Record year of dengue in the Americas: challenges to face

According to the latest report on the epidemiological situation of dengue in the Americas, from the Pan American Health Organization (PAHO), until epidemiological week 22 of 2024, that is, June 22, a total of 9,541,015 suspected cases of dengue were reported, which represents an increase of 230% compared to the same period in 2023 and 421% with respect to the average of the last 5 years. This could be explained by the fact that PAHO considers climate change to be the greatest threat to global health of the 21st century and includes dengue as one of the indirect impacts of the so-called climate-sensitive diseases. To elaborate on the topic, it is necessary to point out that the transmission of dengue is usually seasonal, that is, the number of cases tends to increase in the summer or the rainy season and decrease in the winter or the dry season. But the increase in global temperature means that dengue seasons are lengthening, consequently, there is greater transmission. That same increase in temperature has meant that regions that were once out of reach of Aedes aegypti because they were previously too cold are now infested, meaning that global warming is affecting the distribution of the vector and therefore the possible distribution of cases. In addition to this, the vector is adapting to conditions that were previously adverse to it with records of its presence in waters with high organic content and at altitudes above 2,600 meters above sea level, both conditions unthinkable until a few years ago. There are also social determinants especially linked to inadequate, poorly planned sanitation infrastructure that fails to keep pace with the growth of cities, internal migratory movements, among others. And of course political determinants such as the political instability of some countries in the region, the lack of technical capacity to define and execute public health policies linked to the prevention and control of diseases transmitted by vectors and, of course, corruption. Regarding the challenges that must be faced, let's begin by saying that in terms of vector control, we must consider the ability that Aedes aegypti has demonstrated to develop resistance. In this context, alternatives that are easy to apply, proven effective and community acceptance must be sought. For example, after the use of Temefos as a larvicide and considering the operational problems and the community's rejection of pyriproxyfen (due to its difficult dosage, residuality due to application form and IGR form of action), NATULAR DT (Spinosad) single-dose tablet, larvicide, long-lasting - more than 60 days) emerges as an alternative. For space applications, with the vector being resistant to pyrethroids and organophosphates, the first Neonicotinoid (Imidacloprid) for use in public health, prequalified by WHO with the trade name CIELO, has been developed, successfully used in various countries such as Mexico, Brazil, Ecuador, Paraguay, among others. And since 2019, the use of residual insecticides with the TIRS method has been proposed in a complementary manner. There it is also necessary to identify products that are effective and safe from a toxicological perspective. Likewise, an interesting experimental approach is the release of Aedes aegypti mosquitoes infected with the Wolbachia bacteria, presenting a reduced capacity to transmit viruses to humans. Reproduction of these infected mosquitoes with the wild mosquito population ultimately reduces the number of mosquitoes that are efficient vectors. Another notable experimental strategy is to release billions of sterile male mosquitoes to mate with females in the wild using the sterile insect technique (SIT). Although both strategies have worked at an experimental level, they could be successfully implemented on a mass level in the future. In another approach, the development of the dengue vaccine has also proven to be a challenge due to the existence of four virus serotypes. Dengue vaccines must be quadrivalent and must induce a balanced immune response so that the antibody levels against each of the serotypes are sufficiently high. This is to avoid a phenomenon called antibody-dependent enhancement. This strategy has some limitations such as being contraindicated for some groups such as the use of live attenuated vaccines in pregnant women or immunodeficient patients. Likewise, the need for a cold chain makes it difficult to transport vaccines to populations in remote rural tropical regions, and reluctance to get vaccinated can lead to suboptimal vaccine coverage. Finally, there is the alternative of developing antivirals that act directly on viral targets, also known as direct-acting antivirals. An important advantage of the use of oral antivirals is their possible implementation as antiviral prophylaxis to control outbreaks, acting faster than vaccines and easier to distribute without a cold chain. There are research teams developing antivirals that cover several viruses, let's hope for soon results. In summary, the challenges to face dengue control are the clearest example of the need for comprehensive, interdisciplinary and intersectoral work.