lecture 3- epidemiology of viral infections Flashcards
what is virus transmission?
passing of an infectious virus from an infected host to a susceptible host, regardless of whether the individual was previously infected
what is horizontal transmission
viral transmission between animals within the population at risk
is horizontal transmission direct or indirect?
both
when does vertical transmission occur?
in utero
during birth
colostrum
milk (first few weeks)
example of vertical transmission that can occur before birth (3)
BVDV, blue tongue, feline parvo
example of vertical transmission that can occur during birth
canine herpes virus
example of vertical transmission that can occur after birth
CAE, meadi-visna
consequences of vertical viral transmission
embryonic death/abortion, congenital disease, congenital defects
what are the 6 modes of transmission of horizontal viruses?
direct contact
indirect contact
common vehicles
airborne
vector-borne
iatrogenic
examples of direct contact
licking
rubbing
biting
sexual contact
skin abrasions
disease whose transmission is through biting? what mode of transport?
rabies, direct
disease whose transmission is through sexual contact?
herpes virus, direct
disease whose transmission is through skin abrasions?
papilloma virus, direct
examples of indirect contact
fomites (shared eating containers, beddings, restraint devices, vehicles, clothing, improperly sterilized surgical equipment)
examples of common vehicles
- colostrum and milk
- virus contaminated meat
- virus contaminated bone products
diseases whose transmission is through colostrum/milk? what mode of transport?
caprine arthritis encephalitis virus (CAE), tick borne encephalitis virus
common vehicles
diseases whose transmission is through virus contaminated meat? what mode of transport?
classical swine fever, vesicular exanthema of swine
common vehicles
diseases whose transmission is through contaminated bone products? what mode of transport?
bovine spongiform encephalopathy (BSE)
common vehicles
examples of airborne modes of transport?
droplets, aerospols
large airborne droplets…
settle quickly
microdroplets either…
travel about a meter then evaporate
or
form droplet nucleus then become aerosols and remain suspended in the air for longer periods of time
examples of airborne diseases/their transmission (2 to note- 1 from cough/sneeze and 1 from dust/dander)
cough/sneeze –> influenza
dust/dander –> Marek’s disease virus
what are arboviruses?
arthropod borne
diseases whose transmission is through mosquitos? what mode of transport?
equine encephalitis
arboviruses
diseases whose transmission is through soft ticks? what mode of transport?
african swine fever virus
arbovirus
diseases whose transmission is through culicoides? what mode of transport?
blue tongue virus
arbovirus
what is iatrogenic transmission?
caused by doctor/animal handler
2 examples of iatrogenic diseases?
equine infectious anemia
bovine leukemia virus
what is nosocomial transmission?
acquired from clinics / hospitals
the 1980 epidemic of canine parvovirus infection was caused by what mode of transmission?
nosocomial
feline respiratory infections (calici virus infections) is caused by what mode of transmission?
nosocomial
the 1976/1995 ebola epidemic in Zaire was caused by what mode of transmission?
nosocomial
what are the mechanisms of survival of viruses in nature?
- physical stability/ environment
- maintenance of serial infections- chain of transmission within *animal *
3.
what is the relative stability of viruses transmitted by respiratory route?
low stability
what is the relative stability of viruses transmitted by fecal-oral route?
higher stability
enveloped viruses are generally…. what are the exceptions?
generally labile
exceptions are orf virus and Marek’s disease virus
non enveloped viruses are generally …
stable
example of non-enveloped viruses
adenoviruses, circoviruses
what type of infection (clinical or subclinical) has a more productive source of virus?
clinical infection
what type of infection (clinical or subclinical) has more numerous and more important/better opportunity for virus dissemination
subclinical
why are subclinical infections significant? Explain in regards to BVDV
if a cow is persistently infected with BVDV (is subclinical) then they are still shedding the virus, despite looking healthy
how to viruses maintain serial transmission? (3 patterns)
- acute self limiting
- persistent infection
- vector maintenance
acute self limiting transmissions are affected by…
population size
which serial transmission pattern is described by the following:
- infectious virus disappears with clinical recovery
- high yield of virus during disease
- continuous supply of susceptible hosts recquired
acute self limiting infection (hit and run strat)
what are 3 viral examples of acute self limiting infection?
influenza
rota viral diarrhea
infectious bursal disease
what are the three major types of persistent infection patterns?
- persistant infection
- chronic infection
- latent infection
which serial transmission pattern is described by the following:
- clinical disease and death with result after years of shedding the virus with subclinical infection
persistent infection (with persistent pattern)
what disease example shows a persistent infection with persistent pattern?
BVDV
congenital infection
which serial transmission pattern is described by the following:
- clinical disease and high yield of infectious virus initially resembles acute infection
- clinical recovery follows shedding of a virus at low levels for years
chronic infection (persistent pattern)
what are 2 disease examples that show chronic infection (persistent pattern)?
FMDV (foot and mouth)
feline calici virus
which serial transmission pattern is described by the following:
- intermediate shedding with/without clinical consequences
latent infection (persistent pattern)
during latent periods of latent infection, are viral particles being shed?
no
what is a viral example of latent infection (persistent pattern)?
herpesvirus
where does BHV-1 replication occur?
nasal mucosa
in BHV-1, where is life long latency established?
- trigeminal ganglia-neurons
- tonsillar lymphoid follicles- T cells
what triggers BHV-1 to reactivate? where does productive infection occur?
triggered during stress or when immunity is low
establishes productive infection in primary replication sites (trachea and nasal mucosa)
what 3 factors influence the prevalence of emerging viral diseases?
1) host determinants
2) constant changes in environment
3) viral determinants
how does the evolution of viruses occur via milder genetic changes?
viral replication –> mutations –> antigenic drift
which have a higher mutation rate, RNA or DNA viruses? why?
RNA viruses lack proofreading since most replicate in the cytoplasm, therefore they have a higher mutation rate than DNA
how does the evolution of viruses occur via drastic genetic changes? 2 ways
1) template switching between closely related viruses
2) exchange of entire gene segments (rearrangement)
how does template switching between closely related viruses occur?
co-infection of a cell by genetically distinct viruses can lead to the generation of recombinant viruses
what is an example of template switching
ancient sinbis like viruses + eastern equine encephalitis virus = western equine encephalitis cirus
how does exchange of entire gene segments (reassortment) to create a new virus occur?
co-infection of a cell by genetically distinct strains of a segmented virus can generate different combinations of reassortment progeny
examples of viruses created by reassortment? 4
-arena and birna viruses (2 segments)
- bunyaviridae (3 segments)
-orthomyxoviridae (6-8 segments)
-reoviridae (12 segments)
what kind of receptors are associated with influenza virus
sialic acid
