Hantavirus in Yosemite. West Nile virus in 48 states. Even a case of bubonic plague.

“I hear locusts are next,” says Cathi Soriano of Seattle, who recently took Yosemite National Park off a road-trip itinerary.

Are we under siege?

According to a USA Today report, not really, but the medical victories we’ve experienced over the past 100 years have made Americans forget that such diseases haven’t gone away, says David Dausey, director of the Institute for Public Health at Mercyhurst Universityin Erie, Pa. “It’s unsettling to realize that we’re not entirely safe from these things.”

The rise of hantavirus and West Nile virus, neither even recognized in the United States before 1993, is making people check their window screens, stock up on bug spray and rethink travel plans. In Yosemite this summer, hantavirus has killed three people out of nine sickened. Nationally, West Nile virus is the worst it’s been since the disease arrived on our shores in 1999: more than 3,545 illnesses and 147 deaths as of Thursday.

Extreme weather patterns have played a big role in the two recent outbreaks, and health officials worry more such events could be on the horizon because of climate change.

Climate cycles very clearly play a part in outbreaks, says Michael Osterholm,director of the Center for Infectious Disease Research and Policyat the University of Minnesota in Minneapolis. The question is at what point any given outbreak is being caused by climate change or simply normal weather cycles. However, it’s clear that “eventually (climate change) will affect things, but is it now? We don’t know,” he says.

At the same time, health officials fret that the public health infrastructure of laboratories and public health workers that tracks and responds to outbreaks is being cut. That could make outbreaks harder to detect and control.

“The federal spigot is not just being cut off, it’s being smashed,” Osterholm says. “We’ve got a crash coming. We can see it.”

In the hantavirus outbreak at Yosemite, weather and a move to provide more economical lodging for winter sports enthusiasts could be behind the illnesses. Three deaths are worrisome but doctors are particularly taking notice because they came in a tightly focused geographic cluster.

“It’s never happened before,” says Pierre Rollin, a chief with the Centers for Disease Control and Prevention’s Special Pathogens Branch.