lecture 11

Question 1

virus epidemiology

Answer 1

-study of determinants, frequency, dynamics, and distribution of viral disease in populations

Question 2

why study epidemiology in viral diseases

Answer 2

• risk of infection/disease in animal or animal population is determined by:
• -characteristics of virus (genetic variation from evolution)
• -host and host population (passive, innate, and acquired resistance)
• -behavioral, environmental, and ecological factors that affect virus transmission from one host to another

Question 3

role of epidemiology in viral diseases

Answer 3

• identify/clarify role of viruses in etiology of diseases
• understand interaction of viruses with environmental determinants of disease
• determining factors affecting host susceptibility
• unraveling modes of viral disease transmission
• studying impacts of viral disease on health, economy, and society
• studying role of infectious pathogens in the pathogenesis of chronic non-communicable diseases such as oncogenic viruses in cancer
• large scale testing of vaccines and drugs (clinical trials)

Question 4

how knowing epidemiology helps

Answer 4

• advance our understanding of nature of disease
• alerting and directing disease treatment, control, and prevention activities
• providing early warning systems and tracking disease
• assessment of economic and social impacts of disease
• assessment of efficacy and cost of disease control and prevention programs

Question 5

case fatality rate

Answer 5

• based on outcome of disease in population

- number (%) of deaths among clinically ill animals

Question 6

mortality rate

Answer 6

• based on outcome of disease in population

- number (%) of animals in a population that die from a specific disease over a specific period of time

Question 7

morbidity rate

Answer 7

• based on outcome of disease in population
• percentage of 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)

Question 8

factors based on duration and/or frequency of occurrence

Answer 8

• incidence

- prevalence

Question 9

incidence

Answer 9

-number of new cases that occur in a population over a specified period of time
=number of cases x10^n/population at risk in a specified period of time
-measure of occurrence of infection or disease in a population over time
-especially useful for describing diseases of short duration

Question 10

prevalence

Answer 10

-number of occurrences of disease (old and new cases), infection, or related attributes (antibodies) in a population, at a particular point in time
=number of casesx10^n/population at risk
-at a particular time

Question 11

sporadic viral disease

Answer 11

-occurring occasionally, singly, or in scattered instances, and in a irregular or haphazard manner

Question 12

enzootic viral diseases (endemic in humans)

Answer 12

-constant present of a viral disease within a given geographic area or population group

Question 13

epizootic viral diseases (epidemic in humans)

Answer 13

• occurrence of more cases of viral diseases than expected in a given area or among a specific group of people/animals over a particular period of time
• refers to peaks in disease incidence that exceed the endemic/enzootic baseline or expected incidence of disease

Question 14

panzootic viral diseases (pandemic in humans)

Answer 14

-virus epidemic occurring over a very wide area (several countries or continents) and usually affecting a large proportion of the population

Question 15

asymptomatic carrier

Answer 15

• animals that have contracted an infectious viral disease but display no clinical symptoms
• shed virus, transmit disease to others
• shedding of virus may be continuous or intermittent

Question 16

contagious disease

Answer 16

-disease spread from one person or organism to another by direct or indirect contact

Question 17

period of contagiousness

Answer 17

-refers to time during which an infected animal sheds virus

Question 18

exotic disease

Answer 18

-disease not known to occur in a particular country or geographical area

Question 19

serioepidemiolgy

Answer 19

-simply denotes use of serological data as the basis of epidemiological investigation, as determined by diagnostic serological techniques

Question 20

molecular epidemiology of viruses

Answer 20

-use of molecular biological data as the basis of epidemiological investigation of viral diseases

Question 21

horizontal transmission of viruses

Answer 21

• contact transmission
• vector transmission
• vehicle borne transmission
• iatrogenic transmission
• nosocomial infection

Question 22

horizontal transmission

Answer 22

• spread of infectious agent from one person/animal or group to another person/animal or group
• most viruses transmitted this way

Question 23

contact (horizontal) transmission

Answer 23

-spread of infectious agent by direct or indirect (intermediate object) transmission

