Mycology-Pneumocystis jirovecii infections

1. Name: Purshotam Kumar Sah Kanu
Roll No.: MB 1318/075
Level: M.Sc Microbiology (3rd Sem)
Central Department of Microbiology
Tribhuvan University, Kirtipur
Kathmandu, Nepal
MB 609 Systemic and Diagnostic
Mycology

2. GENUS AND SPECIESTO BE CONSIDERED
Current Name Previous Name
Pneumocystis jirovecii Pneumocystis Carinii
 In 1999, the name of the organism that causes a pneumonia in
immunocompromised humans, commonly called pneumocystis
pneumonia (PCP), was changed from Pneumocystis carinii to
Pneumocystis jirovecii.
 (One of the causative organisms for the rodent form of
pneumocystis is still called P.carinii;the other is Pneumocystis
wakefieldiae.) P.jirovecii is an opportunistic, atypical fungus that
infects immunocompromised hosts and mostly manifests as PCP.

3. Pneumocystosis
 Pneumocystis jiroveci, previously known as Pneumocystis carinii,
is the causative agent of P.carinii pneumonia (PCP).
 PCP is the most common opportunistic infection in HIV-
infected patients.

4. Pneumocystis jiroveci
 Pneumocystis is a unicellular fungus found in the respiratory
tracts of many mammals and humans.
 The genus Pneumocystis was initially mistaken for
trypanosome, then later as a protozoan.
 Biochemical analysis of the nucleic acid composition of
Pneumocystis rRNA and mitochondrial DNA in 1980s
established it as a fungus.
 The cyst wall closely resembles that of fungi.
 However, it does not have ergosterol in its membrane as
do the fungi, but instead has cholesterol.

5. Morphology
 The organism has three distinct morphologic stages:
 Trophozoites: Trophozoites are thin walled (1-5 µm) and is
irregularly shaped. It is thought to reproduce by binary
fission.
 Pre-cyst: The precyst is recognized as an intermediate stage
of the sexual phase of reproduction leading to cyst
development. It is 5 to 8 µm.

6.  Cysts: Cysts are thick walled and spherical (about 8 µm),
contain up to eight intracystic bodies.The cyst collapses,
releasing trophozoites which initiate another cycle of
multiplication, either in the same host, or in another if they
have been spread by coughing.The collapsed cysts can be seen
as irregular crescentic bodies (Fig. 75.10).
 Cysts can be stained with Gomori methenamine silver (GMS)
stain, toluidine blue, Giemsa, and calcofluor white.With
GMS stain, the organisms appear deep blue-black.

7.  Fig. 75.10: Life cycle of Pneumocystis jiroveci.The parasite enters
the lung in respiratory droplets and gets attached to alveolar
epithelium. It divides by binary fission. Some form a thick-walled
cyst withing which sporozoites develop.When mature cyst
ruptures, sporozoites are released which initiate fresh cycles of
infection

8. Epidemiology
 P.jirovecii has a worldwide distribution and most commonly
presents as pneumonia in an immunocompromised host.
 Pneumocystis is transmitted person-to-person via airborne
particles.
 Immunocompetent individuals appear to be the reservoir for
P.jirovecii,which is transmitted to immunodeficient individuals
as a pathogen.
 Most children by age 2 to 4 years have antibodies to Pneumocystis,
suggesting acquisition early in life.
 Vargas et al. showed that Pneumocystis DNA was present in 24 of
72 infants, as determined from nasopharyngeal specimens, and
that seroconversion occurred in 85% of infants by 20 months of
age.

9. Cont….
 Since the onset of the human immunodeficiency virus (HIV)
and acquired immunodeficiency syndrome (AIDS) epidemic
in the 1980s, Pneumocystis has been defined as the most
common opportunistic infection among those with HIV or
AIDS in the United States.
 The introduction of highly active antiretroviral therapy
(HAART) for patients with HIV has reduced the incidence of
disease.
 However, PCP remains a significant medical problem,
because numerous patients with HIV do not respond to
therapy, do not comply with therapy, or do not know they
are infected.

10. Cont….
 The results of DNA testing demonstrate the detection of P.
jirovecii in immunocompetent populations as well as
additional groups of patients with chronic underlying disease.

11. Cont….
 Lungs of healthy individuals are the habitat of the fungus.
Most children are believed to have been exposed to the organism by
age 3 or 4 years.
 PCP causes a mortality of 10–20% in patients with HIV
depending on the stage of the disease. It also causes a considerable
degree of mortality and morbidity in non-HIV patients.
 In developing countries many of the cases are not being reported
due to nonavailability of modern healthcare. Pneumocystis is found to
be responsible for up to 80% of HIV-infected infants with
pneumonia inAfrica.

