Diagnostic Virology Flashcards
(27 cards)
Direct detection methods
Electron microscopy
Cell culture
Immunoassay
Molecular methods
Indirect detection methods
Immunoassay - antibodies to viral proteins
Hepatitis B
Hepadnavirus DsDNA-RT circular Infects liver - cirrhosis, hepatocellular carcinoma Can cause persistent infection Blood borne virus (parenteral) Vaccine preventable
Hepatitis B virus diagnosis
Immunoassay
PCR to detect HBV DNA
Liver function tests
Classical serology techniques
Complement fixation tests Haemagglutination/Haemagglutination inhibition tests Immunofluoresnce techniques Neutralisation tests Single radial haemolysis
Newer serology techniques
radioimmunoassay ELISA Particle agglutination Western Blot Recombinant immunological assay
HBV serology markers
Hepatitis B surface antigen HbsAG
Antibodies to HBV core - anti-HBc and total IgM
HB e antigen - HBeAg and anti-HBe
Antibodies to HBsAG - anti-HBs
Blood service screening
HBsAG Anti-HIV 1/2 Anti-HCV Anti-HTLV Antibodies to troponema pallid up HIV-1 RNA HBV DNA HCV RNA
Diagnostic sensitivity
The probability of an assay detecting samples that contain the Traeger analyte
Non analytical sensitivity
Low number of falsely negative results - high sensitivity
Limit of detection of a test
Diagnostic specificity
The probability of defining samples with a specific analyte and only that analyte as positive
Low number of false positives - high specificity
Human immunodeficiency virus (HIV)
Retroviridae - lentivirus SsRNA-RT (twin strands) Targets CD4 presenting cells Can progress to AIDS Blood-borne virus Anti-retroviral drugs used to treat
HIV diagnosis
Immunoassay
PCR to detect HIV RNA or HIV DNA
CD4 count - indicates immune system health
Western blot
Proteins are prepared
Proteins are separated using gel electrophoresis eg SDS-PAGE
Transferred to solid phase - nitrocellulose membrane
HIV positive status at NRL
1 glycoproteins (ENV) \+ 3 viral proteins (gag or pol)
Togaviridae
SsRNA virus
Enveloped icosohedral
Rubivirus - rubella
Alphaviruses
Rubella
Mild diseas in childhood and adults Severe diseas to a foetus if mother has virus just before or in first 2 trimesters of pregnancy Rash and sub-occipital lymphadenopathy Congenital rubella syndrome Microcephaly- ‘blueberry muffin’
Types of vaccines
Live attenuated
Killed or inactivated
Toxoid based - tetanus and diphtheria
Subunits of virus - hep B
Conjugated to increase effectiveness
Live attenuated vaccines
Passage through cells to ‘weaken’ virus candidate Live in sense it is a functioning virus Eg Oral polio vaccine MMR VZV
Live virus vaccine
Advantages Activates all phases of immune system Provides more durable immunity Low cost Quick immunity Can be easier to administer
Disadvantages
Secondary mutation cause a reversion to virulent wild type
May still be able to cause disease
Manufacture process may cause adverse affect
Susceptible to changes in storage and transport
Inactivated virus vaccine
The DNA/RNA is not functional Heat, chemical or radiation Less immunogenicity so may require more doses Eg Inactive polio vaccine Influenza vaccine
Smallpox
Various
Group I dsDNA complex linear
Most feared infectious disease in history
Fatal 30% cases
Measles
Group V ssRNA enveloped helical
Paramyxoviridae
Only infects humans
Highly contagious - always symptomatic
Influenza
Group V ssRNA segmented
Three types A,B and C
Haemagglutination and neuraminidase spikes
Can undergo
Antigenic drift - seasonal influenza
Antigenic shift - pandemic influenza (A only)
Diagnosis of Influenzavirus
Clinical symptoms Immunofluorescence HA and HAI Cell culture (embryonated eggs) RT-PCR, real-time PCR Sequencing for subtype
