--- MEDICAL VIROLOGY & MYCOLOGY MOUNT KENYA UNIVERSITY — MBCHB YEAR 3 UNIT CODE: MBMM 3300 / MBMM 3333 TARGETED EXAM NOTES — SECTION 1 OF 3 Based on past papers
--- MEDICAL VIROLOGY & MYCOLOGY MOUNT KENYA UNIVERSITY — MBCHB YEAR 3 UNIT CODE: MBMM 3300 / MBMM 3333 TARGETED EXAM NOTES — SECTION 1 OF 3 Based on past papers: 2017/2018, 2018/2019, 2021/2022 and CAT papers. = must know, appears in essays and/or repeatedly across papers. --- VIRAL PATHOGENESISCorrect order of stages : - Viral entry at skin or mucosal surface - Primary replication - Viremia - Replication within target organs - Resistance to infection LEAST depends on: genome size and gender — trick MCQ answers. Persistent infections: viruses evolved to escape host immune detection — NOT just defective immunity. --- VIRUS AND THE RESPIRATORY TRACTImportant factors: mucociliary transport, droplet size, low temperature of upper airways, mucosal IgA. NOT important: M cells — repeated trick answer. Least important early defense: virus-specific cytotoxic lymphocytes — these are late. Early defenses are interferons, NK cells, macrophages. --- HERPES SIMPLEX VIRUS Most tested topic across all papers. Types and transmission - Causes genital herpes: HSV-1 and HSV-2 only. Not HPV, not HTLV1. - Portal of entry: mucous membranes and skin - Target cells: mucous membranes and neurons - Spreads to CNS along nerve fibers, not via blood - Pathogenesis - Most HSV-2 seropositive persons have NO symptoms but shed virus intermittently - Primary episode: lesions present, symptoms severe, NO antibodies present yet - HSV-2 is associated with HIV acquisition - Patient with HSV is ALWAYS at risk for shedding - Herpesviruses replicate in the NUCLEUS not cytoplasm — incorrect statement MCQ trick - Treatment - Acyclovir, Valacyclovir, Famciclovir — all three correct - Transmission - HSV readily inactivated by drying, soap and water - Incubation period is NOT 10 days — trick option - --- VARICELLA-ZOSTER VIRUS- Portal of entry: respiratory epithelium - Most contagious: 1-2 days BEFORE rash appears - --- CYTOMEGALOVIRUS High priority — essay question in multiple papers. Who is most at risk - Most vulnerable group: newborns - Also reactivates in immunocompromised and transplant patients - Congenital CMV causes - Mental retardation - Enlarged spleen - Liver damage - Petechial rash, low birth weight, bilateral cataracts - Answer is always any/all of the above - Pathogenesis - Often asymptomatic in immunocompetent - Establishes latency in mononuclear cells - Reactivates in immunocompromised - Prevention and diagnosis - Prophylaxis: ganciclovir in transplant patients - Screen blood products - Diagnosis: PCR, serology, antigenemia assay, culture - --- EPSTEIN-BARR VIRUS- Causes both Burkitt lymphoma AND infectious mononucleosis — same virus - Niche in humans: lymphoid tissue and salivary glands - Also causes nasopharyngeal carcinoma — TRUE, know for EXCEPT questions - --- HEPATITIS VIRUSES Tested in every paper. Hepatitis A - Transmission: fecal-oral route - Diagnosis: IgM anti-HAV by ELISA - NOT diagnosed by cell culture - Member of Picornaviridae - Immunoglobulin used for post-exposure prevention - Hepatitis B - Only DNA virus that causes hepatitis - Found in blood, semen AND saliva — all three - Transmitted parenterally, sexually, mother to child - Hepatitis C, D, E - All RNA viruses - Hepatitis D needs HBV co-infection - Hepatitis E is fecal-oral like HAV - --- INFLUENZA VIRUS Essay and MCQ — antigenic changes most tested. Antigenic changes - Antigenic drift: minor, gradual, point mutation on surface glycoprotein - Antigenic shift: major, abrupt, genetic reassortment with unrelated strain, new subtype, causes pandemics - What increases antigenic shift: simultaneous infection with two different influenza strains - Surface proteins - HA and NA are glycoproteins contributing to virulence - HA = attachment, NA = release of virus - NOT TRUE about Influenza A — repeated trick - Vaccination confers lifelong protection — this is FALSE - Everything else is true: antigenic changes, pandemics, responds