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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
  • 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
  • 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

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

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
  • Produce flat, waxy colonies which become white and fizzy over time
  • Microscopically:
    • Septate hyphae

Histoplasmosis

  • 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
  • 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
  • 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
  • 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
  • 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

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