MBChB Year 3 Medical Virology Exam Notes: HSV, CMV, EBV

--- 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. Asterisk = must know, appears in essays and/or repeatedly across papers. --- 1. VIRAL PATHOGENESIS Correct order of stages — tested in EVERY paper:- Viral entry at skin or mucosal surface Primary replication Viremia Replication within target organs Resistance to viral infection LEAST likely depends on: size of viral genome and gender of exposed individual. It DOES depend on immunocompetence, history of immunization, and age. Persistent infections: viruses causing them have evolved mechanisms to escape detection and/or clearance by the host immune system. They do NOT require defective immunity to establish persistence. --- 2. VIRUS AND RESPIRATORY TRACTFactors important in virus-respiratory tract interaction:- Mucociliary transport Size of aerosolized droplets Relatively low temperature of upper airways Mucosal IgA production NOT important: M cells — this is the MCQ trick answer used repeatedly. Early host defense (LEAST important in early infection): virus-specific cytotoxic lymphocytes. These are a late response. Early defenses are mucociliary transport, macrophages, interferons alpha and beta, natural killer cells. --- 3. HERPES SIMPLEX VIRUS (HSV) Tested in every single paper. High priority for essays and MCQs.Types that cause genital herpes: HSV-1 and HSV-2 only. Not HPV, not HTLV1, not HIV. Portal of entry: mucous membranes and skin. Target cells: mucous membranes and neurons. HSV establishes latency in neurons and travels to CNS along nerve fibers — this is how it bypasses the blood-brain barrier. Pathogenesis must knows: Most HSV-2 seropositive persons report NO symptoms but still shed virus intermittently from genital area Primary first episode: lesions present, symptoms usually severe, NEITHER HSV-1 nor HSV-2 antibodies are present yet HSV-2 IS associated with HIV acquisition and transmission Patient with HSV is ALWAYS at risk for shedding the virus — this answer appears in essays and MCQs Herpesvirus family — incorrect statement to identify in MCQ: they replicate in host cell NUCLEUS, not cytoplasm. Everything else about them is true — they are enveloped, latent, cause recurrent infections, common in immunocompromised. Treatment — systemic antiviral chemotherapy: Acyclovir Valacyclovir Famciclovir All three are correct. This comes up repeatedly. Transmission facts: HSV is readily inactivated by drying and soap and water Average incubation period is NOT 10 days — this is the trick option Likelihood of transmission does NOT decrease with increased duration of infection --- 4. VARICELLA-ZOSTER VIRUS (VZV)Portal of entry: respiratory epithelium Most contagious period: 1-2 days PRIOR to development of the rash --- 5. CYTOMEGALOVIRUS (CMV)Essay question in 2018/2019 and 2021/2022 — very high priority.Group most likely to develop virulent CMV infection: newborns Congenital CMV infection causes: Mental retardation Enlarged spleen Liver damage Petechial rash, low birth weight, hepatosplenomegaly, bilateral cataracts All of the above can occur. Any of these answers is correct. Pathogenesis of CMV: Primary infection often asymptomatic in immunocompetent CMV establishes latency in mononuclear cells Reactivates in immunocompromised — transplant patients, HIV patients, newborns Diagnosis: detection of CMV pp65 antigen, PCR, shell vial culture Prevention and diagnosis: Preventive measures: antiviral prophylaxis in transplant patients (ganciclovir), screening of blood products, avoid exposure in pregnancy Diagnosis: serology, PCR, culture, antigenemia assay --- 6. EPSTEIN-BARR VIRUS (EBV)Associated with: Burkitt lymphoma AND infectious mononucleosis — both caused by EBV. This is a repeated MCQ.Niche in humans: lymphoid tissue and salivary glands Also associated with nasopharyngeal carcinoma — but note: EBV causing nasopharyngeal carcinoma is TRUE, not false. Know this distinction for the except questions. --- 7. HEPATITIS VIRUSES Tested in every paper.Hepatitis A: Transmission: fecal-oral route — always the answer Diagnosis: detection of IgM anti-HAV by ELISA — most reliable method Initial site of replication: GIT Diagnosis is NOT made by isolating virus in cell culture Member of Picornaviridae family Immunoglobulin used to prevent disease in exposed persons Hepatitis B: Only DNA virus that causes hepatitis — comes up in every paper Found in: blood, semen, AND saliva — all of these Transmitted parenterally, sexually, mother to child Hepatitis C: RNA virus Hepatitis D: RNA virus, requires HBV co-infection Hepatitis E: RNA virus, fecal-oral like HAV --- 8. INFLUENZA VIRUSEssay and MCQ — antigenic changes are very heavily tested.Antigenic drift: minor change, gradual, point mutation affecting major antigenic sites on surface glycoprotein Antigenic shift: major change, abrupt change due to genetic reassortment