Fungal Pathogens I Flashcards
Pathogenic fungi are relatively
Rare
Out of 1.5m species, 8000 plant pathogens and 600 human pathogens
Types of fungi
- Filamentous fungi
2. Yeasts
Filamentous fungi
e.g. Aspergillus
Long hyphae
Airborne spores
Yeasts
e.g. Saccharomyces cerevisiae
Unicellular
Budding
Dimorphic yeast
Switch between filamentous and yeast growth forms
e.g. Candida albicans
Response to change in environment
Human disease types
- Superficial
- Subcutaneous
- Systemic
Mycosis
Fungal disease
Superficial mycoses
Skin, hair, nails, mucous membranes
Subcutaneous mycoses
Through puncture wound
Systemic mycoses
Deep organ or disseminated
Superficial mycoses species
Dermatophytes (athletes foot)
Candida (thrush)
Malasezzia (dandruff, pityriasis versicolor)
Subcutaneous mycoses species
Chromoblastomycosis
Madurella mycetomatis (madura foot)
Rare infections
Primary pathogens
Exposure causes disease in healthy individuals
Opportunistic pathogens
Only cause disease in immunocompromised
Dermatophytes
Medical term ‘tinea’ skin
Named according to site of infection
Tinea corporis - ringworm
Tinea captis - cradle cap
Dermatophyte genera
- Microsporum
- Epidermophyton
- Trichophyton
Filamentous - soil, animals, people
Produce keritinase (virulence factor)
Dermatophytes produce
Keritinase
Can digest keratin so substrate = skin, hair, nails
Virulence factor
Dermatophytes are divided into 3 groups based on habitat:
- Anthropophilic
- Zoophilic
- Geophilic
Anthropophilic dermatophytes
Reservoir is man
Host is man
Trichophyton rubrum (chronic athletes foot)
Zoophilic dermatophytes
Reservoir is animal
Can infect man
Microsporum canis
Geophilic dermatophytes
In soil
Zoophilic species give the most
Severe inflammatory reaction
Candida albicans is present in
50% of population in mouth and GI tract
20% women in genital tract
Commensal
Candida parapsilosis causes disease in
Neonates
Most disease causing candida are in the
CTG clade
Atypical genetic code
Candida infection sites
- Mouth, genitals, skin, nails
Predisposing factors - antibiotics, pregnancy, diabetes
Subcutaneous mycoses are
Geographically limited
Wide range of organisms
Effect subcutaneous layers, though they can’t get in by themselves
Subcutaneous mycoses develop
Slowly
Difficult to treat
Invasive mycoses cause
Systemic life threatening infection
Primary and opportunistic
As many die from top 10 fungal diseases as
TB and malaria
90% of all fungal related deaths are from
Cryptococcus, candida, aspergillus, pneumocystis
Opportunistic mycoses cause the majority of
Deaths from infection
4 main primary pathogens
- Histoplasma capsulatum
- Blastomyces dermatiditis
- Parracoccidioides brasiliensis
- Coccidioides immitis
Inhalation of spores
Geographically limited
Primary fungal pathogens are all
Thermally dimorphic
Saprophytic filamentous at 25 degrees
Parasitic yeast form at 37 degrees
Primary fungal pathogens cause
Mild respiratory infection
But can progress to severe pulmonary or disseminated infection in immunocompromised (10-25% HIV patients)
Disseminated infections predisposing factors
Severely immunocompromised - neutropenia, cancer, bone and organ transplant
major burns, long term catheters, abdominal surgery
Systemic candida infection
Varies with underlying disease (33% bone marrow transplants)
30-50% mortality rate with treatment
Candida auris
Ear pathogen discovered in Japan in 2009
Reached UK in 2013
Candida auris causes both
Superficial and systemic disease
Multidrug resistant
Aspergillosis
Mainly caused by A. fumigatus, A. flavus
Inhalation of spores (sick building syndrome)
Aspergillus disease types
- Allergy (Asthma)
- Toxins
- Invasive bronchopulmonary aspergillosis (opportunistic)
- Disseminated aspergillosis 60-90% mortality
Cryptococcosis species that cause disease
Cryptococcus neoformans
C. gattii
Inhaled
Dimorphic
Capsulate yeast (capsule is a virulence factor)
Soil and avian habitats
Cryptos mainly cause
Pulmonary disease, chronic
Meningitis (disseminated)
AIDS patients
Can be an intracellular pathogen
Pnuemocystis
Pulmonary and disseminated infection AIDS 5-40% mortality VBNC (lacks genes for a.a.biosynthesis) Obligate parasite, originally classed as a protozoan
Emerging fungal diseases in animals
Psuedogymnoascus destructans
White nose syndrome in bats
Batrachochytrium dendrobatiditis
Amphibian skin disease
