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75 Cards in this Set
- Front
- Back
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Metronidazole is effective against? And its SE?
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Entamoeba histolytica, Giardia lamblia, Trichomonas vaginalis and anaerobic cocci and bacilli (Bacteroides fragilis, Clostridum difficile, and Gardnerella vaginalis).
SE: Nausea, antabuse-disulfiram effect, and metallic taste. |
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Who are definitive host of Toxoplasma gondii and how are humans infected?
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Cats are definitive host and oocysts produced in the cat is excreted in feces. Cattle and pigs can feed on the cats feces.
Humans are infected by ingestion of feces or ingesting pseudocysts in undercooked meat (pork, beef, etc.). |
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How common is Cryptosporidium?
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Pretty common, it usually causes self-limiting diarrhea and can be caused by outbreaks due to contaminated city water.
However in AIDS PTs, this causes severe watery diarrhea. |
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Toxoplasma gondii is an obligate intracellular parasite that exist in what forms?
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Proliferative form: banana-shaped tachyzoites that causes chronic infections.
Resting cyst form: slow-growing bradyzoites, found in muscle and brain during (asymptomatic) chronic infection. |
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How is Cryptosporidium parvum ingested?
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As a round oocyst that contains 4 motile sporozoites, which can be seen on a modified acid-fast stain (Ziehl-Neelsen).
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What is a cytosome
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A small mouth on the protozoa used to ingest solid pieces of food.
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What are the clinical presentation of Cryptosporidium parvum?
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Watery, non-bloody diarrhea and abdominal pain which are self-limiting and mild diarrhea (the life cycle takes place only once or twice; therefore, lasts two weeks or less). HOWEVER, in immunocompromised PTs, the symptoms are prolonged, more severe protracted diarrhea, and extreme malabsorption that are life-threatening.
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What is the pathogenesis of Toxoplasma gondii?
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Ingestion of pseudocysts or oocysts, sporozoites are released. Sporozoites transform into invasive tachyzoites in the enterocytes.
It inhibits fusion of lysosome with phagosome. Inside the phagosome, it differentiate into tachyzoites and rapidly divides. |
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How do you treat Cryptosporidium parvum?
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No treatment is necessary other than rehydration for immunocompetent adults and children since the disease is self-limiting. Avoidance of tap water has been considered a good preventive approach in the AIDS community.
Immunocompromised PTs, therapy as been discouraging. IV rehydration and make sure they are on their anti-retroviral therapy. No reliable therapy for cryptosporidiosis. Paromomycin, nitazoxanide, and azithromycin may have partial efficacy. Anti-diarrheal agents may provide relief. |
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What is the most common cause of intracerebral mass lesions, or encephalitis, in AIDS PTs?
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Toxoplasma gondii
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What protozoa are infective on excretion and can permit direct and immediate fecal-oral transmission amongst homosexual acts?
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Cryptosporidium parvum, since the merozoite can undergo sexual reproduction and regenerate oocyts within the same host.
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What is a cyst?
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When a protozoa is exposed to a new environment (temperature change, transit down the GI tract, chemical agent), the protozoa secretes a protective coat and shrink into a armored form.
It is in this form that a protozoa is ingested. |
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What accounts for transmission of Cryptosporidium parvum amongst travelers, and recreational summer activities?
What kind of stool smear do you perform? |
Water-borne transmission of oocysts.
Acid-fast stain |
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PTs with AIDS with CD4+ count less than 200, what is believe to be the cause of Toxoplasma gondii pathology?
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Bradyzoites reactivate and transform into tachyzoites, which evade killing and continue to multiply.
Replicating tachyzoites rupture the brain cells, resulting in focal necrosis. |
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How is Trichomonas vaginalis spread?
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Sexually, and hangs out in the vagina and male urethra.
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What is the DOC for Toxoplasma gondii?
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Sulfadiazine and pyrimethamine--with or without leucovorin.
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What are the symptoms of Trichomonas vaginalis infection?
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Vaginitis: greenish, water and foul-smelling, copious vaginal discharge, pruritus, burning on urination. Cervix has a diffuse, macular erythematous lesion ("strawberry cervix").
Urethritis in males: asmptomatic. |
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What stage follows a cyst?
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Trophozoite, the motile form.
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How do you diagnosis Trichomonas vaginalis?
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Wet mount of vaginal or urethral discharge: tear-drop shaped trophozoites
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What is the clinical features of congenital toxoplasmosis?
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Mental retardation, chorioretinitis, birth defects, the brain may be damaged, causing hydrocephalus.
Note: Congenital toxoplasmosis does not occur in pregnant women who have serologic evidence of previous exposure due to protective immune responses. |
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How do you treat Trichomonas vaginalis?
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Metronidazole and their sexual partner
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What are five intestinal protozoa that causes diarrhea, and which ones cause bloody diarrhea, non-bloody diarrhea, and severe diarrhea in those with a defected immune system (e.g., AIDS)
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Entamoeba histolytica (bloody), Giardia lamblia (fatty and non-bloody) and Cyclospora cayetanensis (non-bloody), and Cryptosporidium and Isospora belli (severe diarrhea in those with AIDS)
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How is Trichomonas vaginalis easily identified?
