Future dengue outbreak risk in Guangzhou under climate change: a mechanistic projection coupling temperature- dependent vector competence with reanalysis and CMIP6 meteorology

In the humid, subtropical south of China, a silent race is constantly underway between a virus and the mosquito that carries it. This is the story of dengue fever, a disease that has shifted from rare, imported cases to frequent local outbreaks in cities like Guangzhou. The key to understanding this shift lies in a biological clock hidden inside the mosquito, known as the extrinsic incubation period. This is the time it takes for a mosquito to become infectious after biting a person with the virus. It is not a fixed number; it is a timer that speeds up as the air gets warmer and slows down when it cools. If the temperature is just right, the virus matures quickly, allowing the mosquito to pass it on to others in a matter of days. If it is too cold, the virus never matures, and transmission stops. As the planet warms, this biological clock is changing, altering not just how long the risk of dengue lasts each year, but how much time public health officials have to stop an outbreak before it spreads.

Researchers in Guangzhou have taken a close look at this changing dynamic, moving beyond simple guesses about future temperatures to build a detailed simulation of how the virus actually behaves inside the mosquito. They combined real-world weather data from the past decade with advanced climate models that project conditions for the middle of this century. Their goal was to see how a warming world would reshape the calendar of dengue transmission. Instead of just asking if the city will get hotter, they asked a more urgent question: how will the speed of the virus change, and how will that affect the window of opportunity for health workers to intervene?

The study reveals that warming is having a two-sided effect on the risk of dengue in Guangzhou. On one hand, the season during which the virus can spread is getting longer. Under current conditions, the virus is capable of spreading for about 33.6 weeks a year, roughly from March to November. By the 2040s and 2050s, as average temperatures rise by about 1.2 degrees Celsius, this window is projected to stretch to 36.4 weeks. If warming continues to a higher level of 2.3 degrees, the season could extend to nearly 40 weeks. This means the city will face a longer annual exposure to the threat of an outbreak, with the virus able to survive and spread during months that were previously too cool for transmission.

However, the second effect is more immediate and dangerous for emergency response. As temperatures rise, the biological clock inside the mosquito speeds up dramatically. In the peak of summer, when the virus is most active, the time it takes for a mosquito to become infectious is shrinking. Currently, during the hottest month of July, it takes about 3.7 days for the virus to mature after a mosquito bites an infected person. In a warmer future, this period could drop to just 2.2 days, and in scenarios with even higher warming, it could fall to 1.6 days. This creates a critical problem for health officials. The time available to detect an imported case, find the mosquitoes, and stop them from spreading the virus is shrinking. The researchers calculated that the "response window"—the total time from when a person gets sick to when local mosquitoes become infectious—is compressing by nearly eight days in the near future and by over twelve days in a high-warming scenario.

This compression is most severe in the middle of summer, exactly when the risk of an imported case sparking a local outbreak is highest. The study highlights that while the total number of weeks with risk increases, the time available to act during the most dangerous weeks is vanishing. In the past, health teams might have had a week or more to react to a new case before the virus could jump to the local mosquito population. In the future, that window could be cut down to just a few days, leaving very little room for error. The researchers emphasize that this shift means the old ways of planning for dengue, which often rely on average temperatures or simple case counts, are no longer sufficient.

The findings suggest that early warning systems need to change. Instead of just watching the weather forecast for a general rise in temperature, officials should monitor the specific speed of the virus's development. When the forecast indicates that the incubation period is dropping below a critical threshold, it signals that the time to act is running out. This requires a shift in strategy, where control measures are pre-positioned and ready to launch the moment an imported case is detected, rather than waiting for the situation to escalate. The study does not predict a specific number of future cases, as that depends on many other factors like mosquito density and human movement, but it clearly shows that the timing of the threat is becoming more urgent.

Ultimately, the research paints a picture of a city where the dengue season is expanding, but the time to fight it is contracting. The virus is becoming faster, and the window to stop it is closing. For Guangzhou, and other cities facing similar climates, the message is clear: the future of dengue control depends on understanding these changing rhythms. By tracking the biological clock of the virus directly, health officials can hope to stay ahead of a threat that is evolving faster than the seasons themselves. The study serves as a reminder that in the face of climate change, the most valuable resource for public health may not be more time, but a better understanding of how little time remains.