Norovirus: Nature’s Perfect Puke’o’genic Pathogen

Todd F. Hatchette MD FRCPC

Director, Virology and Immunology

QEII HSC

November 27, 2008

Overview

• Case

• Outline features of Norovirus– Epidemiology– Transmission– Clinical features– Infection control concerns

Case

• Thursday 1230 AM index case awoken from sleep with projectile vomiting

• Distressed

• Multiple vomiting episodes overnight

• Relocated to more “comfortable” location

• By 800AM was fatigued but otherwise well

• Friday 1700 hrs– Patient #2 feels light headed

and fatigued– Nausea and vomiting begin

at 1745– Associated with

• profuse watery diarrhea• Fever• Chills

• Vomiting resolves by 0300hrs

• Diarrhea resolves next day

Caliciviridae

• Members of the Caliciviridae

• (Calyx; Latin for cup or chalice).

• + sense, single-stranded RNA genome.

• EM: structured.

• Size: 26-40 nm

• Had been referred to by names are derived from the geographic area they are discovered

• Small round-structured virus (SRSV)

• Now classified into genogroups

Caliciviridae

• New classification: four genera1. Norovirus – Found in human, cows and pigs

• Most common cause of human illness

• Includes the “Norwalk-like” agent

2. Sapovirus – Found in Humans and pigs• “Saporo-like” agents

3. Vesivirus:• Animal viruses – feline

4. Lagovirus:• Mainly in rabbits/hares. Rarely has been isolated in humans

The Many Faces of Norovirus

(Zeng et al., 2006 Virology 346:312-323)

Caliciviridae

ORF 1ORF 2

ORF 3

2C 3C 3D 3’5’ AAAAAA

• Genetic variation occurs by recombination

– Occurs at the junction of the NS cassette and capsid regions

– May permit virus to escape host immunity

Norovirus - Epidemiology• Most common cause of sporadic gastroenteritis

– 23 million infections each year in the US

• Causes up to 50% of all food borne outbreaks• Accounts for 54% of Gastro in Hospitals in UK

– Cost 184 million (US) between 2002-2003

• Common cause of travelers diarrhea• Since 2002 PHAC has had approximately 300-

400 outbreaks each year• High attack rate

History

• Zahorsky 1929 describes “winter vomiting disease”– Outbreaks of non-bacterial gastro (NBG)

• Gordon et al 1940’s– Collected stool samples from institutional outbreak of

NBG ; filtrate “fed” to volunteers

– Showed it could be serially passed in humans

– Could not isolate pathogen in eggs

History

• Norwalk Ohio, 1968– Outbreak of “winter vomiting disease” in an elementary

school

– 50% of students and teachers were infected

– Etiology could not be identified but stools saved and filtrates used in subsequent human experimentation

• Kapikian et al., 1972– Able to visualize SRGV in EM from volunteers

infected with filtrate from Norwalk outbreak

Winter Vomiting disease

Lopman et al., 2003 BMC Public Health

Why could it be seasonal?

• Possibly related to virus stability

• Social behaviors that increase the likelihood of person-to-person transmission

• Winter pressures on healthcare

Not Just a Winter Disease

Frankhauser et al., 2002 JID 186:1-7)

Not Just a Winter Disease

Frankhauser et al., 2002 JID 186:1-7)

Norovirusclinical presentation

• Incubation – 12-48hrs

• Onset abrupt or gradual

• adults commonly presents as explosive projectile vomiting, diarrhoea or both but either can occur alone

• myalgias, malaise and occasionally headaches

• low grade fever in 50%

• Illness lasts 12-60 hrs

Clinical Presentation

• Retrospective sturdy looking at large food borne outbreak in children and staff at 30 day care centers in Sweden (Gotz et al., 2001 CID 33:622-628)

– Diarrhea more common in adults– Vomiting is more common in children

• Prospective community cohort study in the Netherlands (Rockx et al., 2002 CID 35:246-253)

Rockx et al., 2002

Duration of Shedding

Correlates with age but not duration or severity of symptoms

Rockx et al., 2002

Duration of Shedding• 71 cases of gastroenteritis, 71 children were positive for

NV by RT-PCR (Murata et al. 2007 Ped Infect Dis J 26:46-49)

• Healthy Pediatric patients can shed for up to 47 days

Shedding and Immunosuppresion• Up to a year in pediatric cancer patients

(Ludwig et al., 2008 J Med Virol. 80:1461-1467)

(Siebenga et al., 2008 JID: 994-1001)

Norovirus – Clinical Presentation

• Clinical criteria for recognizing Norovirus outbreaks (Kaplan et al., 1982; Turcios, et al. 2006)

– (99% specific/68% sensitive)

• Short incubation period (24-48 hours)

• Short symptomatic illness (12-60 hrs)

• High frequency of vomiting (> 50%)

• Absence of bacterial pathogens

• Symptoms vary patient to patient

Norovirus Transmission

• Transmission

– Fecal Oral• Direct contact• Contaminated

fingers/hands • Aerosol

Norovirus - Transmission

• Transmission associated with– Contaminated food

• 9.2/13.8 million cases of food related illness in US secondary to calicivirus

• Any food not served hot (56oC for 30 min before preparation) can be a source of infection.

– Person to person contact– Oysters

• NV can bind to the carbohydrates in the gut of shellfish• Sick crew members contaminated the oyster field

– Contaminated water• Genome has been identified in bottled water

– Mode of transmission sometimes not clear

MMWR 2001 50 RR-9

Mode of transmissionSettings

Outbreaks of Gastroenteritis Reported to CDC Jan 1996–Nov 2000*

N=348

Food as a source

• Calicivirus stable on food for up to 1 week (Mattison et al., 2007 J Food Pro 170:500-503)

4oC Room temp

Why are they so Infectious? Characteristics that facilitate their spread during epidemics

• Low infectious dose• Prolonged asymptomatic shedding• Environmental stability

– Survives <10ppm Chlorine, freezing and heating to 60 oC

• Strain diversity– Multiple antigenic and genetic types

• Incomplete immunity

MMWR 2001 50 RR-9

How Infectious is it?

