As dengue spreads beyond the ‘global dengue belt,’ scientists dispel misconceptions about the disease

Unknowns, dangers and surprises persist regarding dengue viral infection, and now a once-considered conventional wisdom regarding immunity to this mosquito-borne disease may turn out to be incorrect.

New research involving epidemiological models and data from more than 4,400 people in Nicaragua suggests that it is time for immunologists to develop a new framework for understanding population immunity to dengue. For decades, it was believed that once infected with the dengue virus, immunity lasted for life. The dogma persisted despite observational data, which found that previously infected people were more likely to contract severe dengue if they were infected again.

But an international group of researchers has now conclusively demonstrated that immunity not only wanes, but tends to wax and wane – a finding that reveals that dengue infection is much more complex than previously thought. didn’t think so before.

“Infection with multiple serotypes of dengue virus is thought to induce long-lasting protection against dengue,” writes Rosemary A. Aogo, lead author of a new research paper published in Scientific translational medicine. “However, a long-term decrease in antibodies was observed after repeated dengue infections,” Aogo added, referring to his team’s new findings.

The decrease in antibodies was inevitably followed by an increase in antibodies when the next outbreak occurred, Aogo and his colleagues found. His team’s discovery enabled the construction of a new model that best describes population vulnerability to dengue infection, particularly in the known context of the periodicity – the cyclical nature – of dengue epidemics.

When it comes to dengue, people are not permanently immune but susceptible to infection, then immune and finally susceptible again. Hence the model newly proposed by Aogo and his team: “susceptible-infected-recovered-susceptible”.

Dengue is a devastating viral infection transmitted to humans through the bite of Aedes aegypti mosquitoes, flying hypodermic needles that descend prolifically during large outbreaks. Many dengue outbreaks tend to occur in urban settings, scientists say.

Formerly known as fracture fever, dengue viral infection can cause severe headache, high fever, nausea, vomiting, swollen glands, and rash. Yet, perhaps most surprisingly, many infected people show no symptoms. However, in rare cases, dengue can be fatal.

The new research by Aogo and colleagues examined blood samples from 4,478 children and adults in Nicaragua, a country located in the heart of the global dengue belt, which stretches from Central America to the most of South America, then crosses oceans and time zones. to include most of sub-Saharan Africa, India and Southeast Asia.

In 2023, the world’s worst dengue outbreak occurred in a key region of the dengue belt, affecting tens of thousands of people in Bangladesh. There, the mosquito-borne virus has killed nearly 1,500 people as of November 12, and more than 291,000 people have been infected.

Aogo, a viral epidemiologist at the Infectious Diseases Laboratory at the U.S. National Institute of Allergy and Infectious Diseases in Bethesda, Maryland, noted that she and her team uncovered other surprising findings from their Nicaraguan data.

Researchers say they can now confidently predict that infection with the closely related Zika virus can confer protection against dengue and even delay larger-scale dengue outbreaks. Indeed, the most recent Zika outbreak may have delayed the next dengue outbreak, but then led to a resurgence of the dengue virus, which primarily affected susceptible individuals, the study found.

Dengue and Zika viruses both belong to the flavivirus family, which are not only close cousins, they circulate in the same regions and have caused large outbreaks over the past decade. The fact that one can confer immunity against the other is a discovery that has broad implications for the development of antivirals and vaccines.

In their study, Aogo and colleagues analyzed the influence of the devastating Zika epidemic from 2016 to 2017, which showed that the Zika virus was sufficient to boost immunity against dengue. With this knowledge, the team, which included virologists from the Nicaraguan Institute of Sustainable Sciences in Managua, now has a wealth of new data to address flavivirus outbreaks in the future.

Aogo’s research comes as surges of dengue infections have been reported outside of the usual tropical and subtropical regions where dengue is endemic. Last summer, dengue epidemics occurred in parts of Italy and France. Scientists suspect that global climate change has allowed dengue-carrying mosquitoes to expand their range into new, now warmer, regions of the globe.

Additionally, the World Health Organization recently predicted that dengue fever will become a major threat in the southern United States, southern Europe, and new parts of Africa this decade as Aedes aegypti mosquitoes continue to expand their range and carry the dengue virus with them.

Dengue is the most common mosquito-borne virus, infecting up to 390 million people worldwide each year. Most commonly affected countries tend to experience cyclical outbreaks, which is vital information for public health planning as countries develop improved mosquito control efforts and campaigns to help individuals stay safe. security. “This work provides insight into the factors that shape the periodicity of dengue incidence and may inform vaccination efforts aimed at maintaining population immunity,” Aogo and his team concluded.

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