FUNGAL INFECTIONS and ANTIFUNGAL AGENTS

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FUNGAL INFECTIONS and ANTIFUNGAL AGENTS
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AIMS OBJECTIVES

• To provide an overview of the medically important
  fungal infections
• List and classify Antifungal drug classes with
  their modes of action
• Make some key learning points through illustrated
  cases

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The Fungal Kingdom

• Diverse groups of eukaryotic organisms that find
  nourishment from living or dead organic matter
• Their classification is based on their structural
  appearance
• During evolution relied on both sexual and
  asexual reproduction
• Both forms important for identification

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FUNGI

• Saccharomyces cerevisiae is the model organism
  for studying yeast genetics
• Many seen as harmless environmental organisms
• Of the 50-250,000 fungal species less than 200
  cause human disease and only a dozen or so on a
  regular basis

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Fungi of medical importanceClassification

• Based on the colony morphology, vegetative hyphae
  that produce a mycelium and specialised aerial
  hyphae that bear spores (conidia)
• Yeasts unicellular fungi reproduce by budding
• Moulds (filamentous) produce hyphae and mycelium
• Dimorphic grow as moulds (environment) or yeasts
  (in human host)

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YEAST Blastospore hyphae pseudohyphae
MOULD Mycelium hyphae
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Some examples

• Yeast Candida albicans, Cryptococcus neoformans
• Mould Aspergillus, Penicillium, Fusarium,
  Dermatophytes
• Dimorphic Histoplasma capsulatum

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Types of diseases caused by human fungal pathogens

• Mycotoxicosis due to ingestion of the toxic
  metabolites of mould fungi eg, poisonous
  toadstools

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Mycotoxins

• Aspergillus flavus
• A ochraceus
• Fusarium moniliforme
• F graminearum

• Aflatoxin(hepatic ca)
• Ochratoxin (renal tox)
• Fumonisins (oesophageal ca)
• Deoxynivalenol (gastrointestinal toxicity)

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Allergic lung disease

• Due to inhalation of fungal spores
• eg, A fumigatus, causing a type I or type III
  hypersensitivity reaction
• A clinical example is called allergic
  bronchopulmonary aspergillosis
• Farmers lung is another example

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Fungi of medical importance

• Candida albicans
• Other Candida sp.
• Cryptococcus
• Dermatophytes
• Aspergillus spp Zygomycetes
• Dimorphic fungi
• Dematiaceous fungi

Candida albicans x 6049
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Classification of human fungal infections

• Superficial ringworm (dermatophytes) , thrush
  (Candida species), dandruff (Pityrosporum)
• Subcutaneous involve the dermis of the skin,
  deep tissues or bone. Usually found in
  tropics/sub-tropics where caught walking barefoot
  eg, mycetoma
• Systemic due to pathogenic (Histoplasma) or
  opportunistic (Aspergillus) fungi

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Dermatophytes (the cause of RINGWORM)

• Infection of scalp (Tinea capitis), trunk (Tinea
  corporis) or nails (Tinea unguium)
• Causative fungi are Trichophyton, Epidermophyton,
  Microsporum
• Geophilic, zoophylic, anthropophylic
• Clinically red patches on skin, or scalp, scaly,
  hair loss
• Athletes foot an example

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Some other skin fungal infections

• Seborrhoeic dermatitis (Pitysporum)
• Pityriasis versicolor (Pitysporum)
• Candidiasis (Candida albicans)

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Vaginal Candidiasis (Thrush)

• Common in women of child bearing years
• Symptoms are itchy vaginal discharge
• Diagnosed by vaginal examination (white plaques)
  and microscopy/culture
• Treat topical pessary
• Or Fluconazole

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SYSTEMIC (DEEP/INVASIVE) FUNGAL INFECTIONS
MAJOR EXAMPLES

• Candidiasis
• Aspergillosis
• Cryptococcosis
• Other mould infections
• Endemic mycoses
• Emerging fungal infections

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ILLUSTRATION OF SOME CASES
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CANDIDIASIS CASE 1

• A 70-year old man has colonic surgery for
  carcinoma of colon
• Recovery is in the ITU
• He develops high fevers which dont respond to
  antibiotics
• An organism is grown from blood cultures which is
  seen on gram stain

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Candida blastospores (yeast) In blood
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Candidaemia
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GERM TUBE
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CANDIDIASISCASE 1..

