COMEDK 2007 MCQ Answer 14

Pathogenesis:

• P. carinii is a low virulence fungus commonly found in lungs in humans and other mammals.
• Infects host via inhalation of the organism in its trophic form.
• Usually infection occurs in those HIV infected patients with CD4+ counts below 200/mm3, since CD4 + lymphocyte activation of macrophages is critical in host defense.
• Fungus cannot be targeted with usual antifungal agents.

Clinical characteristics:

• Shortness of breath, fever and nonproductive cough.
• Tachypnea and tachycardia characterize an acute ill patient. Alar flaring, intercostal reaction with radiographic findings of bilateral diffuse infiltrates are present.
• The most common finding is hypoxia.
• Extrapulmonary pheumocystosis may occur in cases of advanced HIV infection with involvement of liver, spleen, lymph nodes, GI tract, eyes, thyroid and adrenals.

Diagnostic work-up:

• From identification of organism in respiratory secretions or tissue sections of severely immunocompromised individuals with respiratory symptoms.
• Immunofluerescence is the most widely used technique, while demonstration of P. carinii antigen in serological test and DNA in tissue specimens are of high specificity and sensitivity.

Treatment:

• Key is early diagnosis. Mechanical ventilation along with Trimethoprin-sulfamethoxazole may reduce mortality from 80% -90% to 50%.
• TMP-SMX inhibits folic acid synthesis is relatively inexpensiveavailable in oral and parenteral forms is well tolerated and the drug of choice. Usual IV doses 15-20 mg/kg/day.
• Alternative agents Dapsone 100mg/day PO alone or in combonation with TMP-SMX.
• In patients with AIDS and CD4+ count below 200/mm3, oral candidiasis, unexplained fever of >100 F for more than 2 weeks, or recovered from previous episode of P. carinii pneunitis chemoprophylaxis is recommended and continued for life.