Viruses Flashcards
Virus, size and 3 structures
- Small 20-400nm
- Non-cellular
- Icosahedral (20 faces)
- Helical: protein binds around DNA/RNA in a helical fashion
- Complex: neither icosahedral or helical
Define obligate intracellular pathogens
- Need a host to survive
- Can only replicate inside host cell
- Need a specific host range and only infect host cell types
Taxonomy of viruses
Order
Family
Genus
Species
Classification of virus families
Virion shape/symmetry
Presence/absence of envelope
Genome Structure
Mode of replication
Blood-borne viruses
HIV
Hep B
Hep C
Sexually transmitted virsuses
HIV
Hep B
Hep C increasingly
Vertically transmitted viruses
HIV
Hep B
Faecal-oral route viruses
Hep A
Hep E
Polio
Droplet viruses example and definition
- Large particles and fall within a short distance of a person
- Influenza, Respirtory Syncytial Virus
Airborne example and definition
- Aerosolised, can travel much further in the environmment
- Measles
- Chickenpox
Close contact transmitted viruses
Herpes simplex
CMV (Cytomegalovirus)
EBV - Glandular fever
Vector-borne viruses
Dengue
Yellow fever
Chikungunya
Zoonotic viruses
Rabies
MERS
Ebola
Host range
Some viruses may only infect humans e.g. smallpox, measles
Some may also infect other animals which can result in transmission of a novel virus to humans or coninfection where human and animal strains may recombine to generate a new strain
Consequences of viral infections
- Clearance (with no, short or long term immunity)
- Chronic infection
- Latent infection
- Transformation (long term infection with altered cellular gene expression)
Latent infection life cycle
- How you get cold sores or shingles
- Virus lies dormant after 1ary infection
- Full viral genome is retained in the host cell but it’s expression is restricted, a few viral antigens and no viral particles are produced
- Reactivation of viral replication can occur
- More likely to occur and more severe in immunocompromised
Viruses and cancer, mechanisms
- Viruses can lead to cancer but often need another event to also occur
Mechanisms: - Modulation of cell cycle control, drives cell proliferation
- Modulation of apoptosis, prevention of programmed cell death
- Reactive oxygen species mediated damage, some viral infections cause inflammatory processes which lead to cancer via reactive oxygen species
Viruses and cancer examples
EBV - Glandular fever:
Burkitt’s lymphoma, Hodgkin’s lymphoma, nasopharyngeal carcinoma
Human herpes virus: Kaposi’s sarcoma, primary effusion lymphoma
Human T-cell Lymphotropic virus: Adult T-cell leukaemia/lymphoma
Human Papillomavirus: cervical, anus, oropharyngeal cancers
Hepatitis B and C: hepatocellular carcinoma
Principles of viral culture
You can either detect the whole organism or part of the organism
Whole organism detection method
- Electron microscopy, see the shape and match it
- Culture
but neither are really done anymore
Part of organism detection method
- Antigen detection: you have a specimen coated in antibodies and you look for a reaction with fluoresence
- DNA/RNA detection
- Extraction of genetic material from sample
- Amplification of region of target organism genome: PCR, look for amplification curve that matches the virus
- Immune response to pathogen: look for a sign that they’ve been exposed, opposite of antibody test. Can determine acute/recent infection or prior infection/response to vaccination
Antiviral therapy
- All antiviral agents are virustatic
- Viruses utilise host cell enzymes in order to replicate, there are limited viral proteins that are potential targets for antiviral drugs
- Toxicity to the host cell is not an uncommon side effect
- Only used in the minority of viral infections as there aren’t many available
When you might use an antiviral
- Prophylaxis (preventing infection)
- Pre-emptive therapy, if there’s evidence of infection, replication but no apparent symptoms. Especially in HIV
- Overt disease
- Suppressive therapy, keep viral replication rate low to prevent tissue damage
Prevention of viral infection
- Immunisation: vaccination, passive immunisation with immunoglobulin
- Prophylactic treatment post exposure
- Infection prevention and control measures. Isolate symptomatic patients, PPE, safe use and disposal of sharps
- Blood/tissue/organ screening
- Antenatal screening
What do you need to eradicate a virus?
- No animal reservoir or ability to amplify in the environment
- Clearly identifiable, with accurate diagnostic tool
- No chronic carrier state
- Efficient and practical intervention e.g. vaccination
- Political and social support
