Serological Diagnosis of Infectious Diseases

Serological Diagnosis of Infectious Diseases

• Group A Streptococci (S. pyogenes) are a primary cause of bacterial pharyngitis and impetigo. Untreated infections can lead to complications like acute glomerulonephritis and rheumatic heart disease.

Lateral Flow Immunochromatographic Assays

• Strep A antigen from a throat swab reacts with enzyme-labeled antibodies on a membrane.
• Diagnostically important Streptococcal antibodies include Anti-streptolysin O (ASO), Anti-DNAse B, Anti-NADase, and Anti-hyaluronidase(AHase).

Streptozyme Test

• Detects diagnostically important streptococcal antibodies
• It's a slide agglutination screening test
• Sheep RBCs are coated with streptolysin, streptokinase, hyaluronidase, DNase, and NADase.
• A positive result shows hemagglutination.

Anti-streptolysin O (ASO) Testing

• ASO indicates recent streptococcal infection, potentially leading to acute rheumatic fever or poststreptococcal glomerulonephritis following a throat infection.
• The test measures the ability of antibodies in the patient's serum to neutralize the hemolytic activity of streptolysin O.
• Results are reported as a titer, which is the reciprocal of the highest dilution demonstrating no hemolysis.
• Titer can be reported in Todd units or International units.
• A titer of at least 240 Todd units for adults or 320 Todd units for children is considered moderately elevated.

Nephelometric Method

• Used for ASO testing (currently).

Anti-DNAse B Testing

• Helps diagnose glomerulonephritis preceded by streptococcal skin infections.

Helicobacter pylori Detection

• CLOtest detects urease activity in gastric mucosal biopsy.
• Positive result: hot pink gel; Negative: gel remains yellow.
• Serology is a primary screening method for H. pylori.
• Detects IgG, IgA, and IgM antibodies.
• Most tests for this organism detect IgG class.
• Techniques used involve ELISA, immunoblots, and LFA.

Mycoplasma pneumoniae Detection

• M. pneumoniae-specific antibody detection is possible with ELISA. IgM indicates recent infection.
• Cold agglutinins clump RBCs at 4°C. A titer of 1:64 or greater, combined with clinical presentation, suggests M. pneumoniae infection.

Rickettsial Infection Detection

• Indirect Immunofluorescent assay is the gold standard for serological diagnosis of Rocky Mountain Spotted Fever (due to R. rickettsii).
• The test uses to demonstrate a significant fourfold rise in antibody titers.
• Weil-Felix test detects Rickettsial antibodies, relying on cross-reactivity with polysaccharide antigens present on Proteus species. Relevant antigens are Proteus vulgaris: OX-19 and OX-2; Proteus mirabilis: OX-K. Different results indicate different types of rickettsial infections.

Syphilis Detection

• Caused by Treponema pallidum.
• Transmission routes include sexual, congenital, and parenteral (needles/blood).
• Serological tests can classify as non-treponemal or treponemal tests.

Non-treponemal Tests

• Detects reagin (antibody against cardiolipin). Cardiolipin, lecithin, and cholesterol are used in the test reaction

• Most common tests are the Venereal Disease Research Laboratory (VDRL) test and Rapid Plasma Reagin (RPR) test.

• VDRL and RPR are based on flocculation testing.

• VDRL test involves heating the serum at 56°C for 30 minutes to inactivate complement. Results are microscopically read. A positive VDRL result obtained from spinal fluis is indicative of neurosyphilis.

• A modified VDRL uses charcoal for macroscopic reading.

Treponemal Tests

• FTA-ABS uses Nichols strain of T. pallidum, and is a confirmatory test; specific and sensitive.
• TP-PA uses gel particles sensitized with T. pallidum; less sensitive than FTA-ABS
• It uses gel particles sensitized with T. pallidum sonicate.

Lyme Disease Detection

• Caused by Borrelia burgdorferi.
• Diagnosis is sometimes delayed because IgM antibodies are not detectable until 3-6 weeks after a tick bite and IgG antibody develops later.
• Screening tests include IFA or EIA.
• Confirmatory testing involves Western blot.
• IgM-positive if 2 or more bands are present (23, 39, 41). IgG-positive if 5 or more bands are present.

Fungal Serology (Candida species)

• Current recommendations for Candida species detection combine mannan and anti-mannan antibody detection in serum.

Cryptococcus neoformans Detection

• Cryptococcal polysaccharide antigen can be detected in serum and CSF using LA and enzyme immunoassays (EIA)
• False positives can be caused by rheumatoid factor, but can be reduced with heat and Pronase or 2-mercaptoethanol.

Aspergillus & Histoplasma Detection

• Aspergillus species detection uses galactomannan in serum via EIA, which increases the ability to diagnose invasive aspergillosis. An alternative is B-D-glucan.
• Histoplasma capsulatum uses Complement fixation (CF) and precipitation to detect antibodies. Precipitin band tests for H and M antigens.

Hepatitis Viruses (Hepatitis A, E, B, C, and D)

• Summaries of each hepatitis virus including mode of transmission, serological markers, and molecular testing methods are provided.
  • Hepatitis A: Fecal-oral, IgM anti-HAV, HAV RNA via RT-PCR.
  • Hepatitis E: Fecal-oral, IgM anti-HEV, IgG anti-HEV
  • Hepatitis B: Parenteral, HBsAg, HBeAg, IgM anti-HBc, Total anti-HBc, etc
  • Hepatitis C: Parenteral, Anti-HCV, and HCV RNA determination.
  • Hepatitis D: Parenteral, co-infection with HBV, IgM anti-HDV, IgG anti-HDV, and HDV RNA detection.

Epstein-Barr Virus (EBV) Detection

• EBV causes infectious mononucleosis, and other disorders.
• Transmission is via intimate contact with salivary secretions.
• Hematology findings include lymphocytosis (>50% of total leukocytes) and at least 20% atypical lymphocytes.
• Serology involves detecting IM heterophile antibodies, which are IgM. These antibodies disappear usually within 3 months after symptom onset.

EBV-Specific Antibody Testing

• IgM anti-VCA, Anti-EA-D, IgG anti-VCA, Anti-EBNA and increased anti-EA can differentiate between acute primary infection, convalescent or past infection and reactivation.

Varicella-Zoster Virus (VZV)

• VZV causes varicella (chickenpox) and herpes zoster (shingles).
• FAMA (fluorescent Ab to membrane Ag) is the most sensitive and reliable serological test for antibodies.
• Reference method for antibodies. Live virus-infected cells are required.
• ELISA is a common method for VZV antibodies, does not require live virus infected cells.

Human Immunodeficiency Virus (HIV) Detection

• HIV belongs to the Retroviridae family.
• Transmission is via intimate sexual contact, blood exposure perinatally.
• Hallmark is a decline in CD4+ T cells.
• Testing includes detecting HIV antibodies, antigens, and nucleic acids.
• Screening includes ELISA, 4th generation automated Ag/Ab assays and rapid antibody tests. Confirmation includes Western blot HIV-1, 2 differentiation assays and PCR.

Additional Notes

• Specific tests and interpretations are listed in accompanying tables. These should be studied for details.

Explore the key concepts of serological diagnosis relating to infectious diseases, particularly focusing on Group A Streptococci. This quiz covers diagnostic tests such as Lateral Flow Immunochromatographic Assays, Streptozyme Test, and Anti-streptolysin O Testing. Find out about the implications of untreated infections and the associated complications.