Pneumocystis Jiroveci (Previously Known as Pneumocystis Carinii Pneumonia)



Opportunistic lung infection caused by Pneumocystis jiroveci (PJ). This organism is currently considered a primitive fungus based on DNA sequence analysis. It has two developmental forms (the cysts contain sporozoites that become trophozoites when excised).

  • Although previously known as Pneumocystis carinii pneumonia (PCP), the acronym PCP is still in use and refers to Pneumocystis pneumonia.
  • PCP occurs almost exclusively in the immunocompromised host.
  • PCP is an AIDS-defining illness. It is the most common opportunistic life-threatening lung infection in infants with perinatally acquired human immunodeficiency virus (HIV) disease.
  • PJ causes a diffuse pneumonitis characterized by fever, dyspnea at rest, tachypnea, hypoxemia, nonproductive cough, and bilateral diffuse infiltrates in the roentgenogram. It is a severe condition frequently leading to respiratory failure, necessitating intubation and mechanical ventilation.
  • Chemoprophylaxis against this microorganism has proven successful. Therefore, early identification of the HIV-infected mother becomes essential.
  • Despite advances in therapy, the infection continues to be associated with significant morbidity and mortality.


  • Ubiquitous in mammals worldwide, particularly rodents
  • Growth on respiratory tract surfaces
  • Mode of transmission is unknown:
    • Airborne person-to-person transmission is possible, but case contacts are rarely identified.
    • Environmentally acquired
  • Asymptomatic infection appears early in life; >70% of healthy individuals have antibodies by age 4 years.
  • Primary infection is likely to be the mechanism in infants. Reactivation of latent disease with immunosuppression was proposed as an explanation for disease later in childhood; however, animal models of PCP do not support this proposition.
  • PCP in the HIV patient can occur at any time but usually presents during the 1st year of life. The highest incidence is between 3 and 6 months of age.

Risk Factors

  • Immunocompromised host
    • Children with congenital or acquired immunodeficiency syndrome (AIDS) and recipients of suppressive therapy in the treatment of malignancies or after organ transplantation are at high risk.
    • In leukemic patients, the incidence of PCP has been directly related to the degree of immunodeficiency resulting from chemotherapy.
    • Epidemics of PCP were reported in premature and malnourished infants and children in resource-limited countries and during times of famine.


  • In the immunodeficient child, the pathologic changes occur predominantly in the alveoli. Cysts and trophozoites are seen adhering to the alveolar lining cells or in the cytoplasm of macrophages.
  • As infection progresses, the alveolar spaces are filled with a pink, foamy exudate containing fibrin, abundant desquamative cells, and a large number of organisms. Alveolar septal thickening with mononuclear cell infiltration is also seen.

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