Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
38 Cards in this Set
- Front
- Back
What is the attack rate of diarrhea in children?
|
-10-18 illnesses per child per year in the developed world
-1-3 illnesses per child per year in the developed world |
|
What causes most cases of acute infectious diarrhea?
|
Viruses
|
|
What are the most commonly isolated bacterial pathogens in diarrhea? Which are spread person to person?
|
-Campylobacter (42%)
-Salmonella (32%) -Shigella (19%) -E. coli O157:H7 (7%) -Vibrio (1%) Person to Person: -Shigella -Salmonella typhi |
|
Describe Vibrio
|
-Gram negative bacilli
Grow in esturarine and marine environments -Survive in contaminated waters with increased salinity and temperature -Subclassed based on O antigens -Can cause cholerae (V. cholerae O1 and O139) -Cholera is spread by contaminated food or water |
|
What are the clinical manifestions of cholera? What is treatment?
|
-Variable
-75% asymptomatic -20% abrupt watery diarrhea -5% Severe watery diarrhea, vomiting, and dehydration -No tenesmus, strain, abdominal pain, or fever -Severe dehydration, metabolic acidosis (bicarbonate loss), hypokalemia (low potassium) an hypovolumic shock -Occurs 2-3 days after ingestion of bacilli -Duration: 1-3 days -Mortality: 60% treated, >1% untreated -Treatment: Rehydration: IV followed by oral rehydration solution (glucose and electrolytes) and doxycycline |
|
Describe shigella. What are the species of shigella?
|
Small gram negative bacilli/rods
S. sonnei (developed countries) S. flexneri (developing countries) S. dysenteriae (most severe) S. boydii |
|
What is the reservoir for Shigella?
|
Humans
|
|
Describe the pathogenesis of Shigella
|
-Transmitted fecal-pral
-Low innoculum (<200 organisms) -Invasion of intestinal mucosa, moving from small to large intestines, with multiplication in the cells lining the mucosa and mucosal destruction -Cytotoxin elaboation -Penetration beyond the mucosa is rare |
|
What are the clinical manifestions of Shigella?
|
-12 hours after ingestion, bacterial multiplication begins in small intestines resulting in abdominal pain, cramping, watery diarrhea and fever
-Resolution of fever in a few days -Onset of severe lower abdominal pain, accompanied by urgency, tenesmus, and blood mucoid stools -Illness lasts on average 7 days -Colonic shedding 1-4 weeks -S. dysenteriae results in more serious diarrhea with risk of Hemolytic Uremic Syndrome (HUS) |
|
What enterotoxin does S. dysenteriae produce?
|
Shiga Toxin, which disrupts protein synthesis and produces endothelial damage
|
|
Describe EIEC
|
Causes bloody diarrhea by causing destruction of the epithelial cells in the large intestines
|
|
Describe the clinical presentation of EHEC
|
-Mild, uncomplicated diarrhea to hemorrhagic colitis with severe abdominal pain
-Bloody diarrhea -Little or no fever -Associated with Hemolytic Uremic Syndrome (acute renal failure, thrombocytopenia, microangiopathic hemolytic anemia) (Stx-2, 10% of children under 10, Mortality: 3-5% of children with HUS) -Severe neurological and renal sequelae can occur in as many as 30% of patients |
|
Describe campylobacter?
|
-Small, comma-shaped gram negative bacilli
-Microaerophilic |
|
What are the most common causes of campylobacter gastroenteritis? Where do the bacteria come from?
|
C. jejuni
C. coli C. upsaliensis C. jejuni and C. coli infections occur through consumption of contaminated poultry, milk, and other foods |
|
What is the pathogenesis of C. jejuni?
