A public employee fumigates against the dengue mosquito in a park in Cancun, in the State of Quintana Roo.Elizabeth Ruiz (Cuartoscuro)
EL PAÍS offers the section América Futura open for its daily and global informative contribution on sustainable development.
If you want to support our journalism, subscribe
here
.
One of the first symptoms is a very high fever that can go up to 40 degrees.
And an excruciating pain in the head, behind the eyes, in the muscles.
A horrendous discomfort in the joints accompanied by nausea that does not let you take a little step, or get out of bed.
This is how dengue patients describe the disease.
But that's the milder version.
“Because if the virus attacks the circulatory system and produces
shock
and internal bleeding, it can cause death within hours.
"Dengue acts very quickly," says Luis del Carpio, an internist and virologist from Veracruz who is an expert in this ailment caused by
by the bite of infected mosquitoes.
A zoonosis of tropical origin that, according to the World Health Organization (WHO), affects up to 400 million people annually and whose frequency has grown in recent decades to become the most rapidly spreading insect-borne viral disease worldwide. the planet.
It is an arbovirus that in the 1970s was only found in nine countries and is already endemic in 128. "It is responsible for a chronic epidemic that nobody talks about enough, that increases every year and that only attention is paid when it causes an international alarm”, says the expert, referring to the outbreak that is currently affecting Bolivia, the worst in the last decade.
More information
Dengue plagues children in Bolivia
The epidemiological situation in this region is no exception;
The incidence of dengue in Latin America has not stopped growing, reporting more than 2.8 million cases in 2022, when Brazil recorded the highest number of deaths from the infection.
And Mexico, which currently reports cases in 28 of its 32 states, has been the scene of up to one in five deaths on the continent in the last decade.
"The worst thing is that the rate of severity of the disease has also been increasing," warns the virologist about this zoonosis that uses female Aedes aegypti
mosquitoes as a vector .
Although the Mexican government has been working for years to stop the virus, no strategy has been efficient to checkmate one of its most serious public health problems.
A challenge that has led to the creation of a tool to help identify outbreaks and prioritize pathogen control efforts.
This is a map made by researchers from the Rutgers Institute for Global Health that focuses on the hot spots with the highest incidence of the disease and which, with the collaboration of the Autonomous University of Nuevo León and the University of North Texas, has made it possible to calculate the environmental and socioeconomic risk factors linked to the development of the infection.
"To identify the fever hotspots where the most severe dengue outbreaks occur, we use data from the Mexican Ministry of Health," explains Ubydul Haque, responsible for the tool based on an analysis of more than 70,000 laboratory samples from 2,469 Mexican municipalities. collected between 2012 and 2020, and which included the classification of the serotypes that constitute the range of transmissibility and dangerousness of the virus: DENV-1, DENV-2, DENV-3 and DENV-4.
Each one groups different genetic variants, the most lethal is DENV-2.
“And the most prevalent throughout the country,” explains the author of the map, whose purpose is “to help health officials identify activities to stop it and improve surveillance.
By knowing where severe dengue frequently occurs, we can significantly reduce the number of cases.”
For many years, the direct relationship between the number of people affected by dengue, socioeconomic status and climate has been known.
But, until now, the factors that contribute to the severity of this tropical infection for which there is no specific treatment and which can easily and drastically end life have not been studied.
To delve into the impact of certain determinants, the team led by Haque superimposed clinical data with localized climate and socioeconomic statistics, such as literacy, access to health services, electricity, and sanitation.
“The socioeconomic level is one of the risk factors for the severity of the infection in Mexico.
And some municipalities on our map do not have greater coverage of running water," says the scientist,
The map of dengue in Mexico. Rutgers Institute for Global Health
The poor quality of housing is another of the aggravating factors of the disease.
"In municipalities with more low-quality buildings, infection rates are more likely to be higher," points out the epidemiologist who, based on the data analyzed, created heat maps with the distribution and severity of the dengue virus.
The hot spots of his tool are drawn in the humid coastal regions at lower altitudes: all the DENV serotypes —including the one that causes severe dengue— coincide with municipalities in the northeast, central west, and southeast of Mexico.
