GI 5 Flashcards
4 genera of norwalk virus
NOROVIRUS, SAPOVIRUS, lagovirus, vesivirus
feature of norwalk virus
- naked, + ssRNA
- amorphous surface with feathery ragged outline
causes 66% of gastroenteritis outbreaks in long term facilities
sapovirus (family of calciviridae)
types of patients you see sapovirus
children and adults (elderly)
sapovirus is common in older children and adults. why is it becoming popular in children less than 5 years
because of vaccination to rotavirus
what time of the year is norovirus common
winter
transmission of norwalk virus/norovirus
primarily fecal oral route
but can be air and food borne
food is norovirus commonly seen in
raw shellfish
pathogenesis of norovirus
virus multiplies in the SI –> produces transient lesion of the mucosa –> spares the large intestine –> shed in feces
importance of norovirus sparing the large intestine
there is NO FECAL LEUKOCYTES
clinical manifestation of norovirus: include incubation period, duration, and symptoms
- incubation - it is mild and brief so 24-48 hrs
- duration: lasts 24-60 hours
- abdominal cramps, myalgias, malaise, headache, nausea, low grade fever & 1-2 days diarrhea
- fatalities are rare
how do you diagnose norovirus
- mean duration of 12-60hrs
- mean incubation is 24-48hrs
- greater than 50% of people with vomiting
- no bacterial agent previously found
how do you detect norovirus
not sensitive so must difficult to culture
-virus peaks in stool at about day 2-5 so you can do RT-qPCR assay
where do you commonly see norovirus outbreaks
cruise ships
how do you treat norovirus
- Ligolyte
- 2 doses of IM vaccine taken 3 weeks apart
describe adenovirus
- icosahedral
- naked ds DNA
- 12 vertices pentons with fibers on the end
two serotypes of adenovirus
40 and 41 (Group F)
pathogenesis of adenovirus
- main target is the respiratory tract but infects epithelial cells of pharynx, conjuctiva, SI, and other organs
- if in SI, it will replicate and present in the stool
symptoms of adenovirus
diarrhea with or without vomiting
features of astrovirus
small, naked +ssRNA that has smooth or slight indented outer shell
when are people infected with astrovirus
throughout the year but peak in the winter
feature of Hep A
icosahedra, naked +ssRNA
how is Hep A virus spread
fecal oral route, person to person, poor sanitation, and overcrowding
Hep A is the common cause of what condition and what are the first symptoms
acute hepatitis
nausea, vomiting, and fever
jaundice comes later on and does not subside until all the other symptoms are gone
features of Hep E
naked, symmetrical +ssRNA
where do you find Hep E and what is its incubation period
found in Indian subcontinent
6 weeks which is longer than Hep A
what are inflammatory diarrhea
– Bacterial • Shigella spp. • E. coli (EIEC) • Salmonella Serotypes • Campylobacter spp. • Yersinia spp. • V. parahaemolyticus & V. vulnificus • EAEC & STEC (EHEC) (Non invasive organisms - cytotoxin)
– Parasitic
• Entamoeba histolytica
• Balantidium coli
what is the symptomology of inflammatory diarrhea
bloody diarrhea
how do you get the microbes associated with inflammatory diarrhea and what are the type of toxins released
food borne infection
release enterotoxin and cytotoxins
what are the 4 groups of O antigen of shigella and classify them according to their severity
shigella dysenteriae (most severe)
shigella flexneri
shigella boydii
shigella sonnei (mildest form) –> water diarrhea instead of bloody diarrhea
what is the virulence factors of shigella
- endotoxin (O antigen)
- exotoxin: enterotoxin that act as neurotoxin
- NAD glycohydrolase
what does the enterotoxin and NAD glycohydrolase in shigella do
- enterotoxin which acts as a neurotoxin causes meningismus and coma and ulceration
- NAD glycohydrolase destroys all NAD in human cells hence shutting down metabolism and then cell death
what are the clinical manifestation of shigella sonnei and flexneri
- flexneri: severe abdominal pain and dysentery
- sonnei: vomiting and watery diarrhea common
pathogenesis of shigellosis
- ingest small amount which invades epithelial and M cells in large intestine via invasive induce endocytosis
- multiplies in the cytoplasm
- then spreads to adjacent epithelial cells by actin polymerization –> cell destruction via apoptosis
what is bacillary dysentery
shigella dysenteriae type 1 (shiga bacillus)
what is so important about shigella dysenteriae type 1 (shiga bacillus)
the only species to produce the shiga toxin –> which is a cytotoxin that inhibits protein synthesis leading to cell death
what does the shiga toxin act as?
enterotoxin –> produces diarrhea
exotoxin –> inhibits sugar and AA absorption in SI
neurotoxin –> affects CNS
common population that you see the shigellas in
shigella sonnei - children less than 5 years in day care
shigella flexneri - men who have sex with other men
shigella boydii - rare
pathogenesis of shigella
transmitted the fecal oral route: sanitation break downs (4 Fs - fingers, food, flies, feces)
treatment of shigella
antibiotics
tetracycline - most common
chloramphenicol
ampicillin
how do you diagnose shigella
take sample of stool or water or food
use MacConkey’s agar or S-S agar (salmonella-shigella agar)
what would you see on the S-S agar for shigella – why?
it will grow as colorless or pale due to no lactase fermentation
shigella is non motile, gram negative, no fermentation lactose, no utilization of citric acid, no H2S production (except S. flexnieri), no gas from glucose
