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

• 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

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

Zygomycosis

• 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