The increase in the incidence and geographic distribution of diseases such as chikungunya and dengue, transmitted by hair Aedes aegypti, represents an important public health problem in the region of the Americas. The alert was issued by the World Health Organization (WHO).
Dengue is responsible for the largest number of non-continent cases, with epidemics occurring every three to five years. Dengue fever and chikungunya are endemic in most of the countries of Central America, South America and the Caribbean, in the current summer season, or the increase in transmission and the expansion of two cases of chikungunya have been observed beyond the historical transmission areas.
According to the WHO, 2023 shows intense dengue transmission. Also, higher transmission rates are expected in the coming months in the Southern Hemisphere, due to climatic conditions that favor the proliferation of two mosquitoes.
There were 2.8 million cases of dengue reported in the Americas in 2022, which represents an increase of more than two times when compared to the 1.2 million cases reported in 2021. The same growing trend was observed for chikungunya, with a high incidence of inflammation in the brain (meningoencephalitis) possibly associated with chikungunya.
At the regional level, the WHO assesses the risk as high due to the generalized presence of vector mosquitoes, or the continuous risk of serious illnesses and death, and the expansion into the historical areas of transmission, where the entire population, including risk groups and health professionals , we may not be aware of the clinical manifestations of the disease, including severe symptoms.
Epidemiological panorama in Brazil
An international study details the spread of the chikungunya virus (CHIKV) since its introduction into the country ten years ago. The research, which counts with the participation of the University of São Paulo (USP), analyzes 253,545 laboratory-confirmed cases between 2013 and 2022.
The data suggest that the doença was distributed in the Brazilian territory in a heterogeneous way, being that the more affected cities will present some protection to new surges, while municipalities less exposed to previous waves will remain more suscetive. The results were published in the scientific journal The Lancet Microbe.
“The CHIKV is a great threat to global public health, the virus is transmitted mainly between humans by mosquitoes of species Aedes aegypti and Aedes albopictus, the same vectors of dengue and Zika. During the last 20 years, chikungunya has had more than 10 thousand cases reported in more than 125 countries and territories,” says virologist William Marciel de Souza, from the University of Texas Medical Branch, United States, first author of the article in the statement. .
The disease is characterized by symptoms such as high fever of sudden onset and intense pain in the joints. Despite the similarities in the symptoms, the main difference between dengue and chikungunya is the pain in the joints, much more intense in chikungunya, affecting mainly the hands and feet, usually our fingers and pulses.
The diagnosis must be made by a doctor and can be confirmed by specific laboratory tests, which can be made by the Unified Health System (SUS). As the disease is transmitted by mosquitoes, as a preventive measure I included the elimination of two breeders in the houses and households, which basically consist of places where stagnant water accumulates (go down).
“Chikungunya is a febrile illness typically characterized by acute and chronic human signs and symptoms, usually with severe arthralgia. [dor nas articulações], many times chronic and disabling, but also including some neurological complications and death. Currently there are no licensed vaccines or antiviral drugs available to prevent or treat infection”, explains the researcher.
Aedes aegypti
Researchers estimate that 1.3 billion people live in risk areas for chikungunya virus transmission, and Brazil is the country with the highest incidence of cases in the Americas.
“In this epidemiological study, we use genomic sequencing data, virus vector information, or Aedes aegypti, and aggregated clinical data of chikungunya cases in Brazil, or that represents more than 250 thousand cases confirmed by laboratory tests. Next, we evaluated the spatio-temporal dynamics of chikungunya in Brazil through time series, mapping, age and sex distribution, lethality and genetic analysis, among other factors”, he says.
Between March 2013 and June 2022, 253,545 laboratory-confirmed cases of chikungunya were reported in 3,316 (59.5%) in 5,570 municipalities, distributed mainly in seven epidemic waves from 2016 to 2022. The investigation reveals that Ceará was the state most affected, with 77,418 cases during the three largest epidemic waves, which occurred in 2016, 2017 and 2022.
“Likewise, we sequenced the genomes of the virus and identified that the chikungunya recurrence in 2022 in Ceará, after a four-year hiatus, was associated with a new introduction of an East-Central-South-African lineage, probably originating from other Brazilian states. . The study also estimates that this new CHIKV line was introduced in the State between the middle of and the end of 2021”, adds Souza.
“Based on the epidemiological analysis, we identified that the chikungunya spreads in Ceará, Tocantins and Pernambuco were limited to municipalities with few or no cases reported in previous epidemic waves, indicating that the spatial heterogeneity of the spread of CHIKV and population immunity may explain or travel pattern in the country”, says the specialist.
Not Ceará, the state with the highest number of chikungunya cases (77,418 cases) registered in the country, or the number of deaths from dengue in the last ten years. According to the study, there was 1.3 deaths per thousand diagnosed cases (the dengue mortality rate is 1.1 per thousand).
According to the researchers, the panorama drawn by the study indicates that the subsequent chikungunya epidemics will not be closed without public health interventions – as evidence, we cited the emergence of a new wave this year, this time in Minas Gerais, Mato Grosso do Sul and Tocantins.
According to the virologist, the data suggest that the populations of the two municipalities most affected by chikungunya epidemic waves will present some level of immunological protection against disease and transmission that temporarily prevented a recurrence of explosive outbreaks. In contrast, the populations of municipalities less exposed to previous waves will remain more suscetive. What results from the geographical heterogeneity of the chikungunya dynamics in Brazil.
“Our study shows that chikungunya epidemics will probably continue to occur if no intervention is implemented, causing large epidemic waves with thousands of cases and deaths due to geographic heterogeneity associated with the spread or recurrence of the virus,” warns Souza. “Finally, we highlight that these results will be useful to inform the public health sector to anticipate and prevent future epidemic waves in the country”, he completes.