West Nile virus: What you need to know about Spain’s other ‘deadly’ virus

West Nile virus: What you need to know about Spain's other 'deadly' virus
Credit: Lyle Buss/CC/UF/IFAS
With the news cycle dominated by rolling, twenty-four hour coronavirus coverage in the last six months, you'd be forgiven if news of the West Nile virus in Spain had passed you by.

Although the National Epidemiology Centre registered only seven cases of the Nile virus in Spain over the last decade,52 cases have been recorded in humans in last month alone, clustering in Andalusia, with numbers now increasing and at least four deaths in the province of Sevilla so far.

But what is the Nile virus? What are the symptoms? How is it transmitted, and what can we do to protect ourselves and prevent the spread?

The West Nile Virus

The West Nile virus is a “Flavivirus” – a family of RNA viruses that includes the dengue virus, tick-borne encephalitis virus, the yellow fever and Zika viruses – that have been around since the 1930’s.

First identified in Uganda, it is believed to have remained around the Nile delta area for decades but has now spread across the world. The virus’s ‘reservoir’ (the population of organisms or environment in which infectious pathogens live, reproduce and depend on for its survival) is thought to be birds, not mosquitoes, who instead behave as transmitters of the virus. 


Much like COVID-19, the Nile Virus can be asymptomatic in the vast majority of people. It is believed up to 80 percent of infected people don’t show symptoms, according to the WHO, while the 20 percent who do could experience an array of symptoms ranging from fevers, fatigue, headaches, nausea and muscle pain in mild cases.

More serious cases could experience West Nile encephalitis or meningitis with a high fever, or even comas and seizures in the most severe cases. Patients experiencing these symptoms are usually admitted into hospital. 


Fortunately, unlike COVID-19 the Nile virus cannot be transmitted between people. The transmission process, however, is short and simple: a mosquito bites an infected bird and the virus passes into its salivary glands; the mosquito then bites a human and infects the recipient.

It also affects horses.

Why the recent outbreak? 

Experts blame a particularly wet spring creating stagnant water and the ideal breeding ground for mosquitos. They also blame the coronavirus lockdown, which meant councils may not have conducted fumigations they usually do during spring.

This spring saw an estimated 30 percent rise in the mosquito population in the area around Donaña wetlands – the epicentre of the recent outbreak. 

Regional health minister for Andalucia Jesus Aguirre suggested that the arrival of an invasive species of mosquito known as the Asian Bush mosquito (Aedes Japonicus) may have contributed to the spread of the disease.

Map shows the distribution of cases discovered in horses in Spain. Source: Ministry of Agriculture.


How can we prevent transmission?

Simply put, the best way to stop becoming infected with the Nile Virus is to try and avoid mosquitos. Whilst many Spaniards are well versed in preventative measures – the use of nets, repellents and creams, avoiding buildups of stagnant water and covering the skin, for example – extra vigilance is required because there is, as of 2020, no treatment or vaccine for the Nile virus.

Fumigation has been undertaken in problem hotspots to try to kill off the mosquitos responsible for spreading the virus and Andalusia's regional government has promised an investment of €100,000 on drones to spray inaccessible areas.

Should you be worried?

Although there is no specific profile of at-risk people, like COVID-19 older people with underlying health conditions are at a greater risk of suffering serious symptoms or fatalities.

The four fatalities so far recorded in Spain were all among elderly people; three men aged 70, 77 and 78 and a woman of 85. 

If you are bitten by a mosquito, the incubation period lasts somewhere between 3 and 14 days; medical attention should only be necessary if symptoms appear or you were bitten in one of the high risk areas of Andalusia.

Even so, fortunately it seems that only 0.1 percent of people infected with the Nile virus die from it.

By Conor Faulkner/The Local Spain

READ ALSO:  West Nile virus outbreak spread by mosquitos kills two in Andalusia


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