Almost half of the world’s population is now at risk for contracting dengue fever, also known as “breakbone fever,” an illness carried by a species of mosquitoes (Aedes aegyptia) that has recently expanded its range from tropical regions to more temperate ones in many parts of the United States.
A quarter of the people who become infected with dengue develop symptoms of illness — a potentially high fever, rash and severe muscle and joint pain. About 5% of those with symptoms develop severe dengue, which can become life-threatening within hours. The risk is even higher for infants and pregnant women.
No dengue vaccine is approved for use in the U.S., and no medication specific to dengue is available.
For now, dengue in the contiguous U.S. occurs in mostly isolated cases among travelers returning from the tropics, but that’s changing as the problematic mosquitoes travel northward.
Take a leap forward to the year 2050. You live in Houston with your family, and your favorite hobby is fishing at the nearby nature reserve. Days are averaging about five degrees Fahrenheit warmer than they have for the past decade, and unbeknownst to you and your family, a summer dengue fever outbreak is underway.
You settle your small daughter with toys and begin fishing. The mosquitoes are annoying but not overwhelming. Nonetheless, within a few minutes you notice a mosquito, already swelling with blood, on your child’s arm. Ah well, you think, it’s just a bug bite, and with a little antihistamine and lotion, she’ll be fine. A few days later, your daughter develops a fever and a rash. When she starts vomiting, you take her to urgent care, concerned about the risks of dengue fever now that you’re seeing a few news items on the subject.
You spend a sleepless night holding your daughter in the hospital room as she receives intravenous fluids to rehydrate her. In the morning, the doctor tells you she is not likely to develop severe dengue and you’re given the clear to go home. On the drive back, you remember a time when mosquito bites were not a big deal, just itchy bumps, and the fishing trips were easier.
While this future might be bleak, the good news is Los Alamos National Laboratory scientists are working on a predictive computer model so in the future, you’ll know when outbreaks are happening, and you can take the precautions to protect your family.
Our team recently investigated how changing temperatures could affect dengue transmission under a climate-change scenario. The team extended previous epidemiological models by developing a computer model that allows both the mosquito lifespan and the incubation period to vary with temperature.
The model captures the effects of changing temperatures on mosquito dynamics and dengue transmission. This approach provides a way to explore realistic simulations of potential dengue outbreaks in cities in the southern U.S. where this species of mosquitoes has been observed.
We found that under the assumptions of our model and with an average temperature increase of about five degrees Fahrenheit, dengue risk would double in Los Angeles and Houston. Paradoxically, the risk would decrease in Phoenix, Miami and Brownsville, Texas, due to extreme heat that is actually above the mosquito’s comfort zone. Although the virus travels through the mosquito’s system to the salivary glands quicker as temperatures rise, there is a thermal maximum beyond which the mosquito cannot survive.
Our sensitivity analysis indicated that with rising temperatures, dengue risk factors begin to shift away from mosquito-centered aspects and toward human aspects of disease. Basically, as temperatures rise, the disease dynamics change such that the human part of the transmission cycle—when humans are transmitting dengue from one mosquito to the next—is the key step in the process. This means the most efficient use of resources would be to stop the transmission cycle at the humans, where our intervention would have the most leverage for stopping an outbreak.
This suggests regional public health recommendations for adjusting human behavior may become more important than controlling mosquitoes as temperatures become warmer. Protecting ourselves will be more impactful than attempting to reduce the mosquito populations will be.
So, in that future scenario, before your fishing trip, you might be able to check both the weather and the disease forecasts, letting you plan ahead and take steps to protect yourself and your family.
Julie Spencer is a researcher in the Information Systems and Modeling group at Los Alamos National Laboratory.
