Diarrheal Viruses Flashcards
Do all enteric viruses cause diarrhoea?
NO
- viruses may replicate in the gut and disseminate via viraemia to infect distant organs
e. g. enterovirus –> skin rash/ vesicles, hand food mouth disease, meningitis, encephalitis
e. g. hepatitis A and E –> acute hepatitis with nausea, LOA, jaundice and deranged LFT
General route of transmission of enteric viruses: examples, virus associated with each route, additional route?
Shed in stool –> faecal-oral route of transmission
- human-to-human e.g. food handling, fomites –> norovirus, rotavirus, Hep A/E
- environmental contamination e.g. food and waterborne –> norovirus, Hep A/E
Vomiting may accompany diarrhoea –> additional route of transmission through projectile vomiting
- env contamination
- create aerosol or airborne transmission
especially - NOROVIRUS
General properties of enteric viruses: envelope?, survival advantage, disinfection
mostly non-enveloped
- -> more physically “hard” and survive longer in environment
- -> withstand hard acidic env in stomach
- -> more resistant to disinfection (requires higher concentration)
Acute viral gastroenteritis DDx (4), overview
Norovirus, Rotavirus, Adenovirus, Astrovirus
2nd most common viral illness after respiratory tract infection
Unsafe water, poor hygiene and medical resources are main factors for high incidence and mortality
Rotavirus: structure, subtypes, epidemiology (3), seasonality
Reoviridae - 70-75 nm, “wheel” like
- structural protein VP7 defines G serotype
- among 8 groups, Group A infects humans (B and C rarely)
- minimal cross-species transmission (host-specific)
Epidemiology:
- MOST COMMON cause of viral GE in YOUNG CHILDREN worldwide
- bimodal peak of symptomatic infections - 6-24 mths and >60 yrs old
- asymptomatic in <6 mths (maternal Ab) and >5 yrs (adaptive immunity)
- male predominance
- seasonality: winter in temperate zones, variable in tropical zone
- important nosocomial (hospital acquired) infection
Rotavirus route of transmission, clinical presentation, treatment
Faecal Oral route
- mainly human-to-human (i.e. food handling, fomites)
Short incubation: 1-2 days
Duration: 4-7 days
Present as watery diarrhoea +/- vomiting, fever
–> dehydration is most life threatening consequence
Treatment: no specific tx, oral/IV rehydration
Rotavirus diagnosis (specimen, method, reasons for not using other methods)
STOOL is specimen of choice
- -> direct viral antigen detection by EIA and Latex agglutination
- -> PCR too sensitive (contamination) and EM throughput too low
- -> high viral load in stool (10^11/ml)
Rotavirus prevention: type, route of administration, regime, can give catch-up vaccine?, contraindications (2)
Oral vaccine for G serotype
- RotaRix - live attenuated, monovalent, 2 doses (2 and 4 months)
- RotaTeq - gene reassortment, pentavalent, 3 doses (2-4-6)
First dose between 6-15 wks (not after 15 wks), complete last dose before 32 wks
- don’t give catch-up vaccination as there is RISK OF INTUSSUSCEPTION in older infants
Can be co-administered with injectable inactivated vaccines but NOT ORAL POLIO VACCINE
(live virus in OPV affects gastric motility and increase risk of intussusception)
Contraindicated in severe immunodeficiency
Not part of CIP (gov immunisation program)
Norovirus structure, epidemiology (2), seasonality, common sources
Caliciviridae - 31-35 nm, “Star of David”/ “cup-like” indentations on surface
- ssRNA
- family also includes Sapovirus
Winter Vomiting Disease
Epidemiology:
- MOST COMMON cause of viral GE in ADULTS
- epidemic – common settings for outbreak include cruise ships, nursing homes, hospitals, daycare centres, swimming pools, camps
- seasonality: winter, sometimes in summer
- SEAFOOD is common source (contaminated raw food and inadequate cooking)
Norovirus routes of transmission, outbreak patterns (2)
Faecal Oral route
- very high load in faeces
- 80% human-to-human (fomites - taps, carpets, bed linen; cold food handling)
- environmental contamination (food handling esp seafood, inadequate cooking; drinking water)
Respiratory route
- inhalation of aerosols from projectile vomitus or faecal material
- +/- airborne
Outbreak patterns:
- point/ common source outbreak – e.g. contaminated food and water
- propagated/ person-to-person spread – clusters of cases spread by 1-2 incubation periods
Norovirus clinical presentation, treatment and prevention (4)
Symptomatic infection in all ages
Outbreaks mainly in adults and elderly homes
Short incubation: 0.5-3 days
Duration: 1-4 days
Present as projectile vomiting and nausea mainly
- also diarrhoea, abdominal pain, headache +/- fever
Treatment: rehydration
Prevention:
- no vaccine available
- proper hand hygiene, clean surfaces, wash laundry, gowns and gloves
- not alcohol based sanitisers as non-enveloped virus more resistant
- proper washing and cooking of food
Norovirus diagnosis (specimen, method, reasons for not using other methods)
RECTAL AND STOOL SWABS
–> RT-PCR
- -> EM: not widely available and too technically demanding for routine use
- -> Antigen detection: sensitivity not satisfactory
Enteric Adenovirus: structure, types a/w GE, presentation, lab diagnosis, treatment
Adenoviridae - 70-75 nm, hexagonal
- non-enveloped DNA virus
- types 40 and 41 a/w GE
- 2nd MC cause of viral GE in children
Affect young children and neonates with similar disease to rotavirus (watery diarrhoea)
Lab diagnosis: antigen detection by ELISA
Treatment: Oral/IV rehydration (supportive)
Astrovirus: size, affects what age, lab diagnosis
Small RNA viruses (28 nm)
Affect young children and neonates (10% cases)
No good antigen detection assay (use multiplex PCR)
Other DDx of acute gastroenteritis (6)
Bacteria - foodborne
- salmonella, shigella, campylobacter, E. coli O157, c. perfringens, b. cereus
Parasitic
- giardia lamblia, entamoeba histolytic in immunocompetent
- cryptosporidium, microsporidium in immunocompromised
Traveler’s diarrhea
- enteroinvasive/ enteropathogenic/ enterotoxigenic E.coli
- vibrio cholera
- salmonella, shigella, campylobacter
Non-infectious e.g. drugs, motility disturbances, IBD/IBS
