Fungi

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Fungi General

  • absence of chlorophyll and outer wall containing chitin
  • forms
    • moulds - hyphae (filaments) 2-10microns diameter. mass = mycelium, reproduce by sporulation, hyphae divided up by septae each cells contains nucleus 
    • yeasts - unicellular and 2-8microns in diameter, reprodice by budding 
    • some species are dimorphic 
  • cell walls consist of structural polysaccharides - eg cellulose and chitin and glycoproteins (antigens) with enzymatic functions 
  • type 4 hypersensitivity is important immune response involving CD4 T cells - fungal infections likely to be chronic, granulomas 
  • relatively few fungi are obligate pathogens - most are saprophytes or commensals 
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Drugs used systemically

  • Imidazoles - affect ergosterol synthesis
    • itraconazole
    • clotrimazole
    • enilconazole
    • ketoconazole
    • thiabendazole
  • antifungal antibiotics 
    • griseofulvin - microtubule protein synthesis 
    • natamycin - ergosterol synthesis
    • amphotericin B - binds irreversibly to ergosterol
  • fluorinated pyrimidine - blocks fungal DNA synthesis
    • flucytosine
  • iodides - unknown mechanism
    • sodium iodide IV or potassium iodide orally 
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Dermatophytosis - Obligate Pathogen

  • ringworm - caused by Trichophyton, Microsporum or Epidermophyton
  • dermatomycosis - any other fungal disease of skin
  • obligate pathogens with spores 
  • Trichophyton verrucosum - cattle adapted; Microsporum canis - SA adapted; M. gypseum - geotropic 
  • Pathogenesis - infection of stratum corneum and or hair shafts - exudation and dry crusted lesions. Aerobes - die under scab only active at edges 
  • Clinical Signs - fracture of hairs and loss of coat, crusted lesions face/neck/ears/others; fungal granuloma if ulcerated
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Dermatophytosis - Obligate Pathogen (2)

  • Diagnosis - fluorescence of affected hair under UV, microscopy - chains of arthrospores, culture on DCM or Sabouraud's agar
  • Control - isolation of affected animals, treat environment, vaccine for T. verrucosum in cattle - IM
  • Treatment - topical - natamycin/enilconazole; systemic - griseofulvin; lime sulphur shampoo; lufenuron - interferes with chitin production 
  • Prognosis - good 
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Malassezia pachydermatis - commensal, opportunisti

  • yeast, commensal in cats and dogs, esp. faeces 
  • needs defect in sebum/keratin production to become active
  • pathogenesis - proliferation causes inflammation, increased sebum production and hyperkeratosis 
  • clinical signs - erythema and crusting or scaling of the skin - doggy smelling seborrhoea, greasy surface exudate, otitis externa 
  • diagnosis - oval/bottle-shaped yeast cells in sebum or skin scale - sellotape/direct smear, cultured on sabouraud's agar, trial therapy 
  • control - controlling underlying condition
  • treatment - cleansing of skin with keratolytic shampoo, chlorhexidine with topical antifungal agent, miconazole; systemic ketoconazole/itraconazole if severe
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Candida albicans - commensal, opportunistic

  • yeast, mucous membranes, pathoggen if normal bacterial flora is suppressed by antibiotic usage or immune system compromised 
  • clinical signs - plaques of whitish exudate overlying ulcers on affected mucous membranes, discomfort and pruritis
  • diagnosis - demonstration of organism in exudate, cultured on Sabouraud's agar 
  • control - re-establishing a non-pathogenic bacterial flora - live yoghurt cultures in humans 
  • treatment - topical application of antifungal drugs, clotrimazole or nystatin; possible use of systemic antifungals, itraconaole/amphotericin B
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Aspergillus fumigatus - saprophytic, opportunistic

  • mould, respiratory tract of birds, causes granulomaous inflammatory lesions 
  • clinical signs - young birds, acute infection, high mortality; older birds, chronic infection, loss of condition and dyspnoea
  • diagnosis - culture and morphology of organism, histology of lesions, may be cultured on Sabouraud's agar
  • control - improving environment, removind sources of infection - dirty or cracked eggs 
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Aspergillosis of the nasal cavity

  • well recognised disease in dogs - sporadic in UK
  • clinical signs - unilateral nasal discharge, destruction of turbinate bones on radiography
  • diagnosis - organism demonstrated in exudate, latex agglutination test is specific and sensitive 
  • treatment - irrigation with clotrimazole, severe cases - surgical curetteage of leasion, treatment with oral ketoconazole or itraconazole 
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Cryptococcus neoformans - saprophytic, opportunist

  • yeast, causes cryptococcosis, subacute chronic mycosis of man and domestic animals, found on plants, wood, fruit, grows preferentialy on bird faeces - disease of tropics 
  • thick polysaccharide capsule - anti-phagocytic
  • pathogenesis - enters through respiratory system; invades resp, brain and meninges; immunodeficiency; chronic non-healing skin lesions possible
  • clinical signs - skin disease, nasal disease (cats), pneumonia, meningitis (dogs), generalised disease 
  • diagnosis - organisms in exudate, tissues or CSF; culture on Sabouraud's agar; accurate serological test exists 
  • treatment - systemic itraconazole or amphotericin B & flucytosine
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Sporothrix schenckii - saprophytic, opportunistic

