Viral Infections Flashcards
What is the viral envelope
Lipid bilayer derived from host cell membrane
Not present in all viruses
Contains viral glycoproteins (spikes) that project from the membrane to attach to cells
Interaction between capsid and envelope is mediated by viral matrix protein
What does the viral envelope do
Determines the stability of virions outside the host and correlates with mode of transmission
Non-enveloped viruses are stable in the environment; may be transmitted by food or water (e.g. noroviruses)
Enveloped viruses often survive only transiently outside the host and infectious viruses do not persist in the environment (e.g. HIV)
What does IgM represejnt
acute or recent infection
What is viral hep
Inflammation of the liver
Wide spectrum of clinical diseases
What is type A viral hep
faecal oral transmission
What is type B viral hep
parenteral transmission
What heps cause chronic infection
Hep B +/- D and C can cause chronic infection
Associated with: persistent infection, chronic liver disease, chronic active or persistent hep, cirrhosis, hepatocellular carcinoma
What heps do not cause chronic infection
Hep A does not cause chronic infection
Hep E does not usually cause chronic infection but it can do in immunocompromised patients
Route of transmission, incubation similar
How is viral hep diagnosed
Liver function tests: aminotransferases (high 100s)
Serology: antigen, IgM, IgG, alpha fetoprotein (hepatocellular carcinoma)
Molecular qualitative, quantification, genotyping
Imaging: fibroscan and ultrasound (assess liver fibrosis, fatty deposits and general composition)
Histopathology: liver biopsy
What is hep A
ss RNA unenveloped Hepatovirus (more stable in GI tract)
Endemic worldwide Incubation period 3-5 weeks, median 4 weeks
Faeco-oral transmission
Rare parenteral transmission
Detect HAV IgM in blood samples
How can hep A be prevented
Jaundice: considered infectious from 2 weeks before to 7 days after jaundice onset Sanitary disposal of waste Good hygiene Active - hep A vaccine Passive - human normal immunoglobulin
What is hep E
Ss RNA unenveloped virus
Foodborne zoonosis: undercooked meat products i.e. pork sausages
Evidence of transmission by blood transfusion
Sporadic and epidemic forms
Incubation 6 weeks
How is hep E in immunocompromised px treated
ribavirin (antiviral agent) or interferon (immunomodulator)
How is hep E detected
Detect HEV IgM in blood samples
HEV RNA detection and quantification
What is hep B
Partially ds DNA Hepadnavirus (has reverse transcriptase)
Narrow host range
E antigen is shed, which can be detected
6 weeks to 6 months, median 2.5 months
Sexual intercourse, blood and blood products injecting drug use, tattoos
When hep B surface antigen persists in circulation for over 6 months, classified as a carrier state
What are the two types of acute hep B infection
icteric (resolves just jaundiced) and anicteric (carrier state, causes cirrhosis and hepatocellular carcinoma)
What does HB core antibody contain
IgM and IgG.
What is HBsAg
A protein on the surface of hepatitis B virus; it can be detected in high levels in serum during acute or chronic hepatitis B virus infection. The presence of HBsAg indicates that the person is infectious
What is HB core antibody
Appears at the onset of symptoms in acute hepatitis B and persists for life. The presence of anti-HBc indicates previous or ongoing infection with hepatitis B virus in an undefined time frame.
What is HB core IgM
persists for 3 months after infection
What is anti-HBs
The presence of anti-HBs is generally interpreted as indicating recovery and immunity from hepatitis B virus infection.
What is HB e antigen
is an indicator of active viral replication; this means the person infected with Hepatitis B can likely transmit the virus on to another person
What is delta hep
Ss RNa enveloped by HBsAg
Defective virus
Coinfection, acute delta infection is self-limiting as it cannot survive without HBsAg
What is hep C
ss RNA enveloped Flavivirus, with 6 genotypes
Incubation 6-12 weeks
How is hep B prevented
Passive immunisation: hepatitis B immunoglobulin use if mother is E antigen positive
Active: recombinant vaccine
Antiviral: Lamivudine, adefovir, tenofovir, entecavir, emtricitabine
Immunomodulators: interferon
How is hep c detected and cure
Serology: HCV abx. Molecular diagnostic tests: HCV RNA detection and quantification. HCV genotype. Antiviral resistance.
No vaccine
Antiviral: cure HCV infection to prevent liver cirrhosis and other complications. Aim is undetectable HCV RNA in blood by 12 weeks.
What is VZV
Ds DNA, icosahedral, enveloped, 125 kbp
Only humans are susceptible (no animal reservoir)
Primary infections causes chickenpox
Latent in dorsal root or cranial nerve ganglia
What does VZV reactivation cause
Reactivation causes shingles
During reactivation virus travels down sensory nerves and produce painful vesicles in the area of skin served by infected ganglion
What happens in chickenpox
Prodome: fever, pharyngitis, malaise
Itch/painful lesions appear in crops
Macule (area of skin discolouration) -> papule (a small pimple) -> vesicle (small, fluid filled sac) -> pustule (small blister containing pus) -> crusts (liquid debris that has dried on the surface)
What dermatome is most likely to see shingles
thoracic (50%) and cranial (20%). Ophthalmic singles can cause loss of sight.
