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Orthomyxovirus - Morphology and laboratory diagnosis
- 2. INTRODUCTION • Spherical/ filamentous • Enveloped • Single, segmented RNA • Hemagglutination, Myxovirus – Affinity for mucin • Influenza
- 3. INFLUENZA VIRUSES • 3 serotypes • Type A,B,C • MORPHOLOGY Spherical – 80-120nm, Pleiomorphic + Helical Symmetry – Nucleocapsid RNA genome – Negative sense SS, Segmented – 8 pieces RNA dependent RNA Polymerase
- 4. Envelope – Inner M protein layer Outer Lipid Layer Peplomers – Trans lipid glycoprotein 2 types Haemagglutinin – Neuraminidase –
- 7. N spike H spike SS RNA
- 9. ANTIGENIC CLASSIFICATION • Antigenic Nature of Ribonucleoprotein • M protein • 3 types – A,B,C • Antigenic variation of HA & NAAg – Subtypes • HA – 15 (H1-H15), NA – 9 ( N1-N9) • Human – H1-H3, N1-N2 • Non human virus – Pandemic by assortment
- 10. ANTIGENIC STRUCTURE • Ribonucleoprotein – RNP – Specific for A,B,C • Matrix (M) Protein – Type specific M1, M2 • Haemagglutinin (HA) – Strain specific Antigenic variation HA 1, HA 2 Triangular spike Aggregation of RBC
- 11. • Neuraminidase (NA) – Strain specific Surface Mushroom spike Destroys RBC Rs – Release virion from infected cell
- 13. LIFE CYCLE
- 15. ANTIGENIC DRIFT • Minor Ag changes in HA/NA/ both • Gradual • Regular Intervals • Mutation in HA/NA genes • New Ag – related to old • Epidemics
- 17. ANTIGENIC SHIFT • Major changes in HA (2-3), NA (1-3) • New subtype ( Unrelated to old virus ) • Unlikely due to Mutation • Gene assortment (Recombination ) • Previous Virus Ab cant neutralise new Virus • Major epidemics , Pandemics
- 18. ANTIGENIC SHIFT
- 21. CULTIVATION EGG INOCULATION • Amniotic cavity • 11 – 13 day old chick • After few passages – Allantoic cavity • Detected – Hemagglutination TISSUE CULTURE • Primary monkey kidney , human embryo kidney
- 22. ANIMAL INOCULATION • Intranasal • Ferrets , Mice
- 23. DISEASE • Influenza • Acute Respiratory Distress Syndrome • Mild coryza to Pneumonia • IP – 4 days • Self limiting in 7 days
- 25. LABORATORY DIAGNOSIS • DEMONTRATION OF VIRUS ANTIGEN Immunofluroscence Rapid Viral RNA – RT PCR
- 26. ISOLATION OF VIRUS • Initial 2-3 days • Throat garglings • Amniotic cavity / human embryo kidney / Monkey kidney • Incubate in eggs for 3 days – Amniotic to Allantoic • Hemagglutination • Strains types Identified by antisera • Subtypes - HAI
- 27. Haemagglutination test and haemagglutination inhibition test. The serum from pig "A" contains no antibodies to influenza, which is why haemagglutination occurs. The serum from pig "B" contains influenza antibodies, so agglutination is inhibited.
- 28. The basis of HI assay - antibodies to influenza virus will prevent attachment of the virus to red blood cells. Therefore hemagglutination is inhibited when antibodies are present. The highest dilution of serum that prevents hemagglutination is called the HI titre
- 29. SEROLOGY • CFT • HAI • 4 fold rise in titre of Ab between convalascnt and Acute phase Results of a haemagglutination inhibition test. The antibody titer is 1:80.
- 30. IMMUNITY • 1 strain attack – 1- 2 years protection • Doctrine of Original Antigenic Sin When the body first encounters an infection it produces effective antibodies against its dominant antigens and thus eliminates the infection. But when it encounters the same infection, at a later evolved stage, with a new dominant antigen, with the original antigen now being recessive, the immune system will still produce the former antibodies against this old "now recessive antigen" and not develop new antibodies against the new dominant one, this results in the production of ineffective antibodies and thus a weak immunity.
- 31. EPIDEMIOLOGY • Airborne • Type C – Endemic • Type B – Sporadic , Epidemic • Type A – Pandemics • Winter/ Monsoon • WHO – surveillance - ? – Pandemics • Spanish Flu – 20 million deaths 1918
- 36. PROPHYLAXIS
- 43. THANK UUUUUUU