• Candida albicans is identified
• He is treated with a systemic antifungal drug
  called amphotericin B intravenously
• He develops rigors each time the drug is given
  and after 7 days treatment although he is
  improving kidney failure develops and he requires
  haemofiltration
• Treatment is changed to fluconazole

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SYSTEMIC (invasive) CANDIDIASIS

• Increasing in incidence
• Risk factors are prior colonisation of mucosal
  surfaces, antibiotics, major surgery, leukaemia,
  vascular catheters
• Main pathogenic species is Candida albicans
  (others are C tropicalis, C glabrata, C krusei)

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Distribution of Nosocomial Bloodstream Pathogens
in a Large Teaching Hospital
Crowe et al Eur J Clin Microbiol Infect Dis 1998
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Distribution of candidaemia by species(Hammersmit
h Hospital 1997-2000)
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6
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8
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N50
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General patterns of susceptibility of Candida
species
Candida species Fluco Itraco Vorico Flucy AmB Candins
C. albicans S S S S S S
C. tropicalis S S S S S S
C. parapsilosis S S S S S S (- I?)
C. glabrata SDD - R SDD - R S - I S S I S
C. krusei R SDD - R S I I - R S I S
C. lusitaniae S S S S S - R S
Pappas et al CID 2004 38 161-189
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Interpretive breakpoints for isolates of Candida
species
MIC range (?g/ml) MIC range (?g/ml) MIC range (?g/ml)
Drug Susceptible Intermediately susceptible Resistant
Fluconazole 8 16-32 (SDD) gt32
Itraconazole 0.125 0.25-0.5 (SDD) gt 0.5
Flucytosine 4 8.16 gt16
Pappas et al CID 2004 38 161-189
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Candida biofilms (on vascular catheter) a source
of candidaemia
Courtesy of Dr J Douglas
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Clinical manifestations of candidaemia/invasive
candidiasis

• Infective endocarditis (heart valve surgery,
  IVDAs)
• Endophthalmitis
• Embolic skin lesions (petechial rash)
• Hepatic, renal, cerebral, meningeal infection

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ANOTHER CASE.

• Case no 2 a man who is HIV antibody positive
• He complains of difficulty with swallowing and
  retrosternal burning
• Endoscopy reveals white plaques on the
  oesophageal mucosa typical of Candida (thrush)

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FINALLY SOME LEARNING POINTS ABOUT CANDIDIASIS

• In immunocompromised relapses often occur unless
  underlying problem is removed
• Candida endocarditis often requires surgery
• Fluconazole resistance has been reported in AIDS
  cases because of the high fungal load
• Disseminated candidiasis is difficult to diagnose

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Antifungal Drugs Currently licensed for systemic
therapy

• POLYENES
• examples amphotericin B, nystatin
• Including 3 lipid formulations of amB
  (Ambisome)
• AZOLES
• Imidazoles miconazole, ketoconazole
• Triazoles fluconazole, itraconazole,
  voriconazole
• FLUORINATED PYRIMIDINE flucytosine
• ALLYLAMINE terbinafine
• CANDINS new antifungal class

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CELL WALL SYNTHESIS Caspofungin Anidualfungin Mica
fungin
MEMBRANE FUNCTION Amphotericin B Nyststin
NUCLEIC ACID SYNTHESIS 5-Flucytosine
ERGOSTEROL SYNTHESIS Azoles Fluconazole,
itraconazole, voriconazole ALLYLAMINE Terbinafin
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Targets of action of antifungal drugs
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AMPHOTERICIN B vs FLUCONAZOLE

• Polyene antifungal
• Inhibits cell membrane
• Broad spectrum
• Not absorbed
• Causes rigors
• Causes kidney damage
• Resistance rare

• Azole antifungal
• Inhibits cytochrome p450 ( ergosterol)
• Broad spectrum
• Orally absorbed
• Few side effects
• No kidney damage
• Resistance occurs

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Caspofungin

• New class
• Fungicidal
• Broad spectrum
• not Cryptococcus
• Few side effects
• o.d. regimen
• No cross resistance with azoles polyenes

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Mechanism of Action
b-(1,6)-glucan
Fungal cell wall
Phospholipid bilayer of the fungal cell membrane
b-(1,3)-glucan
Ergosterol
b-(1,3)-glucan synthase
CANDINS
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Antifungal drug resistance

