Systemic Mycoses

FUNGI

Adiaspiromycosis

Aspergillosis

Blastomycosis

Coccidioidomycosis

Coccidioidomycosis spherule histopathology - Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath

• Coccidioides immitis

• Ocurs in the soil
  • Respiratory infections
  • Most commonly seen following dust storms

• Occurs in arid regions
  • E.g. South West USA and Mexico

• Non-contageous, systemic mycosis

• Affects dogs, cattle, sheep and humans

• Mainly affects the lungs
  • Dissemination can occur to other organs

• Causes nodule or granuloma formation
  • Localised
  • Gross lesions resemble Tb in cattle as are usually seen in the bronchial and mediastinal lymph nodes and occasionally lungs
  • Dissemination can occur, especially in primates and dogs, to the lungs, liver, spleen, brain and bones

• Thick-walled spherules in tissue
  • Large sporangia burst leaving 'ghost' spherules

• Saprophytic phase consists of coarse, septate, branching hyphae which fragment into thick-walled, barrel-shaped arthrospores which alternate with empty cells
  • Stained by Lactose Phenol Cotton Blue

• Grows on Sabouraud's Dextrose agar and Blood agar
  • Flat, moist colonies which develop a coarse, cotton-like aerial mycelium which varies from white to brown in colour

• Complement fixation test, latex agglutination and immunodiffusion tests can all be used
  • A positive skin test indicates exposure

Entomophthoromycisus

• Basidiobolmycosis

• Caused by Basidiobolus and Conidiobulus fungi

• Causes ulcerative granulomas in subcutaneous tissue

• Affects the oral and nasal mucous membranes

• Basidiobolus causes large lesions which may involve skin on the head, neck and chest
  • Fistulous tracts
  • Extends to lymph nodes

• Produce flat, waxy colonies which become white and fizzy over time

• Microscopically:
  • Septate hyphae

• Treatment:
  • Surgical excision
  • Amphotericin B or Ketoconazole

Histoplasmosis

Histoplasmosis in a canine spleen Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath

• Histoplasma capsulatum

• Non-contageous, systemic mycosis

• Commonly pulmonary infections occur
  • Other organs can be involved
  • Involves the reticuloendothelial system
  • Intestinal form can also occur

• Acute and chronic disease can occur

• Endemic to the USA
  • Isolated cases have been reported in Europe

• Respiratory infection
  • Infection via ingestion can also occur

• Affects dogs, cats, cattle, horses and humans

• Found in soil contaminated by bird droppings, decaying vegetation and in caves inhabited by bats

Histoplasmosis lesions in lungs Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath

• Fine, branching, septate hyphae with smooth-walled pyriform to spherical microconidia and large, thick-walled tuberculate macroconidia on simple conidiophores

• Dimorphic fungi

• Hard to demonstrate in smears as the organisms is very small
  • Stain with Giemsa or Wright and examine under oil immersion lens

• Present intracellularly in macrophages as oval yeast cells with few buds
  • Clear halo is seen around the darker staining central material

• Grows on Sabouraud's Dextrose agar
  • Creamy white colonies, turning tan coloured and then brown

• Also grows on Blood agar
  • Small, white yeast-like colonies

• Test using immunodiffusion, complement fixation and counterimmunoelectrophoresis
  • Skin test of little value as it only indicates exposure

• Treatment with Amphotericin B
  • If Amphotericin B is contra-indicated, imidazoles can be given orally

• The prognosis is poor in acute and disseminated cases

Histoplasmosis in a canine spleen using silver stain Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath Histoplasmosis phagocyte Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath Histoplasmosis tuberculate chlamydospores Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath

Zygomycosis

Mucor liver Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath

• Also known as mucormycosis, hyphomycosis and phycomycosis

• Caused by strains of Mucor, Absidia, Rhizopus and Mortierella
  • Mucor circinelloides(rare), Rhizomucor pusillus and R. meihi
  • Absidia corymbifera often causes zygomycosis in cattle and pigs
  • Rhizopus arrhizus, R. microsporus and R. rhizopodormis
  • Mortierella wolfi implicated in bovine abortion (mycotic placentitis), M. hygrophila in fowl and M.polycephala in cattle

• Occurs widely in nature

• Infection is by inhalation and ingestion

• Infects lymph nodes of the respiratory and alimentary tract
  • Lymph nodes enlarge and become caseous
  • Can cause stomach and intestinal ulcers

• Granulomatous lesions which can ulcerate

Mucor mould on the ruminal surface Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath</sup?

• Mostly localised lesions but can be generalised
• Pigs
  • Mediastinal and submandibular lymph nodes lesions
  • Embolic tumours in the liver and lungs
  • Can also be present in gastric ulcers

• Cattle
  • Bronchial, mesenteric and mediastinal lymph nodes lesions
  • Ulcers of the nasal cavity and abomasum also occur
  • Often contaminate the placenta

• Horses, dogs, cats, sheep, mink, guinea-pigs and mice can also be infected

• Microscopically:
  • Fragments of non-septate hyphae which are branched and coarse
  • Rhizomucor produce a thick, grey mycelium and have short, black, spherical sporangia
  • Mucor produce thick, colourless mycelium with no rhizoids. Globose spoangia with small spores are present and sporagiospores are simple or branched.
  • Absidia resemble Rhizopus grossly
  • Mortierella produce white, velvet colonies on Sabouraud's Dextrose and Blood agar

• Grows on Sabauraud's Dextrose agar
  • Common contaminants

• Treatment is with Amphotericin B
  • Surgery is also an option in treatment

Saprolegnia salmon Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath Saprolegnia Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath Sporangiospores Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath

Further Links

• Antifungal Drugs