Pneumocystis carinii

Katrina KittlesonSteda Lundak

Parasitology 2007

Introduction

Fungus or Protozoan??Orphan organism, phylogenic position has not yet been established

Opportunistic ParasiteSevere pathology in immunodeficient hosts

Severely malnourished newbornsOne of the initial signs of AIDS emergence

Lives in interstitial tissue of lungsRarely disseminates to spleen, lymph nodes, bone marrow, eyes

Fungus vs. Protozoan

Fungusfrom nucleic acid and biochemical analysisrRNA homologous to that found in fungistains with some fungal stains

Affinity for Grocott’s methenamine silver stain

Produces chitinhas ultrastructural characteristics similar to some fungi

Protozoanother structures similar to Toxoplasma and Plasmodiumis sensitive to a variety of antiprotozoal agents. It’s membrane properties resemble those of amebasShows surface antigenic variation which occurs in protozoa and has not been established in fungi

Geographic Distribution

Worldwide

Most children exposed by the age of 3-4 years

Commonly found in the lungs of healthy individuals, but no disease occurs

Widespread in mammals

Hosts

Humans

Pneumocystis jiroveci(i) alternate names

Pneumocystis carinii hominis

Elderly, malnourished children, primary immunodeficiency disorders, AIDS

Patients receiving cytotoxic or immunosupressive drugs for lymphoresticular cancers or transplants

Other mammals: rabbits, dogs, goats, swine, cats, chimpanzees, owl monkeys, horses

Transmission

Aerosol dropletsDirect contactCongenital infectionHousehold pets

Interspecies transmission?Reactivation of latent infection when immunocompromised

Or, new infection?

Life Cycle

Life cycle is not fully knownAsexual and sexual reproduction (CDC)Four general morphological forms in mammals

Trophozoite (has amoeboid trophozoite form)PrecystsCystsSporozoites (intracystic bodies)

Cyst (diagnostic form)chitinous membrane and 8 intracystic bodiesPore in cyst wall used for releasing sporozoites.Can be spherical or collapsed.

Life Cycle

Clinical Presentation

Causes Pneumonitis, Pneumocystis pneumonia (PCP)

Lung epithelium becomes desquamated

alveoli fill with foamy exudate containing parasites

Fever, non productive cough, breathing difficulty on exertion, respiratory failure, cyanosis

Death by asphyxia

Diagnosis

Clinical symptoms

Sputum or bronchial lavage

Special staining with toluidine blue, methenamine silver

Gram-Weigert stain for cysts

ELISA, immunofluorescence assay, DNA amplification being developed

Diagnosis

Pictures

Trophozoites in BAL material.

Cysts in BAL material

Treatments

Trimethoprim-sulfamethoxazole (TMP-SMZ)Pentamidine isethionate inhalantTreatments can be toxic and patient must be monitored closelyProphylactic treatment if CD4 count is low (<200)HAART regimen to boost immune system function, corticosteroids

Pneumocystis carinii Infection: Update and Review

Questions

Relationship with immunosupression

Taxonomic classification

Morphology

Latent infection or new infection?

Diagnosis, treatment, prophylaxis

Research into a vaccine

More information/References

Parasitology textbook

Discussion article

Familydoctor.org

Aafp.org

National Library of Medicine http://www.nlm.nih.gov/

Center for Disease Control and Prevention http://www.cdc.gov