Two things are needed for a dengue outbreak to start: infected people and mosquitoes. Temples of the Egyptians that, when biting, carry the virus from one to another. Mosquito populations are at the expected values for this time of year, in which they proliferate. The detection of three non-imported cases in the last month does not constitute an outbreak, but it is a warning sign that the virus is circulating. The specialists do not risk predicting whether this will be a season with many or few cases, but as a precaution they suggest checking the houses and their surroundings, and “discarding”; that is, eliminate all reservoirs, no matter how small, in which water accumulates and that could become a breeding ground for these insects.
“I’ve been looking a bit at the statistics over the last few weeks, comparing with previous seasons, and the truth is that we don’t have anything different, and neither in neighboring countries, such as Bolivia, Paraguay or Brazil -says Sylvia Fischer, from Grupo of the Study of Mosquitoes (GEM) of the Faculty of Exact Sciences of the UBA–. It is true that there was a very high peak last year and that the same thing had happened just before our big epidemic. But en this moment the number of cases seems to be normal, or even a little less, both in the region and here. I don’t see anything that allows us to say that this year there will be a major outbreak. Our epidemics are highly correlated with what happens in neighboring countries. The first cases are always coming from areas where there is annual transmission, such as Brazil or Paraguay. I can’t rule it out, but it doesn’t seem very likely.”
In search of Aedes aegypti eggs and larvae
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Fischer (who clarifies that he is a specialist in mosquitoes and not in dengue), explains that Already in this last week the hatching of the eggs rose to quite high values, comparable with those that usually occur at this time of the year. “This is the time when the abundance of mosquitoes starts to increase exponentially. And we know that these numbers are enough so that, if there are cases, they are transmitted. It must be taken into account that there may be underreporting, because some symptoms are similar to those of Covid. Perhaps people, who are quite used to this type of condition, do not go to the hospital and therefore there is less notification than before the pandemic. The fact that there are autochthonous patients is telling us that there is circulation of the virus, although minimal for now.”
a seasonal disease
The researcher stresses that it is not usual for epidemics to arise from one or two events, which should be thought of more as a rain of cases, of which some “ignite”, like the sparks that will unleash a fire. in the presence of Temples of the Egyptians we should increase prevention measures by reducing the places where it can breed and reproduce, using repellent and mosquito nets on the windows and, in the case of having symptoms, reducing our exposure to the open air. In general, at least in my experience, Temples of the Egyptians it is usually more around the houses than inside it”, he comments.
For his part, virologist Mario Lozano, former rector of the National University of Quilmes, disagrees: “It seems to me that there are going to be many cases,” he says. “Dengue outbreaks in Argentina have a dynamic of a couple of years with few cases and then comes a bigger one. The last of these was in 2020, so it is likely that this year will be high again, especially since there are a lot in Brazil and Paraguay, and we depend a little on what happens there It is the people who travel from those territories where the disease is endemic and arrive infected in the country, who start a transmission cycle here. One of the things that must be taken into account is that if there are no mosquitoes it is not transmitted, and That is why in winter there are no more cases, since when temperatures drop, they remain like eggs, inert”.
Dengue has already become a seasonal disease, even in these latitudes. Every year, the peak of cases occurs between February and April. “Prevention has to do with reducing breeding sites,” explains Manuel Espinosa, from the Mundo Sano Foundation. But also, when we are in an outbreak, the population has to be attentive to the symptoms, which are sometimes confused with the flu or a cold: severe headache, muscle and joint pain, high fever, and sometimes a rash. In that case, you have to consult immediately and not self-medicate”.
Containers with water of several days can be breeding grounds for mosquitoes
One goal is to reduce the environmental burden of sites where the mosquito can breed; that is, disused tires or appliances, drums, water tanks without lids, bottles. Even containers as small as a soda cap, if they collect water, can be used for mosquitoes to lay their eggs and larvae to breed.
“It is important to eliminate all this during the year, before the heat and rain begin, which are favorable environmental and temperature conditions, because if not, at the beginning of the dengue season, the municipalities have a significant load of potential hatcheries –says Espinosa–. When an outbreak breaks out, the ‘junk’ can have a negative side effect, which is that carrying those containers around the city can generate dispersion and new sources of infestation. When cases begin to appear, the important thing is that the health system is attentive to take the necessary actions, go to the houses, do the control on the block and the ‘turn’ of [mosquitos] adults. There, the fundamental thing is to react quickly to reduce the number of infected insects, or those that can acquire vectorial capacity and transmit the disease. But when you get to that point, it’s often too late, that’s why there’s so much insistence on working in the previous periods”.
