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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
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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
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By neuronal axons
Infection of endothelial cells
Through capillaries
Infected leukocytes (rare)
Some viruses causing
encephalitis
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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
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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