What Is Valley Fever?

The sometimes dusty conditions in California's Central Valley give the fungus Coccidioides an opportunity to spread. Danita Delmont/Shutterstock

Valley fever is on the rise. Cases of this dangerous and sometimes fatal condition have tripled in the past decade, to the point where the Centers for Disease Control and Prevention (CDC) have dubbed it a "silent epidemic." Fewer than 1,500 cases were reported in California in 2001; by 2017 that number had risen to more than 14,364 with a spike to more than 20,000 cases in 2011. Although Valley fever can be found throughout Mexico, Central and South America and the American Southwest, most cases have turned up in California and Arizona, with a few cases found recently in south-central Washington state.

Cases of Valley fever by year
The number of reported cases of Valley fever spiked in 2011, but it has been rising again in recent years. CDC

So what is Valley fever? Also known as San Joaquin Valley fever or desert rheumatism, it isn't a virus or bacterial condition. The scientific name is coccidioidomycosis, a condition caused by exposure to the airborne fungus Coccidioides, which is common in dry, dusty areas. Although many people who encounter this fungus don't experience symptoms, the fungus can cause a wide range of problems in others, especially those with weakened immune systems. People of African-American or Filipino descent and pregnant women in their third trimester have shown greater susceptibility to Valley fever, which most commonly manifests as flu-like symptoms such as fever, cough, headache, rashes, muscle aches or joint pain. In more advanced cases, valley fever can cause skin lesions, chronic pneumonia, meningitis and bone or joint infections, any of which can be fatal.

How Valley fever is transmitted

Valley fever, The outer wall of this spherule is surrounded by neutrophils and has degenerated and disappeared except on the left side. The endospores are very well seen.
This is what Coccidioidomycosis looks like under a microscope. Yale Rosen of the USA/Wikimedia Commons

Luckily, Valley fever is only transmitted via direct contact with the fungal spores. It can't be transmitted from person to person, so people who experience symptoms don't need to worry about spreading it to friends and family. Unfortunately, it doesn't take much exposure to the fungus to experience problems. As the CDC says, "it only takes one breath" of the fungus to become infected.

For most people, Valley fever will fade and people should recover with little complication, but doctors still don't know why certain groups are more likely to succumb to the worst symptoms, though it might have to do with the concentration of farm workers in the areas where the fungus is concentrated, according to a report produced by Civil Eats and NBC News. Those with severe symptoms or who are likely to get them are treated with antifungals, although this treatment isn't 100 percent effective and relapses are not uncommon. In either case, early diagnosis is critical, especially since Valley fever manifests so similarly to the flu or other respiratory diseases. Valley fever can usually be diagnosed via a blood test, which would show signs of antibodies fighting the fungus, or a culture from coughing, which should show the presence of the fungus itself, according to the Mayo Clinic.

So why is the disease on the rise? The CDC says some scientists are looking into changing weather patterns and hotter temperatures, which may have helped the fungus to spread outside its normal range. Changing rain patterns could also have had an effect, as heavy rainfalls followed by long, dry periods allow more of the fungus to enter the air with dust and wind. It's also possible the increase in cases is a simple side effect of the increased human population in the region.

No vaccine exists for Coccidioidomycosis, but the CDC recommends that people working in or near dusty environments, such as construction sites, wear an N95 mask to reduce the chance of ingesting the fungus. Indoor HEPA filters can also improve air quality and reduce the chance of infection. Finally, they suggest keeping sores and cuts covered and clean, as the fungus has been known to enter through wounds in addition to the lungs.

By the way, humans aren't the only ones at risk of valley fever. Cats and dogs can also contract Coccidioidomycosis, so keep an eye on your critters when conditions are risky.