I. Genetic heterogeneity in Pneumocystis carinii: an introduction

Abstract

Molecular techniques have played an important role in demonstrating a high level of heterogeneity among the different types of organisms which are collectively known as Pneumocystis carinii. Genetic heterogeneity has been observed in Pneumocystis organisms isolated from different host species, suggesting that Pneumocystis infection is host-species specific. On the basis of this genetic divergence a provisional trinomial nomenclature has been adopted, in which different types of Pneumocystis organisms are designated a 'special form'. Multiple special forms of Pneumocystis have been detected in some host species, for example in infected rat and ferret lungs, but not in human lungs. Lower levels of genetic heterogeneity have been observed within each Pneumocystis special form, and in particular in human-derived Pneumocystis. Analysis of the genetic heterogeneity of populations of Pneumocystis is contributing to the understanding of the epidemiology and pathophysiology of this infection.

Phylogeny of Pneumocystis carinii from 18 Primate Species Confirms Host Specificity and Suggests Coevolution

“…Molecular techniques, including karyotyping, DNA sequence analysis, or single-strand conformation polymorphism, have played a significant role in demonstrating the degree of heterogeneity between P. carinii organisms. To date, the mtLSU rRNA sequence has been reported from P. carinii organisms infecting nine different mammalian species: human, rat (two divergent sequence types), mouse, rabbit, pig, horse, shrew, ferret (five divergent sequence types), and rhesus macaque (17,23,37,46). The genetic diversity of P. carinii was examined at other loci such as the mitochondrial small subunit of rRNA (28), the nuclear ribosomal RNA operon (32,46), ␣-and ␤-tubulin (18,43), arom (5), thymidilate synthetase (30,35), DHPS (31), and more recently manganese-dependent superoxide dismutase (16).…”

“…Several Pneumocystis species may be distinguished, each of them residing in a specific mammalian host (29). Isolates of P. carinii infecting different mammals are divergent at the genetic level (specific karyotypic profiles and gene sequences) (29) and at the phenotypic level (antigenic differences, ultrastructure, and isoenzymatic polymorphism) (36,46). The concept of close host specificity has been further supported by the failure of most cross-infection experiments (1,2,3,23,24,47).…”

Pneumocystis carinii f. sp. hominis DNA in Immunocompetent Health Care Workers in Contact with Patients with P. carinii Pneumonia

“…It is now widely accepted that the P. carinii organisms that infect each mammalian species are host specific and that the infection in humans is not acquired from an animal reservoir (32,39). Airborne acquisition of P. carinii infection has been demonstrated by using the rat model (13).…”

Genetic heterogeneity of Pneumocystis carinii from rats of several regions and strains

“…It is a pathogen found mostly in the alveolar spaces, and the rate of infections has risen dramatically over the past years with the advent of aggressive immunosuppressive therapies and increasing infection with human immunodeficiency virus (HIV) (Wakefield et al, 1998).The organism has appeared to infect a wide range of mammals. The hosts which had been reported to be infected by P. carinii were rats, mice, guinea pigs, hamsters, ferrets, rabbits,…”

“…It is a pathogen found mostly in the alveolar spaces, and the rate of infections has risen dramatically over the past years with the advent of aggressive immunosuppressive therapies and increasing infection with human immunodeficiency virus (HIV) (Wakefield et al, 1998).…”