12. Pathogenesis
 After P.jirovecii is inhaled, the trophic form of the pathogen
is believed to adhere to type I pneumocytes (thin squamous
epithelial cells of the lungs).
 The organisms replicate extracellularly while bathed in
alveolar lining fluid.
 With successful replication of the organism, the alveolar
spaces fill with an eosinophilic foamy material, which can be
detected with hematoxylin and eosin staining.

13. Cont….
 Symptoms of PCP include a nonproductive cough, low-grade
fever, dyspnea, chest tightness, and night sweats.
 In patients without HIV infection, the underlying conditions
most commonly seen as risk factors for this opportunistic
infection are asthma, chronic obstructive pulmonary disease
(COPD), cystic fibrosis, systemic lupus erythematosus
(SLE), pregnancy, rheumatoid arthritis, infection with
Epstein-Barr virus, ulcerative colitis, and high-dose
corticosteroid therapy.

14. Cont….
 During treatment with an antiretroviral medication, patients
show an improvement and an increase in CD41 cells.
 However, following a brief period of improvement, the
patients begin to deteriorate because of an exaggerated
immune response referred to as immune reconstitution
inflammatory syndrome.
 Extrapulmonary infection has been reported in 0.6% to 3%
of postmortem samples collected from patients who were
diagnosed with P.jirovecii pneumonia.

15. Cont….
 Extrapulmonary cysts have been identified in lymph nodes,
the spleen, bone marrow, and the liver, predominantly.
 Additional extrapulmonary sites include the adrenal glands,
gastrointestinal tract, genitourinary tract, thyroid, ear,
pancreas, eyes, and skin.
 Multiple sites of infection typically indicate a more rapid
disease progression and fatal outcome.

16. Immunity
 Defects in both cellular immunity and humoral immunity
allow for uncontrolled replication of the organism and
development of the disease.
 Activated alveolar macrophages without CD4 cells fail to
eradicate the organism.

17. Clinical Syndromes
 P.jiroveci causes PCP in HIV patients with their CD4 cells
count below 200/L.
 It also causes PCP in other patients with primary immune
deficiencies including hypogammaglobulinemia and severe
combined immunodeficiency, in organ (e.g., heart, lung, liver
kidney)-transplant recipients’ long-term immunosuppressive
regimens, and in patients with hematologic and
nonhematologic malignancies.
 Most cases of PCP are asymptomatic.

18. Cont..
 In symptomatic cases, sudden onset of fever, nonproductive
cough, dyspnea, and tachypnea are typical manifestations.
 Bilateral rales and ronchi are present.
 Extrapulmonary manifestations are rare.
 It occurs in AIDS patients during their advanced stage.

19. Laboratory Diagnosis
 Chest radiographs in most patients show diffuse bilateral infiltrates
extending from the perihilar region.
 Patchy asymmetric infiltrates and pneumatoceles are less common
finding.
1. Specimens:
 To establish the diagnosis of P.carinii pneumonia, specimens of
bronchoalveolar lavage, lung biopsy, or induced sputum are stained
and examined for the presence of cysts or trophozoites.
2. Staining:
 Appropriate stains include Giemsa, toluidine blue, methenamine
silver, and calcofluor white.
 A specific monoclonal antibody is available for direct fluorescent
examination of specimens.

20. Cont….
 Cyst wall stains black with methenamine silver staining.
 With the Giemsa stain, the organism appears round, and the
cyst wall is barely visible.
 Intracystic bodies are seen around the interior of the
organism.
 Fluorescent monoclonal antibody staining shows
‘honeycomb’ appearance of the cyst. P.carinii cannot be
cultured.

21. 3. Cultivation:
 P.jirovecii is very difficult to cultivate outside the lung;
therefore routine culture methods are not performed.

22. Cont..
4. Serology:
 While not clinically useful, serology has been used to
establish the prevalence of infection.
 Serological tests can be used for diagnosis in suspected cases.
 Complement fixation titers of 1:4 or more is indicative of
active disease.
 Latex agglutination test is also used.
5. Polymerase chain reaction (PCR):
 PCR for amplification of P.carinii DNA is a rapid method for
detection of early infection.

23. Treatment:
 P.jiroveci,although considered a fungus, does not respond
to treatment with antifungal agents.
 A combination of trimethoprim and sulfamethoxazole is the
drug of choice for treatment of PCP.
 Pentamidine and atovaquone are alternative drugs.
 Acute cases of pneumocystis pneumonia are treated with
trimethoprim-sulfamethoxazole (TMP-SMZ) or pentamidine
isethionate. Prophylaxis can be achieved with dailyTMP-SMZ
or aerosolized pentamidine.

24. Prevention and Control
 Chemoprophylaxis with trimethoprim and sulfamethoxazole
or aerosolized pentamidine is useful for prevention of
infection in patients with CD4 counts below 200/L.