PA11- Laboratory diagnosis of viral hepatitis and HIV infection

Laboratory Diagnosis of Viral Hepatitis and HIV Infection

Overview of Hepatitis Viruses

  • Five viruses cause primary hepatic infections:

    • Hepatitis A virus (HAV)

    • Hepatitis B virus (HBV)

    • Hepatitis C virus (HCV)

    • Hepatitis D virus (HDV)

    • Hepatitis E virus (HEV)

Summary of Hepatitis Viruses

Virus

Nucleic Acid

Exposure

Antiviral Treatment

Vaccine

HAV

RNA

Fecal-oral

No

Yes

HBV

DNA

Sexual, blood

Yes

Yes

HCV

RNA

Blood

Yes

No

HDV

RNA

Sexual, blood

No

No

HEV

RNA

Fecal-oral

Yes

Yes

Hepatitis A Virus (HAV
### General Characteristics

  • Non-enveloped RNA virus

  • Three genotypes known to cause human infections

  • Infects hepatocytes

Types of Infections

  • Asymptomatic infections

  • Acute hepatitis

Specimens for Diagnosis

  • Stool (higher concentration of virus detectable 2 weeks before jaundice)

  • Liver biopsy

  • Blood for serology

Direct Methods of Diagnosis

  • Electron Microscopy: Not routinely performed

  • Cultivation: Slow, nonlytic

  • Detection of viral antigens:

    • Immunohistochemistry from liver tissue

    • Immunochromatographic tests from stool

Serological Diagnosis

  • IgM: Appears with symptoms, peaks in 2-3 weeks, undetectable after 3-6 months (indicates acute infection)

  • IgG: Detectable approximately 1 month after infection, persists for life

Hepatitis B Virus (HBV)

General Characteristics

  • Enveloped DNA virus

  • The only DNA virus that primarily infects hepatocytes

  • Eight genotypes (A-H); the complete virus particle is called the Dane particle

Types of Infections

  • Acute hepatitis

  • Chronic hepatitis (risk of cirrhosis and hepatocellular carcinoma)

Specimens for Diagnosis

  • Serum or plasma for serology

  • Liver biopsy

Direct Methods of Diagnosis

  • Electron Microscopy: Not routine

  • Cultivation: Not used for diagnostic purposes due to low cell damage

  • Detection of viral antigens: HBV-specific antigens (HBs Ag, HBc Ag, HBe Ag)

Serological Diagnosis

  • HBs Ag: Indicates active infection and high infectivity

  • HBc Ag: Core antigen

  • HBe Ag: Indicates high viral replication

  • IgM anti-HBc Ab: Positive indicates acute infection

  • Total Anti-HBc Ab: A positive result might indicate various forms of HBV infection

  • Anti HBs Ab: Indicates immunity to HBV post-infection or vaccination

  • Anti HBe Ab: Indicates resolution of infection

Molecular Diagnosis

  • NAATs for evaluation or monitoring chronic infections

Algorithm of Diagnosis

Condition

HBs Ag

Anti-HBs Ab

HBe Ag

Anti-HBe Ab

Anti-HBc Ab

Alanine aminotransferase

Acute Infection

+

-

+

-

+

+

Active Chronic Infection

+

-

+/-

+/-

-

+

Inactive Chronic Infection

+

-

-

+

-

Normal

Vaccinated Patients

-

+

-

-

-

Normal

Hepatitis C Virus (HCV)

General Characteristics

  • Small, enveloped RNA viruses

  • Six genotypes

  • Most common cause of chronic hepatitis worldwide

Types of Infections

  • Acute (often asymptomatic), fulminant disease

  • Chronic (associated with metabolic disorders, cirrhosis, and hepatocellular carcinoma)

Specimens for Diagnosis

  • Blood or saliva for serological tests

  • Plasma for quantitative NAATs

Direct Methods of Diagnosis

  • Electron Microscopy: Not routine

  • Cultivation: Not performed

  • Detection of viral antigens: Rapid tests for core antigen

Serological Diagnosis

  • Anti-HCV Ab: Indicates exposure/infection

  • Molecular diagnosis: NAATs and genotyping

Algorithm of Diagnosis

  1. Screen for anti-HCV antibodies

  2. Confirm active disease via detection of viral RNA with NAATs

Hepatitis D Virus (HDV)

General Characteristics

  • Defective RNA virus that requires HBV for assembly

  • Three genotypes

Types of Infections

  • Asymptomatic, acute hepatitis, chronic progressive

Specimens for Diagnosis

  • Serum, plasma, and hepatic biopsy

Direct Methods of Diagnosis

  • Electron Microscopy

  • Cultivation: specific cell lines (e.g., HepG2, HepaRG, HUH-7)

  • Detection of viral antigens: HDAg (marker of infection)

Serological Diagnosis

  • Total anti-HDV Ab, IgM anti-HDV

  • Molecular diagnosis: NAATs for HDV RNA

Algorithm of Diagnosis

  • Co-infection: detection of Anti-HBc IgM, HBs Ag, Anti-HDV Ab

  • Superinfection: presence of HBs Ag but not Anti-HBc IgM

Hepatitis E Virus (HEV)

General Characteristics

  • Enteric non-enveloped RNA virus, endemic in developing countries

  • Four genotypes

Types of Infections

  • Acute, self-limited in immunocompetent patients

  • Chronic in immunocompromised patients

Algorithm of Diagnosis

  • Serology (IgM, IgG) and NAATs for higher sensitivity and specificity

Human Immunodeficiency Virus (HIV)

General Characteristics

  • HIV-1 and HIV-2; HIV-1 predominantly HIV-1 has four groups (M, N, O, P)

  • Enveloped RNA virus targeting CD4 T lymphocytes

Types of Infections

  • Acute disease (2-4 weeks post-exposure) leading to AIDS

Specimens for Diagnosis

  • Serum and plasma

  • Saliva for antibodies

Direct Methods of Diagnosis

  • Electron Microscopy

  • Cultivation: On lymphocyte cells as routine not common

Serological Diagnosis

  • HIV-specific Abs: Detectable within 1-2 months after infection

  • Corresponding tests include EIAs, chemiluminescent assays, and Western Blot.

Molecular Diagnosis

  • Viral RNA is the first detectable marker, occurring approximately 10 days after infection

  • Viral load assays to monitor efficacy of antiviral therapy and prognostic assessment

Antiviral Susceptibility Tests

  • Genotyping and phenotypic assays to assess viral resistance

Algorithm of Diagnosis

  1. Initial screening with rapid tests for p24 or IgM

  2. Confirmation through NAAT for stage assignment and response monitoring

HIV Progression Phases:

  • Acute retroviral syndrome

  • Asymptomatic period with viral replication

  • Advanced disease (AIDS)