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70 Cards in this Set
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What is Giardia lamblia?
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Common intestinal parasite (20,000 confirmed cases/yr in US; estimated 2 million total/yr in US)
Can cause severe but non-invasive diarrhea |
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What is the transmission of giardia?
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H20
Campers drinking untreated water ("classic" scenario) Travelers to developing nations: contaminated H20 Possible sexual transmission (gay sex) |
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What is a trophozoite and what is a cyst and what do each form look like in giardia?
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Trophozoite: active, often motile, living form
Rapidly die outside host, sensitive to environmental changes Giardia - pear shaped, 2 nuclei, 8 flagella Cyst: dormant, long term "survival mode" Often with thick shell, can survive environmental changes Giardia - has 4 nuclei, but no flagella |
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What is the life cycle for giardia?
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Host: many animals (humans, dogs, etc.)
Transmission: ingestion of cysts; person-to-person Trophozoites excyst in duodenum, migrate to upper intestine, and attach to submucosa via a ventral sucking disc Trophozoites divide by binary fission; form cycst in lower GI tract Cysts are the infective stage |
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What are the symptoms of G. lamblia?
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1. Asymptomatic carries - can still excrete cysts
2. Acute phase - sudden explosive diarrhea, nausea, abdominal distention, cramps with foul flatus, anorexia and greasy stools within 3 wks of exposure 3. Chronic phase - intermittent, loose, foul-smelling stools, abdominal distention, flatulence, epigastric pain, nausea, anorexia 4. Complications - malabsorption, protein malnutrition |
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How is giardiasis diagnosed?
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Microscopy of wet preps/stained smears, Entero-test - at least 3 stool 2-3 days apart, may detect either cysts or trophozoites
ELISA to test stool samples for giardia antigents, also sensitive Serology NOT used |
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How is giardiasis controlled?
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Filtration (purification) or boiling of water - cysts are resistant to chlorine
Hand washing, especially in day-care facilities |
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What is Cryptosporidium parvum?
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Causative agent of cryptosporidiosis - noninvasive diarrhea, nausea, gastric pain
Sporozoite: sexual lifestyle Replicates in human gut, usually found as oocysts |
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How is C. parvum transmitted?
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Contaminated water or food, such as salads
Person-person, or animal-person Ingested oocysts release sporozoites in upper GI tract |
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What is the life cycle of C. parvum?
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Superficially invades mucosal cells, multiplies asexually
Some merozoites differentiate into male/female gametocytes, forming oocysts Mature occysts are excreted in feces; can infect other individuals |
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Who are the risk groups for cryptosporidiosis and how can it be controlled?
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Risk groups: travel, exposure to farm animals, day care and medical institutions possible
Control: purified water, good hygiene Outbreaks often associated with water (drinking water, pools) - cysts resistant to chlorine and iodine |
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What are the clinical signs of C. parvum in a normal immunocompetent pt?
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May be asymptomatic
Profuse watery diarrhea, epigastric cramping pain, nausea and anorexia Primary symptoms due to malabsorption Usually self limiting in about 15 days |
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What are the clinical signs of C. parvum in an immunocompromised pt?
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Can't clear the infection, and C. parvum autoinfects
Severe diarrhea of 3-6 liters/day occur Diarrhea persists for months or years - life-threatening illness, no effective treatment Can disseminate to other organs (resp. tract, biliary tree) |
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How is C. parvum diagnosed?
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Modified acid-fast staining of stool - most frequently used in clinical labs (C. parvum retains red stain after an acidic "destain")
Immunofluorescent staining - more sensitive/specific ELISA tests also available - increasingly used, very sensitive (test stool samples for antigens) |
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What is Entamoeba histolytica?
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Single-celled ameba, causative agent of amebiasis
Occurs primarily in developing countries "Carrier state" common in third world US - mainly seen in travelers and immigrants |
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What is the difference between the trophozoites and cysts in Entamoeba histolytica?
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Trophozoites: motile, active, replicating; chromatin on inside of nucleus, single nucleus; no flagella
Cysts: infective form; small, rounded with up to 4 nuclei; chromatoid body (football shape) |
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How is Entamoeba histolytica transmitted?
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Contaminated food, water; hand-mouth contact
Often food-handlers |
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What is the life cycle of E. histolytica?
