ALL Dimorphic fungi

2 morphological states

Moulds - filamentous - in environment at low temperatures

Yeast - unicellular - form in host tissues at body temperature

Dimorphism is dependent on what

Temperature

How do conidia end up in body

By inhalation

Why does fungus switch to yeast 

To resist phagocytosis

List off dimorphic fungi (5)

Blastomycetes dermatitidis, histoplasma capsulatum, histoplasma farciminosum, coccidioides immitis, sporothric schenckii

What temps for mould and yeast forms

Mould 25

Yeast 37

What is the name of the infection by blastomyces dermatitidis

Blastomycosis

Which host does blastomycosis affect

Dogs and humans

Mould form of blastomyces dermatitidis

Septate hyphae with single conidia

Culture on SDA - methyl blue 

Yeast form blastomyces dermatitidis

Thick walled, broad based budding cells

Culture on BHI agar - gram or methyl blue

Where do blastomyces dermatitidis convert to yeast

Convert in lungs when reach alveoli

What kind of inflammation is caused by blastomyces dermatitidis

Pyogranulomatous inflammation

Blastomyces dermatitidis virulence factor

BAD1 (blastomyces adhesin 1)

Promote adhesion to cell, suppresses host response

Blastomycosis clinical signs 

Chronic cough, fever, weight loss, draining skin lesions, lameness, ocular lesions

What is the disease name of histoplasma capsulatum

Histoplasmosis

Which hosts does histoplasmosis affect

Dogs, cats and humans

Histoplasma capsulatum mould form

Septate hyphae with small conidia and sunflower like macroconidia when cultured

Culture on SDA - methyl blue 

Histoplasma capsulatum yeast form

Small oval budding least cells, can live in macrophages

Where do histoplasma capsulatum turn into yeast

Alveolar macrophages phagocytose macroconidia

Spores convert to yeast and multiply inside macrophages

How does histoplasma capsulatum spread

Via lymphatics and blood and cause granulomatous inflammation 

Histoplasmosis clinical signs

Chronic cough, dyspnea, depression, loss of weight, diarrhea, intestinal ulcers

Histoplasma capsulatum diagnosis

Cytology will show macrophages filled with small yeast with clear halos

What is the disease name of Histoplasma farciminosum

Equine histoplasmosis or Epizootic lymphangitis

What does equine histoplasmosis affect

Horses, mules and donkeys

Mould form of histoplasma farciminosum

Septate hyphae with small conidia and sunflower like macroconidia when cultured

Culture on SDA at 25

Yeast form of Histoplasma farciminosum

Small oval budding yeast cells, can live in macrophages 

How is histoplasma farciminosum transmitted

NOT INHALED

Through skin wounds or abrasions 

What does histoplasma farciminosum target

Lymphatic vessels

What does Histoplasma farciminosum cause

Nodules along lymphatics on limbs, discharge pus, lymphocutaneous lesions

What is the name of the infection caused by Coccidioides immitis

Coccidioidomycosis

What does coccidioides immitis affect

Dogs, horses

What is special about the dimorphism in coccidioides immitis

Not dimorphic but biphasic as it doesn’t transform into true yeast cells

Mould form Coccidioides immitis

Septate hyphae which fragments into arthroconidia with barrel shaped arthrospores

Spherules in coccidioides immitis

Mature spherules are filled with endospores and are found in tissue

Coccidioides immitis pathogenesis

Inhalation arthroconidia which transform into spherules in lungs

They release endospores and new spherules form 

Coccidioidomycosis clinical signs

Dogs - cough, fever, weight loss, lameness, skin lesions 

Horses - pulmonary and cutaneous forms, nasal granulomas

Diagnosis of coccidioides immitis

Microscopy to identify spherules in tissues

What is the name of the infection caused by Sporothric schenckii

Sporotrichosis

Who does Sporothric schenckii affect

Dogs, cats, horses and humans

How does Sporothric schenckii enter body

Traumatic inoculation of spores (splinters, bites, thorns…)

Mould form Sporothric schenckii

Septate hyphae with conidiophores bearing conidia

Yeast form Sporothric schenckii

Cigar shaped pleomorphic budding yeast cells

Where does Sporothric schenckii transform to yeast

Beneath the skin after inoculation 

Nodules spread along lymphatic vessels 

Clinical signs of sporotrichosis in horses, cats and dogs

Horses - nodules ulcerating yellow discharge, subcutaneous edemas 

Cats - nodular skin lesion (often on limb extremities, head and tail)

Dogs - ulcerated, crusted and alopecic cutaneous lesions over head or trunk 

Microscopy and culture Sporothric schenckii