to rimantidine and neuraminidase inhibitors - Related paramyxoviruses - Mumps target site: parotid gland - Paramyxovirus causing serious croup: RSV - --- POLIOVIRUS- Affinity for: nervous system - Survives gastric acid because: naked capsid, no envelope - Transmission: fecal-oral route - --- RABIES VIRUS Essay question in CAT 2018/2019. Pathogenesis - Enters via bite of infected animal - Multiplies in muscle at trauma site for weeks - Travels to spinal cord and CNS via nerve cells - Intensive CNS multiplication - Migrates to salivary glands causing excessive drooling - Post-exposure treatment - Passive: Human Rabies Immune Globulin (HRIG) - Active: Human Diploid Cell Vaccine (HDCV) - --- RETROVIRUSES AND HIV Essay in 2021/2022 — reverse transcriptase and integrase — very high priority. Classification - Retroviruses contain two complete copies of positive strand RNA plus reverse transcriptase - Positive strand does NOT act as messenger — converts to DNA, integrates into host genome - Reverse transcriptase - Converts viral RNA to DNA - Essential for replication - Target of NRTIs and NNRTIs - Integrase - Integrates viral DNA into host genome - Target of integrase inhibitors e.g. raltegravir - Selective toxicity - These drugs target viral-specific enzymes with no human equivalent - Drug classes used in HIV - Synthetic nucleotides - Reverse transcriptase inhibitors - Protease inhibitors - Fusion inhibitors - NOT ribozyme inhibitors — trick MCQ answer - Fastest growing transmission route: sharing of contaminated needles --- ARBOVIRUSES- Nucleocapsid: icosahedral, positive single stranded RNA - Chief vectors: gnats, mosquitoes, flies, ticks - NOT a vector: spiders — repeated trick MCQ - --- POXVIRUSES- False statement MCQ: they are non-enveloped — FALSE, they ARE enveloped - Largest and most complex animal viruses - Multiply in cytoplasm — unlike most DNA viruses - Sites of multiplication appear as inclusion bodies - --- VIROIDS AND PRIONS Viroids - Unusual because: no capsid protein, no envelope - Prions - Cause: Creutzfeldt-Jakob disease, Kuru, Scrapie, Mad Cow disease - Abnormal misfolded proteins, no nucleic acid - Resist standard sterilization - --- BACTERIOPHAGES- Temperate phages: stable long-term relationship with host, lysogeny - Lytic phages: kill host immediately - --- VIRAL ENCEPHALITIS Essay question in multiple papers — high priority. Definition and cause - Inflammation of the brain due to viral infection - Cause: inflammation from infection AND viruses are main agents — both correct together - Symptoms - Fever, vomiting, confusion — all of the above - Viruses that cause encephalitis - HSV-1, HSV-2, VZV, CMV, enteroviruses - Pathogenesis - Virus enters CNS via bloodstream or along nerve fibers - HSV travels along nerve fibers — most important example - Causes inflammation, neuronal death, cerebral edema - Diagnosis - Lumbar puncture/spinal tap — best method - CSF: elevated protein, reduced glucose, mononuclear pleocytosis, antibodies detectable - Treatment - Corticosteroids, mechanical ventilation, anticonvulsants — all of the above - Important distinction - HSV encephalitis = direct viral infection - Measles encephalitis = post-infectious encephalomyelitis - This distinction is specifically tested - --- COVID-19 Transmission - Respiratory droplets, contaminated surfaces, within 1 meter — all correct - Who is at risk - All age groups affected - Mild in children, severe in elderly and those with pre-existing conditions - Symptoms - Mild: fever, cough, shortness of breath — all of the above - Related diseases - MERS and SARS — both caused by coronaviruses - Clinical trials - Transfusing blood from recovered patients: Plasma Therapy - --- VACCINES Essay in 2017/2018 and CAT papers — high priority. Active immunization - Vaccine administered - Stimulates immune system - Produces memory cells - Permanent and long-lasting protection - Passive immunization - Preformed immunoglobulins given - Temporary protection only - Example: HRIG post-rabies exposure - How attenuated vaccine protects - Stimu