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By their ameboid mobility.
They do not have cyst. Note: they replicate by binary fission. |
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What are the complications of Entamoeba histolytica?
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Most are asymptomatic carrier, intestinal amebiasis, and invasive amebiasis (e.g., liver abscess, and can reach other areas).
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What is the only host of Trichomonas vaginalis? What can T. vaginalis cause?
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Humans.
Inflammatory reaction with numerous PMNs. Direct damage to epithelium, leading to ulceration. |
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What are characteristic of asymptomatic carriers of Entamoeba histolytica?
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Trophozoite becomes 4-nuclei cyst as it travels out of the colon, and the stool may be hard
The cyst has four nuclei with a central karyosome and uniformly distributed peripheral chromatin |
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What are characteristics of invasive amebiasis from Entamoeba histolytica?
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Colonic epithelium invasion producing raindrop-shaped ulcers, spreading through portal circulation to form abscess in the liver and may invade diaphragm to create pulmonary abscess. Also results in dysentery.
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How can you distinguish between active and asymptomatic carriers of Entamoeba hisolytica?
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Trophozoites have RBC in the cytoplasm of active disease while cysts or trophozoites without internalized RBC and/or hard stools suggest asymptomatic carriers.
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Treatment of active carriers of Entamoeba histolytica and for the asymptomatic, carriers.
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Metronidazole (tinidazole is equally effective) for active state (systemic therapy) and metronidazole with iodoquinol, or paromomycin, or diloxamide furoate for carriers or symptomatic PTs.
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Backpackers who drink from "clear" mountain streams may catch?
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Giardia lamblia.
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Where does the trophozoite of Giardia lamblia attach to in the GI, and what is the consequence of this?
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To the duodenal wall via a suction disk, but does not invade. It interferes with the intestinal fat absorption and causes damage to the microvilli and causes inflammation. This creates malabsorption (loss of water since its in the upper-GI) and foul-smelling (fatty) diarrhea with flatulence.
The diarrhea precedes as watery, then greasy and foul smelling. |
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The diarrheal specimen (active state) of Giardia lamblia has what morphology?
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Tear-shaped trophozoite with 2 nuclei, 4 pairs of "mustache" flagella
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The Hard stool specimen (carrier state) of Giardia lamblia has what morphology?
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4-nuclei mature cyst.
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How do trophozoites of G. lamblia disrupt the brush border?
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By microvilli injury, causing villus atrophy (via proteinase or mannose-binding lectin), which results in watery diarrhea.
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How does diarrhea occur with G Lamblia?
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Initially watery, then greasy, and foul.
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What is dysentery?
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Diarrhea with blood and mucus in the stool.
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What does the cyst of Entamoeba histolytica look like?
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Spherical with four nuclei with central karyosomes and fine, distributed peripheral chromatin.
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What is the recommended procedure and recovery to identify amebae?
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"Ova and parasite" examination of the stool.
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Describe ingression of the amebae, Entamoeba histolytica.
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Ingestion of cysts in contaminated food or water, excystation occurs with attachment to large intestine mucosal cell wall via lectin-binding receptors. Trophozoites multiply by binary fission and produce cysts, which are passed in feces.
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What do Entamoeba histolytica feed off of and how do they cause damage?
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Trophozoites feed on neutrophils, monocytes, lymphocytes, cells of colonic mucosa, and RBCs to give rise to amebic colits.
Cytotoxins allow it to invade the colon and also lyse PMN which releases hydrolytic enzymes to contribute to damage to the colonic mucosa. |
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Two common infections associated with dysentery associated with traveling in developing countries.
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E. histolytica and S. dysenteriae
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How are Entamoeba histolytica, Giardia lamblia, and cryptosporidium parvum transmitted?
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Fecal-oral route from contaminated food or water, and cryptosporidium parvum can also be transmitted via animals or humans.
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How do Cryptosporidium parvum cause diarrhea?
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They are "intracellular but extracytoplasmic" parasites. Diarrhea develops when the absorption is impaired. Secretion is also enhanced by stimulation of prostaglandin by the intestinal epithelial cells. They mostly infect the jejunum.
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In addition to Entamoeba histolytica, what are two other pathogenic amebas?
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Acanthamoeba and Naegleria fowleri can both cause meningoencephalitic conditions in immunosuppressed and immunocompetent PTs, respectfully. Acanthamoeba can cause keratitis in people wearing contact lenses.
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Metronidazole or tinidazole is the DOC for?
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Severe intestinal wall disease and in hepatic abscess and other extraintestinal amebic disease.
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Nitazoxanide is used for?
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Children who should not be given metronidazole (carcinogenic and metallic test), and instead be given this drug. It can also be given against metronidazole-resistant protozoal strains.
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Light microscopy does not allow distinction between invasive E. histolytica and?
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E. dispar, unless erythrophagocytosis (presence of ingested RBCs in trophozoites)
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What two intestinal parasite can cause diarrhea?
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D. fragilis and E. histolytica.
