The first case of West Nile virus was detected in Spain in 2010, in Cadiz. But since 2020, this emerging disease has left, summer after summer, a never-ending stream of cases, many of them fatal.
This year there are already 65 confirmed cases, 53 of them in Andalusia, the region most affected since the beginning by this virus transmitted by common mosquitoes after biting infected migratory birds.
In addition, there were five deaths. This is expected to be one of the worst years for the virus: it appeared a month earlier than usual, so the end-of-season numbers could set records.
Jorge del Diego He is the Director General of Public Health and Pharmaceutical Regulation for the Andalusian government and is coordinating efforts to contain the virus. He explains that if only 1% of cases are reported, there will be around 5,000 in total if we apply “pure statistics”.
And the April rains did not make the task easy, and the mosquitoes (mainly those of the genus Culex) are more widespread than necessary.
But Del Diego also shows the opposite. If we see more cases, it is because there is now more surveillance. Previously, many deaths from viral meningitis (severe cases of the virus cause life-threatening neurological problems) remained undetermined. Now we have named them.
The year 2020 seems to mark a before and after for the West Nile virus in Andalusia and Spain. What happened that, since then, the cases have not stopped?
It is not 2020 that marks it because, like everything in public health, it is generated [el problema] until there comes a time when it explodes. In Andalusia, for example, we have a reference to cases since 2010. This means that we have had human cases for at least 15 years, and from 2010 to 2020, only passive surveillance was carried out in equines.
This does not seem to have led to vector prevention and control policies, which would have helped, in this case, to ensure that what happened did not happen again in 2020. In the end, circulation accumulates, the radius of action of this vector widens, the circulation of the virus expands and this causes cases to explode abruptly in 2020.
Why is Andalusia the most affected region?
We have the vector, just like other communities such as Catalonia or the Valencian Community. In addition, we have geographical conditions, not only due to the many hectares of rice fields but also the temperature and the fact that it is a transit area for the migration of birds, which are the ones that are infected and the mosquito that bites them incorporates the virus, potentially then biting a human. All this logically allows [el virus del Nilo] is established.
Moreover, this mosquito, of the kind Culexhas good biological plasticity: it entered the United States in 1999 and a few years later, West Nile fever became endemic. We also know that countries like Greece and Italy have many cases every year. The mosquito establishes itself in many places.
There have already been five deaths this year, three last year. Is this problem getting worse?
We have 53 confirmed cases. In 2020, there were 44 confirmed, plus 33 probable. At that time, there were more deaths (eight).
If we know that about 1% of cases show their face, this year we would reach about 5 or 6,000 cases of West Nile fever, if we were to make a pure and uncompromising statistic.
This means that we have five deaths out of 6,000 cases. Every death is a shame and we are extremely sorry but, unfortunately, they are not new. This does not mean that this disease is becoming more aggressive: simply, since 2020, a very powerful surveillance system and network has been set up, where previously many viral meningitis leading to death were left without affiliation, that is, without knowing which pathogen it was. who is responsible, now we can know.
Such a sensitive surveillance system allows us to pick up many more cases, and so it seems that the problem is bigger than it might be if we didn’t give it a name: now we’re afraid of it because we’re afraid of a specific thing.
Therefore, we are at the best time to approach and try to control this disease, with a much better surveillance system, capable of recovering cases whose symptoms previously remained in inconclusive diagnoses, without name or surname.
How is this disease fought or controlled?
In 2020, Andalusia launched the first national program to combat West Nile fever, mandatory for municipalities. We know that there is a lot of controversy around competitions. Each administration must devote itself 100% to what corresponds to it, logically. There are rulings from the High Court of Justice of Andalusia and the Supreme Court that support what we say.
It is essential to know what your land is like. It is important to be very clear about the temperatures and how they vary, because if a winter is milder than expected, you know that more females will survive. And this causes more eggs to be laid.
We also need to monitor the rainfall and the amount of water retained, and know the 23,000 hectares of rice fields. We need to know very well how birds migrate, because that allows us to know how mosquitoes get infected and spread, and year after year we have found that they always leave from one place and head north.
Now, logically, we have to try to control the vector, from the origin (i.e. the larva), trying to make sure that all this retained water is controlled, monitored, that everything is known (to be treated with larvicides in the best possible way) and also where the adults are going.
It’s about identifying all the points, and it’s a difficult job: you have to think about all the space there is where the larvae can lay their eggs and hide the adults, and do the treatments that can reduce the density of mosquitoes to avoid human cases.
Some experts criticize the fact that measures were taken too late.
You mean this season? The first meeting we had with the city councils to warn them that this year could be a more complicated season was on March 14.
When we saw the rains and heat of April, as well as the decision of the Hydrographic Conference to authorize the filling of the rice fields, we quickly called a meeting to work together with the Ministry of Agriculture at the end of May, with the municipalities that have most of the cases (La Puebla del Río, Coria, Dos Hermanas, etc.) and the Provincial Council to provide support.
We have been demanding this action for many months. Keep in mind that since June 10, when we held our first meeting, there has been no formalization of the contract by the Provincial Council and, therefore, the companies have not been able to work until July 23. There has been a month and a half delay.
It is also true that something happened this year that we have never seen before: we detected viral circulation four to five weeks earlier than usual. In the 2020 outbreak, cases started at this time of year. We have had cases since June.
What I don’t want is for this to be interpreted as inter-administration shit, because it’s quite the opposite: Public Health must work for the population and dirty linen is washed at home.
Is the trend towards a continued increase in cases and deaths in the coming years?
What is normal with climate change is that, little by little, it increases, but now we are much more able to know, thanks to traps, passive monitoring, etc. what is happening, to anticipate the next season and act earlier, in collaboration with all the administrations.
The Provincial Council of Huelva works practically all year round in this area. Every year we reinforce surveillance: now we do it from May 15 to November 15. If necessary, it will be increased. We will continue to work with the corresponding administration so that mosquito densities are as low as possible and, therefore, as few cases as possible occur.
