Fungal Pathogens

Question 1

Phytopathogens

Answer 1

(cause rusts, smuts, rots, blights etc)

-huge crop losses

Question 2

Saprophytic fungi

Answer 2

degrade and recycle organic matter (lignin and cellulose)

Question 3

General properties of fungi

Answer 3

yeasts=unicellular, oval, 5-8um, reproduce by budding

moulds= grow as filaments or hyphae (mass of hyphae=mycelium)

Question 4

All fungi are…

Answer 4

eukaryotic, non motile, non-photosynthetic, have rigid cell walls

Question 5

Pityriasis versicolor

Answer 5

=a superficial infection caused by Malassezia species

• transformation of yeast cells to produce hyphae
• climatic factors
• asymptomatic or mildy pruritic with scaling

Question 6

Superficial Candida infections

Answer 6

• mouth, skin, nails
• oral and vaginal thrush and denture stomatitis most prevalent
• antifungal treatment
• remove gut reservoir

Question 7

Suseptible patients of candida infections-

Answer 7

macerated skin, diabetes, immune deficits

Question 8

Dermatophytes (cutaneous)

Answer 8

• seperate branching hyphae
• digest keratin (infect skin, hair, nails)
• Arthrospores in clinical specimens, microcondidia and cacrocondidia in lab culture

Question 9

Sporothrix schenkii (subcutaneous)

Answer 9

• dimorphic
• horses, cats, dogs, man
• chronic cutaneous or lymphocutaneous disease
• fungal spores enter through abrasions (gardeners)

Question 10

SYSTEMIC INFECTIONS

Answer 10

• primary pathogens
• geographically restricted
• spores inhaled, yeasts may remain viable (latent - sub-clinical) in lungs for years

Question 11

Histoplasma capsulatum (systemic)

Answer 11

• endemic in mississippi and ohio river valleys
• man, dogs, cats
• impared CMI
• granulomas in lungs
• infection of macrophages

Question 12

Opportunistic fungal infections

Answer 12

• most serious
• not restricted geographically
• caused by candida, aspergillus and cryptococcus spp.
• infects hosts with impaired defences

Question 13

systemic candida infections

Answer 13

• increasing incidence
• common nosocomial bloodstream infection
• endogenous
• some exogenous

Question 14

Aspergillus infections

Answer 14

• found in air and soil
• not part of human flora
• A.fumigatus=most prevalent airborne fungal pathogen
• produces arial hyphae bearing conidia (spores)
• conidia inhaled, normally destroyed by macrophages
• CAUSE INVASIVE DISEASE IN IMMUNOCOMPROMISED

Question 15

Host defences against aspergillus:lung

Answer 15

• inactive conidia are inhaled
• conida lodge in lower resp. tract
• conidia swell
• blocked by macrophages
• conidia germinate into hyphae
• blocked by neutrophils
• hyphae invade tissue
• hyphae invade blood vessels and disseminate

Question 16

Cryptococcus infections

Answer 16

C.neoformans is only pathogenic member of genus

• occurs worldwide
• pigeon droppings
• yeast with a thick polysaccharide capsule
• during infection, polysaccharide is solublised (used for diagnosis)
• infection follows inhalation of yeasts, then dissemination
• localise in brain and CNS –> cryptococcal meningitis

Question 17

Mucilaginous capsule

Answer 17

india ink stain - virulence factor

Question 18

Antifungal chemotherapy

Answer 18

• polyenes and azoles

- amphotericin B or fluconazole used for treating systemic infections