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Describe the toxins of Entamoeba histolytica
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Cytotoxin allows the trophozoites to invade the colon with lysis of epithelial cells. They can also lyse PMN releasing hydrolytic enzymes that contribute to damage to colonic mucosa.
Extracellular cysteine proteinase degrades collagen and elastin. |
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What do the colonic lesions from E. histolytica look like?
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Range from nonspecific colitis with inflammatory cells to flask-shaped ulcers
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Describe the trophozoite of Giardia lamblia
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Pear-shaped, with four pairs of flagella, to anterior nuclei with with a karosome to give a facelike appearance.
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What is the typical path of transmission of Giardia lamblia?
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Travelers to endemic countries and young children in day care centers.
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How does Giardia lamblia attach to the brush border of the duodenal wall?
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Ventral surface with a "sucking disk", flagella, and receptor-ligand interaction by lectin proteins. But no invasion.
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T cells against Giardia lamblia may cause?
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Crypt hyperplasia
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What is an alternative treat of metronidazole for Giardia lamblia, and why?
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Albendazole and paromomycin in pregnancy.
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What is a highly sensitive and specific test for G. lamblia?
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Stool antigen test
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What is the vector for malaria?
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Anopheles mosquito, carrying it in its salivary glands.
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How often do the RBCs burst in
Plasmodium vivax or P. ovale? P. malariae P. falciparum |
Every 48 h, producing chills and fever, followed by drenching sweats.
72 h Irregularly, between 36 - 48 h |
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What is the sporozoite of malaria?
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Infectious stage of malaria
Is found in the salivary glands of female mosquitoes and invades the liver cells. |
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What is the merozoite of malaria?
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They are released from liver cells. Some will reinfect the liver (vivax, ovale).
Within the RBC, they hydrolyzing hemoglobin. Asexual, haploid forms |
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What is the trophozoite and schizont stage of malaria?
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Trophozoite is the first stage of the parasite in the RBC and defined by presence of a single chromatin mass. The next stage, the schizont, has multiple chromatin masses, each of which develops into merozoites.
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What does the trophozoite look like in the RBC?
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Shaped like a ring with the nuclear material looking like the diamond on the ring.
Note: Nuclear division then occurs with formation of a large multinucleated schizont. |
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What is the gametocyte of malaria?
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The sexual form that infects the mosquito when it takes its blood meal.
In the mosquito, the gametocytes are sucked into the stomach where the male and female gametocytes fuse. DNA is mixed and the fused gametocytes become an oocyst. The oocyst divides into many spindle-shaped wiggling sporozoites. |
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What is the hypnozoite of malaria and what two species does it pertain to?
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Dormant form in the liver, which can grow years alter, causing relapsing malaria.
P. vivax and P. ovale. |
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Describe P. falciparum greater pathogenicity
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P. falciparum is able to infect RBCs of any age, unlike other species that only infects young or old RBCs
They also have greater parasitemia P. falciparum causes infected RBCs to clump together (rosette) by proteinaceous knobs on the surface of the RBC. They will then stick to endothelial cells lining small blood vessels (sequestration), which blocks blood flow--resulting in cerebral malaria. Ischemia due to poor perfusion causes the manifestations of cerebral malaria, which is the main cause of death due to malaria in children Note: Only P. falciparum causes life-threatening infection |
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What is cerebral malaria caused by P. falciparum?
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Brain vessels are plugged with parasitized RBCs.
Characterized by seizures and impaired consciousness, leading to coma. |
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Sickle cell (HbS) protects against?
Absence of Duffy a and b? |
P. falciparum
P. vivax |
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What are the four developmental stages of the plasmodia of malaria?
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1. Ring: early developmental stage
2. Trophozoite: the parasite has lost its "ring". The enlarged infected RBC contains numerous "Schuffner dots" 3. Schizont: late developmental stage, parasite has begun its division into merozoites and characterized by presence of multiple contiguous chromatin dots. 4. Gametocyte: sexual erythrocytic stage. Female is macrogametocyte and male is microgametocyte. |
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What film can differentiate between Plasmodium from Babesia?
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Thin film can, but not thick film.
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Anemia results from malaria by?
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Lysis of infected RBCs, suppression of hematopoiesis, increased clearance of RBCs by the spleen.
Note: over time, malaria infection causes thrombocytopenia. |
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Since malaria consumes glucose faster than RBCs do, what occurs?
How does P. falciparum cause more hypoxia than the other species? |
Hypoglycemia and lactic acidosis
More merozoites are produced, therefore, more RBCs are destroyed. |
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What is the DOC for susceptible strain of Plasmodium species?
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Chloroquine
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What is the DOC for intrahepatic malaria, such as hypnozoites of vivax/ovale?
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Primaquine
Note: must be used to prevent relapse. |
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DOC for chloroquine-resistant straints?
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Mefloquine
Note: usually for P. falciparum. Also, doxycycline or clindamycin may be used in combination with the drugs for P. falciparum. Note: exchange transfusion for P. falciparum when parasitemia is too high. |
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Describe hemozoin.
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Merozoites hydrolyzes hemoglobin. Free heme is toxic to cells, so the parasites convert it into an insoluble crystalline form called hemozoin. In malaria parasites, hemozoin is often called malaria pigment.
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