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