(previously classified as Pneumocystis carinii) was previously
classified as a protozoa. Currently, it is considered a fungus based on
nucleic acid and biochemical analysis.
This is a
generalized life cycle proposed by John J. Ruffolo, Ph.D. (Cushion, MT,
1988) for the various species of Pneumocystis. These fungi are
found in the lungs of mammals where they reside without causing overt
infection until the host's immune system becomes debilitated. Then, an
oftentimes lethal pneumonia can result. Asexual phase: trophic forms replicate
by mitosis to .
Sexual phase: haploid trophic forms conjugate and
produce a zygote or sporocyte (early cyst) .
The zygote undergoes meiosis and subsequent mitosis to produce eight
haploid nuclei (late phase cyst) .
Spores exhibit different shapes (such as, spherical and elongated
forms). It is postulated that elongation of the spores precedes
release from the spore case. It is believed that the release occurs
through a rent in the cell wall. After release, the empty spore case
usually collapses, but retains some residual cytoplasm .
A trophic stage, where the organisms probably multiply by binary fission
is also recognized to exist. The organism causes disease in
Distribution: Worldwide, in
humans and animals. Serologic evidence indicates that most healthy
children have been exposed by age .
Pneumocystis pneumonia (PCP) occurs in immunosuppressed
individuals and in premature, malnourished infants.
Features: The symptoms of
Pneumocystis pneumonia (PCP) include dyspnea, nonproductive cough,
and fever. Chest radiography demonstrates bilateral infiltrates.
Extrapulmonary lesions occur in a minority (<3%) of patients, involving
most frequently the lymph nodes, spleen, liver, and bone marrow.
Typically, in untreated PCP increasing pulmonary involvement leads to
specific diagnosis is based on identification of P. jiroveci in
bronchopulmonary secretions obtained as induced sputum or
bronchoalveolar lavage (BAL) material. In situations where these two
techniques cannot be used, transbronchial biopsy or open lung biopsy may
prove necessary. Microscopic identification of P. jiroveci
trophozoites and cysts is performed with stains that demonstrate either
the nuclei of trophozoites and intracystic stages (such as Giemsa) or
the cyst walls (such as the silver stains). In addition,
immunofluorescence microscopy using monoclonal antibodies can identify
the organisms with higher sensitivity than conventional microscopy.
Trimethoprim-sulfamethoxazole is the drug of choice. Recommended
alternatives include pentamidine; trimethoprim plus dapsone*;
atovaquone; and primaquine* plus clindamycin
* This drug is
approved by the FDA, but considered investigational for this purpose.