These are the very infectious forms of C. immitis are very microscopic, measuring 2 to 5 in length and can be inhaled easily by normal breathing into the lungs. Once past the defence of the upper and lower respiratory tract, arthrospores germinate in the alveoli and branch into the tissues. These reproduce in the host and yield large numbers of endospores. Hundreds of endospores can be released upon maturation of the spherule and begin the cycle all over again. The identification of C. immitis is made by demonstration of these spherules in infected tissue.
Pulmonary coccidioidomycosis is an infection caused by the inhalation of arthrospores.
Arthrospores convert to spherules that contain endospores. The cause of this propensity is not known. Mexicans and American Indians are also at relatively higher risk of dissemination. The pregnant woman is at exceedingly higher risk of dissemination. In endemic areas, C. immitis remains viable for months at a depth of 12 to 14 cm in the soil.