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A campaign began in Puebla del Rio (Seville) on Monday, 5 April to reduce mosquitos and hopefully avoid a repeat episode of last year’s Nile Fever outbreak.

 

Located on the banks of the Guadalquivier, the municipality is vulnerable to mosquitos, prinicipally because of the abundance of water and the cultivation of crops such as rice which involve the flooding of fields and the accompanying network of water channels which present perfect breeding grounds for mosquitos.

Last year the unusually wet spring caused a proliferation in the number of common Culex mosquitos breeding in the wetlands of the Andalusian region, particularly in the area around the national park of Doñana, and on the banks of the Guadalquivir river, where mosquitoes are commonly found, co-inciding with the appearance of the Asian Bush mosquito (Aedes Japonicus), the combination of which is believed to have been the cause of an outbreak which started in Seville province and spread to Cádiz, killing at least four elderly people.

The West Nile Virus (WNV) is commonly found in Africa, Europe, the Middle East, North America and West Asia and is a member of the “Flavivirus”family, which also contains the Zika virus, dengue virus, and yellow fever virus.

WNV is primarily transmitted in a cycle involving transmission between birds and mosquitoes, but does not spread directly from person to person, the transmission to humans normally occurring after a mosquito has bitten an infected bird; the virus passes into the salivary glands of the mosquito, which then bites a human.

Victims are frequently elderly, succumbing to West Nile encephalitis or meningitis, usually accompanied by a high fever, fatigue, headaches, nausea and muscle pain, although in around 80 percent of people the cases are asymptomatic according to the WHO.

 

As WNV is transmitted to humans through mosquitos, preventing the spread of an outbreak is best achieved by intensive fumigation to kill off the mosquitos transmitting the virus in affected areas, as the major problems relating to WNV are that there is no known cure and no preventative vaccine currently available.

 

Last summer efforts to combat the outbreaks in Andalusia were focused around two major risk zones, the first in the municipal area of Puerto Real and a second in an area in which mosquito populations are traditionally high, between Alcalá de los Gazules, Benalup-Casas Viejas and Medina Sidonia, bordering with Vejer, Conil and Barbate.

 

Mayors of the municipalities in which the mosquitos were believed to be breeding most aggressively pressured the regional government to take responsibility for the fumigation work and finally, after prolonged discussions, during which the number of patients, and then deaths, slowly grew, the regional government agreed to fast-track a 100,000 euro contract in order to undertake the necessary fumigation.

 

The regional government was reluctant to assume responsibility for the disinfection work on an ongoing basis, but did agree in principle to support the process in subsequent years in order to try and prevent a repetition of the 2020 fatalities, which occurred in both Seville and Cádiz provinces.
 

The mayor of the town has however, complained about the Andalusian regional government’s lack of action on the matter this year so far and stressed that the local council would do “whatever it takes to protect local residents’ health” although expected the regional government to also play its part in the preventative work this year.

 

The authorities are, therefore, including increased fumigation in the ‘Urban Clean Up Plan’, and workers will be spraying green areas, roundabouts, parks and gardens with insecticides and larvicides.

 

Residents have also been advised to fumigate their private gardens in order to amplify the preventative spraying this year and prevent a repetition of the deaths of last year.

 

It is not known if traces of the virus remain in the resident bird population or whether the campaign last year successfully eradicated the contagious hosts.