Systemic Mycoses
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Aspergillosis
- Worldwide
- Common laboratory contaminants
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- 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
- 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
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- 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
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- 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
- Conidiophores with large terminal vesicles (only visible in the lungs and air sacs where there is access to oxygen)
- Serology:
- Gel immunodiffusion for canine nasal asper
- Treatment:
- Surgery
- Antifungal drugs
- Pathology:
- Aspergillus fumigatus causes rhinitis, respiratory tract inflammation and sinusitis
- Sometimes appears on lesions of ethmoidal haematoma
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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
- On Sabauraud's Dextrose colonies appear moist and grey with a white cotton-like mycelium which turns tan, brown and then black
- Diagnosis:
- Complement fixation test
- Falling antibody titres indicate a poor prognosis
- ELISA and counterimmunoelectrophoresis can also be used
- Treatment:
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
- 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
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- 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
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- 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
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Zygomycosis
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- 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
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- 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
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