The prevailing climatic parameters in this last region position several of its states at greater risk of presenting cases of severe disease, as is the case of Oaxaca.
“These results can guide policies that help allocate public health resources to the most vulnerable municipalities,” says Haque.
Climate change: a dengue precipitator
According to different investigations, the increase in the number of cases of zoonosis has been attributed to the genetic diversification of DENV serotypes and the appearance of new genotypes in Latin America.
"Mexico, especially the southeast, is characterized by large jungle and wooded areas that ensure great biodiversity, including many vector species of epidemiological importance," says Del Carpio, after years dedicated to tracking the different species of the
Aedes aegypti
mosquito
, vector of dengue, Zika and Chikungunya.
The virologist's concerns about the pathogen focus on two intertwined aspects: that there are more vectors than those typically known that demonstrate competence, capacity, and potential to spread the virus, and the new behavior of the transmitters that epidemiologists are observing.
“Theoretically, these vectors do not proliferate at more than 2,000 meters above sea level.
But in Mexico they are succeeding," says Del Carpio, used to receiving many dengue patients at his office in Veracruz, one of the states with the most affected.
"Cases are occurring in Toluca or Puebla, regions where the tropical disease is acclimatizing," says the specialist.
“Due to climate change, Aedes
mosquitoes
They can already survive at higher altitudes in Mexico.
On the other hand, extreme rains, those that are not seasonal, changes in temperature and humidity are important climatic parameters that have a very strong influence on the survival and proliferation of these agents”.
The scientific consensus forecasts an increase in the impact of the virus in Mexico for the next decade due to global warming.
"Some experts have already warned that very soon 20 million people in the capital will be exposed to dengue outbreaks caused by
Aedes
mosquitoes that survive at higher altitudes," says the American researcher, for whom the most effective way to stop the spread of the disease currently goes through vector control.
Insecticide spraying to kill transmitting mosquitoes is one of the most effective means of achieving this.
Precisely the nebulization, through drones that cross the skies over the territories with the highest incidence, is the method that Bolivia is using to stop the transmission of dengue, spread by the overflow of rivers due to intense rains that the country registered.
Among the different programs of the health authorities, efforts have also been made to develop specific vaccines against DENV, such as the one approved in Europe a few years ago.
"But we still don't have a really effective injection," highlights the Mexican virologist.
Another of the control methods that Mexico is committed to, and which has already been implemented in Brazil, Cuba and Argentina, is the sterile insect technology.
Known as SIT, through this technique males incapable of reproducing due to having been subjected to radiation doses are released so that when they mate with wild females they do not produce offspring.
First developed in the United States, this procedure has been very successful in controlling some pests caused by other insects, such as fruit flies, tsetse flies, or cactus moths.
"In some states, such as Chiapas, attempts have been made to carry out pilot programs for the technique, but the results, for the moment, are not decisive," says Del Carpio, who shows great concern about the arrival of new serotypes of the virus in vulnerable populations. .
"The risk of dengue hemorrhagic fever epidemics, the worst, is increasing and we need more extensive surveillance."
In this context, the map designed by Haque's team and the results of their study offer a glimmer of hope for greater control of the infection and guide policies that help allocate public health resources to the municipalities hardest hit by this disease. that has been appearing and disappearing in the last half century.
In 1963,
Mexico was declared free of the
Aedes aegypti
mosquito , the main transmitter of the infection.
But the vector managed to reintroduce itself two years later along its northern border, and a little later, at the end of the 1960s, it did so through the south of the country, expanding in a decade throughout most of the territory.
Since then, the infectious agent, a public health problem shared by most regions of Latin America, has not been eradicated.
“This is an epidemic that never ends, with which the most vulnerable populations, those with the fewest resources, have gotten used to living with it,” says Del Carpio.
"And the rest, those who do not suffer from it, have normalized it because it represents a disease that is far away, dismissing the fact that dengue is one of the most worrisome diseases in our region, a forgotten one."