Diagnosis of viral diseases

Diagnosis of viral diseasesDiagnosis of viral diseases

Diagnosis of viral diseasesDiagnosis of viral diseases

Three General Approaches for Three General Approaches for Laboratory Diagnosis of Viral Laboratory Diagnosis of Viral Infections Infections

1)1) Direct detectionDirect detection-Microscopy or staining-Microscopy or staining

2)2)Virus IsolationVirus Isolation- - PCRPCR

3)3)SerologySerology- - AntibodiesAntibodies

Viral SerologyViral Serology

Detection of SPECIFIC antibodies Indirect Indirect

Primary and secondary responses to viral Primary and secondary responses to viral infectionsinfections IgM antibody during acute phase (1st exposure)(1st exposure) IgG antibody during convalescence (2nd (2nd

exposure)exposure) IgA mucosal antibody (respiratory infections

GI)

Serology Tests

Serology Tests Commonly Used Haemagglutination

Haemagglutination Inhibition

Complement fixation

Indirect Fluorescent Assay (IFA)

Indirect EIA (ELISA)

Viral Serology

Indirect Fluorescent Assay (IFA) Indirect EIA (ELISA)

Viral SerologyViral Serology

Enzyme-Linked Immunosorbent Assays Enzyme-Linked Immunosorbent Assays (ELISAs) (ELISAs) Enzyme-Linked ImmunoSorbent Assay or ELISA is a

biochemical technique used mainly in immunology to detect the presence of an antibody or an antigen in a sample The ELISA has been used as a diagnostic tool in medicine

Enzyme reacts with substrate to produce colored Enzyme reacts with substrate to produce colored product product

Very sensitive Very sensitive Not expensiveNot expensive

ELISA ProceduresELISA Procedures

Advantages of Viral serology

Determine immune status ndash person or population Verify immune response to vaccination Diagnosis of chronic infection reactivation Diagnosis of recent infection (IgM amp IgA) Wide range of tests available Uses serum ndash easily collected and transported (compared with biopsy tissue or DNA )

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Viral markersViral markers

Some common viral markers Some common viral markers detected by serology detected by serology

1)1) HAVHAV

2)2) HBVHBV

3)3) HCVHCV

4)4) CMVCMV

5)5) OTHERSOTHERS

HEPATITIS A

SerologySerology Acute ndash IgM ndash lasts 3-6 months Acute ndash IgM ndash lasts 3-6 months Chronic ndash IgG ndash lifetime Chronic ndash IgG ndash lifetime bull Liver enzymes ndash increases in ALT Liver enzymes ndash increases in ALT

AST bilirubinAST bilirubin

0 1 2 3 4 5 6 7 8 9 10 11 12 13Week

Re

sp

on

se

Clinical illness

ALT

IgM IgG

HAV in stool

Infection

Viremia

EVENTS IN HEPATITIS A VIRUS INFECTION

HEPATITIS B

Serology - acuteSerology - acute HBsAg+ (HBsAb-) = acute infection or HBsAg+ (HBsAb-) = acute infection or

chronic carrierchronic carrier HBeAg+ = highly infectiousHBeAg+ = highly infectious HBsAb = immune ndash naturally or HBsAb = immune ndash naturally or

vaccinevaccine Window phase = HBsAg- and HBsAb-Window phase = HBsAg- and HBsAb-

will be HBcAb+ (IgM ndash acute)will be HBcAb+ (IgM ndash acute)

HEPATITIS C ss +RNA Flavivirus (former non-A non-B)ss +RNA Flavivirus (former non-A non-B) Marked genetic heterogeneity due to hypervariable Marked genetic heterogeneity due to hypervariable

regionregion Mutates under immunologic pressure and becomes Mutates under immunologic pressure and becomes

chronicchronic

Vaccines are difficult to developVaccines are difficult to develop

Immunoglobulin not effectiveImmunoglobulin not effective

Serologic Pattern of Acute HCV Infection with Recovery

Symptoms +-

Time after Exposure

Tit

eranti-HCV

ALT

Normal

0 1 2 3 4 5 6 1 2 3 4YearsMonths

HCV RNA

EBV Serology

EBV VCA IgG Positive EBV VCA IgM Positive EBNA IgG Negative EBV AI lt60 Acute EBV

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