Mycology and Parasitology

Question 1

Definition of mycology

Answer 1

Study of medically important fungi

Question 2

Types of fungi

Answer 2

Moulds:

• further divided into dermatophytes
• Multicellular

Yeasts

• unicellular

Question 3

Dermatophyte moulds infections

Answer 3

Scalp

• Tinea captis
• commonest infection in paeds population
• transfer via infected combs, towels

Nail

• tinea unguium
• increase with age

Feet

• Tinea pedis

Face (males)

• Tinea barbae

Trunk, legs arms

• Tinea corporis

Fingernail and toenails

• Tinea ungium

Groin

• Tinea cruris

Question 4

Laboratory confirmation of a dermatophyte infection

Answer 4

Microscopy

• Interpretation of slides requires experience
• In most cases, cannot tell what type of fungus is causing the infection

Molecular detection

• Sensitive but more expensive than conventional methods

Culture

• Permits species identification
• majority identified by 7-10 days

Question 5

Treatment for dermatophytes

Answer 5

• Terbinafine – inhibits squalene epoxidase resulting in accumulation of squalene & the reduction of ergosterol in fungal cells = altered cell wall function & synthesis
• Griseofulvin - binds to fungal microtubules altering mitosis & deposition of fungal cell walls
• Itraconazole - inhibits the fungal-mediated synthesis of ergosterol via its ability to inhibit cytochrome P450

Question 6

Non dermatophyte moulds

Answer 6

• Aspergiullus species
• Macroaceas noulds

Question 7

Aspergillus mode of infection

Answer 7

Inhalation

Question 8

Aspergiullus species and where they are found

Answer 8

• Found in soil, plants, air
• 200 species, only 20 cause disease
• Most disease caused by Aspergillus fumigatus and Aspergillus flavus

Question 9

Clinical manifestations of aspergillus infection

Answer 9

Immunocompromised

• Widespread growth of fungus in lungs, sinuses and dissemination to other organs & CNS
• Fever, failure to respond to broad spectum antibiotics, low grade chest pain
• CT scans reveal lung lesions, small nodules (halo sign

Immunocompromsed

• allergic sinusitis

Question 10

Mucoraceous moulds species and where found?

Answer 10

• Found in soil, on foods, air-borne
• Affect mostly immunocompromised patients
• Examples include Rhizopus, Absidia

Question 11

Clinical manifestations of mucroaceous moulds

Answer 11

• lung and nasal sinuses
• inoculation of broken skin
• fever, facial swelling, headache, nasal discharge, black lesions on roof of mouth,, black pus from eye
• often lethal

Question 12

Treatment of moulds other than dermatophytes

Answer 12

• Amphotericin B (Ambisome) – binds to ergosterol to impair cell wall function by inducing pores causing ion leakage.
• Itraconazole, Voriconazole, Posaconazole - inhibits the fungal-mediated synthesis of ergosterol via cytochrome P450 inhibition.
• Caspofungin – inhibits β(1,3)-D-Glucan synthase thereby disrupting cell wall synthesis

Question 13

Types of pathogenic yeasts

Answer 13

• Candida species
• Crytpococcus species

Question 14

Yeast infection clinical features

Answer 14

• part of normal flora
• Colonisation in warmth and moist
• Thrush
  
  • Candida albicans
• skin infections
  
  • ​Malazzia species

Question 15

Invasive candida infection features

Answer 15

• fourth most common bloodstream infection
• occurs in high risk patients
• affects:
  
  • kidneys (80%)
  • heart (prosthetic valves)
  • gastrointestinal tract
  • lungs

Question 16

Invasive cryptococcus infections

Answer 16

• Pigeon droppings
  
  • Cryptoccocus neoformans var neoformans
• Gum trees/ tropical regions
  
  • Cryptoccocus neoformans var gattii in
• Acquired via inhalation of spores
• commonly presents as menigitis.
• also, productive cough, chest pain, weight loss, fever

Question 17

Laboratory identification of yeasts

Answer 17

Cultruing on chromogenic agar

• Some yeasts have very similar colour
• Can observe if more than one yeast is present

Maldi-tof

• specific pattern
• mass spec
• 20 seconds

Question 18

Treatment of superficial candida infections

Answer 18

• Fluconazole, itraconazole – both inhibit the fungal cytochrome P450 enzyme thus inhibiting ergosterol formation
• Nystatin, Clotrimazole– binds to ergosterol forming ion pores which lead to leakage

Question 19

Treatment of invasive candida infections

Answer 19

• Amphotericin B (Ambisome) – binds to ergosterol to impair cell wall function.
• *Fluconazole
• Caspofungin – inhibits cell wall synthesis
• *Flucytosine – alters protein & DNA synthesis – resistance is common

Question 20

Types of parasites

Answer 20

Protozoa

• Sporozoa - toxoplasma gondii

Helminths

• trematodes - Shicstomatosis

Question 21

Schistosomaiasis species

Answer 21

Helminth - trematode

5 species infect humans (S species)

Question 22

Schisosome life cycle

Answer 22

1. infected person pees in the water
2. eggs make contact with fresh water
3. miracicila hatches
4. finds snail host
5. cercaria forms
6. penetrate skin
7. becomes itchy
8. go to liver and mature into schistomoluae
9. matures with female and releases eggs

Question 23

Inital symptoms of schistomatosis

Answer 23

• often asymptomatic
• within 24 hours rash develops on skin

Question 24

Chronic schistomiasis (late phase) affects

Answer 24

neurological

• eggs lodge in the CNS/brain -epilepsy

Gential

• females get ulcerative lesions of vagina, vulca, cervix (inferitility)

hepatic

• internal bleeding, usually sudden, massive and fatal

Intestinal

• inflammation of the large bowel and rectum, diarrhoea

Urinary

• ulceration of bladder, blood in urine, calcification of bladder resulting in kidney failure, bladder cancer

Question 25

Diagnosis of schistomatosis

Answer 25

1) Serology to detect egg antigens 2) Microscopy screening of stools & urine

Question 26

Treatment of Schistomatosis

Answer 26

* **Praziquantel** (alters parasite membrane permeability) – paralyses the worm * •No side effects * No effect on immature worms or eggs * Effective for all species

Question 27

Toxoplasmosis species and life cycle

Answer 27

1. Oocysts are shed in cat stools 2. Intermediate hosts include birds, rodents, cattle - become infected after ingesting contaminated soil & water. 3. Oocysts transform into tachyzoites --\> bradyzoite cysts in neural and muscle tissue

Question 28

Humans become infected with toxoplasmosis by?

Answer 28

1. eating undercooked meat of animals 2. consuming food or water contaminated with cat stools 3. blood trasnfusions

Question 29

Clinical features of toxoplasmosis

Answer 29

tissue cysts in skin, heart, brain, eyes

Question 30

Diagnosis of toxoplasmosis

Answer 30

Serology using ELISAs (IgG and IgM detection) Diagnosis of congenital infections can be achieved by detecting T. gondii DNA in amniotic fluid using molecular methods such as PCR

Question 31

Treatment of toxoplasmosis

Answer 31

Pyrimethamine