Viral Infections in Childhood Flashcards
Virion
An entire virus particle, consisting of an outer protein shell called a capsid and an inner core of nucleic acid (either ribonucleic or deoxyribonucleic acid—RNA or DNA)
Nucleic acid
Protein coat (capsid)
+/- envelope
Nucleocapsid
Nucleic acid + protein coat
Viral nucleic acid
Double stranded DNA
(single stranded DNA in parvovirus)
Single stranded RNA (+ or - polarity)
(double stranded RNA in reoviruses)
Viruses as intracellular parasites
Dependent on cells they infect for energy, metabolic intermediates and most enzymes
Steps in Viral Life Cycle
Attachment Entry Uncoating Synthesis of Viral Components Assembly + release
Step 1: Viral attachment
Binding sites on the virus
Receptors (+/- co-receptors) on plasma membrane of cell
“cell tropism”
Cell must be permissive (have all the right intracellular components required by the virus to replicate
Step 2: Entry
Takes from seconds to several minutes
Enveloped viruses undergo membrane fusion
May undergo receptor-mediated endocytosis
Step 3: Uncoating
Can take place in:
–> endosome (receptor mediated endocytosis), due to low pH and lysosomal enzymes
–> cytosol
–> nuclear membrane
Results in transport to right part of cell to begin new virion production
Step 4: Synthesis of viral components
Requires viral mRNA to enable viral polypeptides and nucleic acid to be synthesised by cell machinery
DNA viruses that enter the nucleus can use only cellular enzymes
All other viruses must synthesise their viral mRNA
May carry their own enzymes (e.g. RNA polymerase, reverse transcriptase)
Step 5: Assembly + release
After synthesis of viral proteins + nucleic acid, virions assembled
Released by cell lysis + budding
Important Enveloped DNA viruses
Herpes Viruses
–> herpes simplex, varicella zoster, CMV, Epstein-barr, HHV 6/7/8
Hep B
Poxviruses
Important Non-Enveloped DNA viruses
Papillomavirus
Adenovirus
Parvovirus (ssDNA)
Disseminated Herpes simplex virus in neonates
Sepsis-like syndrome
Hepatitis, coagulopathy
High mortality
IV aciclovir
HSV encephalitis
Fever
Seizures
Haemorrhagic infarction of white matter + cortex
Cytomegalovirus
Self-limiting illness
Severe disease in immunosuppressed