PA11- Laboratory diagnosis of viral hepatitis and HIV infection

Laboratory Diagnosis of Viral Hepatitis and HIV Infection

Overview of Hepatitis Viruses

  • Five viruses primarily infect the liver and cause hepatitis:

    • Hepatitis A Virus (HAV)

    • Hepatitis B Virus (HBV)

    • Hepatitis C Virus (HCV)

    • Hepatitis D Virus (HDV)

    • Hepatitis E Virus (HEV)

  • Categories of viruses based on nucleic acid:

    • HAV: RNA, Fecal-oral transmission, No antiviral treatment, Yes vaccine

    • HBV: DNA, Sexual/blood transmission, Yes antiviral treatment, Yes vaccine

    • HCV: RNA, Blood transmission, Yes antiviral treatment, No vaccine

    • HDV: RNA, Sexual/blood transmission, No antiviral treatment, No vaccine

    • HEV: RNA, Fecal-oral transmission, Yes antiviral treatment, Yes vaccine

  • Chronic hepatic infections are caused by HBV, HCV, and HDV.

Hepatitis A Virus (HAV)

General Characteristics

  • Non-enveloped RNA virus

  • Three genotypes infect humans

  • Primarily infects hepatocytes

Types of Infections

  • Asymptomatic infections

  • Acute hepatitis

Specimens for Diagnosis

  • Stool (highest virus concentration 2 weeks before jaundice)

  • Liver biopsy

  • Blood (serology)

Direct Methods of Diagnosis

  • Electron Microscopy: Not routinely performed

  • Cultivation: Slow and nonlytic

  • Detection of Viral Antigens:

    • Liver tissue (immunohistochemistry)

    • Stool specimens (immunochromatographic tests)

Serological Diagnosis

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

  • IgG: Detected ~1 month post-infection, persists for life

Hepatitis B Virus (HBV)

General Characteristics

  • Enveloped DNA virus

  • Only DNA virus primarily infecting hepatocytes

  • Eight genotypes (A-H)

  • Complete virus particle known as 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

  • Plasma for quantitative Nucleic Acid Tests (using pearl top tube)

Direct Methods of Diagnosis

  • Electron Microscopy: Not routine

  • Cultivation: Not performed for diagnostic purposes

  • Detection of Viral Antigens:

    • HBsAg: Indicates active HBV infection and infectiousness

    • HBcAg: Core antigen, indicating infection

    • HBeAg: Indicates high viral replication

Serological Diagnosis

  • IgM anti-HBc Ab: Indicates acute infection

  • Total Anti-HBc Ab: Positive may indicate acute, resolved, or chronic infection (cannot confirm history of infection if negative)

  • Anti HBs Ab: Indicates immunity or past infection

  • Anti HBe Ab: Indicates resolution of acute infection

Molecular Diagnosis

  • NAATs: For initial evaluation or monitoring chronic infections

  • Typing: for viral classification

Hepatitis C Virus (HCV)

General Characteristics

  • Small, enveloped RNA virus

  • Six genotypes; a primary cause of chronic hepatitis worldwide

Types of Infections

  • Acute infections (often asymptomatic)

  • Chronic diseases (can lead to cirrhosis and hepatocellular carcinoma)

Specimens for Diagnosis

  • Blood

  • Saliva (for antibody testing)

  • Plasma for quantitative tests (using pearl top tube)

Direct Methods of Diagnosis

  • Electron Microscopy: Not routine

  • Cultivation: Not performed

  • Detection of Viral Antigens: Rapid tests for core antigen

Serological Diagnosis

  • Anti-HCV Antibodies: Detected to confirm infection

  • Molecular Diagnosis: NAATs and genotyping

Hepatitis D Virus (HDV)

General Characteristics

  • Defective RNA virus

  • Requires HBV envelope for replication

Types of Infections

  • Asymptomatic

  • Acute hepatitis

  • Chronic progressive disease

Diagnosis Methods

  • Electron Microscopy

  • Cultivation: Usual lines (HepG2, HepaRG, HUH-7)

  • Detection of Antigens: HDAg indicates infection

Serological Diagnosis

  • Total Anti-HDV Ab

  • IgM anti -HDV

  • Molecular Diagnosis: NAATs for HDV RNA

Hepatitis E Virus (HEV)

General Characteristics

  • Enteric non-enveloped RNA virus

  • Mostly endemic in developing countries

Types of Infections

  • Acute, self-limited infections in immunocompetent patients

  • Chronic disease in immunocompromised patients

Human Immunodeficiency Virus (HIV)

General Characteristics

  • Two types: HIV-1 and HIV-2

  • HIV-1 is the most prevalent and has multiple subtypes

  • Enveloped RNA virus, primarily targets CD4 T lymphocytes

Types of Infections

  • Acute disease (2-4 weeks post-exposure)

  • AIDS (Acquired Immunodeficiency Syndrome)

Specimens for Diagnosis

  • Serum, plasma, and saliva

  • Blood tests for point-of-care assays

Direct Methods of Diagnosis

  • Electron Microscopy

  • Cultivation: Rare; can grow on lymphocyte cells

  • Detection of Viral Antigens: p24 antigen

Serological Diagnosis

  • Antibody detection within 1-2 months post-infection

  • HIV IgM: detectable ~5 days post p24, 10-13 days after viral RNA

  • Various testing methods including EIAs, chemiluminescence, point-of-care tests

Molecular Diagnosis

  • Viral Load Assays: Measure HIV RNA levels; monitor therapy response

Antiviral Susceptibility Tests

  • Determining effectiveness against antiviral drugs

Diagnosis Algorithm for HIV

  • Infection phases:

    • Transient acute retroviral syndrome

    • Asymptomatic phase with active replication

    • Advanced disease (AIDS)

  • Monitoring involves initial screening with immunoassays and subsequent NAATs for active disease and therapy response.