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Report Urges P. carinii Name Change

Kate Traynor

A report (PDF) in last month's issue of Emerging Infectious Diseases declared that the causative organism of Pneumocystis carinii pneumonia in humans differs significantly from true P. carinii—which infects rats—and merits a separate species name.

In place of P. carinii, or the sometimes-used interim name P. carinii f. sp. hominis, the report urged that the name P. jiroveci be adopted to refer to the organism. This species name first appeared in the scientific literature in 1999. The name is awarded in honor of Otto Jirovec, the parasitologist credited with first describing the pathogen in humans.

According to the report, genetic analysis strongly supports the conclusion that P. jiroveci is a distinct species. The genetic sequence of Pneumocystis organisms isolated from humans differs from the sequence of Pneumocystis parasites found in other host species. In addition, genetic analysis indicates that the species identified as P. jiroveci is found only in humans.

On the basis of this evidence, the report's authors argued that "it is no longer correct, either biologically or taxonomically, to refer to the human Pneumocystis organism as P. carinii. P. carinii now exclusively refers to the organism formerly known as P. carinii f. sp. carinii, one of the two Pneumocystis species found only in rats."

The report noted that "PCP"—the acronym commonly used in place of "Pneumocystis carinii pneumonia"—can still be used but would now refer to Pneumocystis pneumonia.

P. carinii was first reported in the scientific literature in the early 1900s. The organism was initially believed to be a protozoan parasite but was shown in 1988 to be an unusual fungus. Serological tests indicate that humans are commonly infected with Pneumocystis organisms, but the fungus is problematic only in immunocompromised patients, particularly those infected with HIV.