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

• 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

• 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

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