What is Coccidioides?

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  • Written By: Emma Lloyd
  • Edited By: A. Joseph
  • Last Modified Date: 03 October 2019
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Coccidioides is an infection caused by two similar fungal species called Coccidioides posadasii and Coccidioides immitis. These fungi are common in South America, Central America, Mexico and the driest regions of the southwestern Unites States. The fungi are endemic to these locations, which means they are considered native species, and infection is a common occurrence. The disease caused by these fungi is often given a different name according to the geographical location in which the infection occurs; for example, it has been called valley fever, desert fever, San Joaquin fever and California fever.

The regions where these fungi are most common are similar in climactic and geological terms, with low rainfall; hot summers; mild winters; sandy, salty, alkaline soil; and low elevation. These conditions provide the fungi with ideal growth conditions and help the organism spread. One of the principal ways in which the organism spreads in the environment and infects humans is by becoming airborne. In arid climates, the likelihood of inhalation of C. posadasii and C. immitis increases because soil is drier and the fungi are more likely to become airborne.

In regions where the fungi are endemic, coccidioides infection is a hazard in certain occupations, including construction and agriculture. The main risk factor for infection is engaging in outdoor activities in endemic regions. While most cases of infection occur in endemic areas, it is possible for fungal contamination to cause infection outside of these locations.


C. posadasii and C. immitis cause disease when they are inhaled into the lungs. Fungal infection causes the recruitment of large numbers of granular immune cells to the site, which leads to acute inflammation. In this phase, coccidioides symptoms include chills, fever, cough, chest pain, fatigue, difficulty breathing, night sweats, headache, loss of appetite, weight loss and muscle aches and pains.

If the infection does not resolve in the acute phase, granulomas can form in the lungs. A granuloma is a cluster of immune cells that have surrounded an infectious organism. The immune system reacts this way in an attempt to wall off the infection and prevent it spreading. Chronic infection can cause fever, difficulty breathing and coughing up of blood.

Granulomas are characteristic of chronic inflammation, a condition that can lead to disseminated disease. This type of disease occurs when organisms enter other parts of the body, often via the bloodstream. People with disseminated disease are at high risk of meningitis and other systemic types of infection. Disseminated disease is rare but is often fatal because of the possibility of meningitis or multiple organ involvement.

Standard coccidioides treatment involves the use of anti-fungal medications to kill the invading organisms. Most infections will spontaneously resolve without the use of medication, but people with severe acute symptoms generally receive medication to prevent the development of chronic or disseminated disease. People at increased risk of disseminated disease — such as the very young or old, people with reduced immune system function or those with diabetes — generally are given medication, even for mild infection.


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