The dengue virus is one of the greatest threats to public health in globe tropical regions, and especially in Brazil, where annual epidemics lead to thousands of Brazilians sickness. In the year 2019 alone, there were 2.1 million cases. However, something very intriguing happened in the years 2017-2018, right after the zika, dengue and chikungunya virus’s triple epidemic in 2016. Dengue fever case numbers were reported well below average until its resurgence in 2019.
In the search for an answer to this phenomenon, a study was carried out in cooperation by researchers from Fiocruz Pernambuco; the North American universities of Yale, Florida, and Notre Dame; the University of São Paulo (USP / Ribeirão Preto); and the Rega Institute for Medical Research (Belgium). The group used dengue virus genomic sequencing of samples collected in Northeast and Southeast Brazil to investigate why few cases of the disease were reported in 2017-2018 and what were the viruses’ origins that caused the 2019 epidemic. The results were published (11/5) in the scientific journal Nature Communications, which is part of the respected Nature group, in an article entitled Lying in wait: the resurgence of dengue virus after the Zika epidemic in Brazil.
"Our findings show that the epidemic was mostly caused by dengue 2 in the Southeast and dengue 1 in Northeast Brazil, and that these strains had already been circulating in the country for more than a decade," explains Gabriel Wallau, one of the researchers from Fiocruz Pernambuco who was part of the team responsible for this study. Besides Wallau, researcher Rafael França, from the Department of Virology and Experimental Therapy, and Lais Ceschini and Filipe Zimmer, post-graduation students in Biosciences and Biotechnology in Health at the institution, also participated.
The results suggest that, in line with other previously published studies, much of the population was infected with the zika virus, which may have produced cross-immunity against the dengue virus resulting in a large decrease in the 2017-2018 cases number. This effect may also have been caused by increased immunity in the population due to high rates of infection with the dengue virus itself in the years prior to 2016 and/or these factors combined. "In any case, dengue virus remained circulating at low prevalence until its massive resurgence in the susceptible population in 2019”, adds the researcher.
This study combined genomic, ecological, and epidemiological data to investigate this virus reappearance dynamics. But scientists point out that further research is needed to accurately understand how dengue virus strains can remain undetected for long periods of low transmission.