Epidemiology of viral diseases Flashcards
virus epidemiology
study of determinants, dynamics, distribution and frequency of viral diseases in a population
why study virus epidemiology (3)
- characteristics of virus
- host and host pop
- behavior, envi and ecological facts that affect virus transmission
role of epidemiology in viral diseases
ID role of viruses in disease, understand interaction of virus with envi, affecting host susceptibility, modes of viral disease, impacts of virus on health, economy and society, role of infectious pathogens and vaccines and drug production
how does viral epidemiology help
advance understanding of disease, alert and directing disease treatment, control and prevention, warning systems and tracking disease, assess economical impacts and cost of prevention programs
case fatality rate
number of deaths among clinically ill animals
mortality rate
number of animals in a population that die from a particular disease over a period of time (includes healthy and sick animals)
morbidity rate
percentage of animals that develop clinical signs attributable to a specific virus over a period of time
incidence
number of new cases that occur over a period of time - new cases only
prevalence
number of occurences of disease (new and old) that happen over a point in time
sporadic disease
viral disease occurring occasionally, singly or in scattered instances
enzootic/endemic disease
constant presence of viral disease within an area
epizootic/epidemic
occurrence of more cases than expected in a specific area - large number of cases in very limited area
panzootic/pandemic
large number of cases in large areas
asymptomatic carrier
animals that have contracted the virus but display no clinical signs
3 types of asymptomatic carriers
incubatory (acute): shed virus during incubation period
convalescent (chronic): shed virus during recovery
inapparent: shed virus with no clinical signs of any disease
contagious disease
period of contagiousness
spread from one person to another
period: time during which an infected animal sheds the virus
exotic disease
disease not known to occur in a particular area
methods to study epidemiology (2)
- seroepidemiology: use of serological data, AB-AG presence
- molecular epidemiology: use molecular biological data (PCR) to detect virus – helps with making vaccine so quickly
transmission of viruses 2 types
- horizontal (lateral) - spread from one person to another, most transmitted via this
- vertical - transmit from mom to fetus/embryo/newborn
horizontal transmission: contact transmission
direct contact: actual physical contact between infected and susceptbile - includes sexual contact
droplet transmission: transmission of virus in droplet nuclei that travel LESS than 1 m from source - sneezing, coughing
indirect contact transmission: occurs via fomites - inanimate object that is contaminated and transmits virus
indirect contact- airborne transmission: spread of infectious agents by droplet nuclei in dust that travel MORE than 1 meter
vector transmission
aka arthopod borne transmission, arthropods carry viruses from infected to susceptible host
1. mechanical transmission: passive transport of infectious agent on body of arthropod vector - no multiplication of virus
2. biological transmission: infectious agent undergoes reproduction before transmission
what insect is vector for fowlpox virus and what type of vector
mosquitos, mechanical!
biological transmission stages
arthropod vector gets virus by feeding on blood, virus replicates in the insect gut, spreads to salivary glands, and virions in the salivary secretion are injected into new animals host during blood meals = helps virus to cross species barriers
vector transmission - transovarial transmission and trans stadial transmission
arboviruses
transovarial: virus is transmitted from mom tick through infected eggs to next gen of ticks
trans stadial trans: virus transmitted from larva to next stage of development - but not transmitted vertically
arboviruses: class of viruses transmitted to humans by arthropods such as mosquitos and ticks
types of transmission cycles (3)
- enzootic (sylvatic): transmisstion of virus between while animals and primary insect vectors
- epizootic (rural cycle): virus transmitted between non wild or domestic animals and primary or accessory insect vectors
- urban cycle: virus cycles between humans and insect vectors
amplifying host
dead end host/incidental host
bridge vector
amplifying: level of virus is high enough that an insect vector that feeds on it will become infected
dead end: infectious agents are not transmitted to other susceptible hosts
bridge: arthorpod acquires virus from infected wild animal and subsequently transmits the agent to human (bridges two cycles)
common vehicle transmission
includes fecal contamination of food and water supplies and virus contaminated meat or bone products
Iatrogenic transmission
infection transferred during medical or surgical procedure
happens by: introduction of pathogen on contaminated instrument or contaminated body surface OR intro through therapeutic preparations
nosocomial transmission
occurs while an animal is in vet hospital AKA hospital acquired infection
zoonosis
infections that are transmitted between animals to humans
viruses that are transmitted by respiratory route how what envi stability?
compared to fecal oral route?
respiratory route have lower envi stability, fecal-oral route has higher stability
herd immunity
vaccination of large portion of population protects individuals who are not vaxxed
incubation period
prodromal period
acute period
decline period
convalescent period
time between infection and onset of clinical signs
first signs and feelings of illness
disease is at its highest
clinical signs subsiding
return to healthy
