EXAM: Vaccines & Antivirals, Rabies, CMV & OmpathStudy

Vaccines & Antivirals, Rabies, CMV & EBV, Adenovirus & Enteroviruses 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 Vaccines and Antivirals — types, mechanisms, OPV vs IPV, selective toxicity, stages of antiviral action Rabies Virus — structure, pathogenesis, clinical features, post-exposure prophylaxis CMV and EBV — structure, pathogenesis, congenital infection, oncogenesis, treatment Adenovirus and Enteroviruses — structure, diseases, transmission, prevention, encephalitis --- --- Part 1: Vaccines and Antivirals 1. Introduction Vaccines and antiviral drugs are the two primary strategies for controlling viral infections. Vaccines work by preparing the immune system before infection occurs — they are preventive. Antiviral drugs work by interfering with specific steps in the viral replication cycle — they are therapeutic. Both strategies depend on understanding viral structure, replication, and the host immune response. These topics are among the most consistently examined at MKU, appearing in essays across virtually every past paper, particularly questions on OPV vs IPV, active vs passive immunization, and the mechanism of selective toxicity of antivirals. --- 2. Vaccines What is a Vaccine A vaccine is a biological preparation that induces active immunity against a specific pathogen by stimulating the immune system to produce antibodies and memory cells without causing the disease itself. Mechanism of Protection 1. Vaccine antigen is administered 2. Antigen-presenting cells (dendritic cells, macrophages) process the antigen 3. Presented to CD4+ T-helper cells via MHC class II 4. T-helper cells activate B cells → differentiate into plasma cells 5. Plasma cells produce specific antibodies against the viral antigen 6. CD8+ cytotoxic T cells also activated — important for live vaccines 7. Long-lived memory B and T cells formed 8. On exposure to real virus — rapid, amplified secondary immune response 9. Virus neutralized before disease can develop Types of Vaccines 1. Live Attenuated Vaccines Contain weakened but living virus — reduced virulence, retained antigenicity Produced by: repeated passage of virus in non-human cells until it loses ability to cause disease in humans Advantages: Strongest and most durable immunity — mimics natural infection Both humoral and cell-mediated immunity induced Single dose often sufficient Mucosal immunity produced (especially important for gut/respiratory viruses) Disadvantages: Risk of reversion to virulence — attenuated virus can mutate back Cannot be given to immunocompromised patients — can cause disease Requires cold chain — heat sensitive Cannot be given in pregnancy Examples: OPV (oral polio), MMR (measles, mumps, rubella), Yellow fever vaccine, Varicella vaccine, LAIV (live attenuated influenza) 2. Inactivated (Killed) Vaccines Contain killed virus — treated with heat, formalin, or beta-propiolactone Virus cannot replicate but antigens are preserved Advantages: Cannot cause disease — safer Can be given to immunocompromised patients Stable — does not revert to virulence Disadvantages: Weaker immunity — mainly humoral, less cell-mediated Multiple doses required (boosters needed) Adjuvant often needed to boost response No mucosal immunity Examples: IPV (injected polio), inactivated influenza vaccine, Hepatitis A vaccine, Rabies vaccine 3. Subunit Vaccines Contain only specific viral proteins — not whole virus Examples: Hepatitis B vaccine (HBsAg), HPV vaccine (L1 capsid protein) Very safe — no viral genetic material Requires adjuvant and boosters 4. Toxoid Vaccines Not strictly viral — used for bacterial toxins Inactivated toxin — cannot cause disease but induces antitoxin antibodies 5. mRNA Vaccines Deliver mRNA encoding viral antigen into host cells Host cells produce the antigen → immune response Examples: COVID-19 vaccines (Pfizer-BioNTech, Moderna) Advantages: rapid production, no live virus needed --- OPV vs IPV — The Most Examined Vaccine Comparison This comparison has appeared in essay form multiple times at MKU. Feature OPV (Oral Polio Vaccine) IPV (Inactivated Polio Vaccine) --- --- --- Type Live attenuated Killed/inactivated Route Oral (swallowed) Injected (intramuscular) Developed by Albert Sabin Jonas Salk Immunity type Humoral + cell-mediated + mucosal (gut IgA) Humoral only Herd immunity Yes — vaccine virus shed in stool, spreads to contacts No — does not spread Dose Single dose effective Multiple doses required Cost Cheaper More expensive Risk Vaccine-associated paralytic poliomyelitis (VAPP) — rare but real