6 – How do Viruses Infect and Spread Through the Body? Flashcards
1
Q
Many viruses enter through respiratory tract
A
- Where they are deposited depends on SIZE
- At each level, viruses may infect EPITHELIAL CELLS
o Can lead to disruption of mucociliary escalatory and ‘secondary’ bacterial infections
2
Q
Droplet vs airborne transmission
A
- Droplet: Coughs and sneezes can spread droplets of saliva and mucus
- Airborne: tiny particles are suspended in air for longer and travel further
o **VERY IMPORTANT FOR VIRUSES (ex. dog kennels)
o Ventilation is very important
3
Q
Many viruses are ingested
A
- Many that cause intestinal infection are acid and bile RESISTANT
- Acid may increase infectivity by cleaving capsid
- Peristalsis moves viruses along: provides contact with target cells
- *virus can enter M cells (immune system): parvovirus reach epithelium through blood
4
Q
Viruses enter via the skin
A
- Skin is the longest organ
- Intact keratinized skin=tough barrier, but
o Cuts, injuries provide entry
o Iatrogenic: dirty needles
o ‘flying needles’ (mosquitoes) and other arthropods transmit ‘arboviruses
5
Q
Mechanism of spread in body
A
- Local spread on epithelial surface
- Spread in respiratory tract enhanced by fluid layer
- Spread in GI tract enhanced by fluid layer and peristalsis
- Subepithelial invasion and lymphatic spread
- Spread via blood stream=viremia
- Interact with macrophages
- Interact with endothelial cells
- Multiple within the CNS
6
Q
Local spread on epithelial surfaces
A
- Many pox viruses (ex. myxoma virus, papilloma virus)
7
Q
Spread in respiratory tract enhanced by fluid layer: example
A
- Ex. BRSV
8
Q
Spread in GIT enhanced by fluid layer and peristalsis: example
A
- Ex. coronavirus
9
Q
Subepithelial invasion and lymphatic spread
A
- Facilitated by basolateral budding from epithelial cells
- Ex. mouse hepatitis virus (coronavirus)
10
Q
Spread via blood stream=Viremia
A
- May be free in plasma or associated with cells
- Play a central role in many viral infections, but NOT ALL
- Often viruses with primary and secondary are more ‘susceptible’ to vaccination b/c of LONGER incubation period=gives time for memory response
11
Q
Primary and secondary viremia
A
- Primary: first entry may be subclinical
- Secondary: following replication in target tissue higher sustained levels
- *don’t cause disease right away
12
Q
Viruses interaction with macrophages
A
- Differences amongst isolates of same virus in their ability to infect macrophages
- Ex. feline coronaviruses
13
Q
Virus interactions with vascular endothelial cells
A
- Route to parychymal organs from blood
- Ex. bluetongue virus
14
Q
There are multiple mechanisms of spread within the CNS
A
- Peripheral nerves=one important route of infection for viruses in affect CNS (ex. rabies)
o Don’t need to pass BBB
15
Q
Mechanisms of virus shedding
A
- Shed from respiratory tract
- Shed from oropharynx and GI tract
- From skin
- Urinary tract
- Genital tract
- milk