Climate change is spreading diseases to new areas in the USA, putting millions at risk.

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SACRAMENTO — Software engineer Andres Chavez is used to doing things quickly, efficiently and correctly. So he knew something was seriously wrong when, on a business trip in 2009, he was so confused he could barely sign a stack of paperwork.

"I felt like I was living a quarter-second in the past," he says of the onset of Valley Fever, a disease caused by a soil fungus. It took months for his doctor to finally suggest that might be the cause of Chavez's episodes of "getting stupid," as his wife calls it.

"He called and asked me if I spent any time down in the Central Valley, and I said of course I did, my family lives in Livingston, Calif.," Chavez, 43, remembers.

A FAMILY'S LOSS: Child succumbs to 'brain-eating amoeba'

The soil there and in much of the arid Southwest carries the Coccidioides fungus. In dry months, the dust scatters in the wind and can be breathed into the lungs, infecting humans, dogs and cats and other mammals. The incidence is rising dramatically in the Southwest, where reported cases increased tenfold from 1998 to 2011, according to the Centers for Disease Control and Prevention.

Valley Fever is one of multiple diseases experts say are spreading in part because of climate change. They include a brain-eating amoeba showing up in northern lakes that were once too cold to harbor it and several illnesses carried by ticks whose range is increasing. USA TODAY is looking at the spread of these illnesses as part of a year-long series that explores the places and ways in which climate change affects us.

Chavez's diagnosis led him to the office of George Thompson, an infectious disease specialist who devotes two clinics a week to Valley Fever patients at the University of California-Davis Medical Center in Sacramento.

Almost fully recovered, Chavez still has occasional headaches and bouts of confusion caused by the fungus that invaded his body. In the clinic, Thompson inspected Chavez's hands, knees and ankles. "We worry about your joints with cocci," he said, calling the disease by the short form of its medical name, coccidioidomycosis [cock-sih-dee-oy-doh-my-CO-sis.]

Each year, more than 150,000 people in Arizona, California, Nevada, New Mexico and Utah are infected, and Arizona and California have the most cases, according to the CDC. The incidence of laboratory-confirmed cases rose from 2,265 in 1998 to more than 22,000 in 2011.

About 60% of those infected have no symptoms and never know they have it. An additional 35% have symptoms of fatigue and weight loss and typically miss "a few weeks to a few months of work" but get better, Thompson says. In about 5% of cases, the most extreme, the fungus finds its way into the bones, the brain or the skin, while other people fail to ever clear the organism from their lungs.

For those with the most severe form of the disease, it can be a lifelong illness. Cheryl Rinn, 72, is one of Thompson's patients. The fungus invaded her brain, caused a stroke and left her in a wheelchair, paralyzed on her left side. The former labor and delivery nurse had to move from her home in Lincoln, Calif., to an assisted living facility in Seattle to be near her daughter. "They told me I had lung cancer with brain metastases (sites where the tumor has spread). We were at our wits' end," she says. As is the case with many patients, it took months to get the proper diagnosis. By then, the damage had been done.

Valley Fever is an illness that's moving. Historically, it has been found in the dry areas of California and the Southwest. But Thompson, along with the CDC, reported three cases of cocci in eastern Washington state in 2012.

BRAIN-EATING AMOEBA

The same is true of Naegleria fowleri, "the brain-eating amoeba." It is commonly found in freshwater lakes and rivers, though human infections are rare. They tend to occur in areas where waters warm in the summer. Minnesota had its first ever infection in 2010, 550 miles farther north than an infection had ever been seen before.

Another shift is tick season in the Midwest, which is starting earlier and ending later. This year seems to be one of the worst, says Mary Anne Jackson, director of the infectious disease division at Children's Mercy Hospital in Kansas City, Mo. Ticks carry multiple diseases, but ehrlichiosis and Rocky Mountain Spotted Fever are the ones she sees most.

Ehrlichiosis is a bacterial disease often called "summer flu" by doctors. "Now it can occur any time of year," Jackson says. "I've been here since 1984, and this feels like one of the biggest tick years we've had, with the most children we've had admitted to the hospital."

Three trends contribute to the nation's changing disease map, experts say. The first is overall warming, which makes new areas hospitable to the animals and bugs that can carry disease. The second involves increased extreme weather events such as drought, rainstorms and flooding, which create situations where diseases and insects that carry them can flourish. Finally, Americans are increasingly moving to areas close to wilderness, where they are more exposed to these disease-carrying creatures.

It's impossible to say what specifically causes any single illness. But the overall patterns are clear: Where and when certain diseases strike is changing, and those changes are being affected by the warming, increasingly erratic climate.

One striking example is the movement of the black-legged tick. People in the Northeast got used to doing tick-checks of themselves and their children in the 1970s as word spread that ticks carried Lyme disease. These unpleasant bloodsucking parasites are spreading north, south and west, says Richard Ostfeld, a disease ecologist and Lyme expert at the Cary Institute of Ecosystem Studies in Millbrook, N.Y.

To the north, climate change is making areas of Vermont, Maine and northern New Hampshire and New York suitable for ticks "where they never occurred in recorded history," he says. In the past, these areas got too cold.

In general, temperatures are rising more quickly across the northern USA, according to a draft of the National Climate Assessment released in 2013. From 1895 to 2011, according to the assessment, temperatures in the Northeast increased by almost 2 degrees.

The biting arachnids are actually resettling areas our ancestors pushed them out of more than 200 years ago when forests were cleared for farmland. Farms in New England and the upper Midwest were abandoned when other parts of the country opened to farming. That meant forests began to regrow, bringing back mice and deer and the diseases they carry.

The best known is Lyme, a bacterial illness whose symptoms can include fever, headache and fatigue. Untreated, the infection can travel to the joints, heart and nervous system. Lyme is not the only tick-borne disease. The insects also transmit a range of lesser-known illnesses that more Americans may soon become familiar with. They include anaplasmosis, babesiosis, borrelia miyamotoi and Southern Tick-Associated Rash Illness, or STARI.

PLAYING DEFENSE

Valley Fever infects more than 150,000 people a year, according to the CDC. Part of that increase is due to better testing, part to a doubling of population in the area affected by the disease, says Andrew Comrie, a professor of geography at the University of Arizona who has studied Valley Fever extensively.

An erratic weather pattern Comrie has dubbed "grow and blow" also plays a part. Wetter conditions in the fall and winter allow the fungus to flourish and grow, followed by dry conditions in the summer that dry it out so it can blow in the wind.

No one is saying the Earth is likely to be swept by a new plague that will kill everyone off because of climate change. Nor is climate change the only reason diseases are spreading, but "it's clear that environment change, including climate change, is affecting these populations," says Charles Chiu, director of the viral diagnostics and discovery center at the University of California-San Francisco.

The good news is that the robust public health system in the USA will protect people from some of those changes, says Sonia Altizer, a professor of ecology at the University of Georgia-Athens and co-author of a recent paper in the journal Science on how climate change affects infectious diseases worldwide.

The bad news is "it's going to cost us more money," she says. More mosquito abatement, more deer fences, more vaccination campaigns, more public health clinics, higher medical insurance costs. It all adds up.

"We really have to ask ourselves," she says, "how much harder we'll have to fight to keep diseases out of this country as the climate warms."

Contributing: Doyle Rice

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