XV. Pneumocystosis pathophysiology

Pneumocystis jirovecii pneumonia PCR test on upper respiratory tract swab

OBJECTIVES

Pneumocystis jirovecii pneumonia (PCP) is an opportunistic fungal infection with high morbidity and mortality among people living with HIV. Upper respiratory tract (URT) swabs are routinely taken for testing viral and bacterial pathogens when patients present with respiratory symptoms in our hospital. We conducted a pilot service improvement project to explore the utility of URT swabs for PCP diagnosis using in-house real-time polymerase chain reaction (PCR).

METHODS

Ten URT swab samples obtained from HIV-positive patients with PCP and a positive PCP PCR (AusDiagnostics) from lower respiratory tract (LRT) samples were retrospectively identified. Nine HIV-positive patients with a negative PCR for PCP from LRT samples were identified. Stored aliquots of DNA extracted from these samples were retrieved and tested by an in-house real-time PCR for the presence of PCP DNA. Among PCP-positive cases, URT swabs collected after PCP treatment initiation were excluded from the study.

RESULTS

In all, 10 URT samples from PCP-positive patients and nine URT samples from PCP-negative patients were tested for PCP by real-time PCR. Eighteen out of 19 URT sample had a concordant result with the LRT samples. The sensitivity and specificity for URT sample PCR were 90% [confidence interval (CI): 55.50-99.75%] and 100% (CI: 66.37-100%). The positive predictive value was 100% and the negative predictive value was 90.9% (CI: 60.90-98.47%).

CONCLUSIONS

Upper respiratory tract swab can reliably detect PCP DNA on real-time PCR among people living with HIV with PCP.

Prophylaxis for Pneumocystis jiroveci pneumonia: is it a necessity in pulmonary patients on high-dose, chronic corticosteroid therapy without AIDS?

The benefit of prophylaxis for Pneumocystis jirovecii pneumonia (PJP) is well documented in immunocompromised patients, particularly those with HIV and/or AIDS; therefore, guidelines dictate this as standard of care. However, there is a paucity of literature regarding those without HIV and/or AIDS who are potentially predisposed to PJP, including patients with sarcoidosis, cryptogenic organizing pneumonia, interstitial lung disease, asthma and chronic obstructive pulmonary disease, who may require high dose of prolonged corticosteroids for disease maintenance or to prevent relapses. In this review, the authors examine the available literature regarding prophylaxis in these groups, elaborate on the pathogenesis of PJP, when to suspect PJP in these patients, as well as explore current recommendations that guide clinical practice regarding implementation of PJP prophylaxis, namely with trimethoprim/sulfamethoxazole being the preferred agent. In summary, the role of PJP prophylaxis in non-HIV patients on chronic steroids remains controversial. The authors present a review of the literature to provide better guidance to the clinician regarding the need to initiate PJP prophylaxis in this patient population.

Pneumocystis oryctolagisp. nov., an uncultured fungus causing pneumonia in rabbits at weaning: review of current knowledge, and description of a new taxon on genotypic, phylogenetic and phenotypic bases

The genus Pneumocystis comprises noncultivable, highly diversified fungal pathogens dwelling in the lungs of mammals. The genus includes numerous host-species-specific species that are able to induce severe pneumonitis, especially in severely immunocompromised hosts. Pneumocystis organisms attach specifically to type-1 epithelial alveolar cells, showing a high level of subtle and efficient adaptation to the alveolar microenvironment. Pneumocystis species show little difference at the light microscopy level but DNA sequences of Pneumocystis from humans, other primates, rodents, rabbits, insectivores and other mammals present a host-species-related marked divergence. Consistently, selective infectivity could be proven by cross-infection experiments. Furthermore, phylogeny among primate Pneumocystis species was correlated with the phylogeny of their hosts. This observation suggested that cophylogeny could explain both the current distribution of pathogens in their hosts and the speciation. Thus, molecular, ultrastructural and biological differences among organisms from different mammals strengthen the view of multiple species existing within the genus Pneumocystis. The following species were subsequently described: Pneumocystis jirovecii in humans, Pneumocystis carinii and Pneumocystis wakefieldiae in rats, and Pneumocystis murina in mice. The present work focuses on Pneumocystis oryctolagi sp. nov. from Old-World rabbits. This new species has been described on the basis of both biological and phylogenetic species concepts.

