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46 Cards in this Set
- Front
- Back
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What are teleomorphs and anamorphs?
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A teleomorph is a fungus that produces spores by sexual means. An anamorph is a person who changes into an animal to fight off brain invading aliens... wait, no, it's a fungus that reproduces by asexual spores.
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Which fungal reproduction state is usually isolated in a clinical situation?
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Anamorph (asexual)
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What are the two types of asexual fungal spores? What is the difference between the two?
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The two types of asexual fungal spores are sporangiospores and conidia. Sporangiospores are produced as sporangium structures and generally belong to the class Zygomycetes (genera Rhizopus and Mucor). Conidia are produced outside of a structure, "naked". They are seen in Aspergillus spp. and Penicillium spp.
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What are the three modes of classification for fungi?
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1. Reproductive structures
2. Tissue involvement: superficial vs. cutaneous vs. mucocutaneous vs. subcutaneous vs. systemic 3. Host defenses: Primary vs. opportunistic pathogen |
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How do yeast reproduce?
How do molds reproduce? |
Yeast reproduce by budding or fission.
Molds reproduce either sexually or asexually through spores and conidia, respectively. |
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How do fungi initially escape the immune system?
Which part of the immune response is consequently more important in fighting fungal infection? |
Fungi initially escape the immune system by evading phagocytosis.
This makes cell-mediated immunity more important than humoral immunity. |
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What protein produced by the liver is an important opsonin for fighting fungal infection?
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Mannose binding lectin
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What is the role of macrophages in a healthy person's immune response to fungal infection?
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Macrophages, activated by IFN-gamma, engulf fungal spores.
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Describe the three major methods for diagnosing a fungal infection.
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1. Direct microscopic examination of biopsy specimen: rapid and specific, preferred method
2. Culture: may take a long time, if opportunistic pathogen it is difficult to distinguish normal flora from pathogenic infection 3. Serology: skin tests for Histoplasma capsulatum, Coccidioides immitis, and Paracoccidioides brasiliensis. Agglutination for cryptococcal capsule material. ELISA for Aspergillus cell wall. |
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What is the mechanism of action of polyenes? Name two.
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Polyenes bind to ergosterol in the fungal cell membrane, disrupting osmotic integrity and causing leakage of intracellular potassium and others.
1. Amphotericin B 2. Nystatin (topical for Candida spp. infections) |
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What is the mechanism of action of azoles? Name the two sub-classes and two examples of each.
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Azoles interfere with P450-dependent 1,4-alpha-methylase, leading to diminished ergosterol synthesis and abnormal membrane permeability. They are less toxic than amphotericin, but not as effective.
1. Triazoles: fluconazole and itraconazole 2. Imidazoles: miconazole and ketoconazole |
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What is the mechanism of action of echinocandins? Against what two genera are they active? Name two.
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Echinocandins are large lipopeptides that inhibit beta-glucan synthesis in the fungal cell wall. This molecule is uniquely fungal. They are active against Aspergillus spp. and Candida spp.
1. Capsofungin 2. Micafungin |
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What is the name of the anti-fungal nucleoside analog?
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5-fluorocytosine. It is a fluorinated cytosine analog.
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What is the mechanism of action of griseofulvin?
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Griseofulvin binds microtubule-associated proteins and prevents formation of the spindle at metaphase. It is very affective against dermatophytes and has a high affinity for keratin.
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Classify the following three fungal pathogens as primary or opportunistic. Coccidioides immitis, Candida albicans, Aspergillus spp.
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Primary: Coccidioides immitis
Opportunistic: Candida albicans, Aspergillus spp. |
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Where is Coccidioides immitis found?
Briefly describe its mechanism of pathogenicity. What part of the immune response is important to fight this infection? How is it diagnosed? How is it treated? |
Coccidioides immitis is found in the soil of the southwestern US. Its arthrospores are infectious to all humans. Arthrospores swell into spherules which are too large for phagocytosis. In the lung, the spores transform into the yeast form. 60% of individuals who contract Coccidiodmycosis are asymptomatic. 5% of infections lead to erythema nodosum and another 5% are disseminated. The incidence of symptomatic disease among immunocompromised individuals is higher.
