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?
Viremia
NK cell killing
When to take samples?
Viremia
IgM
IgG
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