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The causative agent of pneumocystis (Pneumocystis jiroveci)
Last reviewed: 23.04.2024
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Pneumocystis is a disease caused by opportunistic fungi; characterized by the development of pneumonia in persons with impaired immunity (prematurity, congenital or acquired immunodeficiency, HIV infection). Pneumocystis jiroveci is classified as a conditionally pathogenic yeast-like fungus. However, morphological and other properties, sensitivity to antimicrobial drugs, they are typical protozoa.
Morphology and physiology Pneumocystis jiroveci
The life cycle of pneumocysts includes the formation of trophozoites, pre-cysts, cysts and intracystic gels. Trophozoite has an oval or amoeboid form, a size of 1.5 ~ 5 microns. It is covered with a pellicle and capsule. Trophozoites with the help of outgrowth pellicles attach to pneumocytes of the 1st order (in contrast to the endogenous stages of Cryptosporidium, which in the lungs live in pneumocytes of the 2nd order). Rounding off, the grophozoites form a thickened cell wall, turning into a pre-cyst and a cyst. The cyst is 4-8 microns in size and has a thick three-layered wall, which is intensely colored by polysaccharides. Inside the cyst there is an outlet from 8 daughter bodies (sporozoites). These intracystic bodies have a diameter of 1-2 μm, a small nucleus and are surrounded by a two-layered shell. After exiting the cyst, they become extracellular trophozoites.
Epidemiology and clinical picture of pneumocystosis
The source of infection are people. The air-dust transmission path. The incubation period is from 1 to 5 weeks. Pneumocystis is an opportunistic infection with lung damage, a leading AIDS marker infection. Pneumocystis pneumonia occurs with shortness of breath, fever and dry cough. Death occurs with respiratory failure. But usually this is an asymptomatic infection; over 70% of healthy people have antibodies to pneumocysts. Most healthy children become infected with fungus at 3-4 years of age.
[Microbiological diagnosis of pneumocystosis
The microscopic method includes microscopy of a smear from a biopsy, pulmonary tissue, sputum, stained by Romanovsky-Giemsa: the cytoplasm of the parasite is blue, and the nucleus is red-violet. To the special methods of coloring, which reveals the cell wall of pneumocysts, the color is toluidine blue and silvering according to Gomori-Grokott. For diagnostics apply also RIF, ELISA and PCR. Detection of IgM or an increase in the level of IgG antibodies in paired sera indicates an acute pneumocystis infection.