Nearly three-quarters of a million fewer dengue cases worldwide occurred in 2020, which may be linked to COVID-19 disruptions limiting mobility and human contact, according to a new study published in Lancet Infectious Diseases.
Researchers from the London School of Hygiene & Tropical Medicine (LSHTM), Peking Normal University and other international partners, funded by the Medical Research Council, analyzed monthly dengue cases from the World Health Organization health (WHO) Weekly reports between 2014 and 2020 from 23 countries – 16 in Latin America and seven in Southeast Asia, the main regions where dengue fever is endemic, as well as climate data on air temperature , relative humidity and precipitation.
They found a strong association between school closures and lower non-residential travel, such as shopping or using public transport, due to COVID-19 and reduced risk of dengue transmission. This indicates that places such as schools and frequently visited public places could be hotspots for dengue transmission and play a key role in the spread of the disease.
More research is needed on how human movement behaviors (the places people visit, how long they spend there, and with whom) impact the risk of dengue transmission. This could help policymakers decide whether measures such as contact tracing, testing or quarantine could help control the spread of the disease.
Dr Oliver Brady, Associate Professor and MRC Fellow at LSHTM and lead author of the study, said: “Currently, dengue control efforts are focused in or around the households of people who become ill. We now know that in some countries we should also focus action on places they have recently visited to reduce dengue transmission. Despite all the damage it has caused, this pandemic has given us an opportunity to inform new interventions and targeting strategies to prevent dengue.
Dengue fever is a viral infection transmitted by Aedes species of mosquitoes, causing flu-like symptoms. It is found in tropical and subtropical climates around the world, and it is more common in urban areas.
It is one of the only infectious diseases to show a sustained increase in cases each year, and the WHO now estimates that around half of the world’s population is at risk of contracting dengue fever.
Transmission is closely linked to meteorological conditions, the surrounding environment and human mobility. It is also closely associated with climate, with hot and humid tropical climates ideal for transmission. Dengue season in many countries occurs between June and September, when spikes in cases can lead to overcrowding in hospitals – much like with COVID-19.
Dengue fever is only transmitted from mosquitoes to humans and vice versa, and is not transmitted from humans to other humans. However, changes in people’s movements and behaviors can have an effect on transmission, for example by reducing exposure to mosquitoes or reducing opportunities for infected people to get out and transmit the virus to uninfected mosquitoes that are there. COVID-19 and the restrictions on human travel that have been imposed during the pandemic therefore provide a unique opportunity to explore how human travel and behaviors contribute to dengue transmission.
The number of dengue cases suddenly started to decline in April 2020 in many countries, following the introduction of public health and social measures targeting the spread of COVID-19 and the resulting change in human and the shift to more time spent in residential settings. In 2020, dengue cases fell by 40.2% in Latin America and 58.4% in Southeast Asia, with just over two million cases recorded in the Americas and Southeast Asia. Is in 2020.
However, unraveling the impacts of the COVID-19 disruption is complex as 2019 saw the largest global dengue outbreak in history, with over 5.2 million cases recorded in the Americas and Asia region. from the South East. This has led to high levels of immunity which is also expected to reduce dengue cases in 2020.
Dr Brady added: “Prior to this study, we did not know whether the disruption of COVID-19 could increase or decrease the global burden of dengue fever. While we can assume that reducing human travel would reduce transmission of the virus, it would also disrupt mosquito control measures already in place. This disruption may lead to long-term impacts on dengue cases that may not be evident until the next outbreak.
The research team looked at two different measures of COVID-19-related disruptions – public health and social measures, such as school and public transport closures, stay-at-home requirements, gathering restrictions; and human movement behavior through time spent in residential and public places. They also took into account the different strengths of lockdown restrictions in different countries around the world.
By combining all of this data and analyzing trends, they were able to show that reduced time spent in public spaces was strongly associated with a reduced risk of dengue fever.
Nine of the 11 countries in Central America, the Caribbean and the Philippines have seen a complete suppression of their 2020 dengue season, with the remaining countries experiencing a greatly reduced season. In countries where COVID-19 restriction measures began at the height of the dengue season, there has been a larger than expected drop in cases, despite above-average incidence recorded earlier in the world. year.
This decline in cases could also be attributed to reduced rates of people seeking treatment, a higher risk of misdiagnosis, and reduced availability for laboratory testing for dengue that can lead to misdiagnosis. However, some countries like Sri Lanka predicted this could be a problem at the start of the pandemic, so they undertook outreach to encourage people to get diagnosed and seek treatment. Despite this, there was no change in the rates of severe cases and reported deaths, suggesting that reduced treatment-seeking was not the cause of the reduction in cases.
A better understanding of how treatment-seeking behaviors change during an outbreak is needed, as access to care and rapid diagnoses change, in order to fully assess and interpret changing case counts. . The team emphasizes the need for longer-term and more systematic measurement of dengue prevalence within each population.
Although overall cases decreased in 2020, Peru and Singapore reported lower than average dengue incidence in 2020. This may have occurred due to unpredictable natural variation in dengue incidence from year to year that occurs due to, for example, the emergence of different cases of dengue fever. variants of the virus, or could allude to the larger role that mosquito bites in the home play in the spread of dengue fever in these countries.
As the climate recorded in 2020 was similar to the average climate of the past six years, the researchers did not find an association between climate and reduced dengue risk in 2020.
The researchers note that it remains to be seen how many of the estimated 0.72 million cases have actually been averted, or simply delayed until years later as human movement returns to pre-COVID levels and say it is critical to continue monitoring dengue trends in 2022 and beyond.
The researchers acknowledge the limitations of this study, including the lack of data on different types of dengue fever, which can lead to outbreaks, and potential changes in dengue reporting resulting from COVID-19 disruptions.
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A copy of the embargoed document is available upon request. The post-embargo link is: https://www.thelancet.com/journals/laninf/article/PIIS1473-3099(22)00025-1/fulltext
Notes to Editors
Yuyang Chen, Naizhe Li, José Lourenço, Lin Wang, Bernard Cazelles, Lu Dong, Bingying Li, Yang Liu, Mark Jit, Nikos I Bosse, Sam Abbott, Raman Velayudhan, Annelies Wilder-Smith, Huaiyu Tian, Oliver J Brady , on behalf of the CMMID COVID-19 Task Force. Measuring the effects of COVID-19-related disruptions on dengue transmission in Southeast Asia and Latin America: a statistical modeling study. Lancet Infectious Diseases. DOI: 10.1016/S1473-3099(22)00025-1
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The Lancet Infectious Diseases
The title of the article
Huaiyu Tian, Oliver J Brady, on behalf of the CMMID COVID-19 Task Force. Measuring the effects of COVID-19-related disruptions on dengue transmission in Southeast Asia and Latin America: a statistical modeling study.
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