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Diagnosis: Pneumocystis Pneumonia

Lab Animal volume 33, pages 22–23 (2004)Cite this article

Pneumocystis is a species-specific pathogen that can cause pneumonia in immunosuppressed or immunodeficient mammals. DNA analysis can differentiate the species of Pneumocystis that infects a specific host. Pneumocystis isolated from one host species cannot cause disease in a different host species. Host specificity has resulted in the recent classification of Pneumocystis organisms into two separate species. Microbiologists refer to the one that infects humans as P. jiroveci, and the one seen in rats as P. carinii. Using P. carinii as an umbrella term for the organism seen in all mammals is no longer acceptable. For example, when it is present in a mouse, we should differentiate the organism by calling it P. carinii special form muris1.

Although P. carinii appears to be a fungus, it has evolved with a set of characteristics that make it a unique organism. Under light microscopy, it exhibits characteristics of both yeast and protozoa1. Its DNA sequence is similar to that of a fungus, but its RNA sequence is similar to that of yeast. The cyst form of the organism exhibits characteristics of a fungus. Its cyst wall contains chitin, and mitochondria are present. However, the trophic form, which is the primarily observed form of the organism, is yeastlike in appearance1. Pneumocystis carinii lacks ergosterol, the primary sterol present in fungi2, causing the organism to be resistant to antifungal drugs. However, antiprotozoan medications are often effective against P. carinii infection. Unlike most fungi, P. carinii has only one copy of the gene for ribosomal RNA and does not proliferate in culture1. Its exotic nature led Kaneshiro2 to conclude that “Pneumocystis is Pneumocystis.”

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Figure 1: Histopathologi-cal alterations in the lung of a 16-week-old female B6;129S2-Tnfsf5tm1Imx mouse with a history of low body weight.
Figure 2

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Authors and Affiliations

  1. Coburn is at the College of Veterinary Medicine, Duck Pond Drive, Virginia Tech, Blacksburg, VA 24061.,

    Amy M. Coburn MS

  2. and Hubbs are in the Health Effects Laboratory Division, Nicolaysen, Simeonova, Moyers, Battelli, Willard, NIOSH, CDC, M/S L2015, 1095 Willowdale Rd., Morgantown, WV 26505.,

    Paul H. Nicolaysen VMD, Petia P. Simeonova MD, PhD, Winnie B. Moyers RVT, RLATG, Lori Battelli BS, RLAT, Patsy Willard & Ann F. Hubbs DVM, PhD, DACVP

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Correspondence to Ann F. Hubbs DVM, PhD, DACVP.

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Coburn, A., Nicolaysen, P., Simeonova, P. et al. Diagnosis: Pneumocystis Pneumonia. Lab Anim 33, 22–23 (2004). https://doi.org/10.1038/laban0204-22

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