Systemic Mycoses

FUNGI

Adiaspiromycosis

Haplomycosis

Emmonsia crescens
- Does not proliferate within the animal body
- Each spore develops into a thick-walled spherule called an adiaspore

Chrysosporium parvum, C. crescens

Non-contageous, pulmonary mycosis

Worldwide

Found in soil

Affects burrowing rodents and small animals

Respiratory infection

Spetate hyphae with large numbers of small, round conidia either singly or in groups on the ends of the short conidiospores can be seen

Dimorphic

Grows on Sabauraud's Dextrose agar and Blood agar

Aspergillosis

Aspergillus cleistothecia - Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath

Aspergillus in a swan - Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath

Aspergillus in vivo - Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath

Aspergillus sporing heads - Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath

Canine nasal aspergillus radiograph - Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath

Worldwide

Widely found in nature
- Colonise a wide range of substrates under different environmental conditions
- Abundant in hay, straw and grain which have heated during storage

Common laboratory contaminants

Pathogenic species include Aspergillus fumigatus, A. flavus, A. nidulans, A.niger and A. terreus

May cause primary or secondary disease
- Infection may be acute, chronic or benign

Avians:
- Diffuse infection of the air sacs
- Diffuse pneumonic form
- Nodular form involving the lungs
- Spores are inhaled
- Yellow nodules in the lungs and air sacs
- The acute form usually affects young birds and is rapidly fatal (within 24-48 hours)
  - Signs include diarrhoea, listlessness, pyrexia, loss of appetite and loss of condition
  - Sometimes convulsions may occur
  - Resembles Pullorum disease
- The chronic form usually occurs in adult birds and is sporadic, presenting with milder clinical signs

Cattle:
- Infection can cause abortion and ocular infections
- Infections involve the uterus, fetal membranes and fetal skin
- Lesions are usually up to 2mm in diameter and contain asteroid bodies with a germinated spore in the centre
  - Acute infection causes miliary lesions
  - Chronic infections causes granulomatous and calcified lesions

Horses:
- Guttural pouch mycosis common
- Infection can cause abortion
- May cause COPD

Dogs, cats and sheep:
- Infections occur, but infrequently
- lungs and nasal cavity most usually affected
- Disseminated form with granulomas and infarcts can occur in dogs
- Pulmonary and intersitital forms can occur in cats

Humans:
- Primary and secondary infections
- lungs, skin, nasal sinuses, external ear, bronchi, bones and meninges all affected
- Infection occurs most frequently in immunocompromised patients

Grows on Sabauraud's Dextrose and Blood agar
- White colonies intitially which turn green, then dark green, flat and velvety
- Colony colour varies with species

Also grows on Czapek-Dox agar and 2% malt extract agar supplemented with antibacterial antibiotics

Microscopically:
- Conidiophores with large terminal vesicles (only visible in the lungs and air sacs where there is access to oxygen)
  - Vesicle shape varies depending on the species
- Is a common contaminant so repeated tests should be done for a definitive diagnosis

Serology:
- Gel immunodiffusion for canine nasal asper

Treatment:
- Surgery
- Antifungal drugs
  - Ketoconazole, Nystatin, Amphotericin B, 5-fluorocytosine, Thiabendazole

Pathology:
- Aspergillus fumigatus causes rhinitis, respiratory tract inflammation and sinusitis
- Sometimes appears on lesions of ethmoidal haematoma

Blastomycosis

North America
- Most common in the North-Central and South-Eastern states

Caused by Blastomyces dermatitidis

Widespread in soil

Respiratory infection

Lesions start in the lungs
- Haematogenous dissemination
- Can be found in lesions in the eyes, brain, bones and genitalia
- Fatal if not treated

Lesions are also found on the skin
These may ulcerate

Granulomatous nodules

Affects mainly dogs (and humans)
- Can affect cats, horses, dolphins, ferrets and sealions but is rare in these species

Microscopically:
- Large, spherical, thick-walled cells
- Single buds connected to a mother cell by a wide base
- Double contoured effect of cells

Grows on Sabauraud's Dextrose and Blood agar
- On Sabauraud's Dextrose colonies appear moist and grey with a white cotton-like mycelium which turns tan, brown and then black
  - Septate hyphae
  - Small, oval/pyriform conidia
  - Older cultures have thickened walls
- On Blood agar colonies are creamy in colour, waxy and wrinkled
  - Thick-walled budding yeast cells can be seen

Diagnosis:
- Complement fixation test
- Falling antibody titres indicate a poor prognosis
- ELISA and counterimmunoelectrophoresis can also be used

Treatment:
- Amphotericin B
- Imidazoles

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}
Histoplasmosis in a canine spleen using silver stain
^{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}
Histoplasmosis phagocyte
^{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

Histoplasmosis tuberculate chlamydospores
^{Copyright Professor Andrew N. Rycroft, BSc, PHD, C. Biol.F.I.Biol., FRCPath}

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

The prognosis is poor in acute and disseminated cases

Zygomycosis

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

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

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

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

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

Further Links

Antifungal Drugs