In Ceará, the state with the most recorded Chikungunya cases (77,418 cases) in the country, the number of deaths from the disease has outpaced that of dengue, which is carried by the same mosquito species, over the past decade aedes aegypti It is Aedes albopictus. There were 1.3 deaths per thousand cases diagnosed (dengue mortality rate is 1.1 per thousand). This is the conclusion of the largest and most comprehensive epidemiological study on this topic, which has just been published in The Lancet Microbe. Based on the analyses, the researchers involved in the work were also able to determine the pattern of disease spread and risk factors, which could serve as a basis for devising effective control, prevention and treatment strategies.
When the virus that causes chikungunya fever (CHIKV) was introduced into Brazil nearly a decade ago, specialists in arboviruses (diseases caused by arthropod-borne viruses) believed it would repeat the dynamics it was already seeing in other countries, such as India: one or at most two short and explosive waves with exposure of a large part of the population, followed by a considerable pause of years. However, what is being observed is back-to-back epidemics and record cases in America – more than 1.2 million registered. It’s important to remember that there are no vaccines or medications to prevent or treat the infection.
Unlike dengue, whose causative virus has four different genotypes and can therefore cause four contamination events, CHIKV should not cause reinfections. And to understand the causes of the differentiated American distribution pattern, researchers from Imperial College (UK), the Public Health Laboratory of Ceará, the Ministry of Health, the State Universities of Campinas (Unicamp), São Paulo (USP) and UFRR ( Federal de Roraima) and the University of Texas Medical White H (United States) reviewed genome sequencing data, vector distribution and epidemiological information on confirmed cases.
The study, supported by FAPESP through three projects (16/00194-8, 18/14389-0 and 19/24251-9), found that between March 2013 and June 2022 the country faced seven epidemic waves, with 253,545 laboratory-confirmed cases in 3,316 (59.5%) municipalities. Each region acted as a “little pocket” of the disease and was affected differently at each moment. In Ceará, the communities that suffered the most in the first two waves were those that added the fewest cases in the third wave.
“The results show that the dynamics of spread of CHIKV differ from those observed in the case of dengue and likely Zika: it does not reinfect the population but causes explosive outbreaks in sites with little prior exposure to the virus,” explains William Marciel de Souza , a researcher at the University of Texas Medical Department who shared first authorship of the study with Shirlene Telmos Silva de Lima, a researcher at Ceará’s Central Public Health Laboratory and in the Department of Genetics, Evolution, Microbiology and Immunology at IB -Unicamp (Institute of Biology). “Because Brazil is a continental country and the mosquito that transmits it is present in virtually every community, we live in an endless cycle.”
“We also changed an important paradigm with this study: that only dengue is a serious disease – chikungunya is not only debilitating, but also deadly,” Lima adds.
The mapping also pointed to risk factors involved in symptomatic infections, which are more common in women, and deaths, which are more common in children and the elderly, who have weaker immune systems.
healthcare
According to the researchers, the panorama outlined by the study shows that the subsequent Chikungunya epidemics will not end without public health interventions – as evidence they cite the appearance of a new wave this year, this time in Minas Gerais, Mato Grosso do Sul and Tocantins.
“Considering Brazil’s continental size with more than 5,000 communities, our work provides insights for further study to identify and prioritize areas that are more susceptible to Chikungunya, which will help guide more targeted action by public health officials,” says de Souza. “Also training physicians who treat groups more prone to death to perform procedures with agility.”
IB Unicamp Professor José Luiz Proença Módena emphasizes the importance of constant surveillance to detect virus pockets and intervene with vector control measures and patient management. “I also draw attention to the importance of genomic surveillance, since many of the conclusions in this work could only be drawn from sequencing the viral genome and we were only unable to delve further because of a lack of data. It is necessary to invest in studies related not only to Chikungunya, but also to other viruses circulating in the country, such as the Amazonian arboviruses,” says Módena, who coordinates the Emerging Virus Studies Laboratory (Leve) at Unicamp .
The research was also supported by institutions such as the Burroughs Wellcome Fund, the National Council for Scientific and Technological Development, the Global Virus Network, the Medical Research Council and the Wellcome Trust.