Viruses Flashcards
Incubation period
Period between start of infection and onset of symptoms
Basic reproduction number (R0)
- Definition
- Rates: avian flu, plague, ebola, influenza, SARS, Measles
The transmission rate of a disease, from one case.
- The number of new infections that arise from one person their infective period.
- Affected by type of infection, mode of transmission and location
Avian flu- 0.7 Plague- 1.3 Ebola= Influenza= 1-3 SARS- 3 Measles= 16
Size of viruses
20-400nm
Structure of virus
Genetic material
- Nucleic acid= DNA or RNA
Protein coat
Envelope/ undeveloped
Viral pathogenesis journey
- Encounter
- Virus encounters the host - Entry
- Mulitplication
- Spread
- Damage
Viral entry into the body
Skin
- Abrasions
- Bites
- Needle punctures
Alimentary tract
- Movement of GIT facilitates entry
Urogenital tract
- Abrasions facilitate entry
Eye
Baltimore system for viral classification 1-7
- Definition
- Types
Classification of viruses based on the type of genome and method of replication.
1- dsDNA
2- ssDNA
3- dsRNA
4- positive ssRNA
5- negative ssRNA
6- positive RNA with DNA intermediate
7- gapped dsDNA
Type 1 virus examples
dsDNA
- Adenovirus
- Herpes simplex virus
- PoxVirus
Type 2 virus examples
ssDNA
- Parvovirus
Type 3 virus examples
dsRNA
- Reovirus
Type 4 virus examples
positive ssRNA
- Poliovirus
Type 5 virus examples
negative ssRNA
- Influenza virus (orthomyoxvirus), rhabdoviruses
Type 6 virus examples
positive RNA with DNA intermediate
- Retrovirus (HIV)
Type 7 virus examples
Gapped dsDNA
- Hep B virus (Hepadnavirus)
Viral spread and release mechanisms
Localised replication
- Within epithelium/ system
Dissemination/ systemic infection
- Haematogenous
- Neurological
Viral release
- Apical (i.e flu)
- Basolateral (i.e rabies), csn invade underlying spread.
Haematogenous spread
- Entry into blood
Entry via
- Capillaries
- Endothelial replication
- Vector bite
- Lymphatic capillaries
Viraemia
- Defintion
- Passive/ active
- Primary/ secondary
Presence of virus in blood
- Can be calculated as %
- Measures viral replication
Passive vs active
- Passive= introduction of virus into the blood stream
- Active= replication of virus in blood stream
Primary
- Spread to blood from primary site of infection
Secondary
- Further infection of other tissues from primary site of infection, via bloodstream
CNS infection of virus
- Neurotrophic
- Neuroinvasive
- Neurovirulent
Neurotropic
- Infection of neural cells
Neuroinvasive
- Viral infection of CNS from peripheral site
Neurovirulent
- Virus that can cause disease of nervous tissue
Determinants of viral tissue tropism
Presence of cell receptors on hosts/ virus allowing entry
- e.g HIV/ CD4
Cell proteases
Cellular proteins that regulate viral transcription
Viral virulence
Determined by genes
- Ability to replicate
- Modification of host’s defence mechanisms (virokines/ viroceptors)
- Ability to spread
- Mechanisms to kill cells
Viral mechanism of cell injury
Cytolytic
- Inhibit host protein/RNA synthesis= loss of membrane integrity= syncytium= apoptosis
Non cytolytic
- Lymphocyte mediated (CD4, CD8, B)
- Free radicals
Examples of acute viral infections
Acute infection
- Non equilibrium between virus and host response
Rhinovirus
Rotavirus
Influenza virus
Examples of persistent viral infections
Lymphocytic choriomeningitis virus
Examples of latent, reactivating viral infections
Herpes simplex