• Rare in Candida albicans except in AIDS patients
• Some fungi are inherently resistant to
  antifungal aspergillus and fluconazole
• Others acquire resistance following exposure eg,
  C albicans in oropharyngeal infection in an AIDS
  patient

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Drug sensitive cell
Azole drug Resistance mechanisms
Drug resistant cell mediated by efflux
or Mutation in target ERG11 gene
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Acquired Resistance to Fluconazole in
HIV-associated Oropharyngeal Candidiasis

• Fluconazole quickly became established as the
  drug of choice
• Effective doses have ranged between 50mg and
  400mg
• Since the late 1980s there have been many
  reports of clinical failure

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ASPERGILLOSIS

• Saprophytic (aspergilloma), allergic (ABPA) and
  invasive forms of this infection
• Environmental fungus Aspergillus is the pathogen
• Acquired by inhalation
• Pulmonary disease is main feature
• Difficult to diagnose high mortality

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Conidia
Hypha and fruiting head Of Aspergillus
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How Aspergillus infection is acquired
Airborne conidia
Alveolar macrophage
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ASPERGILLOSIS CASE STUDY

• A 23-year old man suffering from acute myeloid
  leukaemia undergoes a therapeutic bone marrow
  transplant
• There follows a long period of neutropenia
• He complains of pleuritic chest pain,
  breathlessness and has a fever
• Antibiotics make no difference

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ASPERGILLOSIS CASE CONTD...

• Chest x ray is performed infiltrates
• This is followed by a CT scan
• He also undergoes bronchoscopy which reveals some
  white plaques
• The patient dies despite amphotericin B therapy
  (there was no recovery of his bone marrow)

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Risk groups for Invasive Aspergillosis

• Syndromes/treatments with severe neutropenia
• Haematological malignancy
• Chronic immunosuppression
• Solid organ transplantation
• AIDS
• Chronic granulomatous disease
• Chronic lung diseases sarcoidosis

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Another mould infection Zygomycosis

• Patients with Haematological malignancy at risk
• Diabetic patients also susceptible
• Rhinocerebral infection a feature
• Eye swelling and cellulitis also seen
• Antifungal therapy not effective
• Due to several related mould fungi eg, Rhizopus

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ANOTHER SYTEMIC FUNGAL INFECTION CRYPTOCOCCOSIS

• A man who had a kidney transplant is receiving
  immunosuppression with prednisone and
  azathioprine
• He develops headache over several days, followed
  be photophobia and neck stiffness
• Spinal fluid is obtained which reveals a high
  count of lymphocytes

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CASE CONTD..

• A special stain called India ink reveals the
  presence of round cells surrounded by haloes as
  illustrated
• These haloes are the capsule of the yeast
  Cryptococcus neoformans
• A silver stain of a skin biopsy also shows many
  yeast cells

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Cryptococcosis (India ink stain)
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CRYPTOCOCCOSIS

• A major opportunistic infection in AIDS
• Also occurs in chronically immunosuppressed
  patients eg, organ transplant
• Causes insidious meningitis with lymphocytes in
  spinal fluid
• Treatment is amphotericin B flucytosine (as in
  IDSA treatment guidelines)

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ENDEMIC MYCOSES

• Histoplasmosis (H capsulatum, H duboisii)
• Blastomycosis (B dermatitidis)
• Coccidioidomycosis (C immitis)
• Paracoccidioidomycosis

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HISTOPLASMOSIS

• Has a specific geographical distribution
• For example it is endemic in some mid west states
  in USA
• Evidence of endemicity is from skin testing of
  healthy population
• May cause a self-limiting flu-like illness in
  immunocompetent
• Severe pneumonia in immunocompromised

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Emerging fungal pathogens

• Increasingly being seen in severely
  immunocompromised
• Susceptibility to antifungals unpredictable
• Often these are environmental organisms
• Fusarium is reported to be the 4th most common
  opportunist fungus in some US centres

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SUMMARY POINTS

• Superficial fungal infections are a not uncommon
  presenting complaint in primary care
• Invasive fungal infections are associated with
  compromised patients and are seen in hospital
  practice
• Limited antifungal therapies make them more
  difficult to treat than bacterial infection