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Genetic variation among Pneumocystis carinii hominis isolates in recurrent pneumocystosis
S P Keely1, J R Stringer, R P Baughman
1Cincinnati VA Medical Center, Ohio, USA.
Abstract:
Pneumocystis carinii hominis is a ubiquitous organism that causes pneumonia in immunocompromised persons. Paired P. carinii hominis isolates from human immunodeficiency virus-infected persons who had two episodes of pneumocystosis were examined for genetic heterogeneity. Genetic variation was detected by sequence comparison of a portion of the mitochondrial ribosomal RNA gene. In 5 of 10 patients experiencing two episodes of pneumocystosis, genetically distinct isolates were associated with each episode. These included 4 of 6 patients whose second episode of pneumocytosis occurred > 6 months after their initial bout. The genetic data support the hypothesis that some recurrent episodes of P. carinii hominis pneumonia are caused by reinfection rather than by reactivation of latent infection.
Insights
Genetic analysis of Pneumocystis carinii hominis isolates reveals that recurrent pneumonia in immunocompromised individuals is often due to reinfection, not reactivation. This finding impacts understanding of Pneumocystis pneumonia.
Area of Science:
- Medical Mycology
- Infectious Diseases
- Immunocompromised Host Research
Background:
- Pneumocystis carinii hominis is a significant cause of pneumonia in immunocompromised individuals.
- Recurrent episodes of Pneumocystis pneumonia raise questions about their origin: reactivation or reinfection.
Purpose of the Study:
- To investigate the genetic heterogeneity of Pneumocystis carinii hominis isolates from patients with recurrent pneumocystosis.
- To determine whether recurrent Pneumocystis pneumonia is caused by distinct infections or recrudescence of a prior one.
Main Methods:
- Paired Pneumocystis carinii hominis isolates were obtained from human immunodeficiency virus-infected patients with two episodes of pneumocystosis.
- Genetic variation was assessed by sequencing a portion of the mitochondrial ribosomal RNA gene.
Main Results:
- Genetically distinct Pneumocystis carinii hominis isolates were identified in 5 out of 10 patients with two episodes of pneumocystosis.
- Distinct isolates were more common when the second episode occurred more than 6 months after the initial infection (4 of 6 patients).
Conclusions:
- The genetic data support the hypothesis that reinfection is a common cause of recurrent Pneumocystis carinii pneumonia.
- These findings suggest that strategies to prevent Pneumocystis pneumonia should consider the possibility of repeated exposure and infection.