An expanding population
Until a little over five years ago, in the metropolitan area there were no reports of dengue; However, different studies show that, due to the increase in average temperatures, the Temples of the Egyptians It is present in latitudes increasingly far from the Equator. On the other hand, researchers from the Mosquito Study Group verified that it can complete its development cycle at only 12°C, which extends the transmission season for diseases of which it is a vector (https://academic.oup.com/jme/article-abstract/56/6/1661/5505308). They observed that their larvae can withstand the Buenos Aires winter and reach adulthood.
In 2015, in another work that was published in the Journal of Vector Ecology (https://onlinelibrary.wiley.com/doi/pdf/10.1111/jvec.12181), established that its advance towards the south is notorious, since they detected it in places like San Clemente, San Bernardo and Villa Gesell, in the province of Buenos Aires.
Vertical transmission is also known to exist, although at reduced rates. “That is to say, of all the ‘ovipositions’ of an infected female, only a low percentage of eggs can be. What has not been proven is what is the role of this vertical transmission in an outbreak”, says Espinosa. Mundo Sano’s work on the 2009 epidemic, during which they captured males (which do not bite, therefore cannot be infected from blood) and found positive individuals. That is, they must have already been born with the virus.
Dengue has four serotypes. The one that predominates in our territory is 1, and depending on which region, there may be income from someone else. This poses a health dilemma, since when a person previously infected with one of them acquires another, they can develop what is known as “dengue hemorrhagic fever.” There is a phenomenon called “stimulation mediated by antibodies”: those that one developed against the first strain, when they bind to another, not only do not neutralize it, but also carry the virus to the cell where it replicates; that is, they cause an infection several orders of magnitude more serious than the first. Another work, also local, but by scientists from the Faculty of Pharmacy and Biochemistry of the UBA and the Institute for Biomedical Research on Retroviruses and AIDS, discovered that one in four adults in the AMBA already has antibodies against dengue, which increases the risk of complications in the event of a possible new infection with another subtype.
Vaccines in development
“It is important to be attentive to the symptoms, go to the doctor and not self-medicate,” Espinosa insists. It should also be mentioned that the concern should not only be dengue. Right now, Paraguay is having a chikungunya outbreak [que produce dolor articular, náuseas y vómitos, intenso cansancio, picazón y/o sangrado de encías, y que en algunos pacientes puede derivar en artritis crónica]. We should not be surprised that these infections appear, not only at the border or in Formosa, but also by people who travel to Buenos Aires or other provinces. To give an idea, until the last weeks of November, in the central area of the neighboring country, notifications reached 200 cases. In the last three weeks of December, they went to 700. It is a relevant number for such a short period. That is an outbreak that can become an epidemic.”
Containers with water of several days can be breeding grounds for mosquitoes
For now, the treatment for dengue is symptomatic, but vaccines are being developed. There is one (approved in Argentina and also in other countries), but the World Health Organization indicates it only for those who have already suffered from it, because it does not protect one hundred percent against the four serotypes. So, if one generates antibodies against all of them, but then becomes infected with one against which the protection is 50%, it is as if they had a second infection, but with non-protective immunity, which instead of helping can complicate it. On the other hand, it could only be applied between the ages of 9 and 60. The WHO suggests using it in places where the prevalence is 70% (here it is less than 20%).
“Another immunization, from a Japanese company, appears to be quite effective for all four serotypes and is being submitted for PAHO approval. Espinosa points out. Hopefully it can start to apply. At the Butantán Institute in Brazil, the latest results of phase two tests of a vaccine that could be effective against the four serotypes are also being generated. This would make it easier to control outbreaks, especially in endemic areas.”
According to the WHO, the incidence of dengue fever in the world increased a lot. The number of reported cases has multiplied by eight in the last two decades (There are almost 400 million infections per year, of which about a hundred million are of varying severity.) Currently, the disease is endemic in more than 100 countries in Africa, the Americas, the Eastern Mediterranean, Southeast Asia, and the Western Pacific.