Fungus & Parasites

Question 1

What is the difference between definitive, intermediate, and paratenic host?

Answer 1

definitive: parasite undergoes sexual reproduction in host
intermediate: parasite undergoes larval stage of development, but not sexual reproduction in host
paratenic: parasite passes through without undergoing either

Question 2

What is the difference between infection and infestation?

Answer 2

Infection: parasite in internal organs/tissues. Called Endoparasites. Common entry is oral ingestion or direct penetration of skin.
Infestation: parasites on hair, skin, clothing. Called ectoparasites. E.g. lice or mites

Question 3

List representative intestinal protozoa.

Answer 3

Entamoeba histolytica
Giardia lamblia
Cryptosporidium sp

Question 4

List representative urogenital protozoa.

Answer 4

trichomonas vaginalis

Question 5

List representative free living protozoa.

Answer 5

Naegleria fowleri
Acanthamoeba
They cause CNS issues and corneal ulcers

Question 6

List representative intestinal/tissue cocidium

Answer 6

Toxoplasma gondii (cats)

Question 7

List representative blood and tissue parasites

Answer 7

Hemoflagellates:
Trypanosoma cruzi -Chagas disease
T brucei - sleeping disease
Leishmania sp - cutaneous and mucocutaneous leishmaniasis and visceral
Malaria:
Plasmodium falciparum -most dangerous one of the plasmodiums

Question 8

What is the mechanism of pathogenicity for coccidiodes immitis?

Answer 8

• dimorphic, after inhalation, arthrospores (mold) swell and develop into spherules filled with endospores (yeast) within 48-72 hr. endospores develop into new spherules
• arthospores have anti phagocytic activity
• spherules too big for phagocytosis

Question 9

What diseases do coccidioides immitis cause?

Answer 9

• pulmonary infection (60%)
• erythema nodosum 5%
• disseminated disease 5%: skin, soft tissue abscesses, bone and joint disease, meningitis

Question 10

What is the immune status of coccidioides immitis infections?

Answer 10

primary fungal pathogen, infects both immunocompetent and immunocompromised

Question 11

What are the diseases caused by Candida albicans?

Answer 11

Systemic: urinary tract, endocardium, meninges, blood
non systemic: mucocutaneous: ileum, esophagus, vulvovaginitis, trush
cutaneous: diaper dermatitis, nails

Question 12

What is the immune status of patients with Candida albicans infections?

Answer 12

• Neutropenic patients more susceptible to invasive
• HIV/AIDS increases risk of mucutaeous infections
• patients undergoing antibacterial therapy more susceptible to cutaneous and mucucutaneous infection

Question 13

What is the morphology of Candida albicans?

Answer 13

• Doesn’t have mold form, only yeast form

- can transform into pseudo hyphal and hyphal forms in response to environmental changes

Question 14

What is the host immune status of patients infected with Aspergillus fumigates or flavius?

Answer 14

Immunocompromised only, especially neutropenic patients

Question 15

What is the mechanism of pathogenicity for Aspergillus?

Answer 15

• Mold only

- toxins and extracellular enzymes that lead to hemorrhage and tissue necrosis and may aid in tissue invasion

Question 16

What are the diseases caused by Aspergillus?

Answer 16

• Aspergillosis: disseminates and causes severe symptoms in extrapulmonary organs
• Allergic Bronchopulmonary aspergillosis ABPA
• Aspergilloma-infections of body cavities, fungus ball forms-tangled mass of fungus fibers, blood clots, and WBCs, can infect pre existing lung diseases, e.g. in abscesses

Question 17

What is the route of infection for Aspergillus?

Answer 17

infection of lungs–>invasion of adjacent blood vessels–>speed to brain, kidney, heart, and bone

Question 18

What type of immune response is more important in responding to fungal infections?

Answer 18

Cell mediated immunity involving Th1 responses.

-Th2 help in neutralizing fungi and controlling infection but Th1 is more important.

Question 19

What are some diagnostic methods in identifying parasitic infections?

Answer 19

Examples:
trypanosoma cruzi: demonstration of parasites in blood smears, lymph node aspirates, CSF fluid
Leishmania: visible in stained or cultured bone marrow and spleen samples. Serologic tests.
Plasmodium: identification in blood smears

Question 20

Describe the life cycle of Plasmodium.

