7 Serological Tests for Bacterial and Viral Infections [Autosaved] [Autosaved]

Serologic and Molecular Detection of Infectious Diseases

Test Menu

  • Bacterial Infections

    • Spirochete diseases:

      • Syphilis

      • Lyme Disease

    • Group A Streptococcus

    • Rickettsia Infections

    • Typhoid fever

    • Brucella

    • Mycoplasma pneumoniae

    • Helicobacter pylori

  • Viral Infections

    • Viral Hepatitis

    • HIV

    • Dengue

    • Herpes virus infections:

      • Infectious Mononucleosis

      • Epstein Barr Virus

      • Cytomegalovirus

  • Autoimmune Disorders

    • Rheumatoid Arthritis

    • Systemic Lupus Erythematosus (SLE)

Bacterial Infections

Syphilis

  • Causative agent: Treponema pallidum subspecies pallidum

    • Originally identified as Spirochaeta pallida

  • Antigens:

    • Reiter strain (non-virulent variant)

    • Nichols strain (virulent variant)

  • Modes of Transmission (MOT):

    • Sexual contact

    • Blood transfusion

    • Trans placental route

  • Historical Notes:

    • Known by names: Great pox, Evil pox, French/Italian/Spanish Disease

    • First diagnostic blood test: Wassermann test (1906)

      • Also known as Cardiolipin test, identified membrane phospholipid

    • Treatment evolved from Arsenic, Salvarsan to Penicillin (1940s)

Antibodies in Syphilis

  • Treponemal Antibodies:

    • Specific antibodies produced against T. pallidum antigens

  • Nontreponemal Antibodies (Reagin Antibodies):

    • Based on RPR and VDRL tests

    • Can be produced in other conditions (e.g., leprosy, TB, autoimmune disorders)

Overview of Stages of Syphilis

  • Primary Stage:

    • Chancre: painless, firm lesion, highly contagious

    • Diagnostic tests: Darkfield microscopy, RPR, VDRL

  • Secondary Stage:

    • Most contagious; symptoms include Condyloma lata & rash

  • Latent Stage:

    • Asymptomatic; non-communicable except for vertical transmission

  • Tertiary Stage:

    • Includes Gummata, neurosyphilis, cardiovascular issues

Serological Tests for Syphilis

  • Nontreponemal Tests:

    • VDRL, RPR, USR, TRUST, ART

  • Treponemal Tests:

    • FTA-ABS, FADH, Hemagglutination tests (TPHA, MHA-TP)

Specific Serological Tests

VDRL Test

  • Qualitative and quantitative test for serum and spinal fluid

  • Utilizes Cardiolipin antigen and requires specific preparation conditions

RPR Test

  • Standard screening test, involves agglutination with charcoal

FTA-ABS Test

  • Indirect Immunofluorescence test

  • Uses non-pathogenic strain to minimize false positives

Lyme Disease

  • Characteristic rash: Erythema migrans

  • Causative agent: Borrelia burgdorferi

  • Ixodes scapularis tick as the vector

  • Diagnosis: PCR, Elisa with C6 peptide, and serology tests

Group A Streptococcus (S. pyogenes)

  • Causes URTIs, necrotizing fasciitis, and sequelae like rheumatic fever & glomerulonephritis

  • Features include lipoteichoic acid, M proteins, and various extracellular products

  • Antistreptolysin O (ASO) Test: Neutralization test indicating previous infection

Rickettsial Infections

  • Diseases caused by various Rickettsia species

  • Weil-Felix Test: Differentiates rickettsial infection based on cross-reactivity with Proteus ag

Typhoid Fever

  • Causative agent: Salmonella typhi

  • Transmission by carriers (e.g., Typhoid Mary)

  • Diagnostic tests: Widal test, Typhidot, Tubex

Mycoplasma pneumoniae

  • Causes primary atypical pneumonia, transmitted via respiratory secretions

  • Diagnosis by culture on specialized agars, cold agglutinins testing, and EIA

Helicobacter pylori

  • Urease test: Biopsy or breath tests for detection

  • Antibody testing: EIA targeting IgG or IgM

  • PCR: Amplification of specific DNA for rapid diagnosis

Homework Assignment

  • Prepare short notes on Hepatitis Viruses: HAV, HBV, HCV, HDV, HEV

    • Include name, MOT, causative agent, incubation period, clinical significance, and immunologic markers.