02/27g Introduction to Mycology

Question 1

What are fungi? List five characteristics, especially things that distinguish them from animals and plants

Answer 1

1) Eukaryotic
2) Non-photosynthetic (require a carbon source)
3) Have a cell wall
4) Cell membranes contains ergosterol
5) Often grow as yeasts (round) or moulds (filamentous)

Question 2

List the seven most common pathogenic fungal genera

Answer 2

1) Candidia
2) Aspergillus
3) Cryptococcus
4) Blastomyces
5) Histoplasma
6) Coccidioides
7) Dermatophytes

Question 3

What has there been an increased overall incidence of fungal infection?

Answer 3

More immunosuppressed and “at risk” patients (HIV, steroids, transplants, ICU patients)
Travel

Question 4

What are the four medical problems caused by fungi?

Answer 4

1) Allergic disease
2) Mushroom poisoning (such as amanita)
3) Mycotoxin - poisoning by secondary metabolites
4) Mycoses

Question 5

What are mycoses?

Answer 5

Infection and resulting disease caused by fungi

Question 6

What four types of fungi cause mycoses?

Answer 6

Yeasts
Moulds
Thermally dimorphic fungi
Dermatophytes

Question 7

What is the most common disease-causing yeast?

Answer 7

Candida albicans

Question 8

What two fungi are common colonizers of humans?

Answer 8

C. albicans

Dermatophytes

Question 9

What is mucosal candidiasis?

Answer 9

Locally invasive disease caused by C. albicans
Infects oral and vaginal mucosa in immunocompetent patients
Infects oral and esophageal mucosa in immunocompromised patients

Question 10

What are three manifestations of systemic candidiasis?

Answer 10

Candidemia (from IV catheters)
Intra-abdominal (abdominal surgery)
Disseminated disease (immunocompromised patients)

Question 11

What are three other Candida species that commonly cause infections, particularly in hospitals?

Answer 11

C. glabrata
C. krusei
C. parapsilosis

Question 12

What is Cryptococcosis?

Answer 12

An opportunistic infection by Cryptococcus neoformans
Causes a primary pulmonary infection with CNS tropism
Most pulmonary infections are self-limiting, but CNS disease is fatal if untreated

Question 13

How is Cryptococcosis diagnosed?

Answer 13

Culture
Lumbar puncture
Antigen tests for capsular polysaccharide

Question 14

Where in the environment is Cryptococcus neoformans often found?

Answer 14

Bird excreta
Decaying vegetation
Free-living amoebae

Question 15

What are the two forms of infectious moulds?

Answer 15

Septate

Aseptate (Zygomycetes)

Question 16

What are the two types of infectious septate moulds?

Answer 16

Non-pigmented/hyaline

Pigmented/dematiaceous

Question 17

What are four genera of hyaline moulds?

Answer 17

Aspergillus
Fusarium
Scedosporium-Pseudallescheria
Paecilomyces

Question 18

What is the most common Aspergillus species that causes human disease?

Answer 18

A. fumigatus

Question 19

What are two diagnostic morphological features of Aspergillus?

Answer 19

Uniform hyphal diameter

Regular, frequent septa

Question 20

In which patient population is Aspergillosis a major concern?

Answer 20

Very immunosuppressed patients, particularly those who are neutropenic

Question 21

How does Aspergillus enter the body? Where does it cause disease?

Answer 21

Entry via the respiratory tract

Disseminates to all organs and the CNS

Question 22

How is Aspergillosis diagnosed? List three ways

Answer 22

Chest X-ray
Histopathology
Galactomannan detection

Question 23

How is Aspergillosis treated?

Answer 23

Empiric antifungals

Pre-emptive monitoring is the most effective way to prevent infection

Question 24

What are four types of diseases that are caused by dematiaceous fungi? Name examples

Answer 24

Superficial - tinea nigra, black piedra
Cutaneous and corneal - mycotic keratitis, onychomycosis
Subcutaneous - by traumatic inoculation
Systemic - infects lungs in immunocompromised patients and spreads to other organs, particularly the CNS

Question 25

What are Zygomycetes? What do they look like?

Answer 25

Bread moulds

Have no septa and filaments have variable diameters

Question 26

What are the two most common disease-causing genera of Zygomycetes?

Answer 26

Mucor

Rhizopus

Question 27

With what three conditions is it common to see Mucormycosis?

Answer 27

Hematologic malignancy
Diabetic ketoacidosis
Iron overload syndromes

Question 28

What are the clinical manifestations of Mucormycosis?

Answer 28

Rhinocerebral
Pulmonary
Disseminated

Question 29

How is Mucormycosis treated?

Answer 29

Surgical excision - very important to do
High dose antifungals
Reconstitute immune system

Question 30

What are three species of thermally dimorphic fungi that are common to the US? In what geographical regions are they found?

Answer 30

Histoplasma capsulatum - central US (Ohio and Mississippi River valleys)
Blastomyces dermatitidis - central and eastern US, especially the Great Lakes region
Coccidioides immits - arid desert regions of the southwest US and Latin America

Question 31

What does it mean if a fungi is “thermally dimorphic”?

Answer 31

It exists in the environment as a mould, and in humans as a round/yeast-like form
Morphological transition between the two forms depends on temperature

Question 32

How are thermally dimorphic fungi usually gain access to human hosts?

Answer 32

Inhalation from the environment

Question 33

What diseases are caused by Dermatophytes?

Answer 33

Superficial infections of keratinized tissues (skin, hair, nails, feathers)

Question 34

What is the common name for tinea pedis?

Answer 34

Athlete’s foot