As dengue cases rise, researchers point to a simple solution: cleaning up trash

As dengue fever cases skyrocketed worldwide over the past year, new findings from Stanford researchers and their international collaborators underscore the importance of one measure that can significantly reduce disease risk: cleaning up trash.

Dengue fever is a viral disease spread by mosquito bites. Although cases may be asymptomatic, many people experience high fever and painful body aches. Second infections are often more serious and can lead to hemorrhagic fever, shock and sometimes death. Dengue is thriving in warmer and wetter weather due to climate change and is rapidly spreading to new locations outside its historic tropical range. Dengue cases doubled globally between 2023 and 2024, spreading to several US states in an “unprecedented” way.

Stanford researchers and their international colleagues recently sought to better understand the transmission of dengue and two other diseases spread by the same mosquito — Zika and chikungunya — in children up to age five in two dengue hotspots, Fiji and Indonesia. Their study, published in BMC Infectious Diseases on January 13, it was found that children living in households where waste is regularly cleared away – especially in Indonesia – had a significantly lower risk of contracting dengue than children whose homes had waste around them.

“Waste disposal can have a real impact on dengue risk,” said Joelle Rosser, assistant professor of medicine at Stanford School of Medicine and lead author of the publication. “This highlights an important area where we have the opportunity to intervene and improve people’s health and their environment.”

Rosser believes that waste is a major risk factor for dengue worldwide because many types of waste can collect in shallow standing water, a favorite breeding ground for the dengue-spreading mosquito, Aedes aegypti. Recent research led by Stanford found a similar link between waste and the risk of mosquito-borne diseases in Kenya, while another new publication led by Stanford found that mosquitoes – and the diseases they carry – can spread adapt to higher temperatures.

“We have seen that waste is a major risk factor for dengue, not only in Indonesia, but also in Kenya and probably even in California,” Rosser said.

The high burden of disease affects vulnerable children

The researchers studied children in 24 informal settlements in Fiji and Indonesia. They tested children up to the age of five – a group particularly vulnerable to the virus – for signs of previous infections and asked detailed questions to assess environmental risk factors for these infections.

In addition to the findings on the relationship between waste disposal and infection, the researchers were surprised by the extent of dengue infections among young children in the study. By age 4 to 5 years, 71% of children in Fiji and 51% of children in Indonesia, respectively, were infected with dengue, putting them at risk of a more serious second infection at an early age.

The findings “underline the disproportionate burden of these diseases on children in deprived urban settlements and call for inclusive policies to ensure that all communities benefit from public health interventions,” said Dr. Isra Wahid, a researcher specializing in dengue and other mosquito-borne infectious diseases. diseases at the School of Medicine of Hasanuddin University in Indonesia and the senior author of the paper.

Study sheds light on preventive measures

Wahid noted another surprising study finding: settlements that experienced flooding more often had lower dengue rates, possibly due to the floodwaters washing away mosquito breeding grounds. However, he added that when floods occur in areas where waste collection is poor, the residual flood water trapped in the containers can breed more mosquitoes and increase dengue transmission.

The findings show that environmental changes such as waste management and flood mitigation are important measures for combating dengue and other diseases spread by the same mosquito.

“Beyond these communities, the study provides a model for addressing the transmission of arboviruses through environmental changes, and offers scalable solutions for other high-risk areas worldwide,” Wahid said. Arboviruses are diseases transmitted to humans by infected mosquitoes and ticks.

The research was conducted as part of the RISE (Revitalising Informal Settlements and their Environment) project, which aims to upgrade the entire water infrastructure to build communities that are resilient to the impacts of climate change, including flooding and infectious diseases. For the RISE intervention, Stanford researchers are working with local physician-scientists, ecologists, architects, engineers and community organizers to minimize waste, improve stormwater capture and create natural flood buffers.

These actions can collectively reduce mosquito breeding sites while making communities more resilient to the increased droughts and floods expected from climate change. Both droughts and floods can worsen mosquito-borne diseases, Rosser said.

Rosser will follow a cohort of young children in these communities over several years. She and her colleagues will use these data to assess whether the RISE intervention affects infection rates in children.

Wahid hopes their new findings can help inform local government actions, such as improving waste collection systems, including in informal settlements, and mitigating flood risks. Even now, the work is shedding light on a meaningful way to mitigate the impacts of climate change on human health, Rosser pointed out.

“For many people, climate change is deeply troubling, and it can be daunting to think about how we can impact the problem if we are not climatologists or engineers,” she said. “But there are a whole range of ways we can minimize the impact of climate change on health and wellbeing – and reducing waste is one of them.”