Lecture 3 1/31/24

Question 1

What is adsorption?

Answer 1

the initial interaction between a virus and a cell’s surface

Question 2

What are the characteristics of adsorption?

Answer 2

-contact only, no entry
-reversible
-initiated at random
-mediated by weak bonds and other factors

Question 3

How does viral concentration relate to the chance of infection?

Answer 3

higher viral concentration makes infection of the cell more likely

Question 4

What is viral entry dependent on?

Answer 4

a virus’ ligand interacting with a complementary cell surface receptor

Question 5

Why is it a misnomer to refer to a cell surface receptor as a viral receptor?

Answer 5

-cells do not have receptors that are specific for viruses
-viruses exploit cell surface molecules to gain entry to the cell

Question 6

What are the characteristics of viral attachment through receptors?

Answer 6

-some viruses use different receptors based on the cell type
-some viruses can infect many different animal species by adapting to various receptors
-subtle amino acid changes in the receptor affect species susceptibility

Question 7

What are the two general strategies viruses use to enter the cell?

Answer 7

-endocytosis
-fusion with plasma membrane

Question 8

What factors impact the route a virus uses to enter the cell?

Answer 8

-cellular receptor functions
-factors such as pH

Question 9

How can plasma membrane fusion be involved during viral replication?

Answer 9

-single viral-infected cell can fuse with a neighboring cell due to build up of viral fusion proteins during replication
-this fusion allows for the infected cell to spread the virus to the neighboring cell

Question 10

Why is viral growth not exponential?

Answer 10

one virion is able to make millions of copies

Question 11

What is the infection period?

Answer 11

period in which the virus attaches to and enters the host cell

Question 12

What is the eclipse period?

Answer 12

period in which the viral genetic material is uncoated, and viral particles are no longer detected

Question 13

What is the latent period?

Answer 13

time from the onset of infection to the appearance of virus extracellularly (aka released from the cell)

Question 14

What is pathogenesis?

Answer 14

process by which disease develops in the host

Question 15

What is virulence?

Answer 15

measure of pathogenicity of a virus to cause disease in certain species

Question 16

Does high virulence always indicate high infectivity?

Answer 16

no

Question 17

How do virulence and pathogenicity differ?

Answer 17

-virulence refers to the severity of a pathogen to cause infection, while pathogenicity is the ability of a pathogen to cause infection
-virulence is quantitative in nature, while pathogenicity is qualitative
-virulence is measured by the ability of the pathogen to cause death, while pathogenicity is measured by virulence factors that enhance pathogen’s evasion mechanisms

Question 18

What is a localized infection?

Answer 18

infection that remains at the site or system originally affected

Question 19

What is a disseminated/systemic infection?

Answer 19

infection that spreads beyond the primary site

Question 20

What is viremia?

Answer 20

presence of virions in the blood

Question 21

How does a virus enter the bloodstream?

Answer 21

-virus infects epithelial cell and is able to infect the sub-epithelium through cytopathic effects
-virions enter the ECF/lymph, replicate in lymph node, and enter blood through lymphatic ducts

Question 22

What is passive viremia?

Answer 22

initial wave of viremia in which the virus is introduced into the blood

Question 23

What is active viremia?

Answer 23

result of viral replication within the bloodstream

Question 24

What is primary active viremia?

Answer 24

virus released into blood after initial replication in host

Question 25

What is secondary active viremia?

Answer 25

increased viral replication due to dissemination to other organs

Question 26

What are the factors involved in chain of infection?

Answer 26

-pathogen
-reservoir
-portal of exit
-mode of transmission
-portal of entry
-susceptible host

Question 27

What are the potential routes of transmission?

Answer 27

-droplets through conjunctiva
-inhalation into resp. tract
-direct contact
-fomites
-vertical transmission
-sexual transmission
-insect/arthropod vectors
-iatrogenic

Question 28

How do different body systems shed virus?

Answer 28

-resp. tract: mucus, saliva, aerosols
-GI tract: diarrhea, vomitus
-skin: crusts from lesions, vesicle fluids
-urogenital tract: urine, semen, aborted fetal tissues
-mammary gland: milk

Question 29

How are enveloped viruses best transmitted, since they do not survive in the environment long?

Answer 29

direct contact

Question 30

What other factors can impact viral transmission?

Answer 30

-seasonality
-geography
-humidity
-vector availability

Question 31

What are the characteristics of skin as a barrier/infection site?

Answer 31

-most viruses cannot enter intact skin
-viruses enter through skin defects, such as cuts, bites, via vectors, or iatrogenic means
-infection often seen as a rash
-may infect skin cells directly or cause lesions by infecting underlying blood vessels

Question 32

What are macules?

Answer 32

localized dilated blood vessels

Question 33

What are papules?

Answer 33

solid elevations of skin that may be crusty

Question 34

What are vesicles?

Answer 34

fluid filled popular lesions

Question 35

What are the characteristics of the eyes as a barrier/infection site?

Answer 35

-tears and eyelid movements can flush viruses
-some viruses infect superficial parts of eye and cause conjunctivitis or keratitis
-trauma or immunosuppression can predispose host
-viral uveitis results from systemic viral infection (CAV-1), but seen in eyes

Question 36

What are the characteristics of the resp. tract as a barrier/site of infection?

Answer 36

-most common route of exposure
-coughing/sneezing can aerosolize virus
-ciliated epithelium, mucus, and IgA provide protection in URT
-alveolar macrophages inactivate inhaled virions in LRT
-localized and systemic disease possible

Question 37

What are the characteristics of the GI tract as a barrier/site of infection?

Answer 37

-peristalsis, microbiome, and pH can prevent infection
-GI viruses have evolved to exploit or resist harsh GI environment
-often cause localized disease with vomiting and diarrhea