pneumocystis

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Definition

Pneumocystis pneumonia is a lung infection that occurs primarily in people with weakened immune systems—especially people who are HIV-positive. The disease agent is an organism whose biological classification is still uncertain. Pneumocystis carinii was originally thought to be a one-celled organism (a protozoan), but more recent research suggests that it is a fungus. Although its life cycle is known to have three stages, its method of reproduction is not yet completely understood. The complete name of the disease is Pneumocystis carinii pneumonia, often shortened to PCP. PCP is also sometimes called pneumocystosis.

Description

Pneumonia as a general term refers to a severe lung inflammation. In pneumocystis pneumonia, this inflammation is caused by the growth of Pneumocystis carinii, a fungus-like organism that is widespread in the environment. PCP is ordinarily a rare disease, affecting only people with weakened immune systems. Many of these people are patients receiving drugs for organ transplants or cancer treatment. With the rising incidence of AIDS, however, PCP has become primarily associated with AIDS patients. In fact, as many as 75% of AIDS patients have developed PCP. It has also been the leading cause of death in AIDS patients.

Transmission

The organism that causes PCP is widely distributed in nature and is transmitted through the air. When the organism is inhaled, it enters the upper respiratory tract and infects the tiny air sacs at the ends of the smaller air tubes (bronchioles) in the lungs. These tiny air sacs are called alveoli. Under a microscope, alveoli look like groups of hollow spheres resembling grape clusters. The exchange of oxygen with the blood takes place in the alveoli. It appears that P. carinii lives in the fluid in the lining of the alveoli.

Person-to-person infection does not appear to be very common; however, clusters of PCP outbreaks in hospitals and groups of immunocompromised people indicate that patients with active PCP should not be exposed to others with weakened immune systems. It is thought that many people actually acquire mild Pneumocystis carinii infections from time to time, but are protected by their immune systems from developing a full-blown case of the disease.

— Cindy L. A. Jones, PhD

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n.
A severe lung infection caused by the parasitic protozoan Pneumocystis carinii and affecting primarily individuals with an immunodeficiency disease, such as AIDS. Also called pneumocystis pneumonia.

[From New Latin Pneumocystis, genus name : PNEUMO- + New Latin cystis, cyst; see cyst.]

(nū'mə-sĭs'tĭs, nyū'-)
n.

A severe lung infection caused by the parasitic protozoan Pneumocystis pneumonia and affecting primarily individuals with an immunodeficiency disease, such as AIDS.

A genus of organisms of uncertain status, but considered to be protozoa.

• P. carinii — the causative agent of interstitial plasma cell pneumonia in humans and immunocompromised Arab foals and dogs.

Note: click on a word meaning below to see its connections and related words.

The noun has one meaning:

Meaning #1: pneumonia occurring in infants or in persons with impaired immune systems (as AIDS victims)
  Synonyms: pneumocytosis, pneumocystis carinii pneumonia, interstitial plasma cell pneumonia

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