Introduction to Mycology

Nov. 30, 2015

Bob Slinger, MD, Division of Infectious Disease, CHEO

Objectives231 Recognize the morphological characteristics

of yeasts and filamentous fungal pathogens

232 Recognize the clinical classification, common etiology and impact of human mycoses including superficial, cutaneous, sub‐cutaneous and disseminated infections.

233 Discuss the available treatment options and mechanisms of action of anti‐fungal agents including amphotericin B, the azoles, and echinocandins.

Fungi: eukaryotic= nuclear membrane

Rigid cell wall

Fungal Morphology 12 basic morphological forms: yeasts and

filaments (hyphae)

Yeasts- unicellular, round to oval, reproduce by budding

Hyphae: multi-cellular, groups of hyphae called molds (produce infectious round or oval spores called conidia, these are not yeast)

Dimorphism: fungus can exhibit either the yeast form or the filamentous form (e.g. histoplasmosis)

Hyphae Conidia (Spores) Yeasts

http://www.atsu.edu/faculty/chamberlain/Website/Lects/Fungi.htm

HyphaeIntracellular yeasts.

Who is at risk for Fungal Infections? Some fungi able to affect healthy persons Those with impaired innate immunity: eg change in

Normal bacterial flora caused by antibiotic therapyThose with impaired cellular immunity due to

diseases or medications eg neutropenia caused by leukemia or chemotherapy

for cancerThose with impaired cell mediated immunity eg due

to steroid use ( asthmatics receiving inhaled steroids) or due to diseases that affect T cells eg HIV

Classification of Fungal InfectionsAnatomically, based

on depth of invasionsuperficial cutaneous subcutaneous systemic

Host FactorsCalled

opportunistic/

non-opportunistic= Healthy host vs

non-healthy host)

Superficial Mycosesinfections limited to the

outermost layers of the skin and hair

no invasion of deeper tissues, so no inflammation and no symptoms

E.g Tinea versicolor: Malassezia species

hypopigmented macules, “spaghetti and meatballs" appearance of organism in skin scrapings

Hyphae and conidia

Case: Child with multiple pink circular lesions, itchy, scaly borders, lives on farm, no tick bites

What is diagnosis?A) Lyme disease B) BlastomycosisC) Ring wormD) Candidiasis

Cutaneous Mycoses: Dermatophytesextend deeper into epidermis, or into hair

and nailscellular immune responses may occurinflammation and symptoms (itching,

burning) caused by diseases are referred to as ringworm

identified by appearance +/- microscopic exam and culture

Tinea unguium

Tinea pedis (Athlete’s foot)

What is diagnosis? A) CoccidioidomycosisB) AspergillosisC) Tinea manusD) Sporotrichosis

Fungal culture from biospy of skin nodule: Sporotrichosis

Conidiophores and conidia of the fungus Sporothrix schenckii

http://pathmicro.med.sc.edu/mycology/mycology-6.htm

Subcutaneous Fungal Infectionse.g. Sporotrichosisinvolve the dermis, subcutaneous tissues,

muscle and fascia most infections are chronic initiated after organism is implanted in skin

by trauma spread by lymphatic systemdifficult to treat, surgical excision e.g. Sporotrichosis: Sporothrix schenckii,

from plant thorns, nodules and ulcers along lymphatics at site of inoculation

.

                                                                                                                                                

What is diagnosis?A) BartonellosisB) HistoplasmosisC) Anaplasmosis D) Blastomycosis

Systemic Fungal InfectionBlastomyces dermatitidis: Manitoba,

Northern Ontariousually lung, rare cases of localised skin or

bone lesions

Systemic Fungal Infection agents are inherently virulent, able to

evade host defencesprimary focus of infection is the lung secondary infection may occur

elsewhere in the bodyBlasto, histo, coccidioidomycosis are

top 3May also referred to as “dimorphic” or

“geographic” fungi

Systemic: Dimorphic

Grow as hyphae in environment, but as yeast in humans

Pathogenicity: ability to survive and multiply within phagocytic cells

e.g. Blastomycosis, histoplasmosisHistoplasmosis: bird or bat droppings and soil

central Canada, St. Lawrence valleylocalised lung disease in most patientsdisseminated disease may occur in

immunosuppressed patients

Case: Patient with Leukemia A 4 year old boy with

leukemia develops prolonged fever and neutropenia

Later complains of difficulty eating, and then blurring of vision

Physical exam shows pharynx on right

CT scan of abdomen and photo of fundus are abnormal

CT of abdomen showing multiple lesions. Endoscopic view on right. N Engl J Med 2007; 356:e4January 25, 2007DOI: 10.1056/NEJMicm040112

Fundus ExamWhat fungal

infection do you suspect?

A) AspergillosisB) BlastomycosisC) CandidiasisD) Leptospirosis

Opportunistic Infections: CandidaCandida infections occur

with physiological normal flora disruptions e.g. vaginal candidiasis

as a result of antibiotic therapy disrupting normal flora e.g. Pharyngeal Thrush

in neutropenic patients – disseminated candidiasis

Opportunistic InfectionsCan be yeasts ( Candida) or hyphae (molds)infections in patients with immune

deficiencies, or impaired host defences HIV Alteration of normal flora Diabetes mellitus Immunosuppressive therapy Malignancy Newborns/infants

Satellite lesions

Opportunistic Molds: Aspergillusubiquitous in environment, particularly

spreads during building renovationsinvasive disease in patients with neutropenia,

post-transplant patientsother manifestations: allergic (Allergic

Bronchopulmonary Aspergillosis)www.aspergillus.man.ac.uk

Aspergillosis: AngioinvasionHyphae in blood vessel wall, leads to

infarction

Opportunistic Molds: Mucormycosis,similar to Aspergillus, leads to severe disease in neutropenic patients

Antifungal AgentsAmphotericin B, Lipid Amphotericins

bind to ergosterol in the cell membrane, causing leakage

Azoles : block ergosterol synthesis e.g. fluconazole, voriconazole, posaconazole

Echinocandins (e.g. caspofungin): block glucan synthesis in cell wall

Echinocandins Azoles and Amphotericin

Lab Diagnosis of Fungal InfectionsSpecify on requisition when fungal cultures

required; put down names of suspected agents if possible

Lab will look for fungal elements hyphae and yeast Bacterial gram stain will show yeast (Candida) as

wellCulture on special media (some will grow on

media used for bacteria e.g. candida)Antigen and antibody tests in some cases: send

out to Provincial Lab or to USA for special tests ( can discuss these with Infectious Diseases )

Fungal Infection: Treatment and PreventionSanford Guide to Antimicrobial Therapy -

recommended for treatment informationPrevention:

antifungal medications given to some high risk patients e.g. some leukemia and transplant patients on fluconazole

infection control measures used in hospital to prevent aspergillus inhalation, masks to prevent high risk environmental exposure

Thank you