• Human challenge studies are limited because the starting dose is unknown– Try to quantify by EM but

many particles are in aggregates

• Estimated that 49% of people exposed to a single virus particle will get infected. (Teunis et al., 2008 J Med Virol 1468-1476)

• The higher the dose the more likely people developed illness

(Teunis et al., 2008 J Med Virol 1468-1476)

Norovirus Persistence on Surfaces

(Clay et al., 2006 AJIC 34:41-43)

Norovirus and the cruise ship industry - “the ship of stools”

“The Carnival of crap”

• 2002 – 21 outbreaks of acute gastroenteritis on 17 cruise ships reported to CDC– 9 were laboratory confirmed cases of Norovirus– 9 unknown

• 26 land-based outbreaks reported during the same time

Norovirus and the cruise ship industry

• 3/5 outbreaks described in the MMWR (2002:51(49) 1112-1115) had repeated outbreaks on subsequent cruises after disinfections in accordance with CDC recommendations– Required “aggressive cleaning

and sanitizing” before outbreaks stopped

Caliciviridae diagnosis

• Diagnosis– Culture – not successful*

– EM• laborious and relatively

insensitive (requiring 106 to 107 particles/g or ml of feces).

– RT-PCR• Which gene to target?

– Testing 5 specimens appears to be ideal (Fisman et al, 2008)

RT-PCR performed9 primer sets

Visualize PCR products

Sequencing

Compare with GenBank

Report*Recent 3D culture has some success(Straube et al., 2007 EID 13:396-403)

Norovirus pathogenesis• Pathogenesis is not clear

– Lesions in the small bowel

• Broadening and blunting of intestinal villa

– Transient malabsorption of sugars and fats

– Decreased activity in brush border enzymes

(Hutson et al., 2004 Trends in Microbiol. 12:279-287)

Norovirus

• Long term immunity is not consistent and usually short lived

• Immunity appears to be genotype specific

• Paradoxical association with antibody level– Suggests genetic factors

Norovirus and Human Resistance

Lindesmith et al., 2003 Nat Med 9:548-553

Tan and Jiang, 2007

Norovirus and Mortality

• Illness is generally self limiting• Elderly can succumb to complications of

dehydration• Recent US estimates

– 310/23 million die each year

– 553/1.4 million cases of Salmonella die each year

– Others estimate lower (0-3.7 deaths/year)

Norovirus and Mortality• Case fatality in UK -

7.5/10000 cases• Recent modeling data

suggests that from 2001-2006 there were 228 deaths from norovirus related infections in England and Wales – Represents 20% of deaths from

infectious diseases in >65 yrs

(Harris et al., 2008 EID 14:1546-1552)

Prevention

• Good hand hygiene– Alcohol based hand washes? - controversial

• Good “food hygiene”• Discard stool & vomit and clean with a

bleach solution– H2O2 products can also be used

• Patients to remain off work for 72 hrs after symptoms resolve

Are Noroviruses “Emerging”(Widdowson et al., 2005 EID 11:735-737)

• >2500 foodborne outbreaks of norovirus 1995-1997– <1% attributed to norovirus

– 68% were unknown etiology

• Today– Responsible for up to 50% of food borne outbreaks in

US

– Detected in 35% of persons with sporadic gastroenteritis

The “other” Pandemic• Genogroup II.4

– First identified in mid 1990’s

• Responsible for significant outbreaks in Nursing homes in US and acute care facilities in Europe

• Continues to evolve

Laboratory Reports of Norovirus-Positive Specimens in England and Wales, 1991 to 2006

Lopman et al., 2008 PLoS Med 187-189

How did to arise?• Could new variants arise in chronically

infected patients?

Siebenga et al., JID 2008 198:994-1001

Siebenga et al., JID 2008 198:994-1001

Norovirus the “Gastric Flu”

• Evidence for genetic drift - the surface exposed carbohydrate binding domain is under heavy immunologic pressure

• Examined 176 full length GII.4 sequences from 1987-2005

• Found 5 major clusters

Lindesmith et al., 2008 PLoS Med 5:269-289

Norovirus the “Gastric Flu”

Lindesmith et al., 2008 PLoS Med 5:269-289

Camberwell (1987-1995)

Grimsby cluster (1995-2002)

Farmington Hills (2002-2004)

Hunter (2004-2006)

Sakai (2004-2006)

Den Haag (2006)

Norovirus the “Gastric Flu”

• Genetic drift of H3 Influenza A from 1983-1994

Bush et al., 1999 Science 286:1921-1925

Norovirus the “Gastric Flu”

• Evidence of positive selection in AA in the P2 protein (surface exposed region) but no single pattern was discernable

• VLPs containing representative samples had different binding affinities with different antigens

Evidence for Zoontic transmission

• Noroviruses known to infect pigs, cattle, mice• Cattle and pigs can be infected experimentally

with human strains• Human norovirus GII.4 was detected in fecal

samples from cattle and swine and from retail meat samples (along with animal samples) (Mattison et al., 2007 EID 13:1184-1188)

• Genetic diversity can occur through recombination

Nature’s Perfect Puke’o’genic Pathogen

• The ultimate goal of a virus is not to kill its host but to find a new host to infect so that it can replicate its genetic material. What better way to do this than to induce explosive diarrhea and vomiting.