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Viremia
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  1. Viremia Presence of viruses in the blood stream – biphasic • Primary (prodromal phase of infection) • Secondary replication in target organs

  2. Cell free viremia • Free virus particles in plasma • Accessible to antibodies and immune cells • Parvoviruses • Enteroviruses • Togaviruses • Flaviviruses

  3. Cell associatedviremia • Virus ishidden in bloodcells • Protectedagainstantibodies • Slow virus clearing • Monocytes • Herpesviruses • Retroviruses • Distemper

  4. Lymphocytes • Marek´s disease virus • EB virus • HIV • Erythrocytes • Bluetongue virus (erythroblasts) • Rift Valley fever virus • African swine fever virus • Neutrophils • Short half-life • Anti-microbial mechanisms • May contain phagocyted viruses

  5. Monocytes - macrophages • Prevent access of viruses in the blood and tissues by ingestion of viruses • Antigen presenting cells • Virus replications in macrophages = Trojan horse mechanism • Virulence factor

  6. Virusesreplicating in macrophages • Retroviruses • Circoviruses • Flaviviruses • Coronaviruses • Arenaviruses • Togaviruses • Reoviruses

  7. Samples • Serum samples • Whole blood (EDTA, heparin…) • Intermittent virus shedding

  8. Respiratorytract • Primaryreplication • Tonsil (Aujeszky) • Epithelialcells (Influenza virus) • Alveolarmacrophages (PRRS) • Secondaryreplication • Epithelialcells • Alveolarmacrophages

  9. Respiratorytract - samples • Nasal swabs (samples from upper resp. tract are often sufficient) • Conjunctival swabs • Serum (virus + antibodies) • Transport medium • Rapid transport

  10. Enterictract • Primaryreplication • Tonsil (enteroviruses) • Enterocytes (parvoviruses, coronaviruses) • Secondaryreplication • Matureenterocytes • Usuallyshort term shedding • Somevirusesreplicate in the ET withoutcausingdisease(enteroviruses, FeCOv)

  11. Enterictract - samples • Rectal swabs • Feces

  12. Genitaltract • Transplacental infection • Cell associated viremia • Endothelial tropism • Infertility (porcine enteroviruses, BVDv) • Abortion (EHV-1, EVA, PRRS, PPV, CHV)

  13. Genitaltract - samples • Aborted fetuses (EHV-1, EVA, PPV, PRRS, BVDv) • Placenta (EHV-1) • Serum (virus or antibodies)

  14. Infectionof skin • Protection of skin surface • Keratinisation • Low pH • Permanent renewing • Infection through skin • abrasions, wounds • microtraumatisation • blood sucking insect • Langerhans cells (epidermis) • Lymphatic system, nerve endings

  15. Primary skin infections • Papillomaviruses • Ovine Poxviruses • Vesicular swine disease

  16. Secondary skin infections • generalised infections, hematogenous spread (poxviruses, FMDV, distemper…) • nerves (herpes simplex, herpes zooster) • Marek´s disease virus –virus dissemination by infected keratinised cells

  17. Passive role of skin in virus infections • Entry for viruses transmitted by blood sucking insect • Equine infectious anemia • Myxoma virus • African swine fever virus • Equine encephalitis • Ski lesions due to immunopathologic reactions • PDNS (porcine circovirus)

  18. Skin infection - samples • Tissue for histology (papillomaviruses) • Vesicles, vesicular fluid (FMDv) • Serum samples

  19. CNS infections • Crossing hematoencephal barrier • By neuronal axons • Infection of endothelial cells • Through capillaries • Infected leukocytes (rare)

  20. Somevirusescausingencephalitis • Rabies • Distemper (old dog encephalitis) • Tick borne encepalitis • Herpesviral encephalitis • EHV-1 • Aujeszky disease virus • Maedi-Visna • Teschoviruses • Borna virus disease

  21. CNS infections - samples • Serum (antibodies) • Cerebrospinal fluid (antibodies or virus) Occasional samples • Saliva (rabies) • Section samples are usually necessary

  22. Eyeinfection • Conjunctiva • Distemper, herpesviruses, EVA • Virus replication in the eye • EHV-1, EHV-2 • Immunocomplex • CAV-1, La piedad, EIA Samples: swabs, serum

  23. When to takesamples? NK cell killing Viremia

  24. When to takesamples? IgG IgM Viremia

  25. Diagnostic virology How do we diagnose viral diseases? This can be achieved : Directly – detecting the virus or viral products (proteins, nucleic acids) Indirectly – detecting an immunological response to the virus (antibodies)

  26. Directmethods • Virus isolation • Virus visualisation (EM) • Direct antigen detection • DNA/RNA detection

  27. Indirectmethods • Antibody detection (serology) • Lymphocyte activation • Cytokine release

  28. Virus isolation • Virus has to remain alive • Transport medium • Rapid transport • Keep the sample at 4oC or freeze it at low temperature (at least -50oC)

  29. Virus visualisation - EM • Suitable for viruses with characteristic morphological features • Highly concentrated virus (rota, corona, astroviruses…)

  30. Direct antigen detection

  31. DNA/RNA detection

  32. Antibodydetection