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.