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Cysts and trophozoites passed in feces
Ingestion of mature cysts (fecal contamination) Excystation occurs in small intestine Trophozoites released, which migrate to large intestine They can fully INVADE the mucosa (can disseminate through body as well) |
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What are the clinical manifestations for E. histolytica in symptomatic intestinal amebiasis?
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Incubation period: 1-4 weeks
1. Amebic colitis (non dysenteric) 2. Amebic dysentery - blood in stool and potential for amebic ulcers Both show signs of crampy abdominal pain, watery diarrhea, weight loss, and mucosal necrosis Asymptomatic (90% of infections) - still shed cysts! |
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What are the clinical manifestations for E. histolytica in symptomatic extraintestinal ambiasis?
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May invade mucosa and produce abscesses in liver, lung, and brain (liver dysfunction, pneumonitis, or encephalitis)
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What are the signs for amoebic liver abscess?
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Fever, cough, upper right quadrant pain
Fever with abnormal liver scan - amebiasis should be considered 2/3 of amoebic liver abscess pts have hx of diarrhea Labs: mild to moderate leukocytosis + anemia |
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How is E. histolytica diagnosed?
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Microscopy of stool samples
Demonstration of RBC containing trophozoites in fresh stool is diagnostic Cysts in solid stool; trophozoites in liquid stool Cysts +/- trophozoites lacking RBCs requires confirming (E. dispar is identical but non-pathogenic) Differentiation done by immunoassay (ELISA to detect stool antigen) or PCR |
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What is Enterobius vermicularis?
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Pinworm - infects 200 million annually
Common in temperate regions of N America and Europe Most common helminth infection in US Adult worms tiny, eggs are tinier (elongated-oval and flattened on one side) |
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What is the transmission of E. vermicularis and the hosts?
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Close contact with classmates
Contact with household members (towels, sheets, etc) Eggs most infective for 48 hrs but can remain viable for 20 days Self auto-infection is common Hosts: humans considered only host (dogs, cats NOT source) |
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What is the life cycle for pinworms?
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Adults inhabit cecum and adjacent regions of intestines
Females move to anus Nocturnal migrations to perianal region Air stimulates them to lay eggs Eggs hatch in anal region Resulting infective larvae can crawl back into GI tract |
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What are the symptoms and pathology of pinworms?
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Many infections asymptomatic
Most common symptom is anal pruritis - causes sleep disturbances; can cause psychiatric manifestations Can cause anorexia, abdominal pain, irritability Rare complications: bacterial super-infection (scratching); vulvovaginitis (worm migration) |
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How are pinworms diagnosed and controlled?
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Diagnosis made by recovery of characteristic eggs - cellophane tape test
Up to 5 negative tape tests required to rule out infection Control: personal hygiene, short fingernails, full-length PJs |
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What is Trichuris trichiura and how is it transmitted?
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Whipworm - 1 billion people infected worldwide
Most common in tropical, sub-tropical areas Children most commonly infected Transmission: fecal-oral contamination |
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What is the life cycle of Trichuris trichiura?
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Infective eggs ingested in contaminated food/water
Larvae hatch in upper intestine, penetrate villi cells, migrate to cecum and reach sexual maturity Adults live primarily in colon and cecum Anterior is attached to mucosa Females lay >5000 barrel-shaped eggs/day Eggs embryonate in soil |
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What are the symptoms of tichuriasis?
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Most infections are light with no symptoms
Heavy infections may cause: Bloody stools, anemia, diarrhea Lower abdominal pain, growth retardation Tenesmus Rectal prolapse |
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How is trichuriasis diagnosed?
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ID of barrel (or football) shaped eggs in feces
Concentration procedures may be required in light infections; rarely see worms (attached to cecum lining) Protoscopy of rectal mucosa may visualize worms |
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How is Trichuris trichiura controlled?
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Wash your hands and food
Don't eat dirt (pica) Avoid contaminated food (food fertilized with "night soil") |
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What two nematode species are known as hookworms?
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Necator americanus (found in US - "New world")
Ancylostoma duodenale (not found in US - "Old world") Adults have teeth or cutting plates for tearing intestinal wall allowing for firm attachment |
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What is the hookworm life cycle?
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On human contact, larvae penetrate skin and are carried through veins to lungs
Penetrate alveoli, ascend the bronchial tree to pharynx and are swallowed In small intestine, larvae mature, mate, and females produce ~4000 eggs/day |
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What are the symptoms of hookworm disease?
