Fungus & Parasites Flashcards
What is the difference between definitive, intermediate, and paratenic host?
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
What is the difference between infection and infestation?
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
List representative intestinal protozoa.
Entamoeba histolytica
Giardia lamblia
Cryptosporidium sp
List representative urogenital protozoa.
trichomonas vaginalis
List representative free living protozoa.
Naegleria fowleri
Acanthamoeba
They cause CNS issues and corneal ulcers
List representative intestinal/tissue cocidium
Toxoplasma gondii (cats)
List representative blood and tissue parasites
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
What is the mechanism of pathogenicity for coccidiodes immitis?
- 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
What diseases do coccidioides immitis cause?
- pulmonary infection (60%)
- erythema nodosum 5%
- disseminated disease 5%: skin, soft tissue abscesses, bone and joint disease, meningitis
What is the immune status of coccidioides immitis infections?
primary fungal pathogen, infects both immunocompetent and immunocompromised
What are the diseases caused by Candida albicans?
Systemic: urinary tract, endocardium, meninges, blood
non systemic: mucocutaneous: ileum, esophagus, vulvovaginitis, trush
cutaneous: diaper dermatitis, nails
What is the immune status of patients with Candida albicans infections?
- Neutropenic patients more susceptible to invasive
- HIV/AIDS increases risk of mucutaeous infections
- patients undergoing antibacterial therapy more susceptible to cutaneous and mucucutaneous infection
What is the morphology of Candida albicans?
- Doesn’t have mold form, only yeast form
- can transform into pseudo hyphal and hyphal forms in response to environmental changes
What is the host immune status of patients infected with Aspergillus fumigates or flavius?
Immunocompromised only, especially neutropenic patients
What is the mechanism of pathogenicity for Aspergillus?
- Mold only
- toxins and extracellular enzymes that lead to hemorrhage and tissue necrosis and may aid in tissue invasion
What are the diseases caused by Aspergillus?
- 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
What is the route of infection for Aspergillus?
infection of lungs–>invasion of adjacent blood vessels–>speed to brain, kidney, heart, and bone
What type of immune response is more important in responding to fungal infections?
Cell mediated immunity involving Th1 responses.
-Th2 help in neutralizing fungi and controlling infection but Th1 is more important.
What are some diagnostic methods in identifying parasitic infections?
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
Describe the life cycle of Plasmodium.
- Sporozoites in infected mosquitos injected to host
- Sporozoites invade liver, mature, burst to release merozoites
- Merozoites infect RBCs, mature into gametocytes or into schizont containing merozoites which burst to infect other RBCs
- vector mosquito ingests gametocytes, mature to gametes in mosquito gut, fertilize and mature into sporozoites
How are infections with intestinal worms usually demonstrated?
parasite or its eggs seen in stool
What is the Scotch tape test used to test for?
Pinworm infection
What drug is used for the treatment of helminths?
Praziquantel
Which stage of development of Schistosome life cycle causes pipe stem fibrosis?
- chronic hyper responsiveness to soluble egg antigens
- adult worms mate in hepatic portal vessels and lay eggs
- List differences between eukaryotic fungal cell and prokaryotic bacterial cell
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
- List the 5 primary dimorphic fungi
a. Blastomycosis
b. Histoplasmosis
c. Cocidiomycosis
d. Paracoccidioidomycosis
e. Penecilliosis
- Describe the role of the host’s immunity in the encounter with fungal pathogens
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
- 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.
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.
- Discuss the problems associated with the following fungal identification methods: direct detection, culture identification, and serologic detection
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
Who is most susceptible to Candida albican infections?
HIV
antibiotic therapy use
How does the host response to Candida change depending on what form it is in?
yeast form: th1
pseudohyphae: th2
Explain the classification of fungi.
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
