As dengue cases in the Pacific reach their highest levels in a decade, new James Cook University (JCU) research highlights how human movement and weather patterns contribute to outbreaks in the region.
Dengue fever, a virus carried and spread by mosquitoes, has long been a public health concern for communities in the Pacific, and this year infections hit their highest numbers in years, with outbreaks seeing Samoa, Fiji and Tonga among the worst affected.
The study was conducted collaboratively by researchers at JCU's Australian Institute of Tropical Health and Medicine (AITHM) and the Pacific Surveillance Strengthening for Impact (PacMOSSI) consortium. It was led by JCU Associate Professor Roslyn Hickson and AITHM Adjunct Research Fellow Justin Sexton.
"The number of dengue cases has been increasing over the last decade globally, but particularly in the Pacific Islands, to the point that it has gone from sporadic outbreaks to being endemic in several of the countries," Associate Professor Hickson said.
"There's a lot of questions around what the drivers are for an outbreak starting and continuing to spread."
To better understand these drivers, the researchers analysed data on dengue, climate conditions and human movement from 19 Pacific Island Countries from 2012-2020.
This included information on international and regional travel, flight passenger numbers, mass gatherings such as sports events and international conferences, and meteorological data including temperature, rainfall, and solar radiation.
Dr Sexton and Associate Professor Hickson used machine learning algorithms to classify whether a given month marked the start or continuation of a dengue outbreak. The models identified which factors — such as travel or weather patterns — were most important in describing outbreak dynamics.
"Our research suggests that human movement is one of the key factors in initiating dengue outbreaks in this region, but not their continuation," Dr Sexton said.
"Outbreaks are often triggered by the arrival of an infectious person through international travel or travel between the Pacific Island Countries. However, once an outbreak is established, it doesn't necessarily need infected individuals continuously coming into the country to keep it spreading."
Instead, the results indicated that the ongoing presence of the disease and its continued spread largely depend on weather conditions.
Initially, researchers assumed that the increase in dengue cases was being driven by human movement alone, as many Pacific Island Countries experience relatively stable climates, making it difficult to discern the influence of weather patterns.
However, the study found that climate plays a significant role in both the start and spread of outbreaks in this region.
"The most important factor for predicting a dengue outbreak was the average minimum temperature two months prior, whether it's the start of an outbreak or the continuation of one," Dr Sexton said.
"We also found that rainfall and relative humidity were key factors, with the model identifying rainfall as having an impact on the start of outbreaks and humidity having an impact on their continuation."
Both researchers are optimistic that these findings will lay the groundwork for future research into the complex drivers of dengue outbreaks in this region.
"We hope that this research will guide thinking about future studies and give people an idea of where to look when they are building decision support tools," Dr Sexton said.
This research underscores the importance of a multi-faceted approach to controlling mosquito-borne disease outbreaks. By combining insights from both human movement and climate data, prevention and mitigation strategies can be more targeted to stop the spread of this growing threat.
