Molecular epidemiology of Pneumocystis carinii pneumonia

The Prevalence of Pneumocystis jiroveci in Bronchoalveolar Lavage Specimens of Lung Transplant Recipients Examined by the Nested PCR

BACKGROUND

The use of immune suppressive drugs for organ transplant recipients predisposes them to opportunistic infections, especially by fungal agents. Pneumocystis jiroveci, as an opportunistic pathogen, endangers the patients' life in those with immune system disorders. Early detection of latent Pneumocystis infection in susceptible patients may help choose the optimal treatment for these patients.

OBJECTIVES

The aim of this study was to identify and determine the colonization of latent P. jiroveci infection among lung transplant recipients.

PATIENTS AND METHODS

This cross-sectional descriptive study was conducted on lung transplant recipients. Bronchoalveolar lavage (BAL) specimens were collected from 32 patients undergoing bronchoscopy. The samples were aseptically homogenized by 10 mM dithiothreitol, and their DNA was extracted. The mtLSUrRNA gene of P. jiroveci was amplified using nested PCR in two stages. Nested PCR was performed using external primers of pAZ-102-E and pAZ102-H followed by using the PCR product of the first stage and internal primers of pAZ-102-E and pAZ102-L2.

RESULTS

The genome of P. jiroveci was revealed by a 346 bp PCR product in the initial amplification and a 120 bp product in the nested PCR. The results showed that seven BAL specimens (21.9%) from lung transplant recipients were positive for P. jiroveci.

CONCLUSIONS

In molecular epidemiology studies, nested PCR has higher sensitivity than PCR. Results of this study support the colonization of P. jiroveci in patients receiving lung transplantation. Patients who are carriers of P. jiroveci are at a higher risk of P. jiroveci pneumonia.

Pneumocystis

Pneumocystis organisms can cause pneumonia in mammals that lack a strong immune defense. The genus Pneumocystis contains many different organisms that can be distinguished by DNA sequence analysis. These different organisms are different species of yeast-like fungi that are most closely related to the ascomycete, Schizosaccharomyces pombe. Each species of Pneumocystis appears to be specific for the mammal in which it is found. The species that infects humans is Pneumocystis jiroveci. P. jiroveci has not been found in any other mammal and the species of Pneumocystis found in other mammals have not been seen in humans. Genetic variation among P. jiroveci samples is common, suggesting that there are many strains. Strain analysis shows that adults can be infected by more than one strain, and suggests that pneumonia can be the result of infection occurring proximal to the time of disease, rather than to reactivation of dormant organisms acquired in early childhood. Nevertheless, long-term colonisation may be occurring. A large fraction of normal children and animals show evidence of infection. A Pneumocystis species that grows in rats has been shown to possess a complex genetic system for surface antigen variation, a strategy employed by other microbes that dwell in immunocompetent hosts. These findings, together with strong host specificity, suggest that Pneumocystis species may be obligate parasites. The source of infection is not clear. Pneumocystis DNA is detectable in the air, but is scarce except in environments occupied by individuals with Pneumocystis pneumonia. In a few cases, there is direct evidence of person to person transmission. In general, however, patients and their contacts have been found to have different strains of P. jiroveci.

Genetic variation in Pneumocystis carinii isolates from different geographic regions: implications for transmission

To study transmission patterns of Pneumocystis carinii pneumonia (PCP) in persons with AIDS, we evaluated P. carinii isolates from patients in five U.S. cities for variation at two independent genetic loci, the mitochondrial large subunit rRNA and dihydropteroate synthase. Fourteen unique multilocus genotypes were observed in 191 isolates that were examined at both loci. Mixed infections, accounting for 17.8% of cases, were associated with primary PCP. Genotype frequency distribution patterns varied by patients' place of diagnosis but not by place of birth. Genetic variation at the two loci suggests three probable characteristics of transmission: that most cases of PCP do not result from infections acquired early in life, that infections are actively acquired from a relatively common source (humans or the environment), and that humans, while not necessarily involved in direct infection of other humans, are nevertheless important in the transmission cycle of P. carinii f. sp. hominis.

Pneumocystis carinii pneumonia incidence and chemoprophylaxis failure in ambulatory HIV-infected patients. HIV Outpatient Study (HOPS) Investigators

BACKGROUND

Pneumocystis carinii pneumonia (PCP) remains the most frequently reported serious opportunistic infection in AIDS patients and the second highest cause of mortality among persons with AIDS in the United States, despite the availability of effective chemoprophylaxis.

METHODS

To evaluate incidence of PCP and determinants of PCP chemoprophylaxis failure, we analyzed data from 2842 patients visits to infectious diseases physicians at 10 HIV clinics (eight private and two public) in eight U.S. cities from January 1992 through June 1996 as part of the HIV Outpatient Study (HOPS). We performed a time-dependent regression analysis to examine potential determinants of PCP chemoprophylaxis failure.

RESULTS

The incidence of chemoprophylaxis failure was 4.6 PCP cases/100 person-years on chemoprophylaxis; these cases represent 67% of all incident episodes of PCP. In a multivariate analysis, the only significant predictors of chemoprophylaxis failure were the use of agents other than trimethoprim-sulfamethoxazole (TMP-SMX), history of prior PCP, and a CD4+ T-lymphocyte cell count of <50 cells/microl. Dosing or frequency of TMP-SMX did not seem to influence risk of chemoprophylaxis failure.

DISCUSSION

Chemoprophylaxis failure, especially among those with the most advanced immunosuppression or history of prior PCP, was the most significant source of new PCP cases in the HOPS cohort and thus represents one of the largest contributors to morbidity and mortality in this cohort.

PCR in diagnosis of pneumocystosis of rats

Polymerase chain reaction (PCR) is a powerful technique to detect scanty amount of DNA from living organisms. The present study intended to develop specific primers for PCR diagnosis of pneumocystosis and to evaluate diagnostic efficacy by preparation of template DNAs from invasive BAL fluid and also to screen serum or blood as a non-invasive specimen. Albino rats of Wistar or Fischer strains were experimentally infected by Pneumocystis carinii. Extracted DNAs or cell lysates of their blood, bronchoalveolar lavage fluid, and lung homogenate were used as the template DNA. Primers were synthetic oligonucleotides among 16s rDNA sequences. All of the primer combinations gave PCR products, but the primer pair of #24 and #27 gave best quality product of 666 bp. The sensitivity of PCR with lysates of BAL fluid was 57.7% but it increased to 84.6% with extracted DNAs. None of BAL lysate or DNA was positive among 13 microscopically negatives. The serum DNAs were positive only in 2 cases out of 20 morphologically positive rats. DNAs of human, rat, other parasites, yeast, and microorganisms were negative. The findings suggest that the present primers are specific but simple lysate of BAL fluid is not sensitive. PCR may be used as a routine diagnostic method of pneumocystosis if simple and rapid preparation of non-invasive clinical specimens are available.