BT15 ABW BT15 Lecture Slides PDF

FUNGAL PATHOGENS Dr Gavin Paterson Senior Lecturer in Molecular and Applied Microbiology [email protected]  FUNGI One of 5 kingdoms of life (or 6 if you separate out the Archaebacteria. Eukaryotic Heterotrophic nutrition Many saprophytic Ob...

FUNGAL PATHOGENS Dr Gavin Paterson Senior Lecturer in Molecular and Applied Microbiology [email protected]  FUNGI One of 5 kingdoms of life (or 6 if you separate out the Archaebacteria. Eukaryotic Heterotrophic nutrition Many saprophytic Obtain nutrition by absorption Non-motile  Classification of Fungi Complex and confusing, disagreements and regular changes > 145 000 identified species c. 400 pathogenic species (humans and animals) Based on morphology, types of spore and sexual structures Currently 7 phyla largely accepted Fungi imperfecti – sexual stage no observed  REPRODUCTION Asexual: budding, fragmenting hyphae, conidia production. Sexual: meiosis and then fusion of two haploid nuclei. Parasexual: two diploid nuclei fuse – mitosis and haploidisation (genetic recombination without meiosis).  PATTERNS OF FUNGAL GROWTH - YEAST Larger than bacteria (5-10 m), Unicellular, Oval/round Reproduce by budding e.g. Cryptococcus Saccharomyces cerevisiae  PATTERNS OF FUNGAL GROWTH - MOULDS Filamentous Produce hyphae (some septate) Mat of hyphae = mycelium Grow parallel to surface. When they have exhausted nutrients often produce aerial hyphae.  PATTERNS OF FUNGAL GROWTH - DIMORPHS Transition between two forms dependent on environmental conditions. Yeast in tissue or at 37oC Mould outside host or lower temp e.g. Blastomyces dermatitidis & Histoplasma capsulatum  CELL WALL STRUCTURE Cell wall – polysaccharides of hexoses (glucans), chitin (polymer of N- acetylglucosamine) and mannosylated proteins (mannoproteins/mannans) Plasma membrane contains – ergosterol (different from phytosterol in plants and cholesterol in animals) FUNGAL CELL WALL  SPORULATION Sub-Phyla Asexual spores Sexual spores Chytridiomycota cleavage in a motile gametes sporangium, producing motile, uniflagellate zoospores Zygomycota Sporangium producing zygospores non-motile spores. Ascomycota conidia Ascospores from an Ascus Deuteromycota conidia Absent/unknown Basidiomycota Rare/unknown Basidiosopores on Basidia (e.g. toadstool)  Fungal Reproduction Asexual reproduction Spore- Mycelium producing structures Common method Structures critical for identification Division by mitosis not meiosis Asexual Germination Spores 2 types of asexual spore: Sporangiospores (Zygomycota only) Conidia/conidiospore  Asexual spore examples Arthroconidia Macroconidia Blastoconidia & Chlamydoconidia Phialoconidia Microconidia Conidia (conidiospores) Conidiophore Sporangiospores/. SPORANGIUM conidia Sporangium: Closed structure containing sporangiospores Arthrospores/conidia  FUNGAL INFECTIONS OF VETERINARY IMPORTANCE 1. Contagious cutaneous disease 2. Opportunist cutaneous or mucosal infections endogenously derived. 3. Systemic or tissue infections – environmental opportunist, trauma. 4. Sensitization – inhaled antigenic challenge. 5. Mycotoxic disease- Secondary metabolites of fungi  Some Important Fungi Ascomycota Microsporum sp. Mould Trichophyton sp. Mould Aspergillus sp. Mould Candida sp. Yeast Blastomyces sp. Dimorph Histoplasma sp. Dimorph Coccidioides sp. Dimorph Sporothrix sp. Dimorph Basidiomycota Cryptococcus sp. Yeast Malassezia sp. Yeast Zygomycota Mucor sp. Mould Mortierella sp. Mould  Dermatophytosis (ringworm) Lesions result from host reaction Move away from focus - circular lesion Healing centre – inflamed edge Zoonotic  PATHOGENIC DERMATOPHYTES Dermatophyte Species affected Habitat Microsporum canis Cats, dogs Zoophilic M. equinum Horses Zoophilic