Coccidioidomycosis is an infection caused by breathing in the spores of a fungus Coccidioides immitis found in soil in desert regions of the southwestern U.S., Mexico, and Central and South America. Sometimes called Valley Fever or Desert Fever because of its prevalence in farming valleys, these fungi resist drying and easily become airborne. It usually affects the lungs but can spread and affect many organs.
The disease can have an acute, chronic, or disseminated form. Acute pulmonary coccidioidomycosis is almost always mild, with few or no symptoms, and resolves without treatment. The incubation period is 10 to 30 days and the incidence about 1 out of 100,000 people.
Chronic pulmonary coccidioidomycosis can develop 20 or more years after initial infection which may not have been recognized, diagnosed, or treated. Infections (lung abscesses) can form and rupture releasing pus (empyema) between the lungs and ribs (pleural space). The incidence of chronic disease is also about 1 out of 100,000 people.
In disseminated disease, extension of infection to the bones, lungs, liver, meninges, brain, skin, heart, and pericardium (sac around the heart) may take place. Meningitis occurs in 30 to 50% of cases of disseminated disease. The course of the disease may be rapid for immunosuppressed patients.
When inhaled, as few as 10 surviving spores can cause infection and mature as quickly as 48-72 hours into an active fungal state. Although coccidioidomycosis is not contagious, lab personnel who handle specimens must take precautions to avoid contracting the illness.
Following inhalation and maturation of the cocci, humoral immunity predictably begins with immunoglobulin M (IgM), then IgG. Cellular immunity, particularly T-cells, becomes a key factor in determining recovery from coccidioidomycosis. A respiratory infection ensues.
The majority of patients recover from the respiratory infection with no or minimal consequences. Some develop complications in the lungs, such as tissue death or abscesses. Persistent pulmonary disease may manifest as persistent bronchitis and pneumonia. A subset of patients will develop infection outside the lungs: the infection spreads through blood either during the primary infection or as a reactivation from a chronic pulmonary site.
Areas affected outside of the lungs may include blood cell generating tissues, skin, kidneys, bones, the central nervous system and heart muscle. Disseminated disease can involve nearly every organ and can be especially dangerous in the immune compromised host. More often, in chronic cases, the disease progresses slowly.
Incidence and Prevalence
Coccidioidomycosis affects an estimated 100,000 people each year in the US. Coccidioidomycosis is endemic in the western hemisphere from California to Argentina. Coccidioidomycosis is also being recognized outside these areas as travelers pass through. Former residents of endemic areas suffer reactivation, and natural disasters such as earthquakes and dust storms create new epidemics.
Risk of infection is greatest on windy days when the soil is dry or when the soil is disturbed by activity. An example of such infectivity was noted following a large California dust storm after which 15 counties reported a tenfold or more increase in cases of coccidioidomycosis.
Areas outside of the US with a higher risk are characterized by semiarid climates with hot summers and alkaline soil include northern Mexico and Central and South America.
About 40% of those infected develop symptomatic disease, usually pulmonary. About 90% will resolve their pulmonary maladies without lasting consequences. Some 10% of patients will go on to harbor pulmonary lesions and nodules and about 1% develop disseminated disease.
Diseases and conditions that alter immune responses also predispose those affected to dissemination and serious disease. Pregnant women are at special risk for disseminated coccidioidomycosis.
Filipinos have the highest risk of dissemination, about 10-170 times the risk of whites. Blacks and Hispanics also have a higher risk of dissemination than whites. Blacks have a 5 times higher risk of developing meningitis than whites; Filipinos have a 10 times higher risk of developing meningitis than whites. Mortality rate is 5 times greater for blacks than for whites. The incidence is equal in males and females and persons of any age may be affected. In disseminated disease, the mortality rates in newborns and infants are much higher than those in children, adolescents and adults.
Coccidioidomycosis usually develops 1-4 weeks following exposure. About 60% of infections cause no symptoms and are only recognized by a positive coccidioidin skin test. In the remaining 40% symptoms range from mild to severe. Although the symptoms are very nonspecific, a level of suspicion should be maintained for those who live in or have traveled to endemic areas or have persistent symptoms. Skin tests, blood tests, and sputum cultures can be used for the diagnosis.
The results of medical therapies for coccidioidomycosis are unpredictable. Antifungal therapy for coccidioidomycosis often is less certain than for other fungal diseases. Fortunately, only about 5% of patients require therapy. Common drugs used include Amphotericin B, Diflucan, and Nizoral.