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Viremia Presence of viruses in the blood stream – biphasic Primary (prodromal phase of infection) Secondary replication in target organs Cell free viremia Free virus particles in plasma Accessible to antibodies and immune cells Parvoviruses Enteroviruses Togaviruses Flaviviruses Cell associated viremia Virus is hidden in blood cells Protected against antibodies Slow virus clearing Monocytes Herpesviruses Retroviruses Distemper 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 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 Viruses replicating in macrophages Retroviruses Circoviruses Flaviviruses Coronaviruses Arenaviruses Togaviruses Reoviruses Samples Serum samples Whole blood (EDTA, heparin…) Intermittent virus shedding Respiratory tract Primary replication Tonsil (Aujeszky) Epithelial cells (Influenza virus) Alveolar macrophages (PRRS) Secondary replication Epithelial cells Alveolar macrophages Respiratory tract - samples Nasal swabs (samples from upper resp. tract are often sufficient) Conjunctival swabs Serum (virus + antibodies) Transport medium Rapid transport Enteric tract Primary replication Tonsil (enteroviruses) Enterocytes (parvoviruses, coronaviruses) Secondary replication Mature enterocytes Usually short term shedding Some viruses replicate in the ET without causing disease (enteroviruses, FeCOv) Enteric tract - samples Rectal swabs Feces Genital tract Transplacental infection Cell associated viremia Endothelial tropism Infertility (porcine enteroviruses, BVDv) Abortion (EHV-1, EVA, PRRS, PPV, CHV) Genital tract - samples Aborted fetuses (EHV-1, EVA, PPV, PRRS, BVDv) Placenta (EHV-1) Serum (virus or antibodies) Infection of 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 Primary skin infections Papillomaviruses Ovine Poxviruses Vesicular swine disease 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 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) Skin infection - samples Tissue for histology (papillomaviruses) Vesicles, vesicular fluid (FMDv) Serum samples CNS infections Crossing hematoencephal barrier By neuronal axons Infection of endothelial cells Through capillaries Infected leukocytes (rare) Some viruses causing encephalitis Rabies Distemper (old dog encephalitis) Tick borne encepalitis Herpesviral encephalitis EHV-1 Aujeszky disease virus Maedi-Visna Teschoviruses Borna virus disease CNS infections - samples Serum (antibodies) Cerebrospinal fluid (antibodies or virus) Occasional samples Saliva (rabies) Section samples are usually necessary Eye infection Conjunctiva Distemper, herpesviruses, EVA Virus replication in the eye EHV-1, EHV-2 Immunocomplex CAV-1, La piedad, EIA Samples: swabs, serum When to take samples? IFN, TNF NK cell killing Antibodies Viremia When to take samples? IgG IgM Viremia 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 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) Direct methods Virus isolation Virus visualisation (EM) Direct antigen detection DNA/RNA detection Indirect methods Antibody detection (serology) Lymphocyte activation Cytokine release 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) Virus visualisation - EM Suitable for viruses with characteristic morphological features Highly concentrated virus (rota, corona, astroviruses…) Direct antigen detection DNA/RNA detection Antibody detection