M. nanum Pigs Geophilic M. gypseum Horses, dogs, rodents Geophilic Trichophyton Rodents, dogs, horses & other species Zoophilic T. mentagrophytes var. European hedgehog, dogs Zoophilic erinacei T. equinum Horses Zoophilic T. verrucosum Cattle zoophilic  Dermatophytosis (ringworm) Member of phylum Ascomycota Worldwide distribution; geographical and climatic influences Relatively host-specific and contagious (can be zoonotic) Not part of normal flora but can be found in healthy animals Predisposing factors for carriage/infection: age, immune status, overcrowding, strays  Dermatophytosis Pathogenesis Source: infected animal or env ironment Transmission via direct or indirect contact Infective dose: > 100 arthrospores Arthrospores (a type of conidia) are highly adhesive to keratin structures Clinical signs seen in 1 – 3 weeks Even minor trauma predisposes to infection Trichophyton sp. on skin cells  ANTI-MYCOTIC AGENTS Polyenes - bind ergosterol, ion leakage Azoles – inhibit ergosterol synthesis Allylamines – inhibit ergosterol synthesis Echinocardins – Inhibit b-glucan synthesis Pyrimidines - Disrupts mRNA synthesis Iodides - Mechanism unknown  DERMATOPHYTE PATHOGENESIS Minor trauma (common sites) Entry of conidia, germination and proliferation in stratum corneum Hyphae invade hair follicles Penetrate hair cortex Hyphal proliferation Keratinase, elastase, collagenase Arthrospore/Conidia formation inflammation Hair weakens and breaks Exudative, serous exudation, scab  Diagnosis Hair pluckings/scrapings look for hyphae and/or conidia, stain with lactophenol cotton blue. Woods UV lamp for some M. canis infections Plate onto selective media – e.g. specific agar for fungi such as Sabouraud agar and potato-dextrose agar. Examine culture colour and microscopic shape of macro-conidia  Treatments: topical & systemic + disinfection Control: vaccines e.g. Ringvac-bovis® in cattle Live attenuated conidia www.cartoonstock.com  Yeast and Yeast-like infections Opportunists – hosts with weakened defences: antibiotic usage; innate deficiencies; previous trauma Malassezia pachydermatis Candida albicans Cryptococcus neoformans  Malassezia pachydermatis Commensal of oily skin Lipids promote growth 30% of otitis externa (with Streptococcus, Staphylococcus, Pseudomonas, Proteus) Generalised dermatoses  Diagnosis – microscopy – yeast – flask-shape. “Russian doll” appearance (From Quinn et al 1998 Clinical veterinary Microbiology)  Candida albicans A budding yeast that has a complex lifecycle including a parasexual stage: C. albicans can produce blastoconidia, chlamydospores & pseudohyphae Infections: Dog and cat: mouth, genital, enteric, pyothorax Cattle: mastitis, pneumonia, enteric, Birds: oral “thrush” Horse: genital, ulcerative stomach  (From University of Wisconsin Madison web site) blastoconidia pseudohyphae chlamydospore Localised pyogenic lesions on mucosal surfaces.  Diagnosis Direct microscopic observation Culture Germ tube test -pseudohyphae growth in serum (From University of Wisconsin Madison web site  Cryptococcus neoformans Soil saprophyte, associated with bird & bat faeces Respiratory disease with possible dissemination to other tissues Disease in cats, dogs & humans, occasionally horses Infection via inhalation or inoculation of wounds Antiphagocytic and immunosuppressive capsule. It is a facultative intracellular pathogen. Melanin pigment offers protection from oxidative killing Associated with subcutaneous or nasal granulomas  Cryptococcus neoformans Diagnosis Biopsy material India ink or PAS stain on tissues to demonstrate yeast capsule Culture sabourauds agar/aerobic/37oC/2-3 days Identification Mucoid yeast colonies Budding pattern Capsule production  Dimorphic Fungi Switch