Medical Virology Exam Notes: Pathogenesis, HSV, CMV, Hepa...

--- 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