Concepts used in viral diagnostics

7/28/2019 Concepts used in viral diagnostics

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Diagnosis of viralinfections/diseases

Dr F Noordeen

Department of Microbiology

Faculty of MedicineUniversity of Peradeniya

April 2013


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1. State different methods used in diagnosis of viralinfections

2. Briefly explain the limitations of each method

3. Outline the principles of diagnosis of viral infectionsin Sri Lanka

Dengue Rapid assays for IgM / IgG and PCR for NA

Hepatitis Rapid assays for antigen in hepatitis B

and IgM in hepatitis A

Influenza FAT for antigen, Rapid assays for antigen

and PCR for NA

Rabies Microscopy for inclusion bodies and

FAT for antigen

Learning outcomes


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Diagnosis of viral diseases

1. Identification of Virus

- See virus/virus mediated changes

- Detect antigen or nucleic acid of virus- Grow virus

2. Identify host response to virus- Virus specific antibody detection


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See virus

1. Histological

Stains

Intranuclear Inclusion bodies

Herpes simplex

virus in liver

Cytomegalovirus

in alveolar cells


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ElectronMicroscopy

Herpes virus

Rota virus


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Detect virus products

Antigens

Nucleic acids

Respiratory syncitialRespiratory syncitialvirus infected cellvirus infected cell

Amplification of

viral nucleic acid

PCR


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Grow viruses

ISOLATION OF VIRUSES

1.Tissue culture2. Animal

inoculation

1. Cytopathic effect (CPE)

2. Virus neutralisation

3. Haemadsorption

1. Characteristic disease

2. Death & PM findings


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Inoculation of embryonated eggs


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Tissue culture


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Monolayer of cells(human fibroblasts)

Cytopathic effect(CPE)


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Diagnosis of viral diseases

1. Identification of Virus

- See virus/virus mediated changes

- Detect antigen or nucleic acid of virus- Grow virus

2. Identify host response to virus- Virus specific antibody detection


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Immune System : 2 arms

The innate immune system

a general response to anything other

than recognized self cells

The adaptive immune system

a specific counter-assault against a

known foreign invader


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T and B cell involvement

Antigen presentation

Effector Mechanisms

The adaptive immune system

IgM (Acute) X IgG (Convalescent) >4X

IgM for hepatitis A virus

IgM for dengue virus

With time total antibody titre rises


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Detect host response

Antibody detection

Single titre

Rise in titre

IgMHigh

IgG

N 1/10 1/20 1/40 1/801/5Acute

Convalescence

1/5 1/10 1/20 1/40 1/80N


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Immunoassays

Enzyme linked immunosorbent assay (ELISA)

Immunofluorescence assay (IFA) Rapid immunoassays

Immunohistochemistry

Molecualr assays

Polymerase chain reaction (PCR)

Quantitative polymerase chain reaction (qPCR)

Common assays used in

viral diagnosis


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Documents

Concepts used in viral diagnostics