Wednesday, September 22

A shield against the Nile virus: the plan designed by the experts to prevent another outbreak starts


The control of mosquitoes and birds will be the keys to fight against the disease that caused eight deaths last year in Andalusia

A municipal worker fumigates a
A municipal worker fumigates an area of ​​vegetation in the municipality of Palomares del Ro in August of last year.EFE
  • Infection The outbreak of the Nile virus in Andalusia, that of Seville, has already reached 35 affected without a deadline to control it
  • Health What is West Nile fever? Symptoms and treatment

In a couple of weeks the flooding of the 40,000 hectares of rice fields that unfold south of Seville will begin. Along with the rise in temperature, begin – as every year – the reproduction of mosquitoes Culex pipiens Y very small gnat, natives of Andalusia, but that last year caused eight deaths having fed on birds carrying the Nile virus. The Board affirms that it has established a structure that will allow the presence of the virus in mosquito masses to be detected from the beginning. But as of today, the cause of the extraordinary outbreak of last year is unknown.

At the end of April a greater surveillance in horses, which will also serve as a warning for epidemiologists, Ulises Ameyugo, deputy director of Health Protection of the Board, informs this newspaper. Nile fever is transmitted by mosquitoes to horses and humans, only after they have been infected by birds with the virus. One in 150 people develop symptoms and, in extreme cases, death.

Ameyugo points out that the jobs that carry out the pest control from the Provincial Council of Huelva, the Biological Station of Doana, the University of Cordoba, and technicians from the Regional Ministries of Health, and Agriculture and Sustainable Development, who will analyze birds. At the beginning of May, all the systems will be up and running and, of course, the epidemiological system of the SAS is always on alert, adds the deputy director, admitting that a specific study must still be carried out to know the trigger for the 2020 crisis. For several causes, we had been detecting for years that the virus could be circulating, and that it was becoming endemic.

The Board approved the West Nile Fever Comprehensive Vector Surveillance and Control Program in March. This plan establishes that the town halls those who carry out most of the actions for the control of mosquitoes, an absolutely unfeasible circumstance taking into account the scarcity of economic, technical and human resources at their disposal, affirms the most affected, Coria del Ro, in a motion approved by unanimity.

The best strategy to eliminate Nile virus transmission is to reduce the population of mosquitos in inhabited areas and prevent them from feeding on humans, says Jordi Figuerola, from the Doana Biological Station. For the former, the recommended treatments are preventive and involve larval control using BTI, toxins of bacterial origin that kill the larvae. To avoid contact with humans, mosquito nets are recommended, wear long sleeves and pants, and apply chemical repellants especially in the first and last hours of the day.

Birds are not a problem, but part of the solution. Birds control mosquitoes and insects, so acting on them leads to the opposite effect, the proliferation of insects. In the United States, outbreaks of Nile virus in humans occur when birds migrate and leave residential areas, as mosquitoes no longer have birds to bite and bite humans, explains one of the great European experts in the field .

Figuerola and his team have been in charge of analyzing diseases transmitted by birds for years. In 2020 they received an extra budget to accelerate the results of their analytics in view of the deaths. In 2021 it is not yet official, although it is hoped to have the same means.

The scientists capture animals of the two species of insects involved, identify the females and perform a PCR that detects their viral loadAs in humans with Covid, it is not for nothing that a robot available for extraction was transferred to the Virgen Macarena hospital. Entomological surveillance has been shown to be the best method, since it detects the virus a month before the first cases in humans, adds Figuerola, who deactivates the social alarm caused by some masses of insects in, for example, Seville, when many times it is not. They are mosquitoes, they are other flying insects.

In this 2021 there are similar circumstances to 2020: it has rained with some intensity and human activity was restricted. The only thing missing is the increase in temperature, since in mosquitoes – in addition to becoming active (with cold it does not occur) – the speed with which the virus replicates at 18 degrees is 14 days, and at 28 it takes 4 days to complete the transmission cycle.

The eight deaths in the marshy area of ​​Seville is the result of the worst outbreak ever to occur in Spain. From August 6 to November 30, 2020, the National Epidemiology Center was notified 77 human cases, of which 57 were located in the province of Seville, 14 in Cdiz and 6 in Badajoz. 95% required hospitalization. There are people who have suffered sequelae, such as paralysis of the extremities. More than 130 horses were also affected.

Since July 2020, these species of mosquitoes were much more abundant than normal, and also with many infected specimens: if the normal was 1 in 1,000, last year an infection rate of 1 in 125 was reached. , adds Jordi Figuerola. The reproduction of the common mosquito in the interior of many towns is a fact crtic. It is the inhabited areas where eradication treatments should be accentuated, indicates the expert.

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