TH1 response is important for resolving infection. Coccidioidosis presents with flu-like symptoms. A 10% KOH prep of sputum reveals spherules. It can be grown at 25C on Sabouraud's agar to observe mycelia, and will transform to yeast at 37C. Serological and skin tests may also be used. It is treated with amphotericin B, itraconazole, or fluconazole. |
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Where is Candida albicans found?
Briefly describe its mechanism of pathogenicity. How is it diagnosed? Name five diseases caused by C. albicans. How are these diseases treated? |
Candida albicans is part of normal human flora of the skin, mucous membranes and GI tract, in the yeast form. It becomes pathogenic in immunocompromised patients (ie: HIV), including those whose endogenous flora is out of balance due to antibacterial therapy. When it becomes pathogenic, it transforms into a mold and forms pseudohyphae, which aid in invasion.
A 10% KOH prep of tissue will reveal budding yeast forming pseudohyphae. A skin test is unreliable. Germ tubes are formed when the yeast are incubated in animal serum. Cultures may be done on cornmeal agar to observe pseudohyphae and chlamydoconidia. 1. Thrush 2. Vaginitis 3. Skin invasion 4. Chronic mucocutaneous candidiasis (T-cll deficient patients) 5. Hematogenous candidiasis Treatment: amphotericin B, caspofungin, fluconazole (C. krusei is resistant), 5-fluorocytosine |
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Where is Aspergillus spp. found?
Who does it infect? Describe its mechanism of pathogenicity. Name three diseases caused by Aspergillus spp. How are these diseases diagnosed? Treatment? |
Aspergillus spp. is ubiquitous in the environment. It infects only immunocompromised patients and always remains in its mold form.
Components of its cell wall aid in adherence to the host, and cell wall pigments interfere with phagocytosis. The gliotoxin that it produces slows the ciliary beat of the respiratory epithelium. It also produces other toxins that lead to tissue necrosis and hemorrhage. It spreads to the brain, kidneys, liver, heart, and bones by invading blood vessels. 1. Aspergillosis: pulmonayr, may disseminate to extra-pulmonary organs. 2. Allergic bronchopulmonary aspergillosis 3. Aspergilloma Chest x-ray shows fungus balls, and CTs of other organs may help. 10% KOH prep of sputum shows Y-shaped filaments. Galactomannan may be detected by ELISA. Treatment: IV amphotericin B, caspofungin, surgical removal of fungus balls |
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Describe the basic immune response to fungal infection.
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Dendritic cells phagocytose fungi by a variety of mechanisms, undergo functional maturation (increased MHC II, IL production) and educate protective TH1 cells and non-protective TH2 cells.
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What is the drug of choice for treatment of schistosomiasis and many other helminths?
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Praziquantel
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In general, what does helminth mean?
How are helminths classified? |
Helminth means parasitic worm.
Based on external shape and organs that they inhabit |
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What are the three major groups of helminths?
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1. Flukes: schistosomes
2. Tapeworks: beef and pork tapeworks 3. Roundworms: ascaris, hookworm, whipworm, pinworm |
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Describe some general characteristics of helminths (size, lifespan, etc).
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Helminths may be 1mm-several meters long. They may live for many years and are distributed around the world, although there is a higher infection rate in poor countries. Infection may be symptomatic or asymptomatic.
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What is an easy way for a lab to diagnose the type of worm causing an infection?
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Eggs that are excreted in feces are very characteristic of specific worms.
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Which roundworm is the most common in the US? Which is most common worldwide?
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Pinworm (Enterobius vermicularis)
Roundworm (Ascaris lumbricoides) |
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How is pinworm (Enterobius vermicularis) infection diagnosed?
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Peri-anal swab with Scotch tape
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Describe the infectivity and life cycle of Ascaris lumbricoides.
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Ascaris lumbricoides (roundworm) is ingested orally and then it penetrates the intestinal wall to get into the blood stream, infecting the lung, liver and heart. In the lung it develops further until it is coughed up and re-swallowed. It remains in the intestine for up to a year and lays up to 200,000 eggs/day. A bolus of worms (caused by reinfection, not reproduction) may perforate the intestine and occlude the appendix.