What happens in VZV reactivation
Pain at site may precede eruption of painful vesicles. Unilateral, 1-2 dermatomes involved. Ophthalmic division of trigeminal nerve -> involvement of eye in 50%. Post-herpetic neuralgia especially in the elderly. Incidence increases with age and in the immunocompromised host.
What is horizontal transmission of VZV
respiratory (varicella) commencing 48h before onset of rash. Skin lesions of varicella and zoster are infectious until crusted over
What is vertical transmission of VZV
congenital infection of foetus in utero (maternal varicella in the first 20 weeks of gestation results in foetal defects in <2% of cases) . Perinatal infection causing neonatal varicella (requires urgent treatment) - maternal varicella occurring within 7 days before and 7 days after delivery is associated with a high mortality in the newborn infant.
What is post exposure VZV prophylaxis
Aciclovir
Varivax vaccine (live) - may be contraindicated and administer within 72 hours
VZIG - prevents or ameliorates chicken pox, administer within 7 days of significant contact. Use for pregnant, immunosuppressed, neonate of seronegative mother.
What is Oka varicella vaccine
Live attenuated vaccine
2 does schedule
Recommended in UK for susceptible healthcare workers and susceptible household contacts of IC patients
What is zoster vaccine
Prevent Zoster and post herpetic neuralgia
High does Oka vaccine (14* potent c/w varicella vaccine)
Augments VZV specific T cell immunity
Offer to 70 & 79 year olds
What are DNA viruses
poxvirus, herpesvirus, adenovirus, warts virus, parvoirus
What are RNA viruses
influenza virus, mumps, rotavirus, eastern equine encephalitis, HIV, corona virus, LCM virus, rabies
Why do RNA viruses mutate quickly
RNA dependent polymerases lack proofreading ability
+RNA is essentially equivalent to mRNA and can be immediately translated to protein. Viral polymerase synthesis is the first step.
What cancers does HPV cause
cervical carcinoma, anogential & vulvo-perineal tumour
What cancers does HHV cause
Kaposi’s sarcoma
What cancers does EBV cause
Burkitt’s lymphoma, Nasopharyngeal carcinoma, Hodgkin’s lymphoma, Lymphoproliferative disease
What cancers does hep cause
Hepatocellular carcinoma
What type of cells is in the resp epithelium
ciliated pseudostratified columnar epithelium
What type of cells is in the oral mucosa
stratified squamous epithelium
What are upper resp infections
common cold (nasal obstruction, nasal discharge, sneezing), pharyngitis 9sore throat, inflammation with/out exudates), Laryngitis (hoarseness)
What are airway infections
croup (hoarseness, barking cough), tracheobronchilitis (cough, substernal pain), bronchiolitis (cough, dyspnoea, wheezing - may need surgical intervention)
What causes bronchiolitis
RSV
What causes common cold
Rhinovirus and coronavirus
What causes croup
parainfluenza virus
What causes pneumonia
influenza, RSV, adenoviruses
What is influenza
an envelope virus. 8 cartridges of RNA> Two major proteins: hemagglutinin (binds to sialic acid receptor, determines where in respiratory tract) and neuro-aminidase (catalyses cleavage of glyosidic linkages to sialic acid bonds facilitating exit of new progeny viruses from the cell, major target for current anti-influenza therapies).
What is H1N1
Swine flu
When does influenza A occur
Start of season
When does influenza B occur
End of season
What is antigenic drift
Virus encodes RNA dependent RNA polymerase
Lacks proof reading ability
RNA replication error accumulation
Need for annual influenza immunisation
What is antigenic shift
genetic segment reassortment (influenza A only)
New virus emerges into the population - primed immune response ineffective
Hence origin of influenza A pandemic. New virus must have the capacity for spread directly from human to human
What flu vaccine is given to children
live attenuated intranasal flu vaccine. Increased efficacy compared with inactivated against antigenically drifted influenza. Intranasal route has high acceptability.
What flu vaccine is given to adults
3-4 influenza components
H1n1, H3N2, B components 1-2
Inactivated
What is ebola
single stand enveloped RNA virus, filovirus
Day 1-3: fever, fatigue, myalgia, relative bradycardia
Day 3-10: rash, vomiting, abdominal pain
Day 7-12: shock, oliguria, reduces GCS
What are the lab findings of ebola
hrombocytopenia, coagulopathy, transaminitis AST>ALT, electrolyte abnormalities
What are the symptoms of Zika
Symptoms 2-13 days in infection Viremia very transient Only 25% are symptomatic Fever Maculopapular pruritic rash
How is Zika transmitted
Aedes aegypti
mosquitos, extrinsic incubation period of 10 days. Mother to child. Sexually - detection in semen in 18 days
