Norwalk Virus

1. Norwalk Virus FanazKhairi 1012

2. Family Caliciviridae • Small, nonenveloped RNA viruses • Norwalk virus is the best known of the human caliciviruses • Humans are the only known hosts • No. 1 cause of Gastroenteritis Introduction

3. Primarily in stool, but also in vomitus • Occurs for at least 2-3 weeks • Peaks 4 days after exposure • Infectious dose: 18 to 1,000 viral particles • A droplet of vomitus has enough viral particles to infect over 100,000 people • Virus can survive 12 hours on a surface • 12 days in contaminated fabric • A study demonstrated survival for 61 days in well water.

4. Norwalk and Norwalk-like viruses belong to the genus of Noroviruses and are named after location of outbreak • Norwalk, Ohio • Snow Mountain, Colorado • Taunton and Southampton, England • Otofuke and Sapporo, Japan • Sapovirus • Formerly known as Sapporo-like virus • Genetic homology yet distinct antigenicity among Norwalk and Norwalk-like viruses by immune electron microscopy studies Classification

5. In 1968, 50% of 232 students and teachers at a Norwalk elementary school developed acute gastroenteritis • In 1972, the Norwalk virus was discovered by Dr. Al Kapikan from the National Institute of Allergy and Infectious Disease by immune EM of stool samples from the 1968 outbreak History

6. Classified in 5 genogroups; 31 different clusters of groups • Small, round, 27 nm diameter, nonenveloped • Single linear piece of (+) RNA, 7.5 kb • Organized into 3 Open reading frames (ORF-3) • 5’ encodes for the nonstructural proteins –7 • Main protein is the major structural protein for the capsid • 3’ encodes for 2 structural proteins—this separates the ORF2 and 3 • 5’ end is covalently bound to a viral protein called VPg • 3’ end is polyadenylated • Minor overlap between ORF 1 and 2 where the mRNA lies Structure

7. The precise cell tropism of Noroviruses is unknown • No virus particles have been found during biopsies • Based on recent studies the block to propagation is at the level of receptor binding or uncoating Replication

8. Acute viral gastroenteritis • Infectious dose • Signs and symptoms • Abdominal pain • Vomiting: non-bloody • Diarrhea: watery, non-bloody • Nausea • Headache • Low-grade fever • Malaise • Myalgia Signs and Symptoms

9. Incubation period: 12-48 hours • Acute onset vomiting and/or diarrhea • Watery, non-bloody stools • Abdominal cramps, nausea, low-grade fever • Most recover after 12-72 hours • 10-12% seek medical attention; some require hospitalization and fluid therapy • Severe disease occurs more frequently among older adults, young children, and immunocompromised patients • More severe illness and death possible in elderly and those with other illnesses • 30% of infections are asymptomatic Medical Attributions

11. Person to person • Direct fecal-oral • Ingestion of aerosolized vomitus • Indirect via fomites or contaminated environment • Food • Contaminated by infected food handlers • Point of service or source (e.g., raspberries, oysters, leafy vegetables) • Recreational and Drinking Water • Well contamination from septic tank • Chlorination system breakdown • In healthcare, most likely from direct contact with infected persons or contaminated equipment Transmission

13. Most adults have serum antibodies • No protection against infection • Markers or risk factors • Studies have shown short-term immunity persisting for about 12 weeks • Strain-specific • Repeated infections likely • Further studies • Genetic susceptibility • High risk of severe infection among those with O blood type • Repetitive past exposures Defense

14. 50% of all outbreaks involving acute infectious, nonbacterial gastroenteritis in the U.S. caused by the Norwalk virus • Second most common cause of illness in U.S. after influenza • Occurrence typically in older children and adults • Serum antibodies acquired during early adulthood • Camps, schools, nursing homes, military populations, cruise ships • Infection is worldwide based on seroprevalence studies • Some evidence that Norwalk is spread by the respiratory route • Transmission through aerosolized virus-containing vomitus • Very rapid secondary spread of infection Epidemiology

15. Virus identified in stool specimens • Antibodies measured in serum samples by immune EM or immunoassays • Few research laboratories with necessary reagents from human volunteer studies • Limited diagnosis to community outbreak settings • 27 state public health laboratories can test for virus in stool or contaminated food and water by reverse transcriptase polymerase chain reaction (RT-PCR) Diagnosis

16. Wash fruits and vegetables before preparing and eating them • Cook oysters and other shellfish thoroughly before eating them • Food that might be contaminated with the virus should be thrown out • Keep sick infants and children out of areas where food is being handled and prepared • When sick, do not prepare food or care for others for at least 72 hours after symptoms subside • Clean and disinfect contaminated surfaces • Wash hands Prevention

17. Vaccines focus on the capsid protein expression in various vectors—immunogenic VLP • Require serum IgG and IgA responses—but protective potential has not been determined • A dry powder vaccine—intranasal in conjunction with TLR-4 agonists Treatment and Vaccine