Pneumocystis Pneumonia

                                               Pneumocystis Pneumonia.

                                                  P. K. Ghatak, MD

In 1980, the medical community was challenged by an outbreak of a new disease that was rampant in homosexual communities in the major US cities. Within a few months, it was found to be a viral infection. The patients were the immunocompromised individuals and the virus was called HIV (human immunodeficiency virus). An interstitial pneumonia was almost constantly coexisted with the HIV infection. The organism was Pneumocystis jirovecii, a unicellular fungus, and the pneumonia was called PJP pneumonia.

The history of Pneumocystis is interesting.

In 1090 Dr. Chagas was in pursuit of the causative organisms of Trypanosomiasis of South America. He discovered a few tiny organisms in the respiratory tract of some of the victims. He thought those were immature Trypanosome trophozoites. In 1909, Antonio Carnii found 3 cysts in the lung of children which were similar to Chagas' trypanosome but he did not think they were trypanosomes. In 1910 Delano of the Pasture Institute discovered similar cysts in a rat's lung and found that the organism had many features of a protozoan and named it Pneumocystis carnii. In 1999, molecular analysis of mRNA and mitochondria of the Pneumocystis was conducted by Otto Jiroveci, a parasitologist from Czechoslovakia. He identified Galactosaminogalactan as a signature for a fungus. The organism now classified as a unicellular fungus. Pneumocystis exists in nature in three morphological stages – Protozoite, Sporozoite and Cysts (spores). Distinct genomic variability exists between host-specific members of the genera. For the humans, the pathogenic organism is called pneumocystis jirovecii. It was so named to honor Otto Jiroveci's work.

PJP pneumonia.

This fungus is ubiquitous, and exists as a parasite in the lungs of mammals and humans. The children acquire this fungus by 3 to 4 years of age. It spreads from person to person by being airborne. In good health, no adults or children show any ill effects of this parasitic fungus.

In severely immunocompromised individuals, with a CD4 cell count of less than 200 micro L, the Pneumocystis becomes an opportunist pathogen. In the lung, it produces an interstitial pneumonia. The infiltrates are a perihilar distribution, called a bat wing pattern. Like a viral interstitial pneumonia, the patients become severely hypoxic due to low oxygen diffusion capacity with a wide A-a gradient. Most severe infections produce acute respiratory syndrome. Various systemic symptoms develop due to tissue hypoxemia, specially cerebral manifestations. Other non-pulmonary features are – a. severe bone marrow depression producing pancytopenia, b. lymphadenopathy. c. cotton-wool exudates in the retina, d. thyroid gland enlargement and gastrointestinal symptoms.

Common symptoms are – fever, unproductive cough, chest pain, shortness of breath, cyanosis and tachycardia.

Diagnosis:

High LDH is a characteristic feature. Pneumocystis trophozoites and cysts are recovered by warm saline induced sputum and from bronchoalveolar lavage fluids.

Treatment:

Severely ill patients require tracheal intubation and mechanical ventilation.

PJP are very sensitive to Trimethoprim-Sulfamethoxazole (TMP-SMX). Usually given by IV in an acute situation. In tablet form, it is used as chemoprophylaxis. Alternative to TMP-SMX chemoprophylaxis are Dapsone, Atovaquone and aerosolized Pentamidine.

Prognosis:

Before Retroviral therapy, the mortality from PJP pneumonia was 80-90 %.  The mortality is 10 to 20%.at present.

********************************************