example of inapparent infection? what was the virus and type of virus? how was it spread? symptoms? how was this determined?
Flaviridae family: West Nile Virus
- +ssRNA with envelope
- mosquitos
- mainly no-low symptoms
- sequencing - use phylogenetic tree to find that New York West Nile Virus and Israel West Nile Virus are almost identical
First virus known to cause
disease in humans?
Yellow Fever Virus from US soldiers getting sick when coming back from Cuba
what was learned from yellow fever virus?
- Inject a virus in humans
- Virus can kill humans
- Virus can induce pathogenesis
How does viral pathogenesis occur ?
Cell = susceptible + permissive
The “right” # of virus particles.
This is virus “specific”
what is viral pathogenesis? (2 parts)
To produce a disease.
- EFFECTS OF VIRAL REPLICATION ON HOST
- EFFECTS OF HOST RESPONSE ON VIRUS AND HOST (immune response)
what was the mousepox experiment?
- inject mosepox into footpad
- swelling in site of inocculation
- The host response to replication in the skin results in a rash after viremia
what is viremia?
presence of virions in the blood
what is primary viremia?
progeny virions released in blood
after initial replication at the site of entry
(virions to other organs)
what is secondary viremia?
delayed appearance of virions in the blood
(virions to skin focal infection=rashes)
what are entry points in humans for viruses?
- conjunctiva (outer surface of eye)
- respiratory
- alimentary
- urogenital
- skin breaks
muscal lunings in 2-4 tracts
how are virions inactivated on skin?
- acidic (pH = 5.5) on skin surface
- Anti-viral peptides
- Dryness
how is the skin a virus stopping point?
- outer layer (epidermis) has dead cells which violate the “host requirement”
- skin can be broken by insects (virus enters through blood) to allow dermis access
Mucosal membranes and cells covering the eyes
are lined with
“live” cells (susceptible + permissive)
how is respiratory tract breached by viruses? example?
aerosolized droplets (cough or sneeze) or through contact of saliva breeches** muscus protection**
ex. rhinovirus, influenza virus
how is alimentary tract breached by viruses?
- enter with food but must survive acidic envirn.
- absorbed by SI
ex. reovirus causes gastroenteritis
what is reovirus an example of?
Non-enveloped example for entry
how is lower alimentary tract breached by viruses? example?
- virus does not have to withstand harsh environment of upper alimentary tract
ex. HIV anal intercourse
how is urogenital tract breached by viruses? example?
- sexual activity will create tears and abrasions allowing viral entry
- retrovirus HIV, HPV
how is conjunctiva breached by viruses? example?
- Eye cornea covered by layer of cells called the conjunctiva
- Blinking is a defense mechanism
adenoviruses infect conjunctiva
what is virus shedding?
Release of virions from infected individual (causing transmission)
what is Transmission?
Virus population will survive if many infections in series occur in a host population
ex. of virus shedding?
- feces
- blood
- milk
- urine, semen
- skin lesions
- aerosol
how does non-enveloped vs enveloped viruses compare in terms of shedding and transmission?
non enveloped - hard protein shell
- withstand more things like low pH
- transmission: resp, fecal-oral, fomites
enveloped
- more fragile
- transmission: mainly aerosol
- sensitive to low pH
fomites?
objects contaminated
by virus
