Term
| what are the 2 kinds of diarrhea? |
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Definition
| inflammatory/non-inflammatory |
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Term
| what characterizes non-inflammatory diarrhea? |
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Definition
| watery, osmotic, enterotoxin mediated, and the only kind of diarrhea that viruses can cause (along w/some bacteria) |
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Term
| what characterizes inflammatory diarrhea (2 kinds)? |
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Definition
| hemorrhagic (bloody), OR dysenteric (mucus, blood, and debris from an inflammatory response such as WBCs/fibrin) |
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Term
| what kind of diarrhea do most parasites cause? |
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Definition
| most parasites cause non-inflammatory, watery diarrhea - except for *entamoeba histolytica (which causes inflammatory diarrhea) |
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Term
| what kind of viruses cause non-inflammatory diarrhea? |
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Definition
| rotavirus and calicivirus (norovirus/sapovirus) |
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Term
| what kinds of bacteria can cause non-inflammatory diarrhea? |
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Definition
| vibrio cholerae and enterotoxigenic escherichia coli (ETEC) |
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Term
| what kinds of bacteria can cause inflammatory diarrhea? which of these are most likely to be seen in the US? |
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Definition
| *campylobacter jejuni, *salmonella spp, and *shigella spp are three are the most common in the US. other bacteria which cause inflammatory diarrhea: shiga toxin-producing E. coli, enterohemorrhagic E. coli, clostridium difficile, enteroinvasive E. coli, yersinia enterocolitica, and vibrio parahaemolyticus. |
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Term
| what bacteria can cause food poisoning due specifically to toxins they produce? |
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Definition
| staph aureus, bacillus cereus, and clostridium perfringens |
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Term
| what are the various the modes of transmission for pathogens causing diarrhea? |
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Definition
| fecal-oral and ingestion of contaminated water/food |
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Term
| what kind of settings increase the likelihood of fecal-oral transmission? |
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Definition
| fecal-oral transmission may happen w/crowding & poor hygiene as seen in developing countries, nursing homes/daycares/military barracks - often via various fomites. contamination via food handlers is also a setting w/increased risk (esp with asymptomatic shedding). |
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Term
| what are some common ways in which diarrhea-causing pathogens are ingested in contaminated water? |
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Definition
| pts may be exposed to inadequate water sanitation, swim in contaminated rivers/streams, ingest food washed in contaminated water, and eat shellfish harvested from water contaminated by feces (seen w/vibrio cholera and norovirus) |
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Term
| what are some common ways in which diarrhea-causing pathogens are ingested in contaminated food? |
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Definition
| pts may eat food contaminated by feces during slaughter, drink raw milk which may be contaminated, food may be grown in fields irrigated w/water contaminated by feces or fertilized by animal wastes, and food may have been harvested from areas adjacent to livestock |
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Term
| which viruses are the leading causes of gastroenteritis in the US? |
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Definition
| rotavirus (severe, young children), norovirus (not quite as severe, affects all ages) |
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Term
| what are some other viruses responsible for gastroenteritis less common in the US? |
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Definition
| sapovirus (related to norovirus), astrovirus (children), and adenovirus (children, and may also cause pulmonary problems) |
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Term
| what cells are affected by those viruses causing diarrhea? |
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Definition
| most diarrhea-causing viruses afffect enterocytes in the intestinal villi (the secreting cells) |
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Term
| what characterizes the viruses responsible for diarrhea? |
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Definition
| most are naked icosahedral viruses which can survive low pH and get into the intestines. their final stage of replication involves lysing the enterocytes they infect (cytopathic) which results in sloughing/blunting of the villi. (rotavirus also produces enterotoxin –> chloride and water secretion) |
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Term
| what happens when the intestinal villi are damaged by viral infection? how does this lead to watery diarrhea? |
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Definition
| the intestine enters a state of malabsorption, which the crypts between the enterocytes counteract by increasing division - resulting in hypersecretion/hyperplasia, causing watery diarrhea. as the virus is cleared, the crypt cells re-establish themselves, and the symptoms resolve |
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Term
| what is the incubation period for viruses causing diarrhea? |
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Definition
| rotavirus (1-4 days, a little more severe) and norovirus (1-2 days) |
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Term
| what are the symptoms of gastroenteritis due to viral infection? |
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Definition
| abrupt onset of watery diarrhea and/or vomiting, no blood in stool and low-grade fever/dehydration. (vomiting is more prevalent in children and diarrhea is more common in adults. bacteria are also less likely to cause vomiting except for some types of food poisoning) |
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Term
| what is the duration of symptoms due to the different viruses responsible for gastroenteritis? |
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Definition
| rotavirus (5-8 days) and norovirus (1-3 days) |
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Term
| what is the duration of viral shedding (*asymptomatic) due to the different viruses responsible for gastroenteritis? |
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Definition
| rotavirus: 2-12 days and norovirus: peaks at 1-3 days, but can occur for >1 week |
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Term
| what is the tx for viral gastroenteritis? |
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Definition
| treatment of dehydration and electrolyte imbalance |
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Term
| how is the type of virus detected in a pt w/viral gastroenteritis via electron microscopy? |
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Definition
| often a specific detection is not made. however, when necessary, electron microscopy may be used - though it is not as sensitive and work intensive. |
