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1

Basic characteristics of fungi

Eukaryotic
Unicellular
Aerobic
Heterotrophic
Contain rigid cell wall - chitin + cellulose
Cell membrane - contains ergosterol

2

4 Subclassifications of fungi

Saprobes - live upon dead/decaying organic matter

Symbionts - Live upon another organism, to the mutual advantage of both

Commensals - Live upon another organism with no detriment to the host

Parasites - Live upon another organism, to the detriment of the host

3

Dermatophytes

Superficial fungi that utilize keratin as a substrate for growth and energy production; grows on skin, hair, and nails

Often geophilic (from soil) or zoophilic (from animals)

4

Yeast - Basic Characteristics

Unicellular growth form

Reproduce asexually by blastoconidia (budding) or fission

Ex: Crytptococcus neoformans, Candida albicans

5

Pseudohyphae

Elongated yeast linked together like sausages; they do not have cytoplasmic connections between the compartments

Ex: Candida albicans often forms pseudohyphae

6

Mold - Basic Characteristics

Filamentous growth form in which fungus reproduces via formation of spores

Ex: Dermatophytes, Aspergillosis

7

Hyphae

Filamentous elements of mold; hyphae grow by extension and may form a mat that grows as one multicellular colony, called a mycelium

Hyphae may be septate or non-septate and may grow root-like structures (rhizoids)

8

Dimorphic

Fungi that do not have a fixed morphology but may exist in either yeast or hyphal form; transition is usually triggered by environmental changes, most often temperature

Sporothrix
Coccidioides
Histoplasmosa
Blastomyces
Paracoccidioides

(Some Can Have Both Phases)

9

Conidia

Asexual spores usually borne off of specialized aerial hyphae projections called conidophores

A conidum may be large and multi-nucleated (macroconidia) or small and unicellular (microconidia)

10

Sporangia

Asexual spores similar to macroconidia except that the endospores are enclosed in a membranous sac supported by a sporangiophore

11

Chlamydospore

Asexual spores that are round, thick-walled, and resistant to adverse environmental conditoins; may be terminal (formed at the end of a hyphae) or intercalary (formed along and within the hyphae)

12

Arthrospores

Asexual spores that develop along the hyphae (like chlamydospores) but are more "barrel shaped" - may be consecutive or alternative

13

Spherules

Large, asexual spores; similar to sporangia but without the connection to the hyphae via the sporangiophore

14

Blastoconidia

Asexual spores that form from the asymmetrical budding of yeast

15

Candida albicans

Non-dermatophyte, superficial yeast that utilizes the glucose of interstitial fluids for growth

16

Pityrosporum

Non-dermatophyte, superficial yeast that utilizes breakdown products of sebum for growth

17

Direct microscopic examination of fungi

Done by taking a scraping of affected skin or mucosa; KOH or DMSO is added to denature human material and leave the chitinous walls of fungi more visible

18

Sabouraud's Agar

Sabouraud's agar - non-selective, will grow dermatophytes and non-dermatophytes

19

Periodic Acid Schiff / Diastase (PAS/D)

Highlights the chitinous cell wall magenta/purple; most human tissue doesn't stain

20

Mechanisms that parasites use to avoid immune detection

Encapsulation
Intraluminal location
Immunosuppression
Aquisition of host antigens

21

Definitive vs. Intermediate Host

Definitive Host is the species in which the parasite undergoes sexual replication; intermediate host is any additional species in which asexual replication occurs

22

Epidemiology of Schistosomiasis

Transmitted to humans by exposure to contaminated fresh water, infecting intestinal or urinary system; causes 200,000 deaths/year, second only to malaria; 85% of affected live in sub-Saharan Africa

23

Schistosomiasis - Life Cycle

Eggs are shed in the feces or urine (S. haematobium) of infected humans, hash in fresh water, and release miracidia which infects snails

Miracidia develop into sporocysts within the snail host; free swimming cercaria are released and cercaria penetrate the skin of humans to initiate infection

Cercaria lose their tails and develop into schistosomulae in tissues of humans; they gain access to circulation and migrate to the portal blood where they mature into adult worms

Adult worms migrate to mesenteric veins or venous plexus of the bladder, where sexual mating occurs

Eggs that are produced circulate in the venous blood to the liver, and are released into the intestine or urinary bladder; from there, they are released into the environment

24

Schistosomiasis - Dermatitis

Caused by cercarial invasion into the skin; occurs within 2-3 days of infection

25

Katayama fever

Serum sickness-like illness occurring acutely (4-8 weeks) after infection with schistosomiasis; presents with lymphadenopathy and hepatosplenomegaly

Co-incident with worm maturation and onset of oviposition

26

Schistosomiasis - Chronic Stage

Granulomatous and fibrotic changes in the liver / bladder, leading to the formation of inflammatory infiltrate (primarily eosinophils)

Diarrhea, abdominal pain, and ascites in intestinal disease; hematuria and bladder cancer in urinary disease

27

Malaria - Life Cycle

Sporogony (gamete fusion to form zygotes) occurs in the mosquito and leads to the production of sporozoites in the salivary gland

Infected mosquitos bite humans and inject sporozoites into blood; sporozoites infect liver cells and replicate

After primary replication in the liver, merozoites are released into the blood; they infect erythrocyte and undergo additional asexual replication and release, causing RBC lysis

28

Which malarial species can establish dormant hepatic phase?

P. vivax
P. ovale

May cause recurrent disease

29

Malaria - effects on RBCs

Malarial replication cycle within RBCs becomes synchronized; periodic fever is every 3 or 4 days

Anemia results from lysis of RBCs and RBC phagocytosis in the stimulated RE system; hemolysis may be severe, causing hemoglobinuria

30

Malaria - Physical Exam

Jaundice, hypotension (septic shock), tachycardia, fever, hepatosplenomegaly