General Virology 3- Epidemiology of Viral Infections

Question 1

Definition of viral transmission

Answer 1

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

Question 2

Define horizontal transmission

Answer 2

Direct or indirect contact between animals within the population at risk

Question 3

Define vertical transmission

Answer 3

Transmission in utero, during birth, colostrum or milk (during the first few weeks)

I.e. In embryo, fetus or newborn

Question 4

Diseases that transmit vertically before birth

Answer 4

BVDV
blue tongue
feline parvo

Question 5

Disease that transmit vertically during birth

Answer 5

canine herpes virus

Question 6

Diseases that transmit vertically shortly after birth

Answer 6

Caprine arthritis encephalitis (CAE), and Visna-maedi virus

Question 7

What are the consequences of vertical transmission?

Answer 7

Embryonic death, abortions (PRRS), congenital diseases (BVDV, border disease), and congenital defects (blue tongue and feline Parvo)

Question 8

What congenital defect does feline Parvo cause?

Answer 8

cerebella hypoplasia

Question 9

Give examples of horizontal transmission

Answer 9

-Direct contact
-Indirect contact
-Airborne/Aerosols
-Vector-borne
-Iatrogenic
-Fomites

Question 10

What is a fomite?

Answer 10

non-living objects or materials which are able to carry carry viruses

Question 11

Name some common vehicles for viruses

Answer 11

-Colostrum and milk
-virus contaminated meat
-virus contaminated bone products

Question 12

What are NoSocomial infections?

Answer 12

Animal acquires infection while in clinic/hospital

Question 13

Physical ______ of the virus affects survival of the virus

Answer 13

Physical stability

Question 14

Virus transmitted by respiratory route have what stability?

Answer 14

low

Question 15

Virus transmitted by fecal oral route have what stability?

Answer 15

higher

Question 16

Enveloped viruses are labile, with the exception of? And why?

Answer 16

Orf (pox) virus and Marek’s disease

Thought to be protected by the karatin

Question 17

Pox virus has what distinct histological feature ?

Answer 17

Viral inclusion bodies in the cytoplasm

Question 18

To survive in nature viruses what must be must maintained by ? And how is this done?

Answer 18

Serial infections via Chain of transmission

Serial interval is the time between illness onset in the first case till illness onset in the second

Question 19

What is an example of biological gradient?

Answer 19

Due to close proximity with other species, viruses can mutate to make a variant that infects a new species.

Example: Equine H3N8 that causes equine influenza, the virus mutated and produced canine influenza at the race track both species were at

Question 20

chain of transmission/serial infections depend on what?

Answer 20

clinical and subclinical infections

Question 21

The more productive source of the virus is clinical or subclinical infection

Answer 21

Clinical infection
(is very productive but will also be identified and treated)

Question 22

What is going on during subclinical infection?

Answer 22

more numerous and better opportunity for virus to disseminate

more important

Question 23

What are the three major patterns that allow for serial transmission?

Answer 23

1) Acute self-limiting infection/ hit and run strategy
2) persistant infection
3) vector maintenance

Question 24

Describe acute self-limiting infection

Answer 24

Called hit and run because causes disease then virus is gone (infectious virus disappears w clinical recovery)

• high viral load during disease
• a continuous supply of susceptible hosts are required
• after infection there is a strong antibody response

Question 24

Give 3 example of viruses that cause acute self limiting infection

Answer 24

-Infliuenza -Rota viral diarrhea -infectious bursal disease

Question 25

There are 3 persistent infection patterns. What are they?

Answer 25

-Persistent infection -Chronic infection -Latent infection

Question 26

Describe persistent infections

Answer 26

Animal will have years of shedding the virus with subclinical infection, before clinical disease or death happens. The animal cannot clear the infection

Question 27

What is an example of a persistent infection?

Answer 27

Bovine viral diarrhea virus (BVDV)

Question 28

Describe chronic infections

Answer 28

Initially have clinical disease and high viral load (resembling acute infection) but after clinical recovery there are years of shedding the virus at low levels

Question 29

Give two examples of viruses that are chronic infection patterns

Answer 29

Foot and mouth disease Feline calici virus

Question 29

Describe the latent infection pattern

Answer 29

-cycles of reactivation and latency -will have intermittent shedding with or without clinical signs -reactivation periods happen due to immune response -there is NO shedding (productive infection) during the latency periods -infection is life long

Question 30

Describe how infection and reactivation period in herpes virus can be stimulated

Answer 30

Herpes virus will establish infection in the primary site (ex BHV1 in nasal mucosa), the virus will then establish life long latency trigeminal ganglia (neurons) and lymphoid follicles (t-cells) An immune suppersive event (ex stress) will reactivate the virus and establish a productive period in the primary replication site (ex. nasal mucosa)

Question 31

What is the ONLY virus that has a latent infection pattern

Answer 31

Herpes viruses

Question 32

What are emerging viral diseases?

Answer 32

Diseases that are newly recognized, newly evolved or occurred previously but is showing an increase in incidence

Question 33

What are the three factors that affect emerging viral diseases?

Answer 33

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

Question 34

What are host factors that affect emerging viruses?

Answer 34

The virus must successfully... -invade the host -evade the immune system -enter, replicate and exit the cell -find another cell -find another host

Question 35

What are environmental factors that affect emerging viruses?

Answer 35

-ecological factors- can lead to arthropod borne infections -Human activities- lead to translocations of viruses and vectors

Question 36

What are viral determinants that cause new emerging diseases?

Answer 36

short generation times and higher mutations rates (especially in enzootic variants)

Question 37

What causes minor genetic changes

Answer 37

antigenic drift

Question 38

What is antigenic drift?

Answer 38

the accumulation of a series of minor genetic mutations due to error in copying the viral nucleic acid can be lethal or non lethal to virus

Question 39

What viruses (RNA or DNA) have more mutations? and Why?

Answer 39

RNA viruses. B/c DNA viruses use the cellular machinery in the nucleus to replicate and this has proof reading ability RNA viruses typically have their own transcription enzymes and replicate in the cytoplasm. So no proof reading =every progeny will be different from parent viruses

Question 40

Of all viruses which have the greatest mutation rate?

Answer 40

Retroviruses

Question 41

What is the relationship between genome size and mutation rate

Answer 41

Smaller the genome the greater the mutation rates

Question 42

How can viral variants change in biological transmission and species tropism?

Answer 42

1) There is longterm host and virus co-evelution (ex Virus in bats) 2) because of this co-evolution the virus won't be cleared and prolonged so gives it lots of time to evolve (antigenic drift) 3) This evolution creates a novel pathogen with higher spillover risk and transmission potential 4) Infection in novel host- causing an overreactive immune response with high cytotoxic effects (cytokine storm)

Question 43

What are two things that can cause drastic genetic changes?

Answer 43

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

Question 44

How does template switching occur?

Answer 44

Co-infection of a cell by two different viral strains can lead to the generation of recombinant viruses due to templates switching

Question 45

How does reassortment occur?

Answer 45

Co-infection of a cell by genetically distinct strains of a SEGMENTED virus can generate different combinations of reasserted progenies