Just One Breath: Why valley fever in Washington is cause for concern

The latest edition of the Mortality and Morbidity Weekly Report is out today with some big news on valley fever.

We were given a sneak peek of this news two weeks ago when Washington State University announced that it was working on pinpointing the source of valley fever in the state.

The appearance of valley fever in Washington state isn't the first time the deadly disease has shown up so far north from where it is typically found. In 1996, the Washington State Department of Health in Seattle started tracing a cluster of valley fever cases. But the cases turned out to track back to a fungus in the soil in Mexico, where those infected people had been traveling.

That was what everyone expected since the fungus that causes coccidioidomycosis traditionally only lives in the Southwest U.S. and south of the Mexican border.

This time, though, the fungus is living in Washington, and the new research offers the first significant proof that the fungus is thriving far outside its typical boundaries.

We are likely to see more news like this in the months and years to come as the CDC improves its technological game.

Here’s the chain of events.

In 2010 and 2011, three people were diagnosed with valley fever in eastern Washington, all within a 60-mile radius near the intersection of three counties: Benton, Franklin and Walla Walla.

Those cases were later analyzed and reported in the journal Clinical Infectious Diseases. The authors at the time suspected that the patients had become infected from a fungus growing in the state. They wrote that the low elevation, average temperature, and low annual rainfall all worked in valley fever’s favor:

Established Coccidioides-endemic areas generally have 5–50 cm annual precipitation, hot summers, few winter freezes, and mean annual air temperatures between 0.5°C and 24.4°C, and tend to be at lower elevations with sandy soil. The local environmental conditions and close geographic proximity of cases support local exposure.

But they hedged, saying, “Definitive evidence of Coccidioides in eastern Washington requires further studies.” And now we have those studies.

Soil samples were collected and sent to the CDC’s Mycotic Diseases Laboratory.

At the lab, the CDC identified the valley fever fungus DNA in six of the 22 soil samples. Then researchers used a process involving whole genome sequencing to match the DNA in the valley fever fungus – known as C. immitis – to the DNA isolated from one of the infected patients.

The authors wrote:

This is new direct evidence that the infections were acquired in Washington and that C. immitis exists in this environment clearly outside the recognized endemic area.

But why?

Washington State University professor emeritus Jack D. Rogers, a fungus expert, explained in the university’s news release that while the fungal spores can be transported by strong winds and dust storms, “once deposited on the ground, they need the right climactic and soil conditions to support growth.”

“It’s long been believed that those conditions were geographically maintained in the desert Southwest and parts of Mexico, Central America and South America. Because valley fever is hard to detect and often misdiagnosed by physicians who are not acquainted with it, it’s important to know where cocci’s range is expanding.”

Rogers points to changes in weather patterns and rodents moving north on the hunt for suitable habitat. The rodents dig holes that prove to be good breeding grounds for the fungus, he said.

This clearly isn’t cause for people in eastern Washington to panic. But it is a good prompt for clinicians there to be on the watch for valley fever symptoms. It also should be reason enough for a broader attempt to take soil samples in the Northwest and other parts of the country to see if the fungus shows up elsewhere. We know from previous research that valley fever is greatly underreported. More analyses like these might show just how far the disease is reaching outside the Southwest.

Cropped photo by Bala Sivakumar via Flickr.