Pneumocystis jirovecii colonisation in patients with interstitial lung disease

A prospective study was conducted to determine the prevalence of colonisation by Pneumocystis jirovecii in 80 consecutive patients who required bronchoscopy and bronchoalveolar lavage (BAL) following suspicion of interstitial lung disease (ILD). The mtLSU rRNA gene of P. jirovecii was identified by nested PCR in BAL samples. Patients with ILDs were divided into three groups: group A comprised those with idiopathic interstitial pneumonias; group B comprised those with sarcoidosis; and group C comprised those with other ILDs. The overall prevalence of P. jirovecii carriage was 33.8%, with colonisation rates of 37.8%, 18.8% and 37% in groups A, B and C, respectively (p not significant). There were more smokers among the carriers, but there were no other significant differences between carriers and non-carriers. The high prevalence of P. jirovecii carriers found among immunocompetent patients with ILDs in Spain suggests a possible role of P. jirovecii in the natural history of these diseases.

Association between human-Pneumocystis infection and small-cell lung carcinoma

BACKGROUND

Tobacco smoking is the most important but not the only risk factor in lung carcinoma. There is evidence that certain infections, which cause chronic inflammatory reactions, can also induce tumour development. It has recently been shown that patients with chronic pulmonary diseases present a high rate of subclinical Pneumocystis infection, and that the latter is able to induce inflammatory responses and alveolar cell alterations. The possible role of Pneumocystis infection in the development of lung neoplasms thus deserves consideration.

MATERIAL AND METHODS

Polymerase chain reaction has been used to analyze the presence of DNA of two independent loci of the Pneumocystis genome: the mitochondrial region (mtLSU rRNA) and the gene encoding for the dihydropteroate synthase enzyme, in paraffin-embedded tissue blocks of 10 cases of small cell lung carcinoma (SCLC) and 10 cases of nonsmall cell lung carcinoma (NSCLC) with similar demographic and clinical characteristics. Five cases without lung pathology, and two cases of Pneumocystis pneumonia were also analyzed as controls.

RESULTS

DNA of the microorganism was found in all the cases of SCLC but in only two of the NSCLC, and in none of the controls without pulmonary disease - thus implying a statistically significant association (P < 0.0001) between subclinical Pneumocystis infection and SCLC.

CONCLUSIONS

While the nature of this association is not clear, it nevertheless constitutes an important finding - either the infection is specifically facilitated by this tumour or induces the development of this type of neoplasm in combination with other factors. Eur J Clin Invest 2004; 34 (3): 229-335

Pneumocystis carinii pneumonia in patients with and without HIV infection

Advances in the prevention and treatment of Pneumocystis carinii pneumonia in HIV infected patients have led to a decrease in the incidence and improved outcomes. Pneumocystis carinii pneumonia continues to be problematic in non-HIV infected immunocompromised patients.

Ultrastructural and molecular characterization of Pneumocystis carinii isolated from a rhesus monkey (Macaca mulatta)

High levels of heterogeneity have been observed among isolates of Pneumocystis carinii derived from different mammalian host species. We report the characterization of P. carinii isolated from a rhesus monkey (Macaca mulatta), which was immunosuppressed as a result of infection with a chimeric simian-human immunodeficiency virus (SHIVsbg). Histopathological examination showed evidence of severe P. carinii pneumonia with a large predominance of trophozoite forms. Alveolitis consisted of typical foamy, honeycomb exudate, with only a few alveolar macrophages. The lung inflammatory response was rather moderate without type-2 pneumocyte hyperplasia or collagenosis. P. carinii organisms were sometimes observed in the bronchiolar lumen. Ultrastructurally, macaque-derived P. carinii was more similar to human- or rabbit-derived parasites than to mouse-derived P. carinii. Molecular studies were carried out on the macaque-derived P. carinii DNA at two genetic loci: the genes encoding the mitochondrial large subunit ribosomal RNA (mt LSU rRNA) and the mitochondrial small subunit ribosomal RNA (mt SSU rRNA). Comparison of the DNA sequences with those from P. carinii isolated from eight other host species demonstrated that the macaque-derived P. carinii was genetically distinct at both loci, and was more closely related to human-derived P. carinii than to P. carinii derived from non-primate sources. We propose that macaque-derived P. carinii be named Pneumocystis carinii f.sp. macacae.

Pneumocystis carinii infection in non-AIDS patients

Infection with the opportunist fungus Pneumocystis carinii remains a significant cause of morbidity and mortality in non-HIV-infected individuals immunosuppressed by a wide range of malignancies, transplantation and inflammatory conditions. Glucocorticoid use appears to be an independent risk factor for the development of Pneumocystis carinii pneumonia. Transmission from infected to susceptible patients may occur, albeit infrequently. A diagnosis of Pneumocystis carinii pneumonia may be achieved in the majority of cases by DNA detection using polymerase chain reaction on oropharyngeal mouth washes.