EXAM: Hepatitis Viruses, Oncogenic Viruses, OmpathStudy

Hepatitis Viruses, Oncogenic Viruses, Paramyxoviruses & Arboviruses High-Yield Revision Notes Institution: Mount Kenya University — School of Medicine & Surgery Unit: MBMM 3300 — Medical Virology and Mycology Level: MBChB Year 3 --- Papers & Examinations Covered Exam Date Paper --- --- --- Main Exam January 2022 MBMM 3300 Paper 1 Main Exam February 2021 MBMM 3300 Paper 2 Main Exam July 2019 MBMM 3300 Paper 2 Main Exam January 2023 MBMM 3300 Paper 2 End of Term CAT December 2020 MBMM 3333 Medical Virology CAT II 2018/2019 MBMM 3233 Medical Virology --- Topics Covered Hepatitis Viruses — HAV, HBV, HCV, HEV, transmission, diagnosis, treatment, prevention Oncogenic Viruses — mechanisms of viral carcinogenesis, key oncogenic viruses, associated malignancies Paramyxoviruses — measles, mumps, RSV, parainfluenza, rubella, clinical features, vaccines Arboviruses — dengue, yellow fever, Zika, chikungunya, West Nile, vectors, clinical features --- --- Part 1: Hepatitis Viruses 1. Introduction Hepatitis means inflammation of the liver. Viral hepatitis is caused by a group of viruses that primarily target hepatocytes — liver cells. Despite being caused by completely unrelated viruses from different families, they all share the common clinical feature of hepatitis. Understanding their differences in transmission, natural history, chronicity, and prevention is essential for clinical practice. At MKU, hepatitis viruses appear consistently in MCQs testing transmission routes, diagnostic methods, and specific clinical features. --- 2. Overview — The Five Hepatitis Viruses Feature HAV HBV HCV HDV HEV --- --- --- --- --- --- Family Picornaviridae Hepadnaviridae Flaviviridae Deltaviridae Hepeviridae Genome ssRNA dsDNA (partial) ssRNA ssRNA ssRNA Envelope No Yes Yes Yes No Transmission Fecal-oral Parenteral, sexual, vertical Parenteral Parenteral (needs HBV) Fecal-oral Chronicity Never Yes (5–10% adults) Yes (75–85%) Yes Never (except immunocompromised) Vaccine Yes Yes No HBV vaccine prevents No licensed vaccine Oncogenic No Yes — HCC Yes — HCC Yes No --- 3. Hepatitis A Virus (HAV) Classification Family: Picornaviridae Genome: Single-stranded positive-sense RNA Non-enveloped — survives in water, acidic environments, and on surfaces Transmission: Fecal-oral — contaminated food and water, poor sanitation Pathogenesis Ingested virus survives stomach acid Infects intestinal epithelial cells → enters portal circulation → reaches liver Infects hepatocytes — virus replicates in hepatocytes and is shed into bile → excreted in faeces Liver damage is primarily immune-mediated — cytotoxic T cells destroy infected hepatocytes Clinical Features Incubation period: 2–6 weeks Prodrome — fever, malaise, anorexia, nausea, right upper quadrant pain Jaundice — appears after prodrome; tea-coloured urine, pale stools, pruritis Hepatomegaly and tenderness Self-limiting — complete recovery in most cases No chronic infection — ever Fulminant hepatitis — rare but life-threatening High-Risk Groups Children in developing countries — most infections subclinical Travellers to endemic areas Men who have sex with men Injection drug users Diagnosis — High Yield IgM anti-HAV — gold standard for acute infection; appears early, lasts 3–6 months IgG anti-HAV — indicates past infection or vaccination; persists lifelong Detection of faecal HAV by immunoelectron microscopy — research setting Raised ALT and AST — liver enzymes elevated; ALT more specific for hepatocyte damage Treatment No specific antiviral Supportive — rest, adequate nutrition, avoid hepatotoxic drugs and alcohol Hospitalization for severe cases Prevention Improved sanitation and clean water — most important Handwashing — especially food handlers HAV vaccine — inactivated; two doses; highly effective; recommended for travellers and high-risk groups Passive immunization — normal human immunoglobulin (HNIG) for post-exposure prophylaxis within 2 weeks --- 4. Hepatitis B Virus (HBV) Classification Family: Hepadnaviridae Genome: Partially double-stranded circular DNA — unique among human hepatitis viruses Enveloped virus Replication: Uses reverse transcriptase — unique for a DNA virus; HBV replicates through an RNA intermediate Transmission — High Yield HBV is present in blood, semen, vaginal secretions, saliva, breast milk, and other body fluids. Parenteral — blood transfusion, sharing needles, needlestick injuries Sexual contact — highly efficient sexually transmitted infection Vertical transmission — mother to child during delivery (most important route globally) Horizontal transmission — child-to-child in endemic areas via minor skin breaks Virology — Key Antigens and Antibodies Marker Meaning --- --- HBsAg (surface antigen) Present in active infection — acute or chronic; first marker to appear Anti-HBs Antibody to surface antigen; indicates immunity — from vaccination or recovery HBeAg (e antigen) Marker of active viral replication; high infectivity Anti-HBe Seroconversion from HBeAg; lower replicati