Answer 20

1. Sporozoites in infected mosquitos injected to host
2. Sporozoites invade liver, mature, burst to release merozoites
3. Merozoites infect RBCs, mature into gametocytes or into schizont containing merozoites which burst to infect other RBCs
4. vector mosquito ingests gametocytes, mature to gametes in mosquito gut, fertilize and mature into sporozoites

Question 21

How are infections with intestinal worms usually demonstrated?

Answer 21

parasite or its eggs seen in stool

Question 22

What is the Scotch tape test used to test for?

Answer 22

Pinworm infection

Question 23

What drug is used for the treatment of helminths?

Answer 23

Praziquantel

Question 24

Which stage of development of Schistosome life cycle causes pipe stem fibrosis?

Answer 24

• chronic hyper responsiveness to soluble egg antigens

- adult worms mate in hepatic portal vessels and lay eggs

Question 25

1. List differences between eukaryotic fungal cell and prokaryotic bacterial cell

Answer 25

a. Difference mainly in cell nucleus, and organelles in eukaryotic cells b. Fungal cells: most fungi have cell wall, have chitin c. Bacteria: prokaryotic, peptidoglycan cell wall, sterols absent in cell membrane, endospores for survival, no dimorphism d. Fungi: eukaryotic, chitin and beta glucan in cell wall, ergosterol in cell membrane, spores sexual and asexual for reproduction, some have dimorphism

Question 26

1. List the 5 primary dimorphic fungi

Answer 26

a. Blastomycosis b. Histoplasmosis c. Cocidiomycosis d. Paracoccidioidomycosis e. Penecilliosis

Question 27

2. Describe the role of the host’s immunity in the encounter with fungal pathogens

Answer 27

a. Skin/mucosa, neutrophils, monocytes, NK cells, dendritic cells, T cells, and B cells b. Cell mediated immunity: innate i. Phagocytes with pattern recognition receptors on dendritic cells, macrophages, neutrophils ii. Fungi have PAMP c. Cell mediated: adaptive i. T cells: Th1 cells d. Humoral immunity i. Role: opsonization, prevention of adherence, toxin neutralization, antibody dependent cellular cytotoxicity (ADCC) 1. Neutralizing antibodies doesn’t play a major role

Question 28

3. List the major targets of anti fungal drugs a. Cell wall: i. Glucan synthesis ii. Chitin synthesis b. Cell membrane i. Ergosterol synthesis c. Nucleoside analog: inhibits DNA/RNA synthesis d. Griseofulvin: controls dermatophytes by binding to keratin, good for cutaneous infections. i. Inhibits cell proliferation, and is more specific.

Answer 28

a. Cell wall: i. Glucan synthesis ii. Chitin synthesis b. Cell membrane i. Ergosterol synthesis c. Nucleoside analog: inhibits DNA/RNA synthesis d. Griseofulvin: controls dermatophytes by binding to keratin, good for cutaneous infections. i. Inhibits cell proliferation, and is more specific.

Question 29

4. Discuss the problems associated with the following fungal identification methods: direct detection, culture identification, and serologic detection

Answer 29

i. Direct examination 1. Stain 2. Visualize with KOH prep under microscopy 3. Drawbacks: opportunistic infections hard to identify ii. Culture 1. Grow specimen on various media 2. Drawbacks: may take several weeks to culture, opportunistic infections hard to interpret iii. Serological methods 1. Antibodies a. Drawbacks: hard to tell if active current infection or past infection. b. For opportunistic infections-immunocompromised may not mount cellular response 2. Skin test a. Caused by cell mediated immunity b. Inject intradermally fungal antigens c. Positive skin test indicates exposure d. Drawbacks: same as antibodies 3. Antigens a. Agglutination test 4. DNA probes a. Very specific, can identify at earlier stage b. Drawback: not available everywhere

Question 30

Who is most susceptible to Candida albican infections?

Answer 30

HIV | antibiotic therapy use

Question 31

How does the host response to Candida change depending on what form it is in?

Answer 31

yeast form: th1 | pseudohyphae: th2

Question 32

Explain the classification of fungi.

Answer 32

Classification by reproductive structures: asexual and sexual spores By tissue involvement: superficial, cutaneous, muco-cutaneous, sub-cutaneous, systemic (lung or skin with possible dissemination) By host response: Primary fungi and oppportunistic fungi