Lecture 9- Fungal Infections Flashcards
What is the structure of the fungal genome?
Eukaryotic, contain chromosomes
What are the two groups of fungi?
Ascomycota (majority are this)
Basidiomycota (cause cryptococcal meningitis)
How do fungi acquire their nutrients? what is the term for this?
- secrete hydrolytic enzymes
- break down polymers to be absorbed
- THEY ARE SAPROPHYTES
How do fungi replicate?
- produce larger numbers of spores
- dispersed over large distances
What are the three types of illness caused by fungal diseases?
1) Allergies
2) Mycotoxicoses
3) Mycoses
What causes fungal allergies? Give some examples of fungal allergies?
Inhalation/contact with fungal spores
- rhinitis
- dermatitis
- asthma
- allergic broncho-pulmonary aspergillosis (ABPA)
What causes Mycotoxicosis?
A toxic reaction caused by ingestion or inhalation of a mycotoxin.
What are Mycotoxins?
Mycotoxins are secondary metabolites of moulds that exert toxic effects on animals and humans
What are the symptoms of mycotoxicosis?
Breathing problems, dizziness, severe vomitting, diahorrea, dehydration, hepatic and renal failure 6 days later
What is the therapy for Mycotoxicosis?
- Gastric lavage and charcoal (for adsorption)
- Liver transplant
What is aflatoxin produced by? what does it cause
Aspergillus flavus ( one of the most natural carcinogens)–> HCC especially in people with HepB induced liver damage
Where is aflatoxin found?
It contaminates grain
What are mycoses?
A disease classified by the level of tissue affected- superficial, cutaneous, subcutaneous and systemic
What is infected in superficial mycoses? What are its symptoms?
- Skin and hair shaft
- no living tissue= no cellular response from the host
- increased oleic acid levels –> inflammation of stratum corneum & dandruff
What are cutaneous mycoses?
- Produce EC keratinases which hydrolyse keratin
- causes inflammation because of metabolic by-products
= Dermatomycoses
Give some examples of dermatomycoses
- Tinea capitis: most common paediatric dermatophyte infection
- T. pedis: athlete’s foot = most common dermatophyte
- T. corporis: (aka ringworm) treated by anti fungal cream/ oral
Tinea= worm because initially thought to be worm-like parasites
What are subcutaneous mycoses?
Chronic, localised infections of the skin and subcutaneous tissue after traumatic implantation of etiological agent.
What are the two different types of systemic mycoses?
1) Primary= able to establish infection in a normal healthy host
2) Opportunistic= require a compromised host in order to establish infection
Give an example of a superficial mycoses
Aspergillosis - high MR
Give an example of a superficial mycosis and the parts of the body it infects for different patients
Candida albicans- an opportunistic commensal
HEALTHY- GI tract, GU tract and skin
IMMUNOCOMPROMISED-
- superficial: mouth, throat, skin because of impaired epithelial barrier function (newborn and elderly)
- mucosal: oropharyngeal, oesophageal, vulvovaginal in people with HIV. New born + elderly
- systemic infections: High MR
What are the risk factors for systemic candida infections?
Chemo
Gut related surgery
Catheters
What are the 4 methods of diagnosing fungal infections?
1) Sample acquisition
2) Microscopy
3) Culture
4) Non- culture methods
Where might samples be acquired from?
- skin
- sputum
- lavage
- blood
- vag swab/ smear
- spinal fluid
- tissue biopsy
What are the pros and cons of diagnosing infections through microscopy?
PROS: rapid, cheap
CONS: need to have well established fungal infection to be able to see down the microscope
What are the disadvantages of culture methods?
- slow
- prone to contamination
- retires skilled sample collection methods
- susceptibility testing (seeing which antibiotic kill it)
What are the targets for anti fungal therapy?
1) Cell membrane (use ergosterol instead of cholesterol)
2) DNA synthesis
3) Cell wall
Name two groups of cell membrane anti-fungals and describe how they work
- Polyene antibiotic
- Azole antifungals
- inhibit synthesis of ergosterol in cell membrane
Which drugs are used for DNA synthesis inhibition?
Pyramidine analogues
- Flucytosine
Use combo therapy with azoles
What are the main drugs targeting the fungal cell wall? How does it work?
Echinocandins
- Caspofungin
Inhibits B-glucan synthase
What are fungal cell walls made out of?
Glucans and Chitin
