viral pathogenesis Flashcards
why is skin not a good host for viruses?
because the epidermis (the outer layer of skin) is a dead host and is continuously replacing itself
what are inapparent infections and why are they devastating
when there are no major symptoms yet immune system has been activated
difficult to predict transmission because the infected don’t display symptoms
replication and transmission is still highly likely – virus dependent
describe the West Nile Virus
family: flaviridae; +ssRNA
enveloped virus, thus, flimsy - thus, transmitted thru blood
spread by mosquitoes
1% of infected individuals has neuroinvasive illness caused by the virus breaching the blood brain barrier - this can cause deadly encephalitis (inflammation of the brain)
describe the case study of the West Nile Virus in New York and how it’s an inapparent virus. what were the origins of this virus?
centre for disease control (CDC) was mystified because they have never seen such a virus before in North America… they cannot test for a virus not in their collection and they didn’t consider that viruses move (it most likely came from Israel via mosquitoes)
instead of canceling a major sporting event, they sprayed insecticide in the early morning and provided insect repellant to kill mosquitoes
– a catastrophic epidemic was most likely avoided but it still resulted in 7 deaths
only 20% of infected individuals displayed very acute symptoms and 1% of infected individuals has neuroinvasive illness caused by the virus breaching the blood brain barrier - this can cause deadly encephalitis (inflammation of the brain), easily spread as people who were infected could still donate their blood
the New York West Nile Virus was found to have originated from Israel’s West Nile Virus
discovered due to sequencing (and creation of a phylogenetic tree) where we tested for the presence of the viral genome
what was the first virus known to cause disease in humans? describe how it was researched
yellow fever virus (1901)
the Reed Commission was created after the war due to the prevalence of sickness and infections in soldiers
they believed might’ve been incurred while in Central America
scientists got infected mosquitoes from Central America and recruited health volunteers
they then injected mosquitoes
many died - they realized viruses can induce pathogenesis
describe the components (“two arms”) of viral pathogenesis
to produce a disease it takes two!
- effects of viral replication on host
- effects of host response on virus and host (as we fight off the infection/viral replication)
differentiate between spread and transmission
spread: viruses can travel thru blood and to other organs
transmission: via a process called viral shedding
describe the fenner experiment, an example of viral pathogenesis
mouse pox was injected in the footpad
after local multiplication in the foot, host response leads to swelling/lesions at the site of inoculation
displays viral transmission/spread
- symptoms are seen outside the foot as well, with time
after viremia, the host response to replication in the skin results in a rash (papules or ulceration)
what is viremia? differentiate between primary viremia and secondary viremia
the presence of infectious virions in the blood
primary viremia
- progeny virions released in blood after initial replication at the site of entry
e.g. in this case, footpad
- from the initial site to the spleen and liver
secondary viremia
- delayed appearance of virions in the blood
- from spleen and liver
what are the viral entry routes in humans?
skin, if it breaks
conjunctiva (part of the cornea)
mucosal linings of the respiratory, alimentary, and urogenital tracts – all lined with “live” cells (susceptible and permissive)
describe the viral entry route of skin and the protection it has in place
skin could also break!
viruses are generally unable to infect the epidermal layer of skin as the cells are dead BUT if skin is broken by insects or needles, viruses may enter via blood in the vascularized dermis
virions may also be inactivated by
- the acidity (pH = 5.5) of the skin surface
- anti-viral peptides released by immune mechanisms OR
- the dryness of the skin
describe the viral entry route of the conjunctiva and the protection it has in place
viruses can enter via layer of cells on the surface of the cell
- these outer cells (of the conjunctiva) have receptors
blinking is a defense mechanism, it excretes viruses
certain types of adenoviruses can infect the conjunctiva
describe the viral entry route of the respiratory tract and the protection it has in place
large surface area = increased susceptibility
often viruses enter in the form of aerosolized droplets (cough/sneeze) or thru contact of saliva
respiratory tract has a mucous layer protection of mucus to remove intruders
e.g. rhinovirus (causes common cold)
e.g. influneza virus
describe the viral entry route of the alimentary tract (upper and lower) the protection it has in place
aka fecal-oral route
upper alimentary tract
- viruses can come down with food
- they must be able to survive the harsh acidic environment (the stomach is extremely acidic)
defence
- acidic pH
- proteases
- bile detergents
e.g. reoviruses can survive the upper alimentary tract
- they have multiple layers/shells
any virus that can cause gastroenteritis can survive the upper alimentary tract
- HIV, an enveloped virus would get completely destroyed
lower alimentary tract (anus)
- this way, virus does not have to withstand harsh environment of the upper alimentary tract
e.g. HIV, an enveloped virus enters via anal intercourse
describe the viral entry route of the urogenital tract and the protection it has in place
mucus and pH (specifically low pH of the vagina) provides protection
however, abrasions during sexual activity will create tears, allowing viral entry
e.g. retrovirus, such as HIV
e.g. HPV, human papilloma virus
