Is Pneumocystis carinii a deep mycosis-like agent?

Abstract

Pneumocystis carinii is a widespread eukaryotic microorganism found in the lungs of healthy mammals, including humans. It is able to proliferate extensively in the alveoli, becoming an important agent of severe pneumonitis in immunosuppressed hosts, especially in persons suffering from AIDS. The taxonomic position of P. carinii is uncertain. Typical cytoplasmic organelles of eukaryotic cells have been found and described in the parasite. Biochemical research is hindered by the lack of an efficient in vitro culture system. Results of comparative study of nucleic acid sequences suggest that Pneumocystis is a fungus. However, ultrastructural, biochemical and nucleic acid homology insights appear as clearly insufficient to class Pneumocystis. Pneumocystis infection might be acquired, as deep mycoses, from environmental sources through the respiratory tract. Thus, the hypothesis of an environmental stage of the parasite must be considered. Pneumocystis might be seen as a widespread pathogenic dimorphous fungus. As fungal agents, P. carinii is able to disseminate from the infected lung to other organs. However, deep mycoses and pneumocystosis induce different histopathological changes in the host. Furthermore, deep fungal infections, unlike pneumocystosis, cannot be transmitted from one infested host to another one. Beside these two aspects, pneumocystosis shares many features with deep mycoses. Research on the epidemiology of pneumocystosis is needed.

In vitro attachment of Pneumocystis carinii from mouse and rat origin

“…In spite of the fact that antigenic [10,16], genomic [29] and ultrastructural host-species related differences [8] have been reported between P carinii isolates, in the present work only minor differences were recorded in the kinetics of attachment between mouse-and rat-derived P carinii. However, our results clearly showed that the response of parasites from these two host species to drugs was different ( fig 4).…”

“…Most in vitro studies were performed with rat-derived P carinii. The source of P carinii may be important as genomic [29], antigenic [10,16] and morphological [8] differences were reported between P carinii derived from different host species. What's more, morphological differences involve filopodia, which are directly concerned in the in vitro attachment [7].…”

New Nomenclature for the Genus Pneumocystis

“…Of course, other genes can be used to recognize phylogenetic species, and the more genes that are analyzed the better. Other genes that have been analyzed in more than one Pneumocystis “species” include thymidylate synthase [9,21,22], tubulins [12,49,53], dihydrofolate reductase, mitochondrial small subunit rRNA, 26S rRNA [24], the 5‐enolpyruvyl shikimale phosphate (EPSP) synthase domain [2], dihydropteroate synthase (DHPS) [10], and superoxide dismutase (SOD) [11]. Primers that have been useful for analyzing some of these genes are listed in Table 1.…”

“…The host specificity observed in transfer experiments is accompanied by dramatic genetic differences, including sequence differences at multiple loci, and variation in the sizes and numbers of chromosomes [5,7–9,11,18,20–24,27–42,45–47,50,52]. For instance, chromosomes in ferret‐derived Pneumocystis organisms tend to be larger than those in rat‐derived Pneumocystis organisms [41].…”