Conor Jackson had a big bat and a bright future. But after he contracted a rare illness in 2009 while playing with the Arizona Diamondbacks he was never quite the same.

Last year another major league baseball player – Ike Davis of the New York Mets – was diagnosed with the same thing.

Valley Fever is on the rise in Arizona. And that could become a problem for Major League Baseball's  "Cactus League" – spring training that brings fifteen teams and about 1,000 ballplayers to the Phoenix area from mid-February to late March. A majority of those players are battling for a spot on the major league roster, and an illness that saps your energy is not the way to make that happen. 

"It's the people like professional athletes who I see really struggling" with Valley Fever, said John Galgiani, director of the University of Arizona's Valley Fever Center for Excellence. "The highly motivated, hard working types who aren't used to – and don't want to succumb to – fatigue." 

'Up close and personal'
Valley Fever is a lung disease caused by a fungus – coccidioidomycosis – that thrives in hot, dry areas such as the southwestern U.S. People get the infection if they inhale fungus-released spores.

"In places like California's Central Valley and Phoenix urban populations are getting up close and personal with these desert areas," Galgiani said.

The illness isn't new to the region or limited to just ball players spending time in Arizona. Most people in the Southwestern U.S. are exposed, and the fungus is often spread when desert soils are disturbed. It is prevalent among agriculture and construction workers. 

For many of those infected, Valley Fever usually goes away without major problems. But in severe cases it can cause chronic pneumonia and infections in bones and joints. Pregnant women, the elderly and people with weakened immune systems are at higher risk.  Also, Asian and blacks are at a higher risk for reasons that are unclear, said Benjamin Parke, a medical officer with the U.S. Centers for Disease Control and Prevention.

Inmates killed
California is investigating an outbreak that has sickened 28 workers at two large solar construction projects in the Carrizo Plain, and the CDC is probing outbreaks that killed more than three dozen inmates in two California prisons. The state is fighting a federal official's order to move 3,300 at-risk inmates out of those two prisons.

"Most people recover and everything's fine," Galgiani said, adding that less than 1 percent of those infected by the fungus experience life-threatening impacts.

Jackson and Davis are the only two professional baseball players to have contracted the disease, said Major League Baseball Players Association spokesman Greg Bouris. He said the issue hasn't hit the radar screen of the players as a group yet.

But the athletes may be emblematic of a trend in the Southwest. Valley fever shot from about 2,265 reported cases in 1998 to about 22,000 in 2011, according to the Centers for Disease Control and Prevention. 

A warming Southwest can't be blamed for all of that jump, experts caution.

Development and growth
Development – "bulldoze change" – might contribute as much as climate change to the spread of Valley Fever in the region, said Andrew Comrie, a climatologist at the University of Arizona who studies Valley Fever. And the populations of Tucson and Phoenix, Ariz. – two hot spots for Valley Fever – have grown by 8 percent and 11 percent over the past decade, according to the U.S. Census. 

Arizona in 2009 also increased the sensitivity of its test for the disease, doubling the number of reported cases.

Still, the disease seems ideally suited to take advantage of Arizona's climate of the future. The Southwest is already the hottest, driest region in the country, and it is getting worse: The average temperature has increased about 1.5º Fahrenheit over the last century, compared to 1.3ºF for the rest of the mainland United States. The average annual Southwest temperature is projected to rise an additional 2.5ºF to 8ºF by the end of this century, according to federal estimates. The fungi's heat and drought tolerance allow it to live through conditions that kill other plants, Comrie said.

'Grow and blow'
The fungus also relies on moist winter, and that season is getting slightly wetter – ideal "grow and blow" conditions that researchers believe will make matters worse. Rain prompts fungal growth; heat lets it blow around months later. 

The Valley Fever Center says most infections go unreported and estimates that the truer number of annual infections in the Southwest is closer to 150,000 cases. The United States has a "lion's share" of the total number of infections worldwide, Galgiani said, and 97 percent of all U.S. cases are in California and Arizona. 

After a truncated 2009 season, Jackson bounced around for the next few years, splitting his time between major league and minor league teams. Jackson, 31, retired from baseball on April 14 after spending a few weeks in the minors this spring after the Baltimore Orioles cut him from their major league roster. 

Jackson did not return several calls left with the team and on his cell phone, and his decline can't be directly blamed on Valley Fever. 

Galgiani – who did not treat Jackson but followed his case – said Jackson had a mild form of the disease. But even the mild form can put the healthiest of people out of commission, he said. "I had one patient who couldn't get out of bed for months." 

The Met's Davis, who lives off-season in Arizona, has bounced back well from his 2012 battle with Valley Fever and is starting at first base this year. 

This article originally appeared at The Daily Climate, the climate change news source published by Environmental Health Sciences, a nonprofit media company.