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Understanding Viremia: A Comprehensive Guide to Viruses in the Bloodstream

Explore the complexities of viremia, from primary to secondary replication in various body organs, including cell-free and cell-associated viremia. Learn about key viruses like parvoviruses, herpesviruses, and HIV, as well as sampling methods for effective diagnosis and treatment. Discover how viruses replicate in different bodily systems, such as the respiratory, enteric, genital tracts, skin, CNS, and eyes, and the significance of passive skin infections. Gain insights into diagnosing viral diseases via direct and indirect methods, including virus visualization and antigen detection.

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Understanding Viremia: A Comprehensive Guide to Viruses in the Bloodstream

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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

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