Viral Infection Serology Chapter 4

Viruses

• Characterized as obligate intracellular parasites, exhibiting life only within host cells.
• Outside host cells, viruses are inert and lack enzymatic activity.
• Inside host cells, viral nucleic acids (DNA or RNA) hijack cellular machinery to replicate and produce new virus particles.

HIV Serology

• HIV compromises the immune system, potentially leading to AIDS if untreated.
• Transmission occurs via blood, sexual contact, and from mother to child during pregnancy, delivery, or breastfeeding.
• Common laboratory testing methods include Rapid tests, ELISA, and RT-PCR.

Common HIV Antibody Tests

• Enzyme Linked Immunosorbent Assays (ELISA) include indirect methods.
• Rapid Tests provide quick results.
• Western Blot is a confirmation test for HIV antibodies.

Rapid Assay Testing Principle

• Antigen is coated onto a test strip with a positive control.
• Sample addition triggers a reaction between antigen and antibody, if present.
• Positive result shows two or three colored bars; negative shows one colored bar; invalid results appear without lines.
• Specificity against viral components is crucial for true positive results.

Laboratory Monitoring for HIV

• Peripheral blood CD4 T-cell count: Levels under 200/µL indicate progression to AIDS.
• HIV-1 RNA level (viral load) is detectable as early as 10 days post-infection; highly sensitive tests like qPCR are employed.

Serology of Dengue Fever

• Dengue is a mosquito-borne viral disease prevalent in tropical and subtropical regions, transmitted by Aedes Aegypti mosquitoes.
• The dengue virus (RNA) is part of the Flavivirus genus; four serotypes exist (DEN-1 to DEN-4).
• Infection with one serotype results in lifelong immunity against that type.

Dengue Fever Symptoms

• High fever (40°C/104°F), severe headache, pain behind the eyes, muscle and joint pain, nausea, vomiting, swollen glands or rash.
• Symptoms are self-limiting, usually lasting 2-7 days.

Laboratory Diagnosis of Dengue

• Virus detection via cell culture, antigen detection, and viral RNA detection within 24-48 hours.
• NS1 glycoprotein antigen can be rapidly detected; a strong humoral response noted.
• IgM antibodies appear first, detectable by days 3-5, reaching 99% detection by day 10.
• IgG levels indicate past infection and remain detectable over months to years.

Rapid Antibody Testing for Dengue

• Simple procedure involves adding patient serum and buffer; results interpreted after 15 minutes.
• Positive IgM and negative IgG indicate a current infection; positive IgG indicates a past infection.

Serology of Hepatitis Tests

• Hepatitis refers to liver inflammation, caused by various viruses, primarily hepatotrophic viruses (A, B, C, D, E).
• Each virus has distinct transmission routes and incubation periods.

Hepatitis A Virus

• RNA virus primarily spread via the fecal-oral route; rare transmission via blood.
• Incubation is around one month; does not cause chronic liver disease.
• Effective vaccine available (formalin-killed HAV).

Hepatitis B Virus

• DNA virus spread through blood, sexual contact, and perinatal routes.
• Approximately 3-month incubation; antibodies against HbcAg detectable.
• HBeAg serves as an indicator of acute or chronic infection.

Serological Testing for Hepatitis B

• Reverse passive latex agglutination and chromatographic techniques used for HBsAg detection, with ELISA being the most common method.
• PCR (qPCR) is a confirmatory test for HBV DNA detection.

Hepatitis C Virus (HCV) Antibody Testing

• Diagnosis is achieved by detecting anti-HCV IgG in serum, usually detectable 6-8 weeks post-infection.
• Anti-HCV testing is critical for screening blood donors.