lecture 3- epidemiology of viral infections

Question 1

what is virus transmission?

Answer 1

passing of an infectious virus from an infected host to a susceptible host, regardless of whether the individual was previously infected

Question 2

what is horizontal transmission

Answer 2

viral transmission between animals within the population at risk

Question 3

is horizontal transmission direct or indirect?

Answer 3

both

Question 4

when does vertical transmission occur?

Answer 4

in utero
during birth
colostrum
milk (first few weeks)

Question 5

example of vertical transmission that can occur before birth (3)

Answer 5

BVDV, blue tongue, feline parvo

Question 6

example of vertical transmission that can occur during birth

Answer 6

canine herpes virus

Question 7

example of vertical transmission that can occur after birth

Answer 7

CAE, meadi-visna

Question 8

consequences of vertical viral transmission

Answer 8

embryonic death/abortion, congenital disease, congenital defects

Question 9

what are the 6 modes of transmission of horizontal viruses?

Answer 9

direct contact
indirect contact
common vehicles
airborne
vector-borne
iatrogenic

Question 10

examples of direct contact

Answer 10

licking
rubbing
biting
sexual contact
skin abrasions

Question 11

disease whose transmission is through biting? what mode of transport?

Answer 11

rabies, direct

Question 12

disease whose transmission is through sexual contact?

Answer 12

herpes virus, direct

Question 13

disease whose transmission is through skin abrasions?

Answer 13

papilloma virus, direct

Question 14

examples of indirect contact

Answer 14

fomites (shared eating containers, beddings, restraint devices, vehicles, clothing, improperly sterilized surgical equipment)

Question 15

examples of common vehicles

Answer 15

• colostrum and milk
• virus contaminated meat
• virus contaminated bone products

Question 16

diseases whose transmission is through colostrum/milk? what mode of transport?

Answer 16

caprine arthritis encephalitis virus (CAE), tick borne encephalitis virus

common vehicles

Question 17

diseases whose transmission is through virus contaminated meat? what mode of transport?

Answer 17

classical swine fever, vesicular exanthema of swine

common vehicles

Question 18

diseases whose transmission is through contaminated bone products? what mode of transport?

Answer 18

bovine spongiform encephalopathy (BSE)

common vehicles

Question 19

examples of airborne modes of transport?

Answer 19

droplets, aerospols

Question 20

large airborne droplets…

Answer 20

settle quickly

Question 21

microdroplets either…

Answer 21

travel about a meter then evaporate

or

form droplet nucleus then become aerosols and remain suspended in the air for longer periods of time

Question 22

examples of airborne diseases/their transmission (2 to note- 1 from cough/sneeze and 1 from dust/dander)

Answer 22

cough/sneeze –> influenza

dust/dander –> Marek’s disease virus

Question 23

what are arboviruses?

Answer 23

arthropod borne

Question 24

diseases whose transmission is through mosquitos? what mode of transport?

Answer 24

equine encephalitis

arboviruses

Question 25

diseases whose transmission is through soft ticks? what mode of transport?

Answer 25

african swine fever virus arbovirus

Question 26

diseases whose transmission is through culicoides? what mode of transport?

Answer 26

blue tongue virus arbovirus

Question 27

what is iatrogenic transmission?

Answer 27

caused by doctor/animal handler

Question 28

2 examples of iatrogenic diseases?

Answer 28

equine infectious anemia bovine leukemia virus

Question 29

what is nosocomial transmission?

Answer 29

acquired from clinics / hospitals

Question 30

the 1980 epidemic of canine parvovirus infection was caused by what mode of transmission?

Answer 30

nosocomial

Question 31

feline respiratory infections (calici virus infections) is caused by what mode of transmission?

Answer 31

nosocomial

Question 32

the 1976/1995 ebola epidemic in Zaire was caused by what mode of transmission?

Answer 32

nosocomial

Question 33

what are the mechanisms of survival of viruses in nature?

Answer 33

1. physical stability/ *environment* 2. maintenance of serial infections- chain of transmission within *animal * 3.

Question 34

what is the relative stability of viruses transmitted by respiratory route?

