Experts issue warning as disease-carrying insects appear in new US regions: 'They are locked into humans'

Mosquitoes capable of carrying life-threatening diseases have reached the Mountain West, far from their typical tropical and subtropical habitats.

What's happening?

In Grand Junction, Colorado, public health workers are raising alarms after discovering the Aedes aegypti mosquito there. The insect can be a vector for dengue, Zika, and other viruses.  

As temperatures rise globally and weather patterns shift, the mosquito is moving north into areas like Colorado's Rocky Mountains, according to Inside Climate News. Conditions there have historically been too harsh for the insect to survive. Now, warming winters are enabling mosquito populations to spread.

The area's Grand River Mosquito Control District launched its Aedes aegypti surveillance program in 2024. That year, the climate news outlet reported, it caught 796 adult mosquitoes and found 446 eggs.

Unlike native mosquitoes that tend to breed in ponds and ditches, Aedes aegypti often prefers containers, like those left in yards — plant saucers, watering cans, and old tires. Many residents are unaware that the species is in their neighborhood or that the insects can pose a threat.

"They are locked into humans," Tim Moore of the GRMCD told Inside Climate News. "That's their blood meal."

Why is this concerning?

Mosquitoes are sometimes called the most dangerous species on Earth for their ability to spread diseases such as dengue, Zika, chikungunya, and malaria. Together, these infections kill hundreds of thousands worldwide each year, with the vast majority of these fatalities associated with malaria.

While Aedes aegypti is not the primary vector for malaria — that would be the Anopheles mosquito — the type spreading in the Colorado mountains and beyond can indeed transmit these other viruses through bites.

Dengue cases appear to have increased as much as 25 times since 2000, according to the World Health Organization. The World Mosquito Program, meanwhile, has reported that about half the global population is now at risk of contracting dengue.

As warming temperatures extend mosquito season and as the highly adaptable insect shifts, species like Aedes aegypti are reaching communities historically shielded from these risks. More extreme storms can create new breeding grounds, while drought pushes people to store water in containers — another breeding spot for the bugs. Drought may also spur mosquito biting, researchers have found.

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Although Colorado officials stress that dengue transmission remains unlikely in the area without an infected traveler bringing the virus home, experts say the growing presence of Aedes aegypti is a wake-up call. It highlights how a warming world is creating conditions that can exacerbate disease risks, as seen recently with the spread of Lyme disease via ticks, dengue threats in Europe, and rising chikungunya cases in Kenya.

What's being done about it?

Grand Junction's mosquito control program has expanded trapping, testing, and targeted spraying. In 2025, it invested more than $15,000 in new tools, staff time, and alternative insecticides, according to Inside Climate News.

Communities can help slow the spread by removing standing water from around homes, cleaning gutters, storing containers upside down, and using repellents approved by the Environmental Protection Agency. Wearing long sleeves and pants in outdoor mosquito-prone areas and installing window screens at home may help too.

To address the underlying causes, meanwhile, experts advocate for broader action, including reducing the planet-heating pollution that's making more zones hospitable to the insects. Also critical is strengthening public health systems to support those most vulnerable to vector-borne disease, such as children and pregnant people living in low-income communities and countries.

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