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Term
| how is the type of virus detected in a pt w/viral gastroenteritis via serology? |
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Definition
| serology can be used to look for ab in pts serum, which can confirm a recent illness or be useful when tracking outbreaks (to see if an ab has been upgraded). for rotavirus, an increase in titers is necessary for a dx, b/c everyone has been exposed. |
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Term
| what are the different types of serology which are used in detection of viral causes of gastroenteritis? |
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Definition
| latex agglutination (rotavirus), enzyme immunoassay (EIA - detects antigen in fecal specimens/vomitus, easy/quick/cheap/sensitive), and RT-PCR (more common in research settings and tracking outbreaks) |
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Term
| when tracking viral outbreaks, what are 2 methods of specifically identifying strains/serotypes? why is this important? |
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Definition
| RT-PCR & sequencing (can determine viral genotypes, which generally correlate w/serotype) and pulsed field gel electrophoresis (PFGE - RNA cleaved with enzymes and run on gel -if banding pattern the same, likely from same source). these are important when trying to find the source of an outbreak (need RNA from specimen and take food/environment and look for same subtype to link them) |
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Term
| what characterizes the rotavirus? |
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Definition
| ds RNA, 11 segments, triple-shelled capsid (one of the reasons it is so stable in the GI) |
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Term
| what is the VP2 protein in the rotavirus? |
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Definition
| the inner capsid layer (equivalent to the capsid protein in an enveloped virus) |
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Term
| what is the VP6 protein in a rotavirus? |
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Definition
| the middle capsid layer (equivalent to the matrix protein in enveloped viruses). this helps define the different groups of rotavirus. |
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Term
| what are the VP7 and VP4 proteins in the rotavirus? |
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Definition
| these make up the outer protein layer (equivalent to the envelope in enveloped viruses). the VP4 proteins elict neutralizing antibodies and are targets for vaccines. |
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Term
| which out of the VP6 groups A-E do most human strains of rotavirus belong to? |
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Definition
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Term
| what is the viral enterotoxin produced by rotavirus? |
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Definition
| nonstructural protein 4 (NSP4), which triggers a signal transduction pathway, resulting in Cl secretion. its production can affect unaffected cells. |
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Term
| how are the serotypes/genotypes determined for rotaviruses? |
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Definition
| by the specific type of VP7 and VP4 outer shell proteins which induce neutralizing ab. the antigenicity determines the serotype and sequencing determines the genotype |
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Term
| what are the 5 most common genotypes of rotavirus? |
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Definition
| G1P[8], G2P[4], G3P[8], G4P[8], and G9P[8] |
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Term
| who is rotavirus the leading cause of acute diarrhea in? |
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Definition
| children <5. most severe cases seen between 3-35 mos and 90% of pts acquire ab against rotavirus by age 3 |
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Term
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Definition
| an oral anti-rotavirus vaccine which was only on the market for ~1 year |
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Term
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Definition
| a human/bovine reassortment vaccine for rotavirus a - combination of 5 different viruses, 4 which express the human G protein w/a bovine P protein and 1 expresses the human P protein in bovine background |
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Term
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Definition
| a live attenuated oral vaccine for rotavirus which is monovalent |
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Term
| what is the overall result of using the rotavirus vaccine? are any of the vaccines considered more effective? |
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Definition
| rotavirus seasons are shorter, later, and less cases occur overall. all vaccines available are considered equally effective. |
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Term
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Definition
| porcine circovirus type 1 & 2, which DNA of was found in both rotavirus vaccines. they were eventually determined to present little risk due to lack of evidence that either poses a risk to people. |
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Term
| what characterizes the caliciviridae - specifically noroviruses? |
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Definition
| noroviruses (genus) are RNA, icosahedral, naked, and belong to the caliciviridae family. they are named for a 1972 gastroenteritis outbreak in norwalk ohio. |
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Term
| what characterizes the sapoviruses? |
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Definition
| these viruses also belong to the caliciviridae family and were visualized in sapporo, japan (1977) but bore several similarities to noroviruses. they are associated with sporadic outbreaks in young children |
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Term
| how is a dx of norovirus made? |
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Definition
| generally specifically naming the virus is not done - instead it is a dx of exclusion if stool samples are negative for bacteria/parasites. clinical symptoms can also be a clue, generally consisting of vomiting(big clue)/diarrhea either together or separate. generally disease lasts 12-60 hrs w/incubation time of 24-48 hrs (bacterial time for this is longer, but disease due to preformed toxins will be shorter) |
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Term
| what is the most common cause of nonbacterial gastroenteritis in older children and adults? |
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Definition
| norovirus, which in general is due to most family/community outbreaks as a result of contaminated food/water. secondary cases due to person-person transmission often occur in confined settings such as nursing homes/daycares/cruise ships/long term care facilities |
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Term
| what are factors influencing spread during outbreaks? |
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Definition
| low infectious dose (<100 particles), asymptomatic shedding (difficult to control spread), withstands Cl/freezing/heating (difficult to inactivate), strain diversity (harder to dx, infection by mult types), and lack of lasting immunity |
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