Rotavirus Presented by Group 7 PCL2

Group 7 members: NSABIMANA Venuste 12113664 NYAZIYOSE Ignace 12113538 NZABONIMPA Clarisse 12112932 NZIYOMAZE Elie 12114015 NZAHUMUNYURWA Donat 12113484 RUGIRA Vive 12113869 RUKAMBA Jean de Dieu 12113905 SHABELI Philippe 12113979 SHEMA Origène 12114300 SIMBI Credo Sylvie 12113714 TSEMO Tagne Sandrine 213003054 TUYISENGE Elius 12113225  

Family Reoviridae Genus Rotavirus

Introduction Diarrheal disease has been recognized in humans since antiquity. Until the early 1970s, a bacterial, viral, or parasitic etiology of diarrheal disease in children could be detected in fewer than 30% of cases In 1973, Bishop and colleagues observed a virus particle in the intestinal tissue of children with diarrhea by using electron micrography. This virus was subsequently called “rotavirus” because of its similarity in appearance to a wheel (rota is Latin for wheel).

Introduction First isolated in 1973 from children with diarrhea EM identification from duodenal biopsies Human and animal strains are anti-genetically distinct, and animal strains rarely cause infection in humans.

Introduction cont’ 60-80nm in size Non-enveloped virus Double capsid virus EM appearance of a wheel with radiating spokes Icosahedral symmetry double stranded (ds) RNA in 11 segments

Classification Groups, subgroups, serotypes based on viral capsid proteins : 7 Groups (A through G) Group A is the most common and has 2 subgroups 10 human serotypes based on G protein (VP 7) Classification of rotaviruses is grouped into serogroups and then serotypes , 7 antigenetically different sero-groups – A-G

Group A rotaviruses Group A rotaviruses • Cause most human disease – Further subdivided into subgroups • Principal etiologic agent of severe gastroenteritis in infants and young children • Responsible for 1 billion cases of severe diarrhea • Major cause of mortality among the young Cause most human disease Further subdivided into subgroups • Principal etiologic agent of severe gastroenteritis in infants and young children • Responsible for 1 billion cases of severe diarrhea Major cause of mortality among the young

Other Rotaviruses • Group B – Adult diarrhea • Group C – Primarily veterinary pathogens • Groups D, E, F, G – Only known to infect animals

Epidemiology - Worldwide Millions are affected 600,000-850,000 deaths/year A major cause of diarrhea-associated hospitalizations Seroprevalence studies show that antibody is present in most by age 3.

Rotavirus- Worldwide distribution

Estimated Global Distribution of The 800,000 Annual Deaths Caused By Rotavirus Diarrhea . prevalent area

Epidemiology : U.S No. of children under 5y. affected ~ 2.7 million Physician visits per year ~ 500,000 Hospitalizations per year ~ 50,000 Deaths per year ~ 20 - 40 % cases w/ dehydration ~ 1-2.5%

Epidemiology Age- 4months - 2 years Protection of younger infants through transplacental antibody transfer Asymptomatic infections are common, especially in adults Nosocomial infections Outbreaks

Epidemiology Seasonality Winter months (Nov. through May in US) Gradual spread W to E Year-round in the tropics Incubation period - thought to be <4 days

EPIDEMIOLOGY Differences in Groups Group A infections are most common in human Group B has been associated with outbreaks in adults in China Group C is responsible for sporadic cases of diarrhea in infants around the world

Pathogenesis Targeted host cells- mature enterocytes lining the tips of intestinal villi Intermediate/infective sub-viral particle (ISVP) produced through proteolysis enter host cell by endocytosis

Structure Double capsid (outer and inner capsid) Core with genome Capsid is cleaved by trypsin to form ISVP- infective sub-viral particle

Rotavirus- EM Structure

Rotavirus- 3d structure

ROTAVIRUS- ultrastructure

Rotavirus- details of EM structure

Viral Structural Proteins (VP) Outer structural proteins - VP7 and VP4 VP7=glycoprotein VP4=protease-cleaved, P protein, viral hemagglutinin, and forms spikes from the surface Inner core structural proteins VP 2, 3, 6 VP6 is an important antigenic determinant VP4 determines how virulent the virus is and it determines the P-type of the virus.

Genome is composed of 11 segments of double-stranded RNA coding for six structural and five nonstructural proteins Seven serological groups have been identified (A-G), three of which (groups A, B, and C) infect humans .