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Ground itch: inflammatory reaction at larval penetration site
Larval migration: can produce dry cough, sore throat, and bleeding when many worms involved (eosinophilia during this phase) Heavy infestations: iron deficiency anemia, chronic protein-energy malnutrition, edema, distended abdomen, mental dullness, cardiac failure and death Each adult worm can leach up to 0.05 ml blood/day |
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What is eosinophilia?
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Defined as eosinophil count > 450/microL in peripheral blood
Common manifestation in parasitic infections These cells generate pro-inflammatory molecules Typically seen in helminth infections with systemic migration phase |
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How is hookworm diagnosed?
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Required ID of eggs in feces - concentration may be needed in light infections
Eggs of the two species are morphologically identical Larvae resemble those of Strongyloides |
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How is hookworm controlled?
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Avoid walking barefoot in sandy or dirt areas
Good sanitation practices |
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What is Ascaris lumbricoides?
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Most common human helminthic infection worldwide
Over 1 billion people infected Rural areas of southeastern US Largest intestinal roundworm (30 cm) |
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How is Ascaris lumbricoides transmitted?
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Poor sanitation/hygiene
Ingestion of infective eggs from soil contaminated with human feces |
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What is the life cycle of Ascaris lumbricoides?
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Infective eggs ingested; larvae hatch, invade intestinal mucosa and migrate to lungs
After 2 weeks, larvae penetrate alveolar wall, ascend bronchial tree to throat and are swallowed In intestine, adult worms develop and mate Females pass 200,000 eggs/day into feces In warm, moist soil, fertile eggs embryonate and become infective in ~3 weeks |
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What are the manifestations of A. lumbricoides?
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Pulmonary phase: cough, dyspnea, eosinophilic pneumonitis
Many infections asymptomatic Diarrhea and abdominal pain common High worm burdens can cause intestinal obstruction |
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What are complications of A. lumbricoides?
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Migrating adult worms can cause appendicitis, obstruct the biliary tree or be expectorated
Inducing migration is dangerous (general anesthetics, fever can induce migration) |
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How is ascariasis diagnosed?
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Demonstration of eggs in feces (or after egg conc.)
Eggs are brownish-yellow in color ID of adult worms passed in feces 3 consecutive fecal samples: if neg. will rule out in 99% Worms live for 18 months |
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What are Toxocara canis and cati?
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Dog and cat roundworms
Can cause visceral larva migrans (VLM) and ocular larva migrans (OLM) Serology rates in US in children vary from 3-50% |
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What is the life cycle of toxocariasis?
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Transmission: ingestion of eggs (dog or cat fecal contamination)
Humans are accidental hosts: worms don't fully develop (dead end host) |
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What are the symptoms of toxicariasis?
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Most asymptomatic or self-limiting
VLM: mostly in children, larvae invade various tissues throughout body; can cause fever, anorexia, weight loss, cough, wheezing, rashes, hepatosplenomegaly, and hypereosinophilia OLM: unilateral opthalmologic lesions due to migration of worms through eye |
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How is toxicariasis diagnosed and controlled?
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Serology
Eosinophilia (VLM) Pt history - exposure to puppies (or cats) No eggs found in stools Control: treat pets routinely for worms, cover sandboxes when not in use |
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What is Taenia sp.?
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Taenia solium: pork tapeworm; scolex has sucker and hooks, proglottid 7-13 branches per side
Taenia saginatum: beef tapeworm; scolex suckers only, proglottid 15-20 branches per side Proglottid = reproductive segment Scolex = attachment organ |
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What is the life cycle of taenia sp.?
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2 stages: human and cow/pig
Transmission to pigs through consumption of eggs (contaminated food/water) Transmission to humans through consumption of raw/undercooked meat containing tapeworm larvae |
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What are the clinical features of taeniasis?
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Usually asymptomatic
Pts who report "passing a tape" (dramatic increase in GI "symptoms" vs those who don't pass proglottid) Psychosomatic effect? Complications: appendicitis or cholangitis, due to migrating proglottids |
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How is taeniasis diagnosed?
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Visualization of eggs and proglottids in feces (diagnostic)
Not possible during first 3 months following infection Speciation of Taenia impossible based on eggs alone - need microscopic ID of proglottids or scolex for species |
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What is cysticercosis?
