Medical Virology: Adenoviruses, Hemorrhagic Fever & Viral...

--- MEDICAL VIROLOGY & MYCOLOGY MOUNT KENYA UNIVERSITY — MBCHB YEAR 3 UNIT CODE: MBMM 3300 / MBMM 3333 TARGETED EXAM NOTES — SECTION 3 OF 3 --- ADENOVIRUSES Essay question in 2018/2019 and CAT 2020/2021 — high priority. Modes of transmission Respiratory droplets — most common Fecal-oral route Direct contact with infected secretions Contaminated water — swimming pools Eye-to-eye contact Associated diseases Respiratory: pneumonia, bronchitis, common cold Eye: conjunctivitis, keratoconjunctivitis GIT: gastroenteritis, diarrhea Urinary: hemorrhagic cystitis CNS: encephalitis Pharyngoconjunctival fever Prevention strategies Live oral vaccine available for military personnel Good hygiene and handwashing Avoid sharing towels and personal items Adequate chlorination of swimming pools Isolation of infected individuals --- HEMORRHAGIC FEVER VIRUSES Essay question in CAT 2020/2021. Transmission to humans Contact with infected animals or their excretions Bite of infected arthropod vectors — mosquitoes, ticks Direct contact with blood or body fluids of infected person Nosocomial transmission in healthcare settings Bushmeat handling Viruses that cause hemorrhagic fever Ebola virus Marburg virus Lassa fever virus Yellow fever virus Dengue virus Rift Valley fever virus Crimean-Congo hemorrhagic fever virus --- VIRAL RECEPTORS AND SPIKES Essay question in 2017/2018 — high priority. Clinical importance of viral receptors Attachment: viral spikes/receptors mediate attachment to host cell surface — most important step in viral life cycle Specificity: virus only affects cells expressing specific receptor — determines tissue tropism Entry: receptor binding triggers viral entry into host cell Cell signalling: some viral receptors trigger intracellular signalling Maintenance of cellular structure Complement mediated lysis Vaccine development: receptors and spikes are targets for vaccine design Development of antiviral drugs: blocking receptor-ligand interaction Viral structure proteins and functions Capsid: protection of viral genome Reverse transcriptase: replication Glycoprotein receptors: attachment HA: binding and attachment NA: transmission, cleaves sialic acid, aids release of virus Examples of viral receptors HIV: uses CD4 receptor and CCR5/CXCR4 co-receptors on T-helper cells Influenza: HA binds sialic acid receptors EBV: binds CD21 on B lymphocytes Rabies: binds acetylcholine receptors on neurons Poliovirus: binds CD155 on intestinal cells --- ENTEROVIRUSES Classification Member of Picornaviridae family Naked capsid — survives gastric environment Transmitted via alimentary/fecal-oral route Genera Poliovirus Coxsackievirus — groups A and B Echovirus Enterovirus Diseases caused Poliomyelitis Hand, foot and mouth disease Herpangina Myocarditis Meningitis Hemorrhagic conjunctivitis — caused by enterovirus Hepatitis — Hepatitis A virus Acute hemorrhagic conjunctivitis caused by: enterovirus All following belong to Picornaviridae EXCEPT: Rabies virus — trick MCQ All following viruses disseminated throughout body EXCEPT: Human papilloma virus Viruses transmitted by respiratory routes EXCEPT: Human papilloma virus --- MUMPS AND MEASLES Mumps Caused by paramyxovirus Target site: parotid gland Testes, ovaries and pancreas can also be involved Vaccine exists — MMR vaccine Active immunization prevents disease Second episodes cannot occur — only one serotype Diagnosis NOT made only on clinical grounds — serology available Transmitted by respiratory droplets Measles Caused by paramyxovirus Encephalitis after measles: post-infectious encephalomyelitis — NOT direct Paramyxovirus causing serious croup: RSV Rubella causes teratogenic effects — NOT measles --- RUBELLA- Caused by Rubivirus Only virus that causes teratogenic effects Baby born at 39 weeks with petechial rash, low birth weight, hepatosplenomegaly, bilateral cataracts — acquired in utero: Rubella virus Congenital rubella syndrome — classic presentation --- VIRAL LABORATORY DIAGNOSIS Cell cultures Neutralization test: mainstay of identification of poliovirus isolate Haemagglutination inhibition test: mainstay of identification of respiratory viruses Presence of cytopathic effect is NOT the only way to detect a virus Viruses cannot only be cultured using cell lines — other methods exist Whole blood is NOT specimen of choice for many common viruses Methods to identify virus infected host cell Immunofluorescence test Haemagglutination test Immunoblotting test All of the above Antiviral drugs acting by inhibition of viral DNA polymerase Effective against: Cytomegalovirus NOT influenza, measles, mumps, rabies — these are RNA viruses --- RISK FACTORS FOR FUNGAL INFECTIONS Essay question — appears in multiple papers. Immunosuppression: HIV/AIDS, CD4 below 200 Post-transplantation and use of immunosuppressive drugs Prolonged use of broad-spectrum antibiotics — disrupts normal flora Prolonged use of corticosteroids Diabetes mellitus Malignancies: leukemia, lymphoma Extreme ages: very youn