virology 2 Flashcards
viral epidemiology
diseases in population(s) developed before recognition of a causative agent
three interdependent terms define increasing size of population
enzootic
multiple, continuous transmission, disease presence in a defined population/region/time
epizootic
peaks in incidence exceeding the endemic baseline
nature and degree of expected damage defines whether it is call epidemic (high damage)
panzootic
worldwide epidemics
rate
disease in population
number of cases/population
different diseases, different rates
incidence or attack rate
number of cases over number of subjects over period of time (case:population ratio)
acute, short duration diseases
denominator: population in a time frame: thus person-years or subject-weeks
prevalence
insidious onset with unknown initial date
chronic long duration diseases
no time parameters only number of cases in defined number of subject
Data
acquisition difficult, incomplete and inaccurate; computation easier
surveillance
continuous reporting, reportable diseases
serological survey
antibody, clinical disease-silent, subclinical infection
not informative on current infections
prospective studies
tracking events that are supposed to happen in the future
placebo and treatment groups
number of subjects depending on incidence
very expensive
retrospective studies
cost-effective
only needing limited numbers of subjects
incubation period
moment of infection to onset of clinical signs
variable
generation time
from moment of infection to first day virus shedding
mostly shorter than incubation period
influence in spreading disease
period of infectivity
from first day to last day of virus shedding
may or may not be longer than clinical signs
great influence in spreading disease
chronic viral diseases
distinction between these time periods is difficult
little correlation among disease, generation time, infectivity
modes of transmission by virus
horizontal transmission
vertical transmission
zoonotic transmission
vector-borne transmission
iatrogenic
nosocomical
horizontal
with or without vector, between the same or different host species
common vehicle: water, feed
airborne: droplets, aerosols
direct contact:
licking, rubbing, biting, sexual contact
suitable for transmission of enveloped virus
lipid easier to inactivate
indirect contact
fomites, eating, bedding, vehicles, surgical instruments, needles
non-enveloped virus-usually use this route of transmission
vertical transmission
movement of virus from parents to their offspring during gestation via placenta, perinatally, colostrum, milk
germline transmission
virus integrated into genome of ovum, transcription and replication in offspring
pass from generation to generation
biological vector
virus replicate, magnify in vectors efficient transmission
mechanical vector
no virus replication in vector not efficient for transmission
zoonotic transmission
viral diseases transmissible under natural conditions from vertebrate animals to humans
iatrogenic
patient to patient transmission under veterinary care during the interactions between the vet and the animals
nosocomial
transmission occurs while the animals are in hospital or clinic under the care of veterinarians
acute infection
rapid production of infectious viruses
rapid resolution and elimination of infection by host
acute infections do not always produce disease
persistent infection
infection not cleared efficiently
virus particles are produced for long period of time either continuously or intermittently for months or years
chronic infection
persistent infections that are eventually cleared
Latent infection
persistent infections that last the life of the host
latency
viral genomes integrated into cellular genomes, not expressed
no infectious progeny
Routes of shedding
skin
repiratory secretion
saliva
feces
genital secretions
urine
milk
no shedding
skin
not a major route
contact, abrasion, wound
respiratory secretion
very important
numerous disease, local, systemic
shedding occur before, during after clinical signs
saliva
salivary gland, oral cavity
rabies, FIV
Feces
GI tract virus
many also without intestinal signs
genital secretion
sexual activity, semen, mucus
urine
rinderpest, FMD, canine hepatitis in kidney
hantaviruses: mice to human
milk
not an important route
mammary gland replication
caprine arthritis encephalitis
no shedding
not all virus replications end with shedding
encephalitis (CNS) retrovirus (germ line)
host range
receptors on animal tissue/cells
susceptible for wide range of infections or restricted infections
susceptibility
ability to become infected
permissivitiy
ability to replicate and produce progeny viruses