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Taenia has 2 stages in its life cycle
If a person (instead of pig) ingests embryonated eggs passed by another human, they become "intermediate host" Cysticerci then develop in body, often in places like brain Can only happen with T. solium |
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What are symptoms of cysticercosis?
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Depend on location of cysticerci
Brain = CNS symptoms (seizures, mental changes, death) Cardiac, lung, intramuscular lesions can form as well |
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How is cysticercosis diagnosed?
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Depends on finding cysticerci, not eggs
Serology Imaging (CT, MRI, especially) |
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What is Diphyllobothrium latum?
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Broad fish tapeworm
Northern hemisphere, freshwater areas Largest of human cestodes - up to 10m Adult worms can live > 20 years, shedding 1,000,000 eggs/day Scolex: slit-like groove (sucker) and high # of proglottids |
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What is the life cycle of D. latum?
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Unembryonated eggs passed in feces
Eggs embryonate in water Crustaceans ingest and then are ingested by small freshwater fish Predator fish eats infected fish Human ingests raw or undercooked infected fish Adults in small intestine, proglottids release immature eggs |
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What are the clinical signs of D. latum?
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Usually asymptomatic
Sometimes non-specific abdominal symptoms (pain, diarrhea) Vitamin B12 anemia - D. latum has high affinity for B12 and is absorbed by worm |
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How is D. latum diagnosed and controlled?
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Microscopic ID of eggs in stool (numerous)
ID of proglottids passed in stool also diagnostic Control: cook fish throughly; sanitation |
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What is Echinococcus granulosus?
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Causes echinococcosis (or Hydatid Disease)
Found worldwide, rural grazing areas, wild dogs Larval infection in humans - worms don't develop fully - but disseminate through human host and form cysts that grow |
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What is the transmission of hydatid cysts?
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Ingestion of E. granulosus eggs (from canine feces)
Larvae exit intestine, and lodge in tissues throughout body Mos frequently found in liver and lungs - reach diameter of 1cm in 5-6 months (gradually enlarges over years) |
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What are the clinical signs of hydatid disease?
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Symptoms typically depend on location of cyst
Liver: (most common) abdominal pain, hepatic mass, biliary duct obstruction Lungs: chest pain, cough, hemoptysis Brain: neurological defects |
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How is echinococcosis diagnosed and controlled?
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Imaging techniques to detect cysts
Serology also beneficial No eggs in feces - humans not definitive host Control: good hygiene, treatment of canines, prevent canines from consuming raw meats |
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What is Schistosoma sp.?
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Schistosomiasis - "Blood Flukes"
Afflicts 250 million, one of most important human parasitic diseases Live in mesenteric venules |
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What are the three species of Schistosoma?
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S. mansoni: Caribbean, Venezuela, Brazil, Arabia, Africa - live in venules of colon and portal system of liver
S. japonicum: China, Taiwan, Philippines, & rarely Japan - lives in veins of small intestine S. haemotobium: Africa and India - lives in bladder (RENAL SECTION) |
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How is Schistosoma sp. transmitted?
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Requires direct contact with Schistosome cercariae (larvae)
Swimming in infested waters! The tiny larvae can penetrate human skin then enter blood stream and migrate through body Eventually mature into adult worm |
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What are the clinical signs of schistosomiasis in the acute stage?
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Many asymptomatic
Acute stage: "Katayama fever" 0-7 days localized skin rash at site of larval penetration Usually in people with no prior exposure Acute fever, headache, chills, cough, aches, abdominal pain, hepatosplenomegaly, rt upper quadrant pain History of contact with water (14-84 days prior to onset) Eosinophilia |
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What are the clinical signs of schistosomiasis in the chronic stage?
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Eggs retained in gut - inflammation, ulceration, pain
Fever, diarrhea common (often with blood) Hepatosplenic symptoms - eggs mobilize to liver; granuloma, inflammation, fibrosis; portal hypternsion |
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What are the differences in the schistosoma eggs?
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S. mansoni: prominent lateral spine
S. japonicum: often barely noticeable lateral spine S. hematobium: prominent terminal spine |
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How is schistosomiasis diagnosed and controlled?
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ID of eggs in stool = gold standard; but will be delayed 6 weeks until eggs are produced
Miracidium-hatching test: eggs hatch into larvae when placed in fresh water Serology: specific tests for S. mansoni Abs Control: avoid swimming in fresh water in endemic areas; drink municipal, bottled, boiled water; bio-control (snail control) through molluscicides |
