk Level 4, or high risk municipalities, there’s evidence of the virus circulating among human or animal populations in the past two years within 1.5 kilometres of population centres.

All high risk towns are found in the provinces of Cadiz, Cordoba, Huelva and Sevilla, and include the municipalities of Tarifa, Lepe, Gelves, Utrera, Palomares del Rio and Castilblanco de Los Arroyos, among others.

A list of each Andalucian municipality and their corresponding risk levels can be found on the Junta’s website

The Culex perexiguus mosquito was responsible for a deadly West Nile Virus outbreak in Andalucia in 2020, resulting in eight deaths. Credit: Wikipedia

By the end of the season, 89 Andalucian municipalities had Risk Level 2 or higher, indicating that the virus had been detected among animals in prior years.

In August 2023, an 84-year-old woman in Huelva’s Arroyomolinos de Leon died of West Nile Fever caused by the virus, the year’s first and only fatality. According to EL Pais, the woman had a number of preexisting conditions.

On August 9 2023, a 72-year-old woman from the Valencian town of Pucol was discharged from the hospital after contracting the virus, local media reported.

While 80% of people who contract West Nile Virus show no symptoms, 20% develop West Nile Fever, which can cause — in addition to fever — headache, nausea, disorientation, tremors, and in severe cases, encephalitis, paralysis and death, according to the World Health Organization.

The virus — first identified in Uganda in 1937 — is transmitted by mosquitoes and carried by birds. It is also known to cause severe illness and death in horses.

Outbreaks in horses were detected throughout the summer and fall in the provinces of Sevilla, Cadiz, Huelva, Cordoba and Malaga, while outbreaks among wild birds — mostly raptor chicks which had fallen from their nests — were detected in August and September in Jaen, Cordoba and Sevilla.

However, in the conclusion of the Andalucia Department of Health and Consumer Affairs report released in December 2023, the Junta makes clear there is no cause for alarm.

“Continuing with the trend of data from last week, the female population densities of potentially transmitting mosquito species, in general, are at low or very low levels,” it states.

The Junta decided to close the surveillance season in November after no active circulation of mosquitoes carrying West Nile Virus was detected, and the number of female mosquitoes captured in traps had been decreasing.

The Junta began its annual summer West Nile Virus surveillance program in 2020, after an outbreak attributed to Culex perexiguus mosquitoes that resulted in 77 reported cases and eight fatalities exploded on the banks of the Guadalquivir River in Seville, primarily in the villages of Puebla del Rio and Coria del Rio.

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