Intro to Viruses Flashcards
What is a virus
Non-cellular, genetic element that cannot replicate independently of a living (host) cell
Virology
the study of viruses
What is a virion
extracellular form of a virus:
* exists outside host and facilitates transmission from one host cell to another
* contains nucleic acid genome surrounded by a protein coat and, in some cases, other layers of material
What can viruses only do wigh regards to replication
Only replicate inside host cells: obligate intracellular pathogens
Structure of virus cells
3
- icosahedral: 20 faces, each an equilateral triangle
- helical: protein binds around DNA/RNA in a helical fashion
- complex: neither icosahedral or helical
tissue tropism
Most viruses have a specific host range and only infect specific host cell types
what can virus families be classified according to
- Virion shape / symmetry
- Presence / absence of envelope
- Genome structure
- Mode of replication
Name some structures of a viron
lipid envelope, protein capsid, virion associated polymerase, nucleic acid (DNA or RNA), spike projections
Give steps of viral infection/replication
Not sure if need to know?
- Attachment
- Uncoating
- Replication of genomic nucleic acid
- mRNA sythnthesis, protein synthesis, genomic and nucleic acid synthesis
- Viron assembly
- Insertion of virus proteins into membrane
- Budding and release
- Maturation
capsid
protein coating, virion wraps virus in capsid for transmission. The capsid is the infective form. You can also sometimes get a lipid coating derived from the host cell
examples of viruses transmitted by blood-borne route
HIV, Hepatitis B, Hepatitis C
examples of viruses transmitted by sexual route
HIV, Hepatitis B
examples of viruses transmitted by vertical route (parents to offspring)
HIV, Hepatitis B
examples of viruses transmitted by faecal-oral route
Hepatitis A, Hepatitis E, Polio
examples of viruses transmitted by droplet route
Influenza, RSV
examples of viruses transmitted by airborne route
Measles, Chickenpox
examples of viruses transmitted by close contact route
Herpes Simplex, CMV, EBV
examples of viruses transmitted by vector borne route
Dengue, Yellow Fever, Chikungunya
examples of viruses transmitted by zoonotic route
Rabies, MERS, Ebola
Host range
- Some viruses may only infect humans, e.g. smallpox, measles
- Some may also infect other animals / birds:
- Transmission of a novel virus to humans
- Coinfection of human and animal or bird strains in one organism may lead to recombination and generation of a new strain
examples of respiratory syndromes
Influenza, Measles, Chickenpox
examples of neurological syndromes
Enteroviruses, Polio, Rabies, HSV, VZV
examples of gastroenteritis syndromes
Norovirus, Rotavirus, Adenovirus
examples of hepatitis syndromes
Hepatitis ABCDE, CMV, EBV, Yellow Fever
examples of skin infections
HSV, Enteroviruses
examples of eye infections
HSV, VZV, Adenovirus
examples of congenital abnormalities syndromes
CMV, Rubella, VZV, Parvovirus
examples of arthralgia syndromes
Dengue, Chikungunya, Rubella, Parvovirus
examples of lymphadenopathy syndromes
HIV, CMV, EBV
consequences of viral infection
with examples
- Clearance of virus (with no, short or long term immunity)- measles (long term immunity)
- Chronic infection- HIV, hepatitis B, hepatitis C
- Latent infection: Herpes Virus
- Transformation (long term infection with altered cellular gene expression)- Epstein-Barr Virus, Human Papillomavirus
Explain viral latency
- Following primary infection, some viruses lie dormant in the cell
- The full viral genome is retained in the host cell, but its expression is restricted, such that few viral antigen and no viral particles are produced
- Reactivation of viral replication can occur
- Reactivations may or may not cause apparent disease
- Reactivation more likely to occur and more severe in immunocompromised
Examples of viral latancy
- Herpes simplex virus
- Varicella zoster virus
What can viral infections lead to
cancer
What is the mechanism of viral infection causing cancer
- modulation of cell cycle control (driving cell proliferation)
- modulation of apoptosis (prevention of programmed cell death)
- reactive oxygen species mediated damage (some persistent viral infections can cause persistent inflammatory processes which lead to cancer via reactive oxygen species)
Methods to detect viruses
- Whole organism
- Part of organism - e.g. antigen, nucleic acid
- Immune respone of host to pathogen - e.g. antibodies
Detection method - whole organism
- Microscopy - not suitbale for diagnosis as not specific (can’t identify virus type)
- Culture: unifected vs infected cells
Detection method - part of organism
- Antigen detection
- DNA/RNA detection, extraction of genetic material from sample, amplification of region of target organism genome (if organism present in sample) - PCR
Detection Methods: immune response
- similar methods as those used for antigen detection
- may be used to determine acute (IgM)/ recent infection, prior infection / response to vaccination - IgG
What is antiviral therapy
- All antiviral agents are virustatic, none are virucidal
- As 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 uncommon: side effects
- Only used in a minority of viral infections
In what situations may antivirals be used
- Prophylaxis (to prevent infection)
- Pre-emptive therapy (when evidence of infection/replication detected, but before symptoms are apparent)
- Overt disease
- Suppressive therapy (to keep viral replication below the rate that causes tissue damage in an asymptomatic infected patient)
What are some ways we can prevent viral infection
- Immunisation (vaccination(slow)/passive immunisation with immunoglobulin (quick))
- {rophylactic treatment post exposure
- Infection prevention and control measures (isolate symptomatic pationt, PPE, safe use and disposal of sharps)
- Blood/tissue/organ screening
- Antenatal screening
What properties can viruses have which may lead to their irradication
- No anima resivour or ability to amplify in environment
- Clearly identifiable
- No chronic carrier state
- Efficient and practical intervention (e.g. vaccination)
- Political/social support
give examples of eradicated viruses
3
- Smallpox
- Measles
- Polio
