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Disease. pneumocystosis, PCP (Pneumocystis carinii pneumonia)

Geographic distribution. Cosmopolitan over the world.

Infection rate. Several ten thousands of new patients appear annually in the world.

Life cycle. The organism is transmitted via air. It has two stages, cystic and trophic form. In the lungs, the intracystic bodies grow to trophic forms and proliferate on the surface of the pneumocytes and in the alveolar cavity only in the immunocompromised humans. Some of the trophic forms may grow to cystic forms which have 8 intracystic bodies and cell wall. The intracystic bodies continue to grow as trophic forms and/or cystic forms. The cystic forms may be transmitted between humans.

Morphology. The trophic forms are ameboid of 2-3 ㎛ diameter. It has one nucleus and one tubular mitochondrion. Cystic forms have cyst wall of polysaccharides and globular shape of 6-8 ㎛ diameter. One cystic form includes 8 intracystic bodies which are sickle-shaped after maturation.

Pathology and clinical symptoms. The main pathological finding is exfoliation of pneumocytes and cell infiltration in the interstitial tissue. The mass of organisms, necrotic cell debris, and exudate fills the air space of the alveolar cavity, and thus respiration failure is induced. Major symptoms are fever, non-productive cough and respiration difficulty.

Diagnosis. Detection of organisms from bronchoalveolar lavage fluid or sputum by staining (DQ, GMS, toluidine blue, IFA) or PCR. Pulmonary infiltration in chest radiology may support the diagnosis.

Prevention. Prophylactic medication is effective for immunocompromised hosts.

Impression smeared specimen of the lung of an immune-suppressed rat, showing numerous cystic or trophic forms of Pneumocystis carinii. DQ stained, x1500.

Cyst of Pneumocystis carinii (A) (Toluidine blue stain, 1000x).

In smear of rat lung, cyst containing intracystic bodies is seen. The wall of the cyst is not stained with Giemsa, but the intracystic bodies are clearly seen (Giemsa stain, 1000x).

Cyst of Pneumocystis carinii (C) (Gomori stain, 1000x).

TEM photograph of a trophic form Pneumocystis carinii, which is encysted by the carbohydrate layer. x7000.

TEM photomicrograph of a trophic form Pneumocystis carinii. x7000.

Smear of bronchoalveolar lavage fluid of Pneumocystis carinii pneumonia. The mass is an alveolar cavity material most of which is trophic organisms. Violet dots are nuclei. DQ stained, x1500.

In situ hybridization of the rat lung with a probe of Pneumocystis carinii. Numerous organisms (red) are found in the alveolar cavities and pulmonary interstitium of an immunosuppressed rat. HE stained, x150.

A fatal patient of Pneumocystis carinii pneumonia which was induced by steroid medication. He showed severe emaciation and respiration difficulties.

Chest PA radiography of Pneumocystis carinii pneumonia. The bilateral lower lobes show hazy infiltration.

Lung section of Pneumocystis carinii pneumonia. The alveolar cavity is filled with foamy eosinophilic material which is composed of organisms, necrotic debris and exudate. HE stained, x150.

Smear of bronchoalveolar lavage fluid of Pneumocystis carinii pneumonia. Black round organisms are cystic Pneumocystis carinii. GMS (Groccot's methenamine silver) stained, x1500.

Immunoblotting pattern of human sera to Pneumocystis carinii antigens. Overall positive rate of normal population is high as 80% over the world, but the rate to individual antigenc band is variable by localities in the world.