Answer 34

low stability

Question 35

what is the relative stability of viruses transmitted by fecal-oral route?

Answer 35

higher stability

Question 36

enveloped viruses are generally.... what are the exceptions?

Answer 36

generally labile exceptions are orf virus and Marek's disease virus

Question 37

non enveloped viruses are generally ...

Answer 37

stable

Question 38

example of non-enveloped viruses

Answer 38

adenoviruses, circoviruses

Question 39

what type of infection (clinical or subclinical) has a more productive source of virus?

Answer 39

clinical infection

Question 40

what type of infection (clinical or subclinical) has more numerous and more important/better opportunity for virus dissemination

Answer 40

subclinical

Question 41

why are subclinical infections significant? Explain in regards to BVDV

Answer 41

if a cow is persistently infected with BVDV (is subclinical) then they are still shedding the virus, despite looking healthy

Question 42

how to viruses maintain serial transmission? (3 patterns)

Answer 42

1. acute self limiting 2. persistent infection 3. vector maintenance

Question 43

acute self limiting transmissions are affected by...

Answer 43

population size

Question 44

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

Answer 44

acute self limiting infection (hit and run strat)

Question 45

what are 3 viral examples of acute self limiting infection?

Answer 45

influenza rota viral diarrhea infectious bursal disease

Question 46

what are the three major types of persistent infection patterns?

Answer 46

1. persistant infection 2. chronic infection 3. latent infection

Question 47

which serial transmission pattern is described by the following: - clinical disease and death with result after years of shedding the virus with subclinical infection

Answer 47

persistent infection (with persistent pattern)

Question 48

what disease example shows a persistent infection with persistent pattern?

Answer 48

BVDV congenital infection

Question 49

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

Answer 49

chronic infection (persistent pattern)

Question 50

what are 2 disease examples that show chronic infection (persistent pattern)?

Answer 50

FMDV (foot and mouth) feline calici virus

Question 51

which serial transmission pattern is described by the following: - intermediate shedding with/without clinical consequences

Answer 51

latent infection (persistent pattern)

Question 52

during latent periods of latent infection, are viral particles being shed?

Answer 52

no

Question 53

what is a viral example of latent infection (persistent pattern)?

Answer 53

herpesvirus

Question 54

where does BHV-1 replication occur?

Answer 54

nasal mucosa

Question 55

in BHV-1, where is life long latency established?

Answer 55

- trigeminal ganglia-neurons - tonsillar lymphoid follicles- T cells

Question 56

what triggers BHV-1 to reactivate? where does productive infection occur?

Answer 56

triggered during stress or when immunity is low establishes productive infection in primary replication sites (trachea and nasal mucosa)

Question 57

what 3 factors influence the prevalence of emerging viral diseases?

Answer 57

1) host determinants 2) constant changes in environment 3) viral determinants

Question 58

how does the evolution of viruses occur via milder genetic changes?

Answer 58

viral replication --> mutations --> antigenic drift

Question 59

which have a higher mutation rate, RNA or DNA viruses? why?

Answer 59

RNA viruses lack proofreading since most replicate in the cytoplasm, therefore they have a higher mutation rate than DNA

Question 60

how does the evolution of viruses occur via drastic genetic changes? 2 ways

Answer 60

1) template switching between closely related viruses 2) exchange of entire gene segments (rearrangement)

Question 61

how does template switching between closely related viruses occur?

Answer 61

co-infection of a cell by genetically distinct viruses can lead to the generation of recombinant viruses

Question 62

what is an example of template switching

Answer 62

ancient sinbis like viruses + eastern equine encephalitis virus = western equine encephalitis cirus

Question 63

how does exchange of entire gene segments (reassortment) to create a new virus occur?

Answer 63

co-infection of a cell by genetically distinct strains of a *segmented virus* can generate different combinations of reassortment progeny

Question 64

examples of viruses created by reassortment? 4

Answer 64

-arena and birna viruses (2 segments) - bunyaviridae (3 segments) -orthomyxoviridae (6-8 segments) -reoviridae (12 segments)

Question 65

what kind of receptors are associated with influenza virus

Answer 65

sialic acid