Viral Pathogenesis

Question 1

Why is skin not a good host?

Answer 1

• dead cells

- viruses require machinery form live cells

Question 2

What is Flaviridae?

Answer 2

West Nile Virus

Question 3

What is the West Nile Virus?

Answer 3

• +RNA with an envelope

- spread by mosquitoes

Question 4

Where is the first case of WNV?

Answer 4

• North America
• 1999
• Center for Disease Control was mystified
• cannot test for a virus that you do not have in the collection
• tournaments are almost cancelled but they were sprayed with insecticide

Question 5

Where was the North American Epicenter?

Answer 5

• Queens, NYC, NY, USA

Question 6

The numbers of American WNV

Answer 6

• 80% of infected individuals do not have symptoms
• 20% of infected individuals have very acute symptoms
• 1% of infected individuals develop a neuroinvasive illness
• can cause deadly encephalitis

Question 7

How can WNV be transmitted?

Answer 7

• through the blood

- can create an epidemic through donated blood

Question 8

How did WNV make it to North America?

Answer 8

• tools
• physical measurement
• sequencing
• sequence the entire genome of the virus
• New York WNV and Israel WNV are almost identical

Question 9

What was the first virus known to cause disease in 1901?

Answer 9

• Yellow Fever Virus
• Reed Commission
• Why are US soldiers becoming sick while occupying Cuba
• Inject a virus in humans
• Induce pathogenesis
• Kills humans

Question 10

What are the key points of viral pathogenesis?

Answer 10

• entry
• genome
• spread
• other organs/tissues
• transmission

Question 11

How does viral pathogenesis occur?

Answer 11

• must overcome host immunity
• cells must be susceptible and permissive
• need the “right” amount of virus particles
• the virus needs to be specific

Question 12

How does disease occur?

Answer 12

• effects of viral replication on host

- effects of host response virus and host

Question 13

Pathogenesis of mousepox; The Fenner Experiment

Answer 13

• injected in the foot pad
• after local multiplication in the foot
• host response leads to swelling at the site of inoculation
• after viremia: the host response to replication in the skin results in a rash

Question 14

What is Viremia?

Answer 14

• presence of virions in the blood

Question 15

What is primary viremia?

Answer 15

• progeny virions released in blood after initial replication at the site of entry

Question 16

What is secondary viremia?

Answer 16

• delayed appearance of virions in the blood

Question 17

Types of viral entrances in the body

Answer 17

• Conjunctiva
• Respiratory
• Alimentary
• Urogenital
• Anus
• Broken skin

Question 18

Mucosal linings and viruses

Answer 18

• viruses have evolved to enter vi mucosal linings of the respiratory, alimentary and urogenital tracts
• viruses can enter the other surfaces of the eyes

Question 19

Broken skin

Answer 19

• skin can be broken by insects and viruses may enter via the blood
• the virus gains access to the vascularized dermis
• skin can also get breached via needle punctures

Question 20

How to inactivate virions?

Answer 20

• acid (pH=5.5) on the skin surface
• anti-viral peptides
• dryness

Question 21

Live cells in the respiratory tract

Answer 21

• often viruses enter in the form of aerosolized droplets
• or through contacts of saliva
• mucous layer production of mucus to remove intruders
• ex Rhinovirus
• Influenza virus
• lungs have 140m^2 of surface area for viral absorption

Question 22

Live cells in the upper alimentary tract

Answer 22

• can “come down” with food
• must survive harsh acidic environments
• can get absorbed by the small intestine
• acidic pH
• proteases
• bile detergents
• ex Reoviruses

Question 23

Live cells in the lower alimentary tract

Answer 23

• can also get absorbed
• the virus does not have to withstand the harsh environment of the upper tract
• ex HIV
• entry via anal intercourse

Question 24

Live cells in the urogenital tract

Answer 24

• ex Retrovirus (HIV)
• mucus and pH protection (low pH in vagina)
• however, abrasions during sex will create tears allowing viral entry

Question 25

Live cells in the conjunctiva

Answer 25

- eye covered by a layer of cells - blinking is a defence mechanism - certain types of adenoviruses can infect the conjunctiva - the cornea is partially covered by a layer of cells termed the conjunctiva

Question 26

What is virus shedding?

Answer 26

- release of virions from infected individuals | - virus population will survive if many ifection in series occur in a host population

Question 27

What are some aeorsol secretions?

Answer 27

- coughing - sneezing - talking - travels up to 50m

Question 28

What are some types of viral shedding?

Answer 28

- aerosol secretion - feces - blood - milk - urine or semen - skin lesions

Question 29

What is transmission?

Answer 29

- can be in the same species or from insect to vertebrates

Question 30

Facts about non-enveloped viruses

Answer 30

- withstand a lot including low pH - mostly transmitted in respiratory, fecal-oral route - fomites - abjects contaminated by viruses

Question 31

Facts about enveloped viruses

Answer 31

- more fragile - mostly aerosol transmission - sensitive to low pH

Question 32

What is Iatrogenic transmission?

Answer 32

- heath care worker infects a patient

Question 33

What is nosocomial transmission?

Answer 33

- patients infected while in a hospital

Question 34

What is vertical transmission?

Answer 34

- patient to offspring

Question 35

What is germline transmission?

Answer 35

- genomic transfer

Question 36

What is horizontal transmission?

Answer 36

- transmission between two same or different species