Transcript محاضرة 8

Systemic mycoses
General characters
1) Fungi that cause systemic mycoses are:
o Histoplasma capsulatum causing histoplasmosis.
o Blastomyces dermatidis causing blastomycosis.
o Paracoccidiodes brasiliensis causing paracoccidiodomycosis.
o Coccidiodes immitis causing coccidiodomycosis.
2) All these fungi are DIMORPHIC:
o In the soil or culture at 25 degree: hyphae with spores.
o In the tissues or culture at 37 degree: yeast cells.
3) Infection by these fungi occurs as follows:
o These fungi grow as hyphae in the soil.
o They release spores into air.
o These spores are inhaled by man.
o Inside the human body: spores will grow as yeast
cells.
Epidemiology
 Infection by these fungi is restricted to certain
areas in the world.
 So, SYSTEMIC mycoses is called ENDEMIC mycoses.
 Histoplasmosis and blastomycosis are endemic in
vast areas that drain into Mississippi river.
 Paracoccidiodes brasiliensis is endemic in South
America especially Brazil.
 Coccidiodes immitis is endemic in Southwestern USA
(Arizona, New Mexico, South California) and North
Mexico.
Pathogenesis
 These fungi are acquired by inhalation of spores
residing in the soil. (NO PERSON TO PERSON)
 Once inhaled, spores will grow as yeast cells that
infect the lungs.
 Dissemination may occur.
Histoplasma capsulatum (non capsulated ) grows in areas contaminated
with birds & bats excreta. So, outbreaks of histoplasmosis occur during
clearing chicken coops or spelunking.
Blastomyces dermatidis is isolated from the soil and rotten wood.
Clinical picture
Asymptomatic: the majority of cases.
 Pneumonia:
o Mild pneumonia with fever & coughing.
Histoplasma lesions may heal with calcification of granuloma
o A small percent will develop severe pneumonia.
o A smaller percent will progress to chronic cavitary
pneumonia.
 Disseminated lesion: occurs in immunodeficient
patients. Spread occurs to:
o
o
o
o
o
Lung.
CNS causing meningitis.
Bone causing lytic lesions.
Skin causing ulcers.
Other organs.
NOTE THAT
Blastomycosis is the hardest to get & the hardest to have
Blastomycosis is the rarest systemic infection. Mostly
present as chronic disseminated disease.
Blastomycosis
Blastomycosis
Skin lesions resulting from the dissemination
of the fungus from the lungs
Laboratory diagnosis
Tissue is the issue
 Specimen: BIOPSY from the affected tissue.
 Direct microscopic examination of the tissue
after staining with PAS (periodic Acid Schiff),
silver to see the yeast phase.
 Culture on SDA at:
 At 25 degree: hyphae with characteristic spores.
 It converts to yeast after incubation at 37 degree.
 Serological diagnosis: detect the antibodies against
fungi.
The tests used are:
o Complement fixation test.
o Immunodiffusion test.
Serological diagnosis of blastomycosis is not reliable
because these antigens are:
o Poorly defined.
o Cross reactive with other fungi.
PAS stain showing Histoplasma capsulatum yeast cells
in liver specimen
Histoplasma capsulatum
Macroconidia and microconidia
Rough-walled macroconidia
Blastomycosis
Tissue sections showing large,
broad-base, unipolar budding
yeast-like cells
Blastomyces dermatitidis
One-celled conidia formed
on short conidiophores.
Broad based budding and
thickened cell walls and globose
shape are characteristic of the
yeast form of Blastomyces
dermatitidis
COCCIDIOIDOMYCOSIS
Disease •
Coccidioides immitis causes coccidioidomycosis.
Properties •
C. immitis is a dimorphic fungus that exists as a mold in
soil and as a spherule in tissue
Coccidioides immitis showing typical single-celled, hyaline,
rectangular to barrel-shaped, alternate arthroconidia
Transmission & Epidemiology
Coccidioide
The fungus is endemic in arid regions of the
southwestern United States and Latin America.
People who live in Central and Southern California,
Arizona, New Mexico, Western Texas, and Northern
Mexico.
 In soil, it forms hyphae with alternating arthrospores
and empty cells.
Arthrospores are very light and are carried by the
wind.
They can be inhaled and infect the lungs.
Pathogenesis of Coccidioide
In the lungs, arthrospores form spherules that are
large, have a thick, doubly refractive wall, and are
filled with endospores.
 Upon rupture of the wall, endospores are released
and differentiate to form new spherules.
The organism can spread within a person by direct
extension or via the bloodstream.
Granulomatous lesions can occur in virtually any organ
but are found primarily in bones and the central
nervous system (meningitis)
Dissemination from the lungs to other organs occurs in
people who have a defect in cell-mediated immunity.
Pathogenesis of Coccidioide
Most people who are infected by C. immitis develop
a cell-mediated (delayed hypersensitivity) immune
response that restricts the growth of the organism.
One way to determine whether a person has
produced adequate cell-mediated immunity to the
organism is to do a skin test (see below).
