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FAMILY CALICIVIRIDAE: Noroviruses

FAMILY CALICIVIRIDAE: Noroviruses. To Be Discussed:. Taxonomy, structure and genome Disease manifestations and clinical symptoms Diagnosis Transmission Epidemiology and incidence Environmental resistance Prevention and Control. Noroviruses Taxonomy. Previously- Family Caliciviridae

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FAMILY CALICIVIRIDAE: Noroviruses

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  1. FAMILY CALICIVIRIDAE:Noroviruses

  2. To Be Discussed: • Taxonomy, structure and genome • Disease manifestations and clinical symptoms • Diagnosis • Transmission • Epidemiology and incidence • Environmental resistance • Prevention and Control

  3. Noroviruses Taxonomy Previously- Family Caliciviridae Genus: 1. Norwalk-Like Viruses (NLVs) 2. Sapporo-Like Viruses (SLVs) Recently- Genus Noroviruses (formerly Norwalk-Like Viruses)

  4. The Norovirus Genus • Norwalk Virus • Desert Storm Virus • Southampton Virus • Snow Mountain Agent • Hawaii Virus • Toronto Virus • Bristol Virus • Jena Virus

  5. Viral Morphology • Non-enveloped, icosahedral • 27-40 nm • Single structural capsid protein, 60kD - 180 molecules, folds into 90 dimers • Distinguishing characteristic: 32-cupped shaped depressions on the axes of the icosahedron

  6. Norovirus Structure by EM www.pubmed.gov PMID: 13679618

  7. Genome • (+) ss RNA, 7900 nt in length • 3 Open Reading Frames: ORF1= non-structural proteins- RdRp + helicase ORF2= structural capsid protein ORF3= small protein, function unknown ORF1 ORF2 ORF3 hel cap ? 5’ RdRp 3’

  8. Genome www.allthevirologyonthewww.com www.pubmed.gov; PMID: 13679618

  9. RdRp Structure Crystal structure from www.pubmed.gov PMID: 12706072

  10. Replication Strategy Replication suggested- Typical of positive-sense ss RNA viruses, unconfirmed Wagner et al. Basic Virology. www.netlibrary.com

  11. Replication of the Genome Wagner et al. Basic Virology. www.netlibrary.com

  12. Disease Manifestations • Infects small intestines and causes gastroenteritis • Expansion of the villi at proximal small intestine and shortening of the microvilli -epithelial cells remain intact • Incubation period: 24-48 hours • Mistakenly termed- “stomach flu”

  13. Path of Infection Wagner et al. Basic Virology. www.netlibrary.com

  14. Clinical Symptomology Non-bloody diarrhea Nausea Vomiting Abdominal cramps Malaise Myalgias Headache Low-grade fever • Symptoms last 12-60 hours. • Children tend to suffer from vomiting, while adults tend to suffer from diarrhea.

  15. Transmission • Fecal-Oral • Typically in contaminated drinking water • Many sources found : poorly maintained municipal supplies wells recreational lakes swimming pools cruise ship water food handled by infected person or washed with contaminated water

  16. Prevalence of Sources of Transmission

  17. Epidemiology and Incidence • Found Worldwide. • Burden: - ca. 267,000,000 annual cases - 612,000 hospitalizations - 3,000 deaths • Highly contagious: fewer than 100 virus particles can cause infection • 2002- Cruise ship bound for Alaska- 13% of 1266 on board were affected; contaminated drinking water

  18. Epidemiology Frankenhauser et al. www.cdc.gov

  19. Prevention and Control • Highly Stable in environment- resistant to: freezing heating to 60ºC disinfection w/ chlorine acidic conditions vinegar alcohol high sugar concentration

  20. Prevention and Control • Infection produces IgG, IgA and IgM, but antibodies are not protective. • No lasting immunity or protection from reinfection. Transient immunity- lasting 3-4 months. • Vaccine not likely. • No current antiviral drugs, however complete recovery is most common. • Prevent by hand-washing, good hygiene, proper water management, preparation of food.

  21. Things to Remember for Exam • Defining structural characteristic(s). • Nucleic acid/ genome type. • How many open reading frames and what each one contains (general). • Cell tropism and effects; hint- Does Norwalk virus kill intestinal epithelial cells? • Infectious dose; environmental stability • Lasting immunity?; protective antibodies produced?

  22. References Centers for Disease Control and Prevention. “Norwalk-Like Viruses:” Public health consequences and outbreak management. MMWR 2001; 50 (No. RR-9): [inclusive page numbers]. www.cdc.gov - MMWR, 2003, Outbreaks on Cruise ships. www.pubmed.gov suggested articles, PMID: 13679618; 14499247; 14557646; 14715308; 12791850; 12706072 Wagner, E.K.; Martinez, H. Basic Virology. Malden, MA. Blackwell Science, 1999. www.netlibrary.com Dorlands Online Medical Dictionary. www.dorlands.com

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