viruses and their hosts (4) (Leanne) Flashcards
pathogenicity
how virulent
diff strains have diff virulence
pathogenesis
mode of development of disease - mechanism by which pathogen causes disease
systemic effect
whole body affected if virus enters lymphatic/circulatory system
measles
respiratory system systemic effect enveloped virus single stranded non segmented negative sense RNA genome
what cells are susceptible to viruses?
cell with receptors
intrinsic features of immune system
gender
MHC molecules - show viral particles
physiological variation
nutrition
age
stress
physical health
how does age affect immune system?
thymus gland vanishes over time
can’t produce new T cells
3 outcomes of infection
acute + death
acute + recovery
persistent
persistent infection
continuous virus production with or without chronic disease
because virus changes - antigenically stable virus types, surface protein slightly diff version (serotypes)
constantly diversifying virus population
chronic - constant virus production
or latent - no detectable virus but production may re-activate
herpes simplex virus
type 1 - cold sores
type 2 - genital
2 processes can trigger it from latent stage
human papilloma virus
can lead to cervical cancer
can be asymptomatic
latent infections may occur
in epithelial stem cells in basal layer of epithelium
cells driven into cell cycle, genome amplification and new virion production
low level protein production by virus allows it to evade immune detection
immune regression, infiltration of predominantly T cells, viral gene expression shut off, lesion regression occurs
horizontal transmission
host to host
direct or indirect
has recognised routes like respiratory, oral-faecal, sexual, conjunctival (eye)
respiratory route
airborne transmission like cold/measles
humidity affects desiccation rate
oral-faecal
direct or indirect
contaminated water, poor hygiene, swimming pools
e.g. poliovirus, rotavirus, hepatitis A
saliva and urine transmission
aerosols, zoonotic
e.g. CMV
fomites, skin, conjunctiva
objects, surfaces, money, skin damage, hand-to-eye contact
indirect transmission
1 or more species, vectors
reservoir species
host for pathogen but survives without disease (asymptomatic)
insect-borne viruses
yellow fever, West Nile, dengue fever
yellow fever
replicates in mosquitoes and monkeys
sylvatic cycle - between these 2 species
urban cycle - to humans
but can’t transmit human to human
vertical transmission
mother to child
intrauterine - across placenta, congenital rubelle syndrome
perinatal - during delivery because blood, HIV
postnatal - breast feeding, HIV
2 types of vaccine
live attenuated
killed non-replicating
serial passage
passed along hosts, growth in wrong host selects variants which are no longer virulent but still replicate in autologous (the usual host for specific virus)
epidemic vs pandemic
rapid spread over short time
cross borders and affect huge populations
influenza subtypes
18 haemagglutinin (H) - aids in viral entry, binds to RBC 11 neuraminidase (N) - aids in viral exit
why do viruses have high mutation rates?
poor proofreading
antigenic drift vs shift
drift - small change
shift - big difference, 2 viruses combine to mosaic, genome segments exchanged during replication
5 techniques in studying viruses
cell culture and viral propagation plaque assays haemagglutination assay antibody detection - IMF, ELISA molecular techniques - PCR, RT-PCR, detect nucleic acids
primary cell lines
taken from organ tissue
actual cells that virus targets
passage
cells differentiate limited times
cell lines
less differentiated so more capability of dividing and growing, more passages
continuous cell lines
HeLa, immortal
cpe
cytopathic effect - phenotypic effect of infection
PFU
plaque forming unit