In general, a person who has a positive skin test
reaction has developed sufficient immunity to
prevent disseminated disease from occurring.
If, at a later time, a person's cellular immunity is
suppressed by drugs or disease, disseminated
disease can occur.
Clinical Findings of Coccidioide
 Infection of the lungs is often asymptomatic and is evident
only by a positive skin test and the presence of antibodies.
 Some infected persons have an influenza like illness with fever
and cough.
 About. 50% have changes in the lungs (infiltrates, adenopathy,
or effusions) as seen on chest x-ray.
 10% develop erythema nodosum (see below) or arthralgias.
 This syndrome is called "valley fever" or "desert
rheumatism"; it tends to subside spontaneously.
 Disseminated disease can occur in almost any organ; the
meninges, bone, and skin are important sites.
Clinical Findings of Coccidioide
The overall incidence of dissemination in persons
infected with C. imrnitis is 1%, although the
incidence in Filipinos and African Americans is 10
times higher.
Women in the third trimester of pregnancy also have
a markedly increased incidence of dissemination.
Erythema nodosum (EN) manifests as red, tender
nodules ("desert bumps") on extensor surfaces such
as the shins.
It is a delayed (cell-mediated) hypersensitivity
response to fungal antigens and thus is an indicator
of a good prognosis.
Clinical Findings of Coccidioide
There are no organisms in these lesions; they are not
a sign of disseminated disease. EN is not specific for
coccidioidomycosis; it occurs in other granulomatous
diseases, eg, histoplasmosis, tuberculosis, and
leprosy.
In infected persons, skin tests with fungal extracts
cause at least a 5mm induration 48 hours after
injection (delayed hypersensitivity reaction).
Skin tests become positive within 2-4 weeks of
infection and remain so for years but are often
negative in patients with disseminated disease.
Coccidioidomycosis
Tissue section showing typical endosporulating spherules of
C. immitis
Coccidioidomycosis
Chronic cutaneous
granulomatous lesions of the
face, neck and chin
Extension of pulmonary
coccidioidomycosis
showing a large superficial
ulcerated lesion
Laboratory Diagnosis of Coccidioide
In tissue specimens, spherules are seen
microscopically.
Cultures on Sabouraud's agar incubated at 25 °C show
hyphae with arthrospores
(Caution: Cultures are highly infectious; precautions
against inhaling arthrospores must be taken.)
Laboratory Diagnosis of Coccidioide
In serologic tests, [gM and IgG precipitins appear
within 2-4 weeks of infection and then decline in
subsequent months.
Complement-fixing antibodies occur at low titer
initially, but the titer rises greatly if dissemination
occurs
PARACOCCIDIOIDOMYCOSIS
Paracoccidioides
brasiliensis
causes
paracoccidioidomycosis, also known as South
American blastomycosis.
Properties of Paracoccidioides
 P. brasiliensis is a dimorphic fungus that exists as a
mold in soil and as a yeast in tissue.
 The yeast is thick walled with multiple buds, in
contrast to B. dermatidis, which has a single bud .
Transmission & Epidemiology of
Paracoccidioides
The spores are inhaled, and early lesions occur in the
lungs.
Asymptomatic infection is common.
Alternatively oral mucous membrane lesions, lymph
node enlargement, and sometimes dissemination to
many organs develop.
Paracoccidioidomycosis
Extensive destruction
of facial features
Ulcerated lesion on
the pharyngeal
mucosa
Ulcerated lesion on
the nasal mucosa
Laboratory Diagnosis of Paracoccidioides
In pus or tissues, yeast cells with multiple buds are
seen microscopically.
A specimen cultured for 2-4 weeks may grow typical
organisms.
Skin tests are rarely helpful.
Serologic testing shows that when significant
antibody titers (by immunodiffusion or complement
fixation) are found, active disease is present.
Paracoccidioidoes brasiliensis
Multiple, narrow base, budding yeast cells
"steering wheels" of P. brasiliensis
Paracoccidioidoes brasiliensis
Multiple, narrow base, budding yeast cells
"steering wheels" of P. brasiliensis
Summary
Agent
infection
Dissemination
Drug of choice
Blastomyces
dermatitidis
Blastomycosis
Skin and bone
Later nervous system and visceral
organs
Amphotericin B
itraconazole
Coccidioides immitis
Coccidioidomycosis
Skin, bones, joints, subcutaneous
tissues, and visceral organs
Amphotericin B
Paracoccidioidoes
brasiliensis
Paracoccidioidomycosis
Oro-nasal mucosa
latter spleen, liver, intestine and
skin
Amphotericin B +
sulfas or azoles
Histoplasma
capsulatum
Histoplasmosis
Acute pneumonia (cave disease)
Amphotericin B
Chronic pneumonia (smoker)
Disseminated
(immunocompromised)
Primary cutaneous
(lab accidents)
Systemic Mycoses
PARACOCCIDIOIDES BLASTOMYCES
HISTOPLASMA
COCCIDIOIDE