  • sporothricosis - occurs in horses, cattle, other domesticated species and rarely humans in india, southern USA and southern Europe 
  • pathogenesis - mycelium form is a soil saprophyte, enters skin via wounds and causes exudative, ulcerative nodules containing yeast form - spreads along lymphatics
  • clinical signs - painless small cutaneous nodules which extend proximally from fetlock region, ulcerate, discharge then heal - further crops of nodules 
  • treatment - systemic iodides or ketoconazole 
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Blastomyces dermatiditis - saprophytic, opportunis

  • blastomycosis - dogs and humans in USA and Canada, also occured in Africa, Europe and Middle East; soil saprophyte, requires sandy acid soil and proximity to water 
  • pathogenesis - confined to skin or generalised - enters through resp. tract; chronic granulomatous lesion develops and metastasises to other tissues throughout body
  • clinical signs - weight loss, chronic cough, uveitis, skin lesions, lameness, pyrexia 
  • diagnosis - yeast like organism in tissues and by culture - growns as mycelium on Sabouraud's agar - 25C
  • treatment - itraconazole, flucytosine, plus amphotericin B if severe
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Histoplasma farciminosum - saphrophytic, opportuni

  • epizootic lymphangitis, equids in mediterranean, Africa and parts of Asia
  • pathogenesis - soil saprophyte, enters skin or respiratory mucous membranes and forms an ulcer. regional lymphatics become swollen and local lymph nodes ulcerate and discharge pus
  • clinical signs - exudative skin lesions, interstitial pneumonia, keratitis, weight loss; most animals recover
  • immunity - solid immunity in recovered animals - cell mediated
  • diagnosis - yeast in exudate, and culture 
  • treatment - iodides or ketoconazole 
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Histoplasma capsulatum - saprophytic, opportunisti

  • histoplasmosis, disease in cats, dogs and humans; reservoir host is bats and birds 
  • transmission by saliva, pus, urine, faeces, and vomit 
  • free living form as mycelium in soil, can act as obligate pathogen
  • pathogenesis- resp. tract as air borne conidia, spreads via reticulo-endothelial system to other organs 
  • clinical signs - chronic cough, pyrexia, hepatomegaly, splenomegaly, can affect CNS or gut
  • diagnosis - yeast in exudate, tissues stained with periodic acis - Schiff's (PAS), culture - highly infectious to man - SAFETY
  • treatment - itraconazole, flucytosine, amphotericin B if severe 
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Chronic obstructive pulmonary disease COPD

  • disease of horses - allergic response to inhaled mould spores - esp Faenia rectivirgula, Aspergillus fumigatus, Thermoactinomyces vulgaris; associated with poor ventiltion, esp straw bedding or mouldy dry hay; irritant gases/head position may increase severity
  • pathogenesis - sensitisation after viral resp. disease compromising clearence of mucus and damage to resp. epithelium - T helper cells get to fungal antien; mould spores penetrate resp. tract up to terminal bronchioles - Type 1 and 3 hypersensitivity reactions - excessive mucus production and bronchospasm
  • clinical signs - increased respiratory effort, nasal discharge, coughing, reduced performance
  • control - environmental management, bronchodilators, mucolytics 
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Aflatoxicosis - fungal toxin (mycotoxin) disease

  • caused by aflatoxins - Aspergillus flavus toxin - fungal metabolites related to dicoumarins - produced by growth of A. flavus and other fungi in animal feedstuffs - esp peanuts, cottonseed, sorghum, corn or bread; mostly cattle and pigs - can be transmitted in milk 
  • pathogenesis - hepatosis, hepatic insufficiency; mutagenic and teratogenic effects in lab anaimlas 
  • clinical signs - depression, anorexia, trembling and weakness, blindness, haemorrhagic diarrhoea, collapse, seizures and death 
  • diagnosis - assay of levels in urine, blood or tissues and feedstuffs, may take weeks for disease to show in pigs 
  • treatment - symptomatic support of hepatic insufficiency 
  • control - dont feed spoilt feedstuff 
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Rye grass staggers - fungal toxin (mycotoxin) dise

  • exposure to tremorgens - Neotyphodium lolii, grows in perennial ryegrass especially in lower outer leaf sheaths - end of summer when grass is short - sheep/cattle/horses 
  • pathogenesis - reversible biochemical toxicosis - no lesions 
  • clinical signs - fine tremor, nodding of head, bounding gait when driven - fall and make convulsive efforts to rise 
  • diagnosis - based on clinical signs, epidemiology and detection of high levels of fungal hyphae in leaf sheaths 
  • control - pasture management 
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Ergotism - fungal toxin (mycotoxin) disease

  • Claviceps purpura growth on seed heads of rye - warm, wet conditions favour growth of fungus; housed cattle fed on grain, can occur at pasture/silage fed cattle - sheep less commonly affected 
  • patho - arteriolar spasm, endothelial damage, restrict circulation 
  • clinical signs - (one of three)
    • lameness, reddening, coldness, swelling, hair loss, dry gangrene of extremeties, sloughing of necrotic tissues, diarrhoea
    • hyperthermia - drop in growth rate/milk production 
    • reproductive syndrome - embryonic loss/abortion/agalactia 
  • diagnosis - clinical and necropsy findings, ergot alkaloids in feed - chromatography/mass spectrometry
  • treatment - vasodilators control - avoiding ergotised grain/pasture 
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