Viral causes of diarrhea Flashcards
Which bug is the most common cause of severe diarrhea in children worldwide?
Rotavirus
Describe the characteristics of rotavirus
Member of REOvirus family
ds RNA, non-enveloped but has an inner and outer capsid
segmented genome allows for reassortment which impacts vaccine development
What are 4 important proteins in the structure of Rotavirus?
VP7 and VP4 - outer capsid proteins for neutralization
**VP7 is the major neutralization protein that gets cleaved byGI proteases thereby activating the infection**
VP4 - responsible for binding and neutralization as well; aka P protein (protease cleaved)
VP6 is an inner capsid protein and is the basis of immunoassay testing (Group A is the most common protein worldwide)
NSP4 - enterotoxin that causes watery diarrhea
Which Rotavirus serotype is the most common worldwide?
G1P8
**G1, G2, G3 and G9 comprise most of the infections**
Describe the replication of rotavirus
attachment via VP4 (not sure if G protein cleavage of VP7 happens before or after attachment) >> release of core into cytoplasm >> transcription/translation >> inner capsid entry into ER >> acquisition of VP7 + temporary envelope >> mature virus released by cell lysis
Describe how rotavirus causes watery diarrhea
Which toxin is implicated in the production of this watery diarrhea
cytolytic infection of villus tips - causes blunting of microvilli which decreases absorption of water and sugars (so that’s part), then there’s also migration of secretory crypt cells to the vilus tips which increases secretion of water and ions (and that’s part two)
NSP4: activates the enteric nervous system to induce secretion of water and ions (watery diarrhea);
also NSP4 causes actin rearrangement >> no tight junctions >> paracellular leakage >> watery diarrhea
How is rotavirus transmitted?
Primarily fecal-oral
(can also be transmitted via other routes:fomites, respiratory, contaminated food/water)
What time of the year would you expect a pt to present with rotavirus infection?
Rotavirus infection primarily occurs in the winter
Describe the following for rotavirus:
incubation time
duration of symptoms
symptoms
Incubation: avg 2 days (12 hrs - 4 days)
Illness: 4 to 8 day duration
Symptoms:
Vomiting (often just at beginning of illness)
Watery diarrhea (no gross blood or fecal WBC)
Low grade fever (~50%)
Typically no fecal leukocytes
The primary complication of rotavirus infection is __ (hint: this is the major thing that oral rehydration seeks to address)
Dehydration
**
other complications:
Electrolyte abnormalities
Acidosis
Persistent diarrhea (immunocompromised/malnourished)
Carbohydrate malabsorption (common, but <10% clinically significant)
T/F: There’s no rotavirus vaccine
What is the basis of the immunogenicity of rotavirus vaccines?
Falasehood. There are a few vaccines but all of them are oral, live-attenuated vaccines. Main one is RotaTeq: pentavalent rotavirus vaccine that contains G1-G4 and VP4
Basis of immunogenicity of rotavirus vaccines: based on human rotavirus antigens being expressed on monkey rotavirus. The vaccine can induce immunity in the human host without causing disease b/c its not technically human rotavirus
Which enteric adenovirus serotypes are associated with diarrheal disease?
Describe the characteristics of enteric adenovirus
Adeno serotypes 40 and 41
ds DNA icosahedral viruses; Have penton fiber projections that help with binding/attachment to host cell
Contrast enteric adenovirus with rotavirus in terms of transmission, seasonality, incubation period and illness duration
Note that transmission here is person to person in contrast to rotavirus which is fecal-oral
Also note: no seasonality, longer incubation (1+ week as opposed to 2 days and about 1.5 week illness duration as opposed to 1 week for rotavirus)
Describe the characteristics of astrovirus
small, smooth-surfaced, non enveloped, ss (+) sense RNA virus that looks like a 5 or 6 pointed star on EM
Astrovirus can be transmitted from ___ or contaminated food/water. The incubation period is ___ and the virus causes sporadic diarrheal disease in ___ (population)
Astrovirus can be transmitted from person to person or contaminated food/water. The incubation period is 4-5 days and the virus causes sporadic diarrheal disease in kids over a year old (population)
Describe the characteristics of human caliciviruses
non-enveloped, (+) RNA, cup (calix)-shaped surface depressions
human CVs can’t be cultured; virus replicates in cytoplasm; viral particles released by cytolysis
What effects does norovirus have on the jejunal tissue which results in diarrhea?
Blunts them pretty much, rendering them unable ro reabsorb anything (see image below)