Nonstructural viral proteins NSP1, the product of gene 5, is a nonstructural RNA-binding protein. NSP2 is an RNA-binding protein that accumulates in cytoplasmic inclusions (viroplasms) and is required for genome replication. NSP3 is bound to viral mRNAs in infected cells and it is responsible for the shutdown of cellular protein synthesis.

NON STRUCTURE PROTEINS NSP4 is a viral enterotoxin to induce diarrhoea and was the first viral enterotoxin discovered. NSP5 is encoded by genome segment 11 of rotavirus A and in virus-infected cells NSP5 accumulates in the viroplasm. NSP6 is a nucleic acid binding protein, and is encoded by gene 11 from an out of phase open reading frame.

ROTAVIRUS Structure

Gene coding assignment

Rotavirus - Properties Virus is stable in the environment Relatively resistant to hand washing agents Susceptible to disinfection with 95% ethanol, ‘Lysol’, formalin

Replication There are two possible ways of entry in the cell: Direct penetration of the virion across the plasma membrane Endocytosis

Early events Early transcription, translation, and assembly of double-layered particles. Some of the (+) RNA that is synthesized functions as mRNA . NSP2 and NSP5 play roles in the assembly of viroplasms, where cores are assembled from VP1, VP2 and VP3. Some of the (+) RNA functions as templates for synthesis of (−) RNA. VP6 is added to the core to form a progeny double-layered particle.

Late events Late transcription, translation and virion assembly. NSP4 is synthesized in the endoplasmic reticulum,where it binds VP4 and a double-layered particle . This complex buds into the endoplasmic reticulum, where the final stages of assembly occur. VP7, also synthesized in the endoplasmic reticulum, is added to form the outer layer of the capsid and the VP4 spikes are added. Virions are released from the cell either by lysis or by exocytosis

Clinical Features Incubation period - thought to be <4 days Fever- can be high grade (>102F in 30%) Vomiting, nausea precede diarrhea Diarrhea - usually watery (no blood or leukocytes) - lasts 3-9 days - longer in malnourished and immune deficient indiv. - NEC and hemorrhagic GE seen in neonates

Histopathology Mature enterocytes lining the tips of intestinal villi are affected Villous atrophy and blunting Death of the mature enterocytes

Histopathology Infiltration of lamina propria with mononuclear cells Repopulation of the villous tips with immature secretory cells [crypt hyperplasia]

Histopathology

Mechanism of diarrhea Watery diarrhea due to net secretion of intestinal fluid Activation of the enteric nervous system - possible role of enterotoxin

Clinical Features (contd.) Dehydration is the main contributor to mortality. Secondary malabsorption of lactose and fat, and chronic diarrhea are possible

CONT’ Recovery is usually complete. However, severe diarrhea without fluid and electrolyte replacement may result in dehydration and death .

Immunological Aspects Immunoglobulin (Ig A) , in the lumen of the gut immunity to infection . Actively or passively acquired antibodies (including antibodies in colostrum and mothers milk) lessen the severity of disease but does not consistently prevent reinfection . Absence of antibody small amounts of virus infection and diarrhea .

Diagnosis Antigen detection in stool by ELISA, Latex Agglutination (for Group A rotavirus) EM- non-Group A viruses also Culture- Group A rotaviruses can be cultured in monkey kidney cells Serology for epidemiologic studies

Transmission Mainly person to person via fecal-oral route Fomites Food and water-borne spread is possible Spread via respiratory route is speculated

Treatment and Prevention Supportive - oral, IV rehydration Prevention Hand washing and disinfection of surfaces

Rotavirus vaccine • Rotarix which is the latest(licensed in 2008) RotaTeq(Rhesus rotavirus tetravalent vaccine) licensed in 2006 – Serotypes 1, 2, 3, 4 for VP7 – Reassortant strains – Protective against 80% of the cases of severe diarrhea, 100% of the dehydration cases Rotashield • Was recommended at 2, 4 and 6 months of age • Risk of intussusception (a bowel blockage that is treated in a hospital and may require surgery) 1 in 12,274 infants

REFERENCES Links: www.ncbi.nih.gov/pmc www.diarrhea.emedtv.com/rotavirus www.bvgh.org/biopharmaceutical www.pubmed.com www.cdc.com Book: Lange microbiology and Immunology review (10th Edition)

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