Sporozoites often cause infection when the body’s immune system is weakened. Vulnerable populations include patients with AIDS, patients on long-term immunosuppression, and patients with end-stage oncological disease. The lungs are often involved and the clinical manifestations are mainly an irritating cough, mainly dry. It may be accompanied by fever, usually high, and progressive shortness of breath after activity. Imaging studies may reveal diffuse, glassy changes in both lungs. Blood gas analysis is often suggestive of intractable hypoxemia, and treatment with conventional oxygen and antibiotics against infection is usually ineffective. In patients without a history of sulfonamide allergy, treatment with compounded sulfamethoxazole can be remarkably effective. In some patients with significant hypoxemia, a combination of methylprednisolone may also be used for treatment.