Amid concern over the dengue outbreak, one of the questions many have is not
why most of those who become infected are asymptomatic
, while only a quarter of people show symptoms.
In addition, what depends on whether the manifestation is serious.
And, at the same time,
what does it really mean to be asymptomatic
?
Here, the answers, according to four specialists in the subject.
Going from the most to the least important (the "most" is contracting severe dengue), the first guidelines were drawn up by
Jorge Geffner
, a Conicet researcher at the Institute for Biomedical Research in Retroviruses and AIDS (INBIRS) and head of the Immunology course. at the Faculty of Medicine of the UBA.
Following the "international literature" (the way scientists call scientific publications on a certain subject),
"it is clear that between 5% and 7% of those infected by dengue have a severe course"
.
However, the variations that this percentage can have -as well as the lethality, data that none of the respondents dared to report, due to the multiple variables that interact in the outbreaks- depend a lot on how many serotypes circulate in the
region
.
Even when talking about "asymptomatic",
Victoria Micieli
, entomologist, Conicet researcher at the Center for Parasitological and Vector Studies (CEPAVE), clarified the terms: "If a mosquito has the serotype 1 virus, it will infect a person with the serotype 1".
"After the period that we call 'viremia', which lasts from 7 to 10 days and is the time when
the outbreak can amplify
because it could infect healthy mosquitoes that bite them, that person will manufacture their antibodies against serotype 1," clarified.
It means that “if another mosquito infected with serotype 1 comes along and bites it, it will not get infected because it already has antibodies against that strain of the virus.
However, if a mosquito with serotype 2 comes, there can be symptoms of dengue, from severe forms -because there could be an
overreaction of the antibodies-
to a form of common disease”.
Micieli highlighted two central issues: one,
surveillance of serotypes
circulating in the region.
The second, in addition to
messing around
, use repellent.
Just in case, let's clarify that this includes the four obvious scenarios, and their combinations: 1) have dengue and know it, 2) have dengue and don't know it, 3) have had dengue and don't know it;
and 4) have had and are aware of it.
From severe to asymptomatic dengue
The question that arises from the above is whether it can be deduced that all or most cases of severe dengue correspond to people who already had the disease in asymptomatic form, with another serotype.
The answer is no, or rather, not necessarily.
In the first place because, as
Juan Manuel Carballeda
, a Conicet researcher at the Hurlingham National University's Molecular Virology Laboratory, explained, "asymptomatic people who later have a second infection
have their nuances
."
In this sense, he assured, “
it is not that a second dengue infection implies that one is in trouble
.
The fact of reinfecting ourselves with a second serotype different from the first infection increases the chances of developing severe dengue, but it is not exhaustive that it should be like that”.
Secondly, because, as explained by
Adrián Díaz
, an expert virologist in arboviruses, a Conicet researcher at the "JM Vanella" Institute of Virology (Faculty of Medical Sciences of the National University of Córdoba), the severity of the condition in which it can lead the infection “is
multicausal
”.
Why some have severe dengue
So, what does it depend on to fall on one side or the other on the gray scale that starts with "asymptomatic" and ends with a severe or funereal picture?
Is it the viral load of the mosquito?
Is it the health of the host, that is, us?
According to Díaz,
the subtlety of multicausality
is such that "if we are in an outbreak with several serotypes, on the one hand, each one could be generating a different degree of virulence."
In addition, "if the populations of mosquitoes that are in a place are different,
some could be inoculating a higher viral load than others
."
Micieli had a similar opinion: "The viral load of the mosquito can vary because the virus replicates inside it and the same amount does not always reach the saliva."
However, even with all these subtleties, Díaz concluded that "
it is the genetic and social factors that best define the immunological status of the host
, and possibly that is what mainly defines the appearance of symptoms."
Genetics, the key against dengue
Geffner agreed with that look: “Could it be the viral load that the mosquito injects?
Actually, that doesn't seem to be the case.
Even if the load is small, the virus rapidly multiplies, and it multiplies so much that it reaches levels that are generally comparable.”
“
It is genetics
”, he summarized, before explaining: “In genetics there is a set of very differential factors that make how the immune response is induced and what susceptibility the target tissue of the infection has with respect to the virus reproducing with more or less easily.
In addition, he said,
the "whole" of genetics seems to exceed the sum of its parts
: "It is very difficult to understand and put names to each of the genes that, together, determine this level of susceptibility."
Symptomatic dengue: the tip of the iceberg
Putting it simply, assuring that someone with a severe dengue condition had the infection before, asymptomatically and with another serotype, is risky.
Of the multicausality that defines how much and how the disease “hits”, most of it is taken away by the subjective genetics of the host.
What is known is that, in epidemiological terms,
"we only see the tip of the iceberg
," Díaz warned.
"When one is seeing cases of a viral disease, we always say that
underneath the virus is surely circulating asymptomatically
, something that the health system cannot detect," he added.
For this reason (in coincidence with Micieli) he remarked that "it is so important to have
good surveillance systems
, not only clinical but also virological".
According to the last report released on Saturday by the Ministry of Health, 16,143 cases have already been recorded.
But Carballeda pointed out that "there are many more because there are not only asymptomatic but also
mild symptomatic
, who may not access the health system."
Geffner directly released a figure: "It is impossible to know for sure how many susceptible to the second infection there are, but if you talk about 10,000 diagnosed with symptoms, there will undoubtedly be about
40,000 to 50,000 infected hanging around
."
Against dengue, healthy apples
Genetics exceed us and mosquitoes, even when there is no "invasion" in the metropolitan area, are there.
To do?
Carballeda is concerned: "The circulation of the disease is very strong and
there are still many days of circulation of the mosquito
."
“If these temperatures continue, with more than 20 degrees,
the mosquito perfectly reaches adulthood in four days
.
If it bites a person who has a high viremia, it will be infected and it will carry the disease to another person, ”he said.
But he placed a hope.
“You have to use repellent, discard and know that we are facing a mosquito that does not fly very far.
It does not reach more than 100 meters from the place where it takes place.
If in the block where we live we avoid having containers where it can develop,
we can take care of each other and avoid contagion
, ”he proposed.
"The concept of
a healthy apple
is very interesting to avoid contagion."
Geffner added two additional measures.
On the one hand, he said that “
spraying is necessary
.
It has the limitation that it does not kill the eggs and larvae, but it would be necessary to fumigate in the most affected areas”.
The second, offer
accessible repellents
: “They are expensive and should be taken like medicine.
They cost quite a lot to acquire."
ACE
look also
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