Question bank 2
There are four types of mycotic diseases:
1. Hypersensitivity - an allergic reaction to molds and spores. Indoor air pollution
2. Mycotoxicoses - poisoning of man and animals by feeds and food products
contaminated by fungi which produce toxins from the grain substrate.
3. Mycetismus- the ingestion of pre-formed toxin (mushroom poisoning).
4. Pathogenic fungi can exist in the yeast or mycelial form. 5. Yeasts are unicellular organisms, which reproduce by budding, and hyphae are
multicellular filamentous structures, constituted by tubular cells with cell walls.
6.The terms "hypha", "mycelium" and “mold” are frequently used interchangeable.
7. Some fungi may occur in both the yeast and mycelial forms. These are called
dimorphic fungi.
8. The dimorphic fungi have two forms:
a) YEAST - (parasitic or pathogenic form). This is the form usually seen in tissue
sections, in some exudates, or if cultured in an incubator at 37ºC.
MyceliumYeastyeast
Mycelium
Dimorphic fungi
b) MYCELIUM - (saprophytic or mold form). The form observed in nature or
when cultured at 25ºC. Conversion to the yeast form appears to be essential
for pathogenicity in the dimorphic fungi.
9. Fungi are identified by several morphological or biochemical characteristics,
including the appearance of their fruiting bodies. 10. The asexual spores may be large, macroconidia, chlamydospores or
small ,microconidia, blastospores, arthroconidia.
11. Label the picture
macroconidia & microconidia blastospores
arthrospores chlamydospores
12.Dimorphic fungi are confirmed by converting to the alternate form and some dimorphic fungi can be confirmed by molecular methods.
Blastospores
13. Fungi are ubiquitous in nature and human beings are constantly exposed to
them.
Most mycotic agents are soil saprophytes and mycotic diseases are generally
not communicable from person-to-person (occasional exceptions: Candida and some dermatophytes).
Outbreaks of fungal disease may occur, but these are due to a common
environmental exposure, not communicability.
The establishment of a mycotic infection usually depends on the size of the inoculum and on the resistance of the host.
14. The severity of the disease seems to depend mostly on the immunologic status
of the host.
15. Pathogenesis: the relative ability/degree of an organism to cause disease, It
involves interaction (and sometimes modification) of factors on the side of the host
and the fungus. Therefore:
16. Virulence: is a complex interrelationship between the infecting organism and the
host.
17.a) The complex interplay between fungal virulence factors and host defence factors will determine if a fungal infection will cause a disease.
b) Infection depends on inoculum size and the general immunity of the host.
18. Following are the Virulence factors:
Ability to adhere to host cells by way of cell wall glycoproteins Production capsules allowing them to resist phagocytosis Production of a cytokine called GM-CSF by Candida albicans that suppress the
production of complement.
Ability to acquire iron from red blood cells as in Candida albicans
Ability to damage host by secreting enzymes such as keratinase, elastase,
collagenase
Ability to resist killing by phagocytes as in dimorphic fungi
Ability to secrete mycotoxins Having a unique enzymatic capacity
Exhibiting thermal dimorphism Ability to block the cell-mediated immune defences of the host.
Exhibit Surface hydrophobicity
19. CLINICAL CLASSIFICATION OF THE MYCOSES
Superficial mycoses Subcutaneous mycoses and
Systemic mycoses
Opportunistic mycoses 20. Superficial mycoses: The Superficial mycoses (or cutaneous mycoses) are
fungal diseases that are confined to the outer layers of the skin, nail, or hair, (keratinized layers) rarely invading the deeper tissue or viscera. The fungi
involved are called dermatophytes.
21. a)Subcutaneous mycoses: it is confined to the subcutaneous tissue and
only rarely spread systemically.
b) Subcutaneous mycosis is usually form deep, ulcerated skin lesions or fungating
masses, most commonly involving the lower extremities. The causative
organisms are soil saprophytes, which are introduced through trauma to the feet or legs.
22. Systemic mycoses: it may involve deep viscera and become widely disseminated.
23. Opportunistic mycoses: it is caused by ubiquitous saprophytes and occasional pathogens that invade the tissues of those patients who have:
1) Predisposing disease like diabetes, cancer, leukemia, etc. or
2) Predisposing conditions such as agammaglobulinemia, steroid or antibiotic therapy.