between two forms yeast form in tissue or enriched culture at 37°C mould in environment or culture at 25°C Important species include: Sporothrix schenkii, Histoplasma capsulatum, Coccidioides immitis, Blastomyces dermatitidis General pathogenesis: inhalation – primary lung lesion – dissemination – secondary lesion in specific organ systems  Dimorphic Fungi – Blastomycosis North American Blastomycosis Blastomyces dermatitidis Exotic to UK; endemic in eastern USA infection from environment Affects dogs-sporting breeds and man Aerosol - lung lesions - secondary lesions in skin & other sites. Granulomas Clinical signs: anorexia, weight loss, cough, exercise intolerance, skin lesions Poor prognosis Ubiquitous fungal/mould infections Aspergillus spp. Penicillium spp. Mucor spp. Rhizopus spp. Absidia spp.  Aspergillosis Phylum Ascomycota A. fumigatus a common pathogenic species Saprophytic fungi, ubiquitous in environment Air-borne spores; inhalation as common route of infection Opportunistic infections; localised or generalised Allergies and Mycotoxicoses (covered next) Several virulence factors, extracellular toxins, enzymes – proteases, haemolysins, but none disease specific Immune status of host determines outcome of infection Host Disease Comments Birds Brooder pneumonia Newly hatched chicks Air sacculitis Young chicks Generalised aspergillosis Older birds Horses Guttural pouch mycosis Nasal granulomas Corneal infection Secondary to trauma Recurrent airway obstruction Allergic condition; may involve Aspergillus sp Intestinal aspergillosis Chronic diarrhoea in foals; rare Cattle Mycotic abortion Sporadic Mycotic pneumonia Mycotic mastitis Iatrogenic Dogs Sino-nasal aspergillosis Disseminated aspergillosis Uncommon Otitis externa Part of mixed infection Equine Aspergillosis Rhinitis Guttural pouch mycosis The mycotic infection can invade the underlying carotid artery and be fatal due to haemorrhage. Can also affect the vagal and glossopharyngeal nerves (Horner’s syndrome)  Diagnosis of Aspergillus – Culture A. fumigatus A. niger Diagnosis of Aspergillus –imaging of conidiophores and conidia  Inhalation sensitivity Air-borne conidia - hypersensitivity Mucor spp., Penicillium spp., Aspergillus spp. Chronic obstructive pulmonary disease (COPD) - Horses (heaves) Not all sensitivities caused by fungi. Micropolyspora faeni, thermophilic actinomycete produce high levels of spores  COPD Chronic obstructive pulmonary disease (COPD) is a combination of immediate and delayed hypersensitivity reactions (type I and type IV) to inhaled (spore) allergens, The natural defence mechanisms in the airways of COPD horses becomes over-activated resulting in inflammation that leads to bronchi-constriction and over production of mucus that also contributes to airway obstruction. Environmental management is often the solution.  Mycotoxicosis Acute or chronic intoxications Usually moulds. Mycotoxins are normal metabolic by-products. Heat resistant, non- antigenic Sporadic – seasonal Most animals susceptible. Especially affects young. Low levels chronic toxicity High levels acute toxicity  Factors affecting occurrence of Mycotoxicoses Region Season Climate Fungal growth Storage or pasture Crop conditions Mycotoxin production Host factors Mycotoxicosis  Ergotism Claviceps purpurea Colonises seed head of grasses & cereals Toxins: Ergotamine & Ergometrine Acute – convulsions Chronic – gangrene due to constriction of blood vessels in the extremities  Aflatoxicosis Aspergillus flavus Aspergillus parasiticus Ingestion – absorption – liver metabolism – toxic Turkeys very susceptible Fusarium spp. Grows on corn Mycotoxin is oestrogenic Infertility, pseudopregnancy, vulval hyperaemia Impact on mammals and birds