1. FUNGAL INFECTIONS and ANTIFUNGAL AGENTS

2. 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

3. 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

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

5. Fungi of medical importance: Classification
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)

6. YEAST:
Blastospore; hyphae;
pseudohyphae
MOULD:
Mycelium; hyphae

7. Some examples Yeast: Candida albicans, Cryptococcus neoformans
Mould: Aspergillus, Penicillium, Fusarium, Dermatophytes
Dimorphic: Histoplasma capsulatum

8. Types of diseases caused by human fungal pathogens
Mycotoxicosis: due to ingestion of the toxic metabolites of mould fungi eg, poisonous toadstools

9. Mycotoxins Aspergillus flavus A ochraceus Fusarium moniliforme
F graminearum
Aflatoxin(hepatic ca)
Ochratoxin (renal tox)
Fumonisins (oesophageal ca)
Deoxynivalenol (gastrointestinal toxicity)

10. 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

11. Fungi of medical importance
Candida albicans
Other Candida sp.
Cryptococcus
Dermatophytes
Aspergillus spp Zygomycetes
Dimorphic fungi
Dematiaceous fungi
Candida albicans x 6049

12. 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

13. 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

14. Some other skin fungal infections
Seborrhoeic dermatitis (Pitysporum)
Pityriasis versicolor (Pitysporum)
Candidiasis (Candida albicans)

18. 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

19. SYSTEMIC (DEEP/INVASIVE) FUNGAL INFECTIONS: MAJOR EXAMPLES
Candidiasis
Aspergillosis
Cryptococcosis
Other mould infections
Endemic mycoses
Emerging fungal infections

20. ILLUSTRATION OF SOME CASES

21. 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 don’t respond to antibiotics
An organism is grown from blood cultures which is seen on gram stain

22. Candida
blastospores (yeast)
In blood

23. Candidaemia

24. GERM TUBE

25. CANDIDIASIS:CASE 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

26. 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)

27. Distribution of Nosocomial Bloodstream Pathogens in a Large Teaching Hospital
26% 9%
5.5%
17% 6%
4.5%
19.5%
Crowe et al: Eur J Clin Microbiol Infect Dis 1998

28. Distribution of candidaemia by species (Hammersmith Hospital 1997-2000)2% 6%
44% 8%
14%
N=50
24%

29. General patterns of susceptibility of Candida species
Fluco
Itraco
Vorico
Flucy
AmB
Candins
C. albicans S
C. tropicalis
C. parapsilosis
S (- I?)
C. glabrata
SDD - R
S - I
S – I
C. krusei R
I - R
C. lusitaniae
S - R
Pappas et al CID 2004; 38:

30. Interpretive breakpoints for isolates of Candida species
MIC range (g/ml)
Drug
Susceptible
Intermediately susceptible
Resistant
Fluconazole ≤8
16-32 (SDD)
>32
Itraconazole
≤0.125
(SDD)
> 0.5
Flucytosine ≤4
8.16
>16
Pappas et al CID 2004; 38:

31. Candida biofilms (on vascular catheter): a source of candidaemia
Courtesy of Dr J Douglas

32. Clinical manifestations of candidaemia/invasive candidiasis
Infective endocarditis (heart valve surgery, IVDAs)
Endophthalmitis
Embolic skin lesions (petechial rash)
Hepatic, renal, cerebral, meningeal infection

33. 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)

34. 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

35. 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

36. NUCLEIC ACID SYNTHESIS
CELL WALL SYNTHESIS
Caspofungin
Anidualfungin
Micafungin
MEMBRANE FUNCTION
Amphotericin B
Nyststin
NUCLEIC ACID SYNTHESIS
5-Flucytosine
ERGOSTEROL SYNTHESIS
Azoles:
Fluconazole, itraconazole, voriconazole
ALLYLAMINE:
Terbinafine
Targets of action of antifungal drugs

38. 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

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

40. Mechanism of Action CANDINS Fungal cell wall Phospholipid bilayer
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

41. 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

42. Drug sensitive
cell
Azole drug
Resistance
mechanisms
Drug resistant
cell mediated
by efflux or
Mutation in
target ERG11 gene

43. 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 1980’s there have been many reports of clinical failure

44. 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

45. Conidia
Hypha and
“fruiting head”
Of Aspergillus

46. How Aspergillus infection is acquired
Airborne conidia
Alveolar macrophage

48. 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

49. ASPERGILLOSIS CASE CONT’D……...
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)

50. 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

51. 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

52. 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

53. CASE CONT’D………..
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

54. Cryptococcosis (India ink stain)

55. 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)

56. ENDEMIC MYCOSES Histoplasmosis (H capsulatum, H duboisii)
Blastomycosis (B dermatitidis)
Coccidioidomycosis (C immitis)
Paracoccidioidomycosis

57. 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

58. 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

59. 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