The rise of dengue

Dengue is common in many parts of the tropics and subtropics, and almost half the world’s population is at potential risk of infection. The World Health Organization estimates that up to 400 million dengue infections occur each year.

Argentina is going through a historic outbreak of this disease. Because?

More than 56,000 cases and 48 deaths have already been registered in the country, figures that, as far as is known, have never been reached before in an outbreak of this type. Particular environmental conditions and a variant of the virus that accelerates the contagion processes are some of the causes that explain the problem. Some specialists are investigating the genetics of the vector, which could be the key to designing new control strategies.

In recent weeks, a significant increase in dengue infections in Argentina has set off warning signs in the health system. According to a recent Epidemiological Bulletin, issued by the National Ministry of Health, 56,324 cases were registered and 15 jurisdictions in the country confirmed autochthonous circulation. The sad record of 48 deaths is also recorded.

Argentina has three dengue epidemiological milestones, which occurred in 2009, 2016 and 2020. Each of them exceeded the previous one in numbers and the current numbers are on track to lead the podium. “We are seeing that, compared to the same period in 2020, this peak is noticeably more important,” said Victoria Micieli, director of the Center for Parasitological and Vector Studies (CEPAVE), attached to the National University of La Plata (UNLP) and to the National Council for Scientific and Technical Research (CONICET), in Argentina.

A female Aedes aegypti mosquito, an important vector of dengue. (Photo: James Gathany/CDC)

The increase in dengue cases is common in the summer period, but what caused it to exceed registered records in previous years? For the CONICET researcher, when dengue manifests itself as an epidemic, it has multiple causes. “When we talk about communicable diseases, we always refer to a triad made up of the environment, the vector and the host. And they all have a great incidence, ”she explained, in dialogue with the CTyS-UNLaM Agency.

The high temperatures, and the subsequent rains, which marked the climatic panorama of the last months, affected the dynamics of the vector, generating a more favorable scenario for the increase in viral circulation. According to Micieli, in addition to environmental conditions, another factor could have had an impact on the transmission dynamics: the serotypes and genetics of the viral strains that entered the country this year.

It is that there is not only one dengue virus, but four so-called serotypes (DEN 1, DEN 2, DEN 3 and DEN 4). Although they share many characteristics, they present variations that make them unique and, therefore, their interaction with the organism they enter will be different. “In Argentina, 1 is circulating and strongly 2, which is associated with severe forms of dengue,” the researcher specified.

In this sense, Arturo Lizuain, Associate Professional of CONICET and member of CEPAVE, pointed out that Argentina depends exclusively on the viral circulation that exists in neighboring countries such as Brazil, Paraguay and Bolivia, where, in the last year, there has been an increase very important cases.

“In the country there are all the conditions for the vector to reproduce, and if we add that strain 2 circulates with a genotype associated with more serious problems and faster transmission, that would explain why we have an outbreak today.” so important,” he said.

In 2017, an international team led by experts from Yale University in the United States, in which Dr. Micieli participated on behalf of CEPAVE, sought to determine the genetic diversity of the Aedes aegypti mosquito, a dengue vector. Thanks to the researcher’s contribution, they were able to discover that, in Argentina, there is a genetic mixture of two subtypes of this species: Aedes aegypti formosus, a variety of jungle origin, and Aedes aegypti aegypti, the domestic form.

However, the study to deepen this finding was interrupted until this year. According to Micieli, they are in the process of preparing data using genomics to understand the origin and behavior of this vector in Argentina, thanks to a current collaboration between CEPAVE professionals and the team of Dr. Andrea Gloria-Soria and Dr. Jeffrey Powell .

“We detected an important variability in its genome and different from the rest. That jungle subform would have been introduced into the country from Africa. This is important to study if this genetic variability can affect the behavior of the vector and lead to an increase in the invasion capacity”, he explained.

A problem to combat all year round

Dengue has no cure or treatment. People who contract it should rest and monitor their symptoms. For this reason, the best way to combat it is with prevention. Using repellents on the skin, wearing light-colored clothing with long sleeves, placing mosquito nets on doors and windows, and eliminating possible breeding sites are general recommendations.

For Lizuain, one of the keys to preventing dengue is to continue with dissemination and eradication campaigns during the winter. “What happens is that the mosquito survives during the cold in the form of an egg, waiting for the temperature to rise again. That is why it is crucial to discard useless containers that can accumulate water and clean the surfaces of animal drinking troughs, vases, buckets, etc. ”, she pointed out.

Lastly, regarding the control methods, he maintained that spraying is often required in a preventive manner, for which reason he clarified that this is not recommended, since it can generate resistance to insecticides, as well as being harmful to the environment. . “The only time when fumigations should be carried out is when these outbreaks occur in specific places, such as a neighborhood where we know there is transmission and we have to stop it,” he clarified. (Source: Marianela Ríos (CTyS-UNLaM Agency))