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Describe the infectivity and life cycle of Necator americanus (hookworm).
Describe the associated symptoms. |
Necator americanus penetrates the skin and gets into the blood stream, then infects the lungs. It is then coughed up and re-swallowed, and develops into an adult worm in the small intestine. It feeds on blood.
Rash, pneumonitis, nausea, vomiting, diarrhea, anemia, bleeding |
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Who does Enterobius vermicularis (pinworm) primarily infect?
Where might eggs be found? |
Enterobius vermicularis primarily infects children.
Eggs can survive in dust (ie: under bed, on window sills). |
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Describe the infectivity and life cycle of Enterobius vermicularis.
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Infection occurs with ingestion of eggs. The worm lives in the intestine. Often at night or early in the morning, the female migrates to the anus and lays 10-20K eggs, causing severe itching. The host will then scratch and get eggs under the fingernails and spread infection to others.
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Describe the infectivity of Trichuris trichiuria (whipworm).
Describe associated symptoms. |
Trichuris trichiuria eggs are ingested on dried goods or vegetables. It partially burrows into the intestinal wall.
With a light worm burden (<80 worms, there may be no symptoms. Heavy worm burden leads to pain in the lower abdomen and bloody diarrhea. |
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What is the common name for schistosomes?
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Blood flukes
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Are the pathogenic effects of flukes mainly due to eggs or worms?
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Both- it depends on the species. Liver flukes cause damage to the bile duct, which schistosomes cause damage due to granuloma formation around eggs.
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What drug is used to treat fasciola hepatica?
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Bithional
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What are the three major schistosome species to infect humans?
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S. mansoni
S. japonica S. haemotobium |
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Where in the host do schistosomes live?
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In the lumen of the blood vessel. The female lives within the tegumental fold of the male.
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Describe the life cycle of schistosomes.
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The male and female mate in the hepatic portal vessels. S. japonicum and S. mansoni live in mesenteric venules. S. haemotobium lives in vessels around the bladder. They lay 300-3,000 eggs/day for 4-35 years. The eggs are passed in the urine or stool, then hatch into the miracidium (larval) stage in freshwater. Miracidia penetrate snail soft tissue and differentiate into sporocysts which produce thousands of cercarie which emerge from the snail and seek a vertebrate host. Cercariae penetrate the skin of the host and differentiate into schistosomula, which migrate into the vasculature of the heart, lungs, and hepatic portal system.
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What happens to some schistosome eggs that are not excreted?
What is the result of this phenomenon? |
Some eggs are swept into the hepatic lobules, eliciting an immune response, which results in granulomas and "clay pipe fibrosis".
As a result, portal hypertension, hepatomegaly, splenomegaly, and esophageal varices often occur. (Hydronephrosis and uremia with haemotobium.) |
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What are the three major syndromes of schistosomiasis?
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1. Schistosomiasis dermatitis
2. Acute schistosomiasis 3. Chronic schistosomiasis |
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Why are schistosomes difficult for the immune system to kill?
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The varying life stages of the schistosomes have different antigenic composition, making it difficult for the immune system to keep up.
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In what part of the body are these protozoa medically important?
Entamoeba histolytica, Giardia lamblia, Crptosporidium sp. |
Intestines
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In what part of the body is this protozoan medically important?
Trichomonas vaginalis |
GU tract
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In what part of the body are these amoebas important?
Naegleria fowleri, Acanthamoeba spp. |
They are free-living. Acanthamoeba is important in the cornea.
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What is pneumocystis jiroveci?
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It is a protozoan/fungus that causes bilateral diffuse pneumonitis in immunocompromised patients.
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Name three hemoflagellates and the diseases they cause.
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1. Trypanosoma cruzi (Chagas disease)
2. T. brucei (Sleeping sickness) 3. Leishmania spp. (Leishmaniasis) |
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Name the four malaria parasites.
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1. Plasmodium falciparum
2. Plasmodium vivax 3. Plasmodium malariae 4. Plasmodium ovale |
