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Coccidioidomycosis is the infection
caused by the dimorphic fungus Coccidioides immitis. The
history of the identification of this organism and the clinical
study of the infections caused by this agent have been the subject
of a number of comprehensive reviews.1-2 Although it
was initially believed that coccidioidomycosis was an invariably
lethal infection, by the mid-1930s, it was recognized that the organism was
in fact responsible for a very common, acute, and generally self-limited
disease that was known as the San Joaquin Valley fever. In regions
where coccidioidomycosis is endemic, Valley fever continues to be
an important public health problem. In addition, coccidioidomycosis
has emerged in recent years as an important cause of disease in
immunocompromised patients, particularly those with human immunodeficiency
virus (HIV) infection.
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The life cycle of C immitis is complex (reviewed
in Parish and Blair4) and demonstrates 2 distinct
phases: a saprophytic (vegetative) phase and a parasitic phase.
In soil, the organism grows as a mycelium, with branching septated
hyphae. As they mature, the mycelia develop rectangular spores (arthroconidia); at this
stage, the hyphae become very fragile, and arthroconidia easily
become airborne. When inhaled, the arthroconidia begin the parasitic
phase, and spherules form. Spherules are round,
double-walled structures that reproduce by formation of spherical
internal spores, termed endospores. A single spherule
may produce thousands of endospores, and as the spherule ruptures,
each endospore may in turn develop into a new spherule, perpetuating
the parasitic phase.
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In general, C immitis appears to be confined
to the Western hemisphere. The endemic areas lie in the southwestern
United States, encompassing west Texas, New Mexico, Arizona, and
California. The organism can also be found in northwestern Mexico
and a few small areas of Central and South America. These endemic
areas have arid climates, hot summers, few winter freezes, low altitude,
and alkaline soil—ecological conditions that favor C
immitis. The organism is drought resistant, and periodic
increases in cases are observed when prolonged drought is followed
by periods of heavy rain. Arthroconidia may become airborne after
windstorms or disruption of soil by farming or construction work.
Since infection requires that arthroconidia be inhaled, person-to-person
transmission does not play a role in acquisition of coccidioidomycosis.
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Hospitalizations for coccidioidomycosis are common, particularly
in endemic areas. County of residence, older age, black race, male
sex, intercurrent HIV infection, and pregnancy are all risk factors
strongly associated with an increased risk for hospitalization.5
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Clinical Manifestations
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The primary portal of entry in most patients is the lung, although
the organism may enter through the skin. Accordingly, signs and symptoms
of respiratory tract infection represent the major clinical manifestations
of acute coccidioidomycosis in most patients.6 Pulmonary coccidioidomycosis
occurs in 95% of all cases. The majority of individuals
with acute coccidioidomycosis will have either asymptomatic infection
or mild upper respiratory tract symptoms. Approximately ...