Question 24

direct (horizontal)-

contact virus transmission

Answer 24

• involves actual physical contact between infected animal and susceptible animal (licking, rubbing, biting) also includes sexual contact
• droplet transmission: transmission of virus in droplet nuclei (saliva or mucus) that travels less than one meter to source of susceptible host

Question 25

indirect (horizontal) contact transmission

Answer 25

-occurs via fomites (inanimate object/substance contaminated with infectious agent and capable of transmitting it), such as shared eating containers, bedding, dander, restraint devices, vehicles, clothing, improperly sterilized surgical equipment, or improperly sterilized syringes/needles

Question 26

indirect-contact (horizontal) transmission- airborne

Answer 26

-spread of infectious agents by droplet nuclei in dust that travels more than one meter, sometimes for miles, from the infected to susceptible host

Question 27

vector transmission

Answer 27

- can be mechanical or biological transmission | - arthropods can carry virus

Question 28

mechanical transmission

Answer 28

-passive transport of the infectious agent on the feet or other body parts of the arthropod vector

Question 29

biological transmission

Answer 29

-infectious agent undergoes either a necessary part of its life cycle, or multiplication in the vector before transmission to susceptible host

Question 30

arboviruses

Answer 30

class of viruses transmitted to humans by arthropods such as mosquitoes and ticks

Question 31

types of transmission cycles

Answer 31

- enzootic cycle (sylvatic or jungle cycle) - epizootic cycle (rural cycle) - urban cycle

Question 32

enzootic cycle (sylvatic or jungle cycle)

Answer 32

natural transmission of virus between wild animals/birds (vertebrate hosts) and primary insect vectors

Question 33

epizootic cycle (rural cycle)

Answer 33

-virus transmitted between non-wild or domestic animals and the primary or accessory insect vectors

Question 34

urban cycle

Answer 34

virus cycles between humans and insect vectors

Question 35

amplifying host

Answer 35

-in which the level of virus can become high enough that an insect vector such as a mosquito that feeds on it will probably become infectious

Question 36

dead end host/incidental host

Answer 36

- host from which infectious agents are not transmitted to other susceptible hosts - they do not develop sufficient viremia to be picked up by insect vectors

Question 37

common-vehicle transmission

Answer 37

includes fecal contamination of food and water supples (fecal-oral transmission) and virus-contaminated meat or bone products -can contaminate meat or meat products

Question 38

iatrogenic transmission

Answer 38

- infection transferred during medical or surgical practice - can happen by: introduction of pathogens by contaminated instruments (non-sterile surgical instruments, syringes) or contaminated body surface (inadequate handwashing) - example: spread of equine infectious anemia virus via multiple-use syringes and needles - introduction of pathogen through contaminated prophylactic or therapeutic preparations

Question 39

nosocomial transmission

Answer 39

- occurs when an animal is in a vet hospital or clinic | - hospital acquired infection

Question 40

vertical transmission

Answer 40

-usually used to describe infection that is transferred from dam to embryo or fetus, or newborn before, during, or shortly after parturition (colostrum, milk, or fecal contamination of teats)

Question 41

zoonosis

Answer 41

used to describe infections that are transmissible from animals to humans

Question 42

example of physical stability of a virus

Answer 42

-viruses that are transmitted by the respiratory route have low environmental stability, whereas those transmitted by fecal-oral route have higher stability

Question 43

herd immunity

Answer 43

-form of immunity that occurs when the vaccination of a significant large portion of a population (or herd) provides a measure of protection for individuals who have not developed immunity

Question 44

incubation period

Answer 44

- interval between infection and the onset of clinical signs | - in many diseases there is a period during which animals are infectious before they become sick

Question 45

predromal period

Answer 45

- first signs and feelings of illness after incubation period - period of early symptoms of disease occurring after the incubation period and just before the appearance of the characteristic symptoms of the disease

Question 46

acute period

Answer 46

- when disease is at its height | - severe clinical signs

Question 47

decline period

Answer 47

-period when clinical signs begin to subside

Question 48

convalescent period

Answer 48

the body gradually returns to pre-diseased state and health is restored