Viremia

1
Viremia

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

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Cell free viremia

• Free virus particles in plasma
• Accessible to antibodies and immune cells
• Parvoviruses
• Enteroviruses
• Togaviruses
• Flaviviruses

3
Cell associated viremia

• Virus is hidden in blood cells
• Protected against antibodies
• Slow virus clearing
• Monocytes
• Herpesviruses
• Retroviruses
• Distemper

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• Lymphocytes
• Mareks 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

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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

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Viruses replicating in macrophages

• Retroviruses
• Circoviruses
• Flaviviruses
• Coronaviruses
• Arenaviruses
• Togaviruses
• Reoviruses

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Samples

• Serum samples
• Whole blood (EDTA, heparin)
• Intermittent virus shedding

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Respiratory tract

• Primary replication
• Tonsil (Aujeszky)
• Epithelial cells (Influenza virus)
• Alveolar macrophages (PRRS)
• Secondary replication
• Epithelial cells
• Alveolar macrophages

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Respiratory tract - samples

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

10
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)

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Enteric tract - samples

• Rectal swabs
• Feces

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Genital tract

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

13
Genital tract - samples

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

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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

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)
• Mareks disease virus virus dissemination by
  infected keratinised cells

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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)

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Skin infection - samples

• Tissue for histology (papillomaviruses)
• Vesicles, vesicular fluid (FMDv)
• Serum samples

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CNS infections

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

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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

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CNS infections - samples

• Serum (antibodies)
• Cerebrospinal fluid (antibodies or virus)
• Occasional samples
• Saliva (rabies)
• Section samples are usually necessary

22
Eye infection

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

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When to take samples?
NK cell killing
Viremia
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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)

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Direct methods

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

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Indirect methods

• Antibody detection (serology)
• Lymphocyte activation
• Cytokine release

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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)

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Virus visualisation - EM

• Suitable for viruses with characteristic
  morphological features
• Highly concentrated virus (rota, corona,
  astroviruses)

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Direct antigen detection
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DNA/RNA detection
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Antibody detection