31: Norovirus

Question 1

salmonella vs. norovirus

Answer 1

salmonella is more about exceptional infection whereas norovirus is very common

number of infections much greater for norovirus

Question 2

norovirus lifetime risk in the US

Answer 2

leading cause of hospitalisation for children

small chance of death but causes many cases of acute gastroenteritis

19-21M cases annually

responsible for 96% of viral gastroenteritis cases

Question 3

norovirus worldwide statistics

Answer 3

most common cause of acute gastroenteritis

685M cases annually
- 200M in children < 5

leading cause of death in children under 5

over 90% of children in the world have norovirus by the time they are 2

Question 4

is norovirus a zoonosis?

Answer 4

no, only human-human

Question 5

norovirus characteristics

Answer 5

single stranded RNA virus with no envelope
- very stable as a cecal-oral pathogen

category B agent on list of possible bioterrorism agents
- can be put into the food supply
- very stable and easy to disperse

10 genogroups and 48 genotypes
- 3 genogroups primarily found in humans (group I, II and IV)

Question 6

norovirus symptoms

Answer 6

vomiting

diarrhoea

cramps

Question 7

how does norovirus infect?

Answer 7

binds to carbohydrates on mucosal epithelial cells, infects cells, replicates quickly and lyses cell

causes inflammation to trigger vomiting/diarrhea for reelease

Question 8

genogroups vs. genotypes vs. strains

Answer 8

challenge of vaccine production

great antigenic variation (like influenza)

10 genogroups with 1-15 genotypes in each group

VP1 as the main antigen that varies and results in a high number of genotypes and strains

GII-4 as the predominant genotype in outbreaks

Question 9

antigenic variation and GII-4

Answer 9

causes 80% of infections

endless number of noroviruses that can infect us as humans

antigenic drift
- constant mutations of norovirus, constant new strains, constant antigenic drift

Question 10

norovirus seasonality

Answer 10

GII is the main one that is seasonal, while GI is present at low amounts

winter seasonality in the US (and other temperate zones) but outbreaks can occur at any time of the year

5-15% of individuals found to be infected even in summer months
- not a virus that disappears

epidemic in the winter season, endemic in between

Question 11

norovirus transmission

Answer 11

more than just fecal-oral, also aerosol transmission
- norovirus very hardy outside the body and survives well

two very big outbreaks with raspberries and oysters
- oysters as filters of dirty sewage water in the ocean

Question 12

aerosol transmission and outbreaks

Answer 12

non-foodbourne outbreaks

schools, nursing homes, cruise ships and prisons
- concentrated places

Question 13

norovirus disease vs. no disease

Answer 13

after 1-2 day incubation period, 65-85% of infected individuals have symptoms for 1-3 days
- doesn’t always cause disease

severe cases are rare but require hospitalisation for dehydration

symptomatic individuals shed high amounts in the first 2-5 days with symptoms, but can remain infected after symptoms pass and shed virus for weeks

15-35% of infected people have asymptomatic infections

Question 14

attributes that allow norovirus to repeatedly cause outbreaks

Answer 14

highly contagious
- one of the most infectious viruses in humans

extremely stable in the environment
- survives on surfaces, food and water
- resistant to alcohol, vinegar, etc.

many different genotypes
- hard to build up protective immunity

Question 15

immune response to norovirus

Answer 15

protective IgA antibodies that prevent reinfection with that strain

protective immunity only lasts 6 months
- not a great memory response because it doesn’t get past intestines

less herd immunity against any specific norovirus in any given population

Question 16

norovirus in immunocompromised hosts

Answer 16

in healthy adults, symptoms only last 2-3 days and the virus clears in less than a week

can become chronic in immunocompromised individuals with infection lasting 6-12 months

Question 17

norovirus vaccines

Answer 17

new tetravalent vaccine using 4 different genotypes in clinical trials

virus-like particle containing proteins but no RNA
- similar to HPV as a recombinant protein vaccine making VLPs

Question 18

norovirus cruise ship outbreaks

Answer 18

in a 10-year period in the US, 250 outbreaks in nursing homes and 135 outbreaks in cruise ships

Question 19

difficulties in studying norovirus

Answer 19

difficult to grow in laboratories
- difficult to understand/diagnose

detection of antibodies tells you if someone’s been infected, but doesn’t say that it is active infection

diagnosis of active infection only down by detection of viral RNA in stool