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New insights for fight against dengue as pandemic restrictions also curbed transmission

Covid restrictions were linked to nearly 750,000 fewer dengue infections during the first year of the pandemic, offering new insights about how best to control the potentially fatal virus.

Dengue, often described as “breakbone fever” because of the severe muscle and joint pain it can trigger, is on the rise across the globe – especially in Latin America and South Asia. The World Health Organization, estimates that half of the world’s population is at risk of contracting the virus. 

But, according to research published in Lancet Infectious Diseases, prevalence fell drastically across 23 countries where the disease is endemic in 2020. Cases fell by roughly 45 per cent in Latin America and almost 60 per cent in South East Asia – with 2 million reported, compared to 5.2m in 2019. 

Part of this was because a record-breaking year of infections in 2019 was not sustained in 2020. This was expected, as high levels of immunity would offer some protection against reinfection.

However, researchers were able to directly link a fall of 750,000 cases to Covid restrictions. 

In nine of 11 countries studied in Central America and the Caribbean there was a complete suppression of the 2020 dengue season. Nations that introduced pandemic measures at the peak of virus transmission also saw a sharper than expected drop-off in new cases – despite above average incidence earlier in the year. 

“Before this study, we didn’t know whether Covid-19 disruption could increase or decrease the global burden of dengue,” said Dr Oliver Brady, associate professor of epidemiology at the London School of Hygiene and Tropical Medicine, and senior author of the study. 

He added that the research found a strong association between school closures, declining mobility and reduced dengue transmission, indicating for the first time that schools, shops and public transport could be hotspots for the spread of the virus.

Although also an infectious disease, dengue is unlike Covid-19 in that it is transmitted by mosquitoes, not directly between humans. There are ongoing efforts to target these mosquitoes, by infecting them with a bacteria called Wolbachia to make it harder for them to also carry the dengue virus. 

But experts now believe changes in movement may reduce the opportunities for infected people to pass the virus to uninfected mosquitoes. 

“Currently dengue control efforts are focused on or around the households of people who get sick,” Dr Brady said. “We now know that, in some countries, we should also be focusing measures on the locations they recently visited to reduce dengue transmission. 

“For all the harm it has caused, this pandemic has given us an opportunity to inform new interventions and targeting strategies to prevent dengue,” he added. 

But the study said further research is needed to establish how different human behaviours impact transmission – for instance, where a person visits and how long for. 

This could help decide whether measures such as contact tracing, testing and isolation would help control the disease.

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