|
-Produces histologic damage throihg invasion into intestinal cells
-Exact role of the adhesions, cytotoxins, and nterotoxins are not well defines -Rarely associated with Guillaine-Barre syndrome -Pathogenesis believed to be related to antigenic cross-reactivity between the oligosaccharides of Campylobacter and glycosphiniolipids present on neural tissues |
|
Describe salmonella
|
-Gram negative bacilli
More than 2400 unique serogroups -Typhoid species: S. typhi and S. paratyphi -Nontyphoidal species: S. enteritidis and S. typhimurium |
|
Explain the pathogenesis of S. typhi
|
-Only reservoir is human
-Causes typhoid fever -Produces a febrile illness -Passes through the intestinal lining -S. typhi is engulfed by macrophages, where it replicates and is sent to the liver, spleen, and marrow -5-21 days later patients experience fever, headache, malaise, myalgias, and a salmon pink rash on the abdomen |
|
Explain the pathogenesis of S. enteritidis
|
-Colonized the GI tract of virtually all animals
-Large inoculum required for development of symptomatic disease -Infections occur in people when contaminated foods are improperly stored -However in high risk populations (elderly, immunocompromised) -Characterized by fever, nausea, vomiting, bloody or non-bloody diarrhea, abdominal cramps |
|
Describe E.coli
|
-Gram negative bacillus
-Facultative anaerobe -6 groups -Enterotoxigenic (ETEC) -Enteropathogenic (EPEC) -Enteroinvasive (EIEC) -Enterohemorrhagic -Shiga-like toxin producing E. coli (STEC) -Enteroaggregative (EAEC) -Diffusely adherent E. coli (DAEC) |
|
Describe ETEC
|
-Traveler's diarrhea
-Produces heat-labile, heat-stable enterotoxins which affect the small intestine sand cause a secretory diarrhea -Seen mostly in infants in developing countries |
|
Describe EHEC
|
-Inoculum <1000 organisms
-Hemorrhagic colitis, associated with HUS in children -Produces cytotoxic Shiga Toxins (Stx-1 and 2) that destroy intestinal villi and cause dysentery -Serotype O157:H7 is responsible for most of the E. coli gastroenteritis in the US -More common in warm months from meats, water, milk or fruit juice |
|
Describe EPEC
|
-Children's diarrhea
-Causes diarrhea by destroying microvilli in the small intestine -Seen mostly in infants in developing countries |
|
Describe EIEC
|
Causes bloody diarrhea by causing destruction of the epithelial cells in the large intestines
|
|
Describe the clinical presentation of EHEC
|
-Mild, uncomplicated diarrhea to hemorrhagic colitis with severe abdominal pain
-Bloody diarrhea -Little or no fever -Associated with Hemolytic Uremic Syndrome (acute renal failure, thrombocytopenia, microangiopathic hemolytic anemia) (Stx-2, 10% of children under 10, Mortality: 3-5% of children with HUS) -Severe neurological and renal sequelae can occur in as many as 30% of patients |
|
Describe the Cholera Toxin
|
-Enterotoxin
-A subunit: enzymatic activity -B subunit: binds to enterocyte surface receptor, the ganglioside Gm1 -After binding to enterocyte, A subunit translocates across cell membrane, catakyzed ADP ribosylation of a GTP-binding protein resulting in persistent activation of adenylate cyclase -Inhibits Na reabsorption and new flux of fluid from the gut -Doesnt affect sodium glucose transport |
|
Describe Shiga toxin
|
-Produced by S. dysenteriae
-B subinit binds to host cell glycolipid (Gb3) and facilitates transfer of A subunit -A subunit disrupts protein sunthesis by preventing binding of aminoacyl-transfer RNA to the 60S ribosomal subunit -Results in destruction of intestinal cells and villi, decreasing intestinal absorption |
|
Describe S. aureus enterotoxin
|
-Neurotoxin
-Heat-stable -Increases peristalsis by autonomic activation, results in intense vomiting |
|
Describe Bacillus Cereus enterotoxic
|
-Two enterotoxins
-Emetic: incubation period of 1-6 hours -Diarrheal: Incubation period of 10-12 hours |
|
Describe ETEC toxin
|
-LT-1
-Similar to cholera toxin -1 A subinit -5 B subunites |
|
Describe EHEC Shiga toxin
|
-Stx-1 identical to Shigella Shiga toxin
-Stx-2 has 60% homology, A internalized and binds to 28S ribonucleic acid, disrupting protein synthesis |
|
Which bacteria can invade tissues? What is the mechanism?
|
-E. coli, Shigella, and Salmonella all share a common effector system
-Type III secretion system -Salmonella has two: SPI-1 and 2 -After binding M cells, SPI-1 secretion system introduces salmonella-secreted invasion proteins (Sips and Ssps) into M cells -Results in rearrangement of host cell actin and subsequent membrane ruffling -Ruffled membrane engulfs Salmonella -Salmonella replicates in host cel and spreads to adjacenet cells -Shigella system has 4 proteins (IpaA-D) -Shigella lyses phagocytic vacuole and replicates in host cell cytoplasm |
|
Contrast watery diarrhea, Dysentery and enteric fever
|
-Watery diarrhea is usually localized to the small intestines and is enterotoxin-mediated
-Dysentery is localized to large intestine and is caused by secreted cytotoxins or bacterial invasion -Enteric fever is from bacterial invasion and systemic dissemination |
|
What causes watery diarrhea?
|
-V. cholerae
-ETEC -Bacillus cereus -C. perfringens |
|
What causes dysentery?
|
-Shigella
-EHEC -C. jejuni -C. difficile -E. histolytica |
|
What causes enteric fever?
|
-Salmonella
-Yersinia |
|
What bacteria is in beef/gravy? Shellsfish? Sushi?
|
Beef gravy: Salmonella, Campylobacter, EHEC
Sushi: Campylobacter Shellfish: Vibrio species Fried rice: B. cereus |
|
What bacteria is in water? milk? Eggs? Undercooked chicken?
|
Water: Giardia, Norwalk virus, Campulobacter
Milk: Salmonella, Campylobacter, Yersinia Eggs: Salmonella Chicken: Salmonella, Campylobacter |
|
For which cases are antibiotics recommended? What is used?
|
-Traveler's diarrhea (ETEC)
-Fluoroquinolones -Empiric therapy for those with moderate to severe disease in the absence of C. difficile and EHEC -3-7 day course of fluoroquinolone |