Epidemiology Flashcards
important strains of SARS
SARS 1: bats
SARS 2: civets
SARS 3 and 4: humans
virus epidemiology
study of determinants, frequency, dynamics, and distribution of viral diseases in populations
disease triad
host - pathogen - environment
case fatality rate
% deaths among clinically ill animals
mortality rate
% animals in a population that die from a particular disease over a specified period of time
morbidity rate
% animals in a population that develop clinical signs attributable to a particular virus over a defined period of time (commonly the duration of an outbreak)
incidence
new cases that occur in a population over a specified period of time (attack rate)
prevalence
occurrences of disease (old and new cases), infection, or related attributes (antibodies) in a population, at a particular point in time
T/F incidence is easy to measure for chronic diseases
F: for chronic diseases will usually measure prevalence instead
sporadic viral diseases
viral diseases occurring occasionally, singly, or in scattered instances, and in a irregular and haphazard manner
enzootic viral diseases (endemic)
constant presence of a viral disease within a given geographic area or population group
ex. Louping Ill
epizootic viral diseases
occurrence of more cases of viral diseases than expected in a given area or among a specific group of animals over a particular period of time; peaks in disease occurrence that exceed the enzootic baseline or expected incidence of disease
panzootic viral diseases
virus epidemic occurring over a very wide area (several countries or continents) and usually affecting a larger proportion of the population
carrier
animals that have contracted an infectious viral disease, but display no clinical symptoms
T/F A carrier can shed a virus continuously or intermittently.
T
incubatory carriers
aka acute
animals that shed virus during incubation period of the disease
convalescent carriers
aka chronic
animals that shed virus during recovery from disease
inapparent carriers
carrier state may exist in an animal with an infection that is inapparent throughout its course
contagious disease
disease that is spread from one person or organism to another by direct or indirect contact
period of contagiousness
time during which an infected animal sheds virus
exotic disease
disease not known to occur in a particular country or geographical area
reservoir
habitat in which an infectious agent normally lives, grows, and multiplies; can be human, animal, or environmental
T/F reservoirs can be animate or inanimate
T
surveillance
systematic collection, analysis, interpretations, and dissemination of health data on an ongoing basis, to gain knowledge of the pattern of disease in the community
seroepidemiology
use of serological data as the basis of epidemiological investigation, as determined by diagnostic serological techniques
T/F seroepidemiology can only determine prevalence of a particular infection
F: prevalence and incidence
molecular epidemiology of viruses
use of molecular biological data as the basis of epidemiological investigation of viral diseases
T/F molecular epidemiology can be used for conclusive evidence for transmission of viruses from animals to humans
T (or vice versa)
horizontal transmission
aka lateral
spread of an infectious agent from one person/animal or group to another person/animal or group
*most viruses transmitted this way
contact transmission
spread of infectious agent by direct or indirect contact
direct contact transmission
involves actual physical contact between an infected animal and a susceptible animal; includes sexual contact (as in HIV, herpes)
droplet transmission
transmission of a virus in droplet nuclei (saliva or mucus) that travel less than 1 meter from the source to susceptible host (sneezing, coughing)
indirect contact transmission
occurs via fomites
fomite
inanimate object or substance that is contaminated with the infectious agent and is capable of transmitting infectious organisms from on individual to another
airborne transmission
spread of infectious agents by droplet nuclei in dust that travel more than 1 meter, sometimes miles, from infected to susceptible host
T/F airborne transmission is indirect contact
T
T/F droplet transmission is indirect contact
F
vector transmission
aka arthropod-borne transmission
arthropod vectors carry viruses from infected host to susceptible host
*can be mechanical or biological
mechanical transmission
vector transmission *
passive transport or the infectious agent on the feet or other body parts of the arthropod vector
biological transmission
*vector transmission
infectious agent undergoes either a necessary part of its life cycle, or multiplication, in the vector before transmission to susceptible host
How does an arthropod vector acquire the virus for biological transmission?
by feeding on the blood of a viremic animal
extrinsic incubation period
time it takes a virus inside an arthropod vector to get from the gut to the salivary gland (several days)
*bio transmission
What is important about biological transmission?
helps virus to cross species barriers
overwintering
survival of virus from one vector season to the next (period during which arthropods hibernate)
What are the 2 mechanisms of overwintering?
- transovarial transmission
2. trans-stadial transmission
transovarial transmission
virus transmitted from mother tick through infected eggs to the next generation of ticks
trans-stadial transmission
virus transmitted from larva or nymph to next stage of development (nymph or adult); ex. tick-borne flaviviruses
arboviruses
class of viruses transmitted to humans by arthropods such as mosquitoes and ticks; complex life cycles
- sylvatic
- rural
- urban
sylvatic cycle
aka enzootic or jungle
natural transmission of virus between wild animals/birds (vertebrate hosts) and primary insect vectors
rural cycle
aka epizootic
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
level of virus can become high enough that an insect vector such as a mosquito that feeds on it will probably become infectious
dead-end host
aka incidental host
host from which infectious agents are not transmitted to other susceptible hosts; do not develop sufficient viremia to be picked up by insect vectors
bridge vector
arthropod that acquires virus from an infected wild animal and subsequently transmits the agent to human or secondary host
WEEV transmission
- enzootic cycle between passerine birds and mosquito vector (C. tarsalis)
- domestic and wild birds are reservoir and epizootic amplifying hosts
- lagomorphs and rodents can amplify
- horses and human are dead-end hosts
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 practice
- contaminated instruments or body surface
- contaminated prophylactic or therapeutic preparations
nosocomial transmission
occurs while an animal is in a vet clinic; hospital acquired infection
ex. parvo
vertical transmission
infection that is transferred from dam to embryo, fetus, or newborn before, during, or shortly after parturition (colostrum, milk, or fecal contamination of teats)
What can vertical transmission cause?
- early embryonic death or abortion
- congenital disease
- congenital defects
vertical transmission of retroviruses
via integration of proviral DNA directly into DNA of germ line of fertilized egg
vertical transmission of cytomegaloviruses
to the fetus via the placenta, whereas other herpesviruses are transmitted during passage through birth canal
T/F viruses transmitted by fecal-oral route have low environmental stability
F: they have higher stability; respiratory route has low environmental stability
Which routes of transmission avoid exposure to external environment?
- vertical transmission
- venereal transmission
- vector transmission
herd immunity
occurs when the vaccination of a significant portion of a population provides a measure of protection for individuals who have no developed immunity
incubation period
interval between infection and onset of clinical signs
prodromal period
first signs and feelings of illness after incubation period; period of early symptoms of a disease occurring after the incubation period and just before the appearance of the characteristic symptoms of the disease
acute period
disease is at its height; severe clinical signs
decline period
period when clinical signs begin to sub side
convalescent period
body gradually returns to its pre-diseased state, and health is restored
