Population Structure of Rat-Derived Pneumocystis carinii in Danish Wild Rats

Abstract

The rat model of Pneumocystis carinii pneumonia is frequently used to study human P. carinii infection, but there are many differences between the rat and human infections. We studied naturally acquired P. carinii in wild rats to examine the relevance of the rat model for human infection. P. carinii DNA was detected in 47 of 51 wild rats and in 10 of 12 nonimmunosuppressed laboratory rats. Evidence for three novel formae speciales of rat-derived P. carinii was found, and these were provisionally named Pneumocystis carinii f. sp. rattus-secundi, Pneumocystis carinii f. sp. rattus-tertii, and Pneumocystis carinii f. sp. rattus-quarti. Our data suggest that low-level carriage of P. carinii in wild rats and nonimmunosuppressed laboratory rats is common and that wild rats are frequently coinfected with more than one forma specialis of P. carinii. We also examined the diversity in the internally transcribed spacer (ITS) regions of the nuclear rRNA operon of Pneumocystis carinii f. sp. carinii by using samples from wild rats and laboratory rats and spore trap samples. We report a lack of variation in the ITS1 and ITS2 regions that is consistent with an evolutionary bottleneck in the P. carinii f. sp. carinii population. This study shows that human-and rat-derived P. carinii organisms are very different, not only in genetic composition but also in population structure and natural history.Animal models have been widely used as a source of Pneumocystis carinii organisms and for studying many aspects of P. carinii infection. This is because sustained in vitro cultivation of P. carinii has not been possible (1, 38), although recently a new method has been reported which is now being evaluated in a number of centers (25). The rat model has been particularly useful in studies of epidemiology (11, 50), drug sensitivity (59), immunology (51), and the biology of the organism (42). Ratand human-derived P. carinii organisms, however, are known to differ significantly in many respects. Considerable divergence has been shown between the genes of rat-and humanderived P. carinii (36,43), as well as antigenic (9) and ultrastructural (5) differences.Two genetically divergent types of P. carinii organisms, known as Pneumocystis carinii f. sp. carinii and Pneumocystis carinii f. sp. ratti, have been found in rat lungs (34). These were originally identified by differences in electrophoretic karyotype (7) and subsequently by DNA sequence variation at a number of genes, including those for the nuclear 26S rRNA (21, 29), the mitochondrial large-subunit (mt LSU) rRNA (14), the mitochondrial small-subunit rRNA (12), the TATA binding factor (45), BiP chaperonin (40), thymidylate synthase (14), and ATPase (24), and the ␣ subunit of the G protein (39). The level of genetic divergence between these two types of ratderived P. carinii was sufficiently high for them to be classed as different formae speciales (34, 44). Although eight different electrophoretic karyotypes of P. carinii f. sp. carinii and two of P. carinii f. sp. ratti have been identifi...

Distribution ofPneumocystis carinii f. sp. hominisTypes in the Lung of a Child Dying ofPneumocystisPneumonia

“…hominis is not present in P. carinii f. sp. carinii (rat-derived P. carinii) [7]. Mixed infections of P. carinii, however, have been observed in rats but consisted of a mixture of different formae specialis of rat-derived P. carinii, which were much more divergent than the different ITS genotypes observed in this study.…”

“…Samples of tissue (∼1 cm 3 ) were mechanically disrupted using sterile scalpels and digested with 1 mg/mL Proteinase K, in 10 mM EDTA pH8.0, and 0.5% sodium dodecyl sulphate at 60ЊC overnight, after which a further 1 mg/mL Proteinase K was added and the sample was incubated for a further 24 h. DNA was purified by phenol-chloroform extraction, followed by a DNA binding resin (Wizard DNA Clean-Up System, Promega) [7] . All precautions were taken throughout these procedures to eliminate the possibility of cross-contamination of samples.…”

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).…”

Pneumocystis murina MSG gene family and the structure of the locus associated with its transcription

“…Disease is seen only when the immune system is debilitated. The same seems to be true in other host species, including wild and laboratory animals, and humans (Mazars et al, 1997;Bishop et al, 1997;Nielsen et al, 1998;Laakkonen, 1998;Weisbroth et al, 1999;Denis et al, 2000;Palmer et al, 2000;Vargas et al, 2001;Demanche et al, 2001;Icenhour et al, 2001;Durand-Joly et al, 2003). Therefore, the function of the MSG system